/*
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
"use strict";

/*
 * This file is generated from kinto.js - do not modify directly.
 */

// This is required because with Babel compiles ES2015 modules into a
// require() form that tries to keep its modules on "this", but
// doesn't specify "this", leaving it to default to the global
// object. However, in strict mode, "this" no longer defaults to the
// global object, so expose the global object explicitly. Babel's
// compiled output will use a variable called "global" if one is
// present.
//
// See https://bugzilla.mozilla.org/show_bug.cgi?id=1394556#c3 for
// more details.
const global = this;

var EXPORTED_SYMBOLS = ["Kinto"];

/*
 * Version 13.0.0 - 7fbf95d
 */

(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
  typeof define === 'function' && define.amd ? define(factory) :
  (global = global || self, global.Kinto = factory());
}(this, (function () { 'use strict';

  /**
   * Base db adapter.
   *
   * @abstract
   */
  class BaseAdapter {
      /**
       * Deletes every records present in the database.
       *
       * @abstract
       * @return {Promise}
       */
      clear() {
          throw new Error("Not Implemented.");
      }
      /**
       * Executes a batch of operations within a single transaction.
       *
       * @abstract
       * @param  {Function} callback The operation callback.
       * @param  {Object}   options  The options object.
       * @return {Promise}
       */
      execute(callback, options = { preload: [] }) {
          throw new Error("Not Implemented.");
      }
      /**
       * Retrieve a record by its primary key from the database.
       *
       * @abstract
       * @param  {String} id The record id.
       * @return {Promise}
       */
      get(id) {
          throw new Error("Not Implemented.");
      }
      /**
       * Lists all records from the database.
       *
       * @abstract
       * @param  {Object} params  The filters and order to apply to the results.
       * @return {Promise}
       */
      list(params = { filters: {}, order: "" }) {
          throw new Error("Not Implemented.");
      }
      /**
       * Store the lastModified value.
       *
       * @abstract
       * @param  {Number}  lastModified
       * @return {Promise}
       */
      saveLastModified(lastModified) {
          throw new Error("Not Implemented.");
      }
      /**
       * Retrieve saved lastModified value.
       *
       * @abstract
       * @return {Promise}
       */
      getLastModified() {
          throw new Error("Not Implemented.");
      }
      /**
       * Load records in bulk that were exported from a server.
       *
       * @abstract
       * @param  {Array} records The records to load.
       * @return {Promise}
       */
      importBulk(records) {
          throw new Error("Not Implemented.");
      }
      /**
       * Load a dump of records exported from a server.
       *
       * @deprecated Use {@link importBulk} instead.
       * @abstract
       * @param  {Array} records The records to load.
       * @return {Promise}
       */
      loadDump(records) {
          throw new Error("Not Implemented.");
      }
      saveMetadata(metadata) {
          throw new Error("Not Implemented.");
      }
      getMetadata() {
          throw new Error("Not Implemented.");
      }
  }

  const RE_RECORD_ID = /^[a-zA-Z0-9][a-zA-Z0-9_-]*$/;
  /**
   * Checks if a value is undefined.
   * @param  {Any}  value
   * @return {Boolean}
   */
  function _isUndefined(value) {
      return typeof value === "undefined";
  }
  /**
   * Sorts records in a list according to a given ordering.
   *
   * @param  {String} order The ordering, eg. `-last_modified`.
   * @param  {Array}  list  The collection to order.
   * @return {Array}
   */
  function sortObjects(order, list) {
      const hasDash = order[0] === "-";
      const field = hasDash ? order.slice(1) : order;
      const direction = hasDash ? -1 : 1;
      return list.slice().sort((a, b) => {
          if (a[field] && _isUndefined(b[field])) {
              return direction;
          }
          if (b[field] && _isUndefined(a[field])) {
              return -direction;
          }
          if (_isUndefined(a[field]) && _isUndefined(b[field])) {
              return 0;
          }
          return a[field] > b[field] ? direction : -direction;
      });
  }
  /**
   * Test if a single object matches all given filters.
   *
   * @param  {Object} filters  The filters object.
   * @param  {Object} entry    The object to filter.
   * @return {Boolean}
   */
  function filterObject(filters, entry) {
      return Object.keys(filters).every(filter => {
          const value = filters[filter];
          if (Array.isArray(value)) {
              return value.some(candidate => candidate === entry[filter]);
          }
          else if (typeof value === "object") {
              return filterObject(value, entry[filter]);
          }
          else if (!Object.prototype.hasOwnProperty.call(entry, filter)) {
              console.error(`The property ${filter} does not exist`);
              return false;
          }
          return entry[filter] === value;
      });
  }
  /**
   * Resolves a list of functions sequentially, which can be sync or async; in
   * case of async, functions must return a promise.
   *
   * @param  {Array} fns  The list of functions.
   * @param  {Any}   init The initial value.
   * @return {Promise}
   */
  function waterfall(fns, init) {
      if (!fns.length) {
          return Promise.resolve(init);
      }
      return fns.reduce((promise, nextFn) => {
          return promise.then(nextFn);
      }, Promise.resolve(init));
  }
  /**
   * Simple deep object comparison function. This only supports comparison of
   * serializable JavaScript objects.
   *
   * @param  {Object} a The source object.
   * @param  {Object} b The compared object.
   * @return {Boolean}
   */
  function deepEqual(a, b) {
      if (a === b) {
          return true;
      }
      if (typeof a !== typeof b) {
          return false;
      }
      if (!(a && typeof a == "object") || !(b && typeof b == "object")) {
          return false;
      }
      if (Object.keys(a).length !== Object.keys(b).length) {
          return false;
      }
      for (const k in a) {
          if (!deepEqual(a[k], b[k])) {
              return false;
          }
      }
      return true;
  }
  /**
   * Return an object without the specified keys.
   *
   * @param  {Object} obj        The original object.
   * @param  {Array}  keys       The list of keys to exclude.
   * @return {Object}            A copy without the specified keys.
   */
  function omitKeys(obj, keys = []) {
      const result = Object.assign({}, obj);
      for (const key of keys) {
          delete result[key];
      }
      return result;
  }
  function arrayEqual(a, b) {
      if (a.length !== b.length) {
          return false;
      }
      for (let i = a.length; i--;) {
          if (a[i] !== b[i]) {
              return false;
          }
      }
      return true;
  }
  function makeNestedObjectFromArr(arr, val, nestedFiltersObj) {
      const last = arr.length - 1;
      return arr.reduce((acc, cv, i) => {
          if (i === last) {
              return (acc[cv] = val);
          }
          else if (Object.prototype.hasOwnProperty.call(acc, cv)) {
              return acc[cv];
          }
          else {
              return (acc[cv] = {});
          }
      }, nestedFiltersObj);
  }
  function transformSubObjectFilters(filtersObj) {
      const transformedFilters = {};
      for (const key in filtersObj) {
          const keysArr = key.split(".");
          const val = filtersObj[key];
          makeNestedObjectFromArr(keysArr, val, transformedFilters);
      }
      return transformedFilters;
  }

  const INDEXED_FIELDS = ["id", "_status", "last_modified"];
  /**
   * Small helper that wraps the opening of an IndexedDB into a Promise.
   *
   * @param dbname          {String}   The database name.
   * @param version         {Integer}  Schema version
   * @param onupgradeneeded {Function} The callback to execute if schema is
   *                                   missing or different.
   * @return {Promise<IDBDatabase>}
   */
  async function open(dbname, { version, onupgradeneeded }) {
      return new Promise((resolve, reject) => {
          const request = indexedDB.open(dbname, version);
          request.onupgradeneeded = event => {
              const db = event.target.result;
              db.onerror = event => reject(event.target.error);
              // When an upgrade is needed, a transaction is started.
              const transaction = event.target.transaction;
              transaction.onabort = event => {
                  const error = event.target.error ||
                      transaction.error ||
                      new DOMException("The operation has been aborted", "AbortError");
                  reject(error);
              };
              // Callback for store creation etc.
              return onupgradeneeded(event);
          };
          request.onerror = event => {
              reject(event.target.error);
          };
          request.onsuccess = event => {
              const db = event.target.result;
              resolve(db);
          };
      });
  }
  /**
   * Helper to run the specified callback in a single transaction on the
   * specified store.
   * The helper focuses on transaction wrapping into a promise.
   *
   * @param db           {IDBDatabase} The database instance.
   * @param name         {String}      The store name.
   * @param callback     {Function}    The piece of code to execute in the transaction.
   * @param options      {Object}      Options.
   * @param options.mode {String}      Transaction mode (default: read).
   * @return {Promise} any value returned by the callback.
   */
  async function execute(db, name, callback, options = {}) {
      const { mode } = options;
      return new Promise((resolve, reject) => {
          // On Safari, calling IDBDatabase.transaction with mode == undefined raises
          // a TypeError.
          const transaction = mode
              ? db.transaction([name], mode)
              : db.transaction([name]);
          const store = transaction.objectStore(name);
          // Let the callback abort this transaction.
          const abort = e => {
              transaction.abort();
              reject(e);
          };
          // Execute the specified callback **synchronously**.
          let result;
          try {
              result = callback(store, abort);
          }
          catch (e) {
              abort(e);
          }
          transaction.onerror = event => reject(event.target.error);
          transaction.oncomplete = event => resolve(result);
          transaction.onabort = event => {
              const error = event.target.error ||
                  transaction.error ||
                  new DOMException("The operation has been aborted", "AbortError");
              reject(error);
          };
      });
  }
  /**
   * Helper to wrap the deletion of an IndexedDB database into a promise.
   *
   * @param dbName {String} the database to delete
   * @return {Promise}
   */
  async function deleteDatabase(dbName) {
      return new Promise((resolve, reject) => {
          const request = indexedDB.deleteDatabase(dbName);
          request.onsuccess = event => resolve(event.target);
          request.onerror = event => reject(event.target.error);
      });
  }
  /**
   * IDB cursor handlers.
   * @type {Object}
   */
  const cursorHandlers = {
      all(filters, done) {
          const results = [];
          return event => {
              const cursor = event.target.result;
              if (cursor) {
                  const { value } = cursor;
                  if (filterObject(filters, value)) {
                      results.push(value);
                  }
                  cursor.continue();
              }
              else {
                  done(results);
              }
          };
      },
      in(values, filters, done) {
          const results = [];
          let i = 0;
          return function (event) {
              const cursor = event.target.result;
              if (!cursor) {
                  done(results);
                  return;
              }
              const { key, value } = cursor;
              // `key` can be an array of two values (see `keyPath` in indices definitions).
              // `values` can be an array of arrays if we filter using an index whose key path
              // is an array (eg. `cursorHandlers.in([["bid/cid", 42], ["bid/cid", 43]], ...)`)
              while (key > values[i]) {
                  // The cursor has passed beyond this key. Check next.
                  ++i;
                  if (i === values.length) {
                      done(results); // There is no next. Stop searching.
                      return;
                  }
              }
              const isEqual = Array.isArray(key)
                  ? arrayEqual(key, values[i])
                  : key === values[i];
              if (isEqual) {
                  if (filterObject(filters, value)) {
                      results.push(value);
                  }
                  cursor.continue();
              }
              else {
                  cursor.continue(values[i]);
              }
          };
      },
  };
  /**
   * Creates an IDB request and attach it the appropriate cursor event handler to
   * perform a list query.
   *
   * Multiple matching values are handled by passing an array.
   *
   * @param  {String}           cid        The collection id (ie. `{bid}/{cid}`)
   * @param  {IDBStore}         store      The IDB store.
   * @param  {Object}           filters    Filter the records by field.
   * @param  {Function}         done       The operation completion handler.
   * @return {IDBRequest}
   */
  function createListRequest(cid, store, filters, done) {
      const filterFields = Object.keys(filters);
      // If no filters, get all results in one bulk.
      if (filterFields.length == 0) {
          const request = store.index("cid").getAll(IDBKeyRange.only(cid));
          request.onsuccess = event => done(event.target.result);
          return request;
      }
      // Introspect filters and check if they leverage an indexed field.
      const indexField = filterFields.find(field => {
          return INDEXED_FIELDS.includes(field);
      });
      if (!indexField) {
          // Iterate on all records for this collection (ie. cid)
          const isSubQuery = Object.keys(filters).some(key => key.includes(".")); // (ie. filters: {"article.title": "hello"})
          if (isSubQuery) {
              const newFilter = transformSubObjectFilters(filters);
              const request = store.index("cid").openCursor(IDBKeyRange.only(cid));
              request.onsuccess = cursorHandlers.all(newFilter, done);
              return request;
          }
          const request = store.index("cid").openCursor(IDBKeyRange.only(cid));
          request.onsuccess = cursorHandlers.all(filters, done);
          return request;
      }
      // If `indexField` was used already, don't filter again.
      const remainingFilters = omitKeys(filters, [indexField]);
      // value specified in the filter (eg. `filters: { _status: ["created", "updated"] }`)
      const value = filters[indexField];
      // For the "id" field, use the primary key.
      const indexStore = indexField == "id" ? store : store.index(indexField);
      // WHERE IN equivalent clause
      if (Array.isArray(value)) {
          if (value.length === 0) {
              return done([]);
          }
          const values = value.map(i => [cid, i]).sort();
          const range = IDBKeyRange.bound(values[0], values[values.length - 1]);
          const request = indexStore.openCursor(range);
          request.onsuccess = cursorHandlers.in(values, remainingFilters, done);
          return request;
      }
      // If no filters on custom attribute, get all results in one bulk.
      if (remainingFilters.length == 0) {
          const request = indexStore.getAll(IDBKeyRange.only([cid, value]));
          request.onsuccess = event => done(event.target.result);
          return request;
      }
      // WHERE field = value clause
      const request = indexStore.openCursor(IDBKeyRange.only([cid, value]));
      request.onsuccess = cursorHandlers.all(remainingFilters, done);
      return request;
  }
  class IDBError extends Error {
      constructor(method, err) {
          super(`IndexedDB ${method}() ${err.message}`);
          this.name = err.name;
          this.stack = err.stack;
      }
  }
  /**
   * IndexedDB adapter.
   *
   * This adapter doesn't support any options.
   */
  class IDB extends BaseAdapter {
      /* Expose the IDBError class publicly */
      static get IDBError() {
          return IDBError;
      }
      /**
       * Constructor.
       *
       * @param  {String} cid  The key base for this collection (eg. `bid/cid`)
       * @param  {Object} options
       * @param  {String} options.dbName         The IndexedDB name (default: `"KintoDB"`)
       * @param  {String} options.migrateOldData Whether old database data should be migrated (default: `false`)
       */
      constructor(cid, options = {}) {
          super();
          this.cid = cid;
          this.dbName = options.dbName || "KintoDB";
          this._options = options;
          this._db = null;
      }
      _handleError(method, err) {
          throw new IDBError(method, err);
      }
      /**
       * Ensures a connection to the IndexedDB database has been opened.
       *
       * @override
       * @return {Promise}
       */
      async open() {
          if (this._db) {
              return this;
          }
          // In previous versions, we used to have a database with name `${bid}/${cid}`.
          // Check if it exists, and migrate data once new schema is in place.
          // Note: the built-in migrations from IndexedDB can only be used if the
          // database name does not change.
          const dataToMigrate = this._options.migrateOldData
              ? await migrationRequired(this.cid)
              : null;
          this._db = await open(this.dbName, {
              version: 2,
              onupgradeneeded: event => {
                  const db = event.target.result;
                  if (event.oldVersion < 1) {
                      // Records store
                      const recordsStore = db.createObjectStore("records", {
                          keyPath: ["_cid", "id"],
                      });
                      // An index to obtain all the records in a collection.
                      recordsStore.createIndex("cid", "_cid");
                      // Here we create indices for every known field in records by collection.
                      // Local record status ("synced", "created", "updated", "deleted")
                      recordsStore.createIndex("_status", ["_cid", "_status"]);
                      // Last modified field
                      recordsStore.createIndex("last_modified", ["_cid", "last_modified"]);
                      // Timestamps store
                      db.createObjectStore("timestamps", {
                          keyPath: "cid",
                      });
                  }
                  if (event.oldVersion < 2) {
                      // Collections store
                      db.createObjectStore("collections", {
                          keyPath: "cid",
                      });
                  }
              },
          });
          if (dataToMigrate) {
              const { records, timestamp } = dataToMigrate;
              await this.importBulk(records);
              await this.saveLastModified(timestamp);
              console.log(`${this.cid}: data was migrated successfully.`);
              // Delete the old database.
              await deleteDatabase(this.cid);
              console.warn(`${this.cid}: old database was deleted.`);
          }
          return this;
      }
      /**
       * Closes current connection to the database.
       *
       * @override
       * @return {Promise}
       */
      close() {
          if (this._db) {
              this._db.close(); // indexedDB.close is synchronous
              this._db = null;
          }
          return Promise.resolve();
      }
      /**
       * Returns a transaction and an object store for a store name.
       *
       * To determine if a transaction has completed successfully, we should rather
       * listen to the transaction’s complete event rather than the IDBObjectStore
       * request’s success event, because the transaction may still fail after the
       * success event fires.
       *
       * @param  {String}      name  Store name
       * @param  {Function}    callback to execute
       * @param  {Object}      options Options
       * @param  {String}      options.mode  Transaction mode ("readwrite" or undefined)
       * @return {Object}
       */
      async prepare(name, callback, options) {
          await this.open();
          await execute(this._db, name, callback, options);
      }
      /**
       * Deletes every records in the current collection.
       *
       * @override
       * @return {Promise}
       */
      async clear() {
          try {
              await this.prepare("records", store => {
                  const range = IDBKeyRange.only(this.cid);
                  const request = store.index("cid").openKeyCursor(range);
                  request.onsuccess = event => {
                      const cursor = event.target.result;
                      if (cursor) {
                          store.delete(cursor.primaryKey);
                          cursor.continue();
                      }
                  };
                  return request;
              }, { mode: "readwrite" });
          }
          catch (e) {
              this._handleError("clear", e);
          }
      }
      /**
       * Executes the set of synchronous CRUD operations described in the provided
       * callback within an IndexedDB transaction, for current db store.
       *
       * The callback will be provided an object exposing the following synchronous
       * CRUD operation methods: get, create, update, delete.
       *
       * Important note: because limitations in IndexedDB implementations, no
       * asynchronous code should be performed within the provided callback; the
       * promise will therefore be rejected if the callback returns a Promise.
       *
       * Options:
       * - {Array} preload: The list of record IDs to fetch and make available to
       *   the transaction object get() method (default: [])
       *
       * @example
       * const db = new IDB("example");
       * const result = await db.execute(transaction => {
       *   transaction.create({id: 1, title: "foo"});
       *   transaction.update({id: 2, title: "bar"});
       *   transaction.delete(3);
       *   return "foo";
       * });
       *
       * @override
       * @param  {Function} callback The operation description callback.
       * @param  {Object}   options  The options object.
       * @return {Promise}
       */
      async execute(callback, options = { preload: [] }) {
          // Transactions in IndexedDB are autocommited when a callback does not
          // perform any additional operation.
          // The way Promises are implemented in Firefox (see https://bugzilla.mozilla.org/show_bug.cgi?id=1193394)
          // prevents using within an opened transaction.
          // To avoid managing asynchronocity in the specified `callback`, we preload
          // a list of record in order to execute the `callback` synchronously.
          // See also:
          // - http://stackoverflow.com/a/28388805/330911
          // - http://stackoverflow.com/a/10405196
          // - https://jakearchibald.com/2015/tasks-microtasks-queues-and-schedules/
          let result;
          await this.prepare("records", (store, abort) => {
              const runCallback = (preloaded = []) => {
                  // Expose a consistent API for every adapter instead of raw store methods.
                  const proxy = transactionProxy(this, store, preloaded);
                  // The callback is executed synchronously within the same transaction.
                  try {
                      const returned = callback(proxy);
                      if (returned instanceof Promise) {
                          // XXX: investigate how to provide documentation details in error.
                          throw new Error("execute() callback should not return a Promise.");
                      }
                      // Bring to scope that will be returned (once promise awaited).
                      result = returned;
                  }
                  catch (e) {
                      // The callback has thrown an error explicitly. Abort transaction cleanly.
                      abort(e);
                  }
              };
              // No option to preload records, go straight to `callback`.
              if (!options.preload.length) {
                  return runCallback();
              }
              // Preload specified records using a list request.
              const filters = { id: options.preload };
              createListRequest(this.cid, store, filters, records => {
                  // Store obtained records by id.
                  const preloaded = {};
                  for (const record of records) {
                      delete record["_cid"];
                      preloaded[record.id] = record;
                  }
                  runCallback(preloaded);
              });
          }, { mode: "readwrite" });
          return result;
      }
      /**
       * Retrieve a record by its primary key from the IndexedDB database.
       *
       * @override
       * @param  {String} id The record id.
       * @return {Promise}
       */
      async get(id) {
          try {
              let record;
              await this.prepare("records", store => {
                  store.get([this.cid, id]).onsuccess = e => (record = e.target.result);
              });
              return record;
          }
          catch (e) {
              this._handleError("get", e);
          }
      }
      /**
       * Lists all records from the IndexedDB database.
       *
       * @override
       * @param  {Object} params  The filters and order to apply to the results.
       * @return {Promise}
       */
      async list(params = { filters: {} }) {
          const { filters } = params;
          try {
              let results = [];
              await this.prepare("records", store => {
                  createListRequest(this.cid, store, filters, _results => {
                      // we have received all requested records that match the filters,
                      // we now park them within current scope and hide the `_cid` attribute.
                      for (const result of _results) {
                          delete result["_cid"];
                      }
                      results = _results;
                  });
              });
              // The resulting list of records is sorted.
              // XXX: with some efforts, this could be fully implemented using IDB API.
              return params.order ? sortObjects(params.order, results) : results;
          }
          catch (e) {
              this._handleError("list", e);
          }
      }
      /**
       * Store the lastModified value into metadata store.
       *
       * @override
       * @param  {Number}  lastModified
       * @return {Promise}
       */
      async saveLastModified(lastModified) {
          const value = parseInt(lastModified, 10) || null;
          try {
              await this.prepare("timestamps", store => {
                  if (value === null) {
                      store.delete(this.cid);
                  }
                  else {
                      store.put({ cid: this.cid, value });
                  }
              }, { mode: "readwrite" });
              return value;
          }
          catch (e) {
              this._handleError("saveLastModified", e);
          }
      }
      /**
       * Retrieve saved lastModified value.
       *
       * @override
       * @return {Promise}
       */
      async getLastModified() {
          try {
              let entry = null;
              await this.prepare("timestamps", store => {
                  store.get(this.cid).onsuccess = e => (entry = e.target.result);
              });
              return entry ? entry.value : null;
          }
          catch (e) {
              this._handleError("getLastModified", e);
          }
      }
      /**
       * Load a dump of records exported from a server.
       *
       * @deprecated Use {@link importBulk} instead.
       * @abstract
       * @param  {Array} records The records to load.
       * @return {Promise}
       */
      async loadDump(records) {
          return this.importBulk(records);
      }
      /**
       * Load records in bulk that were exported from a server.
       *
       * @abstract
       * @param  {Array} records The records to load.
       * @return {Promise}
       */
      async importBulk(records) {
          try {
              await this.execute(transaction => {
                  // Since the put operations are asynchronous, we chain
                  // them together. The last one will be waited for the
                  // `transaction.oncomplete` callback. (see #execute())
                  let i = 0;
                  putNext();
                  function putNext() {
                      if (i == records.length) {
                          return;
                      }
                      // On error, `transaction.onerror` is called.
                      transaction.update(records[i]).onsuccess = putNext;
                      ++i;
                  }
              });
              const previousLastModified = await this.getLastModified();
              const lastModified = Math.max(...records.map(record => record.last_modified));
              if (lastModified > previousLastModified) {
                  await this.saveLastModified(lastModified);
              }
              return records;
          }
          catch (e) {
              this._handleError("importBulk", e);
          }
      }
      async saveMetadata(metadata) {
          try {
              await this.prepare("collections", store => store.put({ cid: this.cid, metadata }), { mode: "readwrite" });
              return metadata;
          }
          catch (e) {
              this._handleError("saveMetadata", e);
          }
      }
      async getMetadata() {
          try {
              let entry = null;
              await this.prepare("collections", store => {
                  store.get(this.cid).onsuccess = e => (entry = e.target.result);
              });
              return entry ? entry.metadata : null;
          }
          catch (e) {
              this._handleError("getMetadata", e);
          }
      }
  }
  /**
   * IDB transaction proxy.
   *
   * @param  {IDB} adapter        The call IDB adapter
   * @param  {IDBStore} store     The IndexedDB database store.
   * @param  {Array}    preloaded The list of records to make available to
   *                              get() (default: []).
   * @return {Object}
   */
  function transactionProxy(adapter, store, preloaded = []) {
      const _cid = adapter.cid;
      return {
          create(record) {
              store.add(Object.assign(Object.assign({}, record), { _cid }));
          },
          update(record) {
              return store.put(Object.assign(Object.assign({}, record), { _cid }));
          },
          delete(id) {
              store.delete([_cid, id]);
          },
          get(id) {
              return preloaded[id];
          },
      };
  }
  /**
   * Up to version 10.X of kinto.js, each collection had its own collection.
   * The database name was `${bid}/${cid}` (eg. `"blocklists/certificates"`)
   * and contained only one store with the same name.
   */
  async function migrationRequired(dbName) {
      let exists = true;
      const db = await open(dbName, {
          version: 1,
          onupgradeneeded: event => {
              exists = false;
          },
      });
      // Check that the DB we're looking at is really a legacy one,
      // and not some remainder of the open() operation above.
      exists &=
          db.objectStoreNames.contains("__meta__") &&
              db.objectStoreNames.contains(dbName);
      if (!exists) {
          db.close();
          // Testing the existence creates it, so delete it :)
          await deleteDatabase(dbName);
          return null;
      }
      console.warn(`${dbName}: old IndexedDB database found.`);
      try {
          // Scan all records.
          let records;
          await execute(db, dbName, store => {
              store.openCursor().onsuccess = cursorHandlers.all({}, res => (records = res));
          });
          console.log(`${dbName}: found ${records.length} records.`);
          // Check if there's a entry for this.
          let timestamp = null;
          await execute(db, "__meta__", store => {
              store.get(`${dbName}-lastModified`).onsuccess = e => {
                  timestamp = e.target.result ? e.target.result.value : null;
              };
          });
          // Some previous versions, also used to store the timestamps without prefix.
          if (!timestamp) {
              await execute(db, "__meta__", store => {
                  store.get("lastModified").onsuccess = e => {
                      timestamp = e.target.result ? e.target.result.value : null;
                  };
              });
          }
          console.log(`${dbName}: ${timestamp ? "found" : "no"} timestamp.`);
          // Those will be inserted in the new database/schema.
          return { records, timestamp };
      }
      catch (e) {
          console.error("Error occured during migration", e);
          return null;
      }
      finally {
          db.close();
      }
  }

  var uuid4 = {};

  const RECORD_FIELDS_TO_CLEAN = ["_status"];
  const AVAILABLE_HOOKS = ["incoming-changes"];
  const IMPORT_CHUNK_SIZE = 200;
  /**
   * Compare two records omitting local fields and synchronization
   * attributes (like _status and last_modified)
   * @param {Object} a    A record to compare.
   * @param {Object} b    A record to compare.
   * @param {Array} localFields Additional fields to ignore during the comparison
   * @return {boolean}
   */
  function recordsEqual(a, b, localFields = []) {
      const fieldsToClean = RECORD_FIELDS_TO_CLEAN.concat(["last_modified"]).concat(localFields);
      const cleanLocal = r => omitKeys(r, fieldsToClean);
      return deepEqual(cleanLocal(a), cleanLocal(b));
  }
  /**
   * Synchronization result object.
   */
  class SyncResultObject {
      /**
       * Public constructor.
       */
      constructor() {
          /**
           * Current synchronization result status; becomes `false` when conflicts or
           * errors are registered.
           * @type {Boolean}
           */
          this.lastModified = null;
          this._lists = {};
          [
              "errors",
              "created",
              "updated",
              "deleted",
              "published",
              "conflicts",
              "skipped",
              "resolved",
              "void",
          ].forEach(l => (this._lists[l] = []));
          this._cached = {};
      }
      /**
       * Adds entries for a given result type.
       *
       * @param {String} type    The result type.
       * @param {Array}  entries The result entries.
       * @return {SyncResultObject}
       */
      add(type, entries) {
          if (!Array.isArray(this._lists[type])) {
              console.warn(`Unknown type "${type}"`);
              return;
          }
          if (!Array.isArray(entries)) {
              entries = [entries];
          }
          this._lists[type] = this._lists[type].concat(entries);
          delete this._cached[type];
          return this;
      }
      get ok() {
          return this.errors.length + this.conflicts.length === 0;
      }
      get errors() {
          return this._lists["errors"];
      }
      get conflicts() {
          return this._lists["conflicts"];
      }
      get skipped() {
          return this._deduplicate("skipped");
      }
      get resolved() {
          return this._deduplicate("resolved");
      }
      get created() {
          return this._deduplicate("created");
      }
      get updated() {
          return this._deduplicate("updated");
      }
      get deleted() {
          return this._deduplicate("deleted");
      }
      get published() {
          return this._deduplicate("published");
      }
      _deduplicate(list) {
          if (!(list in this._cached)) {
              // Deduplicate entries by id. If the values don't have `id` attribute, just
              // keep all.
              const recordsWithoutId = new Set();
              const recordsById = new Map();
              this._lists[list].forEach(record => {
                  if (!record.id) {
                      recordsWithoutId.add(record);
                  }
                  else {
                      recordsById.set(record.id, record);
                  }
              });
              this._cached[list] = Array.from(recordsById.values()).concat(Array.from(recordsWithoutId));
          }
          return this._cached[list];
      }
      /**
       * Reinitializes result entries for a given result type.
       *
       * @param  {String} type The result type.
       * @return {SyncResultObject}
       */
      reset(type) {
          this._lists[type] = [];
          delete this._cached[type];
          return this;
      }
      toObject() {
          // Only used in tests.
          return {
              ok: this.ok,
              lastModified: this.lastModified,
              errors: this.errors,
              created: this.created,
              updated: this.updated,
              deleted: this.deleted,
              skipped: this.skipped,
              published: this.published,
              conflicts: this.conflicts,
              resolved: this.resolved,
          };
      }
  }
  class ServerWasFlushedError extends Error {
      constructor(clientTimestamp, serverTimestamp, message) {
          super(message);
          if (Error.captureStackTrace) {
              Error.captureStackTrace(this, ServerWasFlushedError);
          }
          this.clientTimestamp = clientTimestamp;
          this.serverTimestamp = serverTimestamp;
      }
  }
  function createUUIDSchema() {
      return {
          generate() {
              return uuid4();
          },
          validate(id) {
              return typeof id == "string" && RE_RECORD_ID.test(id);
          },
      };
  }
  function markStatus(record, status) {
      return Object.assign(Object.assign({}, record), { _status: status });
  }
  function markDeleted(record) {
      return markStatus(record, "deleted");
  }
  function markSynced(record) {
      return markStatus(record, "synced");
  }
  /**
   * Import a remote change into the local database.
   *
   * @param  {IDBTransactionProxy} transaction The transaction handler.
   * @param  {Object}              remote      The remote change object to import.
   * @param  {Array<String>}       localFields The list of fields that remain local.
   * @param  {String}              strategy    The {@link Collection.strategy}.
   * @return {Object}
   */
  function importChange(transaction, remote, localFields, strategy) {
      const local = transaction.get(remote.id);
      if (!local) {
          // Not found locally but remote change is marked as deleted; skip to
          // avoid recreation.
          if (remote.deleted) {
              return { type: "skipped", data: remote };
          }
          const synced = markSynced(remote);
          transaction.create(synced);
          return { type: "created", data: synced };
      }
      // Apply remote changes on local record.
      const synced = Object.assign(Object.assign({}, local), markSynced(remote));
      // With pull only, we don't need to compare records since we override them.
      if (strategy === Collection.strategy.PULL_ONLY) {
          if (remote.deleted) {
              transaction.delete(remote.id);
              return { type: "deleted", data: local };
          }
          transaction.update(synced);
          return { type: "updated", data: { old: local, new: synced } };
      }
      // With other sync strategies, we detect conflicts,
      // by comparing local and remote, ignoring local fields.
      const isIdentical = recordsEqual(local, remote, localFields);
      // Detect or ignore conflicts if record has also been modified locally.
      if (local._status !== "synced") {
          // Locally deleted, unsynced: scheduled for remote deletion.
          if (local._status === "deleted") {
              return { type: "skipped", data: local };
          }
          if (isIdentical) {
              // If records are identical, import anyway, so we bump the
              // local last_modified value from the server and set record
              // status to "synced".
              transaction.update(synced);
              return { type: "updated", data: { old: local, new: synced } };
          }
          if (local.last_modified !== undefined &&
              local.last_modified === remote.last_modified) {
              // If our local version has the same last_modified as the remote
              // one, this represents an object that corresponds to a resolved
              // conflict. Our local version represents the final output, so
              // we keep that one. (No transaction operation to do.)
              // But if our last_modified is undefined,
              // that means we've created the same object locally as one on
              // the server, which *must* be a conflict.
              return { type: "void" };
          }
          return {
              type: "conflicts",
              data: { type: "incoming", local: local, remote: remote },
          };
      }
      // Local record was synced.
      if (remote.deleted) {
          transaction.delete(remote.id);
          return { type: "deleted", data: local };
      }
      // Import locally.
      transaction.update(synced);
      // if identical, simply exclude it from all SyncResultObject lists
      const type = isIdentical ? "void" : "updated";
      return { type, data: { old: local, new: synced } };
  }
  /**
   * Abstracts a collection of records stored in the local database, providing
   * CRUD operations and synchronization helpers.
   */
  class Collection {
      /**
       * Constructor.
       *
       * Options:
       * - `{BaseAdapter} adapter` The DB adapter (default: `IDB`)
       *
       * @param  {String}    bucket  The bucket identifier.
       * @param  {String}    name    The collection name.
       * @param  {KintoBase} kinto   The Kinto instance.
       * @param  {Object}    options The options object.
       */
      constructor(bucket, name, kinto, options = {}) {
          this._bucket = bucket;
          this._name = name;
          this._lastModified = null;
          const DBAdapter = options.adapter || IDB;
          if (!DBAdapter) {
              throw new Error("No adapter provided");
          }
          const db = new DBAdapter(`${bucket}/${name}`, options.adapterOptions);
          if (!(db instanceof BaseAdapter)) {
              throw new Error("Unsupported adapter.");
          }
          // public properties
          /**
           * The db adapter instance
           * @type {BaseAdapter}
           */
          this.db = db;
          /**
           * The KintoBase instance.
           * @type {KintoBase}
           */
          this.kinto = kinto;
          /**
           * The event emitter instance.
           * @type {EventEmitter}
           */
          this.events = options.events;
          /**
           * The IdSchema instance.
           * @type {Object}
           */
          this.idSchema = this._validateIdSchema(options.idSchema);
          /**
           * The list of remote transformers.
           * @type {Array}
           */
          this.remoteTransformers = this._validateRemoteTransformers(options.remoteTransformers);
          /**
           * The list of hooks.
           * @type {Object}
           */
          this.hooks = this._validateHooks(options.hooks);
          /**
           * The list of fields names that will remain local.
           * @type {Array}
           */
          this.localFields = options.localFields || [];
      }
      /**
       * The HTTP client.
       * @type {KintoClient}
       */
      get api() {
          return this.kinto.api;
      }
      /**
       * The collection name.
       * @type {String}
       */
      get name() {
          return this._name;
      }
      /**
       * The bucket name.
       * @type {String}
       */
      get bucket() {
          return this._bucket;
      }
      /**
       * The last modified timestamp.
       * @type {Number}
       */
      get lastModified() {
          return this._lastModified;
      }
      /**
       * Synchronization strategies. Available strategies are:
       *
       * - `MANUAL`: Conflicts will be reported in a dedicated array.
       * - `SERVER_WINS`: Conflicts are resolved using remote data.
       * - `CLIENT_WINS`: Conflicts are resolved using local data.
       *
       * @type {Object}
       */
      static get strategy() {
          return {
              CLIENT_WINS: "client_wins",
              SERVER_WINS: "server_wins",
              PULL_ONLY: "pull_only",
              MANUAL: "manual",
          };
      }
      /**
       * Validates an idSchema.
       *
       * @param  {Object|undefined} idSchema
       * @return {Object}
       */
      _validateIdSchema(idSchema) {
          if (typeof idSchema === "undefined") {
              return createUUIDSchema();
          }
          if (typeof idSchema !== "object") {
              throw new Error("idSchema must be an object.");
          }
          else if (typeof idSchema.generate !== "function") {
              throw new Error("idSchema must provide a generate function.");
          }
          else if (typeof idSchema.validate !== "function") {
              throw new Error("idSchema must provide a validate function.");
          }
          return idSchema;
      }
      /**
       * Validates a list of remote transformers.
       *
       * @param  {Array|undefined} remoteTransformers
       * @return {Array}
       */
      _validateRemoteTransformers(remoteTransformers) {
          if (typeof remoteTransformers === "undefined") {
              return [];
          }
          if (!Array.isArray(remoteTransformers)) {
              throw new Error("remoteTransformers should be an array.");
          }
          return remoteTransformers.map(transformer => {
              if (typeof transformer !== "object") {
                  throw new Error("A transformer must be an object.");
              }
              else if (typeof transformer.encode !== "function") {
                  throw new Error("A transformer must provide an encode function.");
              }
              else if (typeof transformer.decode !== "function") {
                  throw new Error("A transformer must provide a decode function.");
              }
              return transformer;
          });
      }
      /**
       * Validate the passed hook is correct.
       *
       * @param {Array|undefined} hook.
       * @return {Array}
       **/
      _validateHook(hook) {
          if (!Array.isArray(hook)) {
              throw new Error("A hook definition should be an array of functions.");
          }
          return hook.map(fn => {
              if (typeof fn !== "function") {
                  throw new Error("A hook definition should be an array of functions.");
              }
              return fn;
          });
      }
      /**
       * Validates a list of hooks.
       *
       * @param  {Object|undefined} hooks
       * @return {Object}
       */
      _validateHooks(hooks) {
          if (typeof hooks === "undefined") {
              return {};
          }
          if (Array.isArray(hooks)) {
              throw new Error("hooks should be an object, not an array.");
          }
          if (typeof hooks !== "object") {
              throw new Error("hooks should be an object.");
          }
          const validatedHooks = {};
          for (const hook in hooks) {
              if (!AVAILABLE_HOOKS.includes(hook)) {
                  throw new Error("The hook should be one of " + AVAILABLE_HOOKS.join(", "));
              }
              validatedHooks[hook] = this._validateHook(hooks[hook]);
          }
          return validatedHooks;
      }
      /**
       * Deletes every records in the current collection and marks the collection as
       * never synced.
       *
       * @return {Promise}
       */
      async clear() {
          await this.db.clear();
          await this.db.saveMetadata(null);
          await this.db.saveLastModified(null);
          return { data: [], permissions: {} };
      }
      /**
       * Encodes a record.
       *
       * @param  {String} type   Either "remote" or "local".
       * @param  {Object} record The record object to encode.
       * @return {Promise}
       */
      _encodeRecord(type, record) {
          if (!this[`${type}Transformers`].length) {
              return Promise.resolve(record);
          }
          return waterfall(this[`${type}Transformers`].map(transformer => {
              return record => transformer.encode(record);
          }), record);
      }
      /**
       * Decodes a record.
       *
       * @param  {String} type   Either "remote" or "local".
       * @param  {Object} record The record object to decode.
       * @return {Promise}
       */
      _decodeRecord(type, record) {
          if (!this[`${type}Transformers`].length) {
              return Promise.resolve(record);
          }
          return waterfall(this[`${type}Transformers`].reverse().map(transformer => {
              return record => transformer.decode(record);
          }), record);
      }
      /**
       * Adds a record to the local database, asserting that none
       * already exist with this ID.
       *
       * Note: If either the `useRecordId` or `synced` options are true, then the
       * record object must contain the id field to be validated. If none of these
       * options are true, an id is generated using the current IdSchema; in this
       * case, the record passed must not have an id.
       *
       * Options:
       * - {Boolean} synced       Sets record status to "synced" (default: `false`).
       * - {Boolean} useRecordId  Forces the `id` field from the record to be used,
       *                          instead of one that is generated automatically
       *                          (default: `false`).
       *
       * @param  {Object} record
       * @param  {Object} options
       * @return {Promise}
       */
      create(record, options = { useRecordId: false, synced: false }) {
          // Validate the record and its ID (if any), even though this
          // validation is also done in the CollectionTransaction method,
          // because we need to pass the ID to preloadIds.
          const reject = msg => Promise.reject(new Error(msg));
          if (typeof record !== "object") {
              return reject("Record is not an object.");
          }
          if ((options.synced || options.useRecordId) &&
              !Object.prototype.hasOwnProperty.call(record, "id")) {
              return reject("Missing required Id; synced and useRecordId options require one");
          }
          if (!options.synced &&
              !options.useRecordId &&
              Object.prototype.hasOwnProperty.call(record, "id")) {
              return reject("Extraneous Id; can't create a record having one set.");
          }
          const newRecord = Object.assign(Object.assign({}, record), { id: options.synced || options.useRecordId
                  ? record.id
                  : this.idSchema.generate(record), _status: options.synced ? "synced" : "created" });
          if (!this.idSchema.validate(newRecord.id)) {
              return reject(`Invalid Id: ${newRecord.id}`);
          }
          return this.execute(txn => txn.create(newRecord), {
              preloadIds: [newRecord.id],
          }).catch(err => {
              if (options.useRecordId) {
                  throw new Error("Couldn't create record. It may have been virtually deleted.");
              }
              throw err;
          });
      }
      /**
       * Like {@link CollectionTransaction#update}, but wrapped in its own transaction.
       *
       * Options:
       * - {Boolean} synced: Sets record status to "synced" (default: false)
       * - {Boolean} patch:  Extends the existing record instead of overwriting it
       *   (default: false)
       *
       * @param  {Object} record
       * @param  {Object} options
       * @return {Promise}
       */
      update(record, options = { synced: false, patch: false }) {
          // Validate the record and its ID, even though this validation is
          // also done in the CollectionTransaction method, because we need
          // to pass the ID to preloadIds.
          if (typeof record !== "object") {
              return Promise.reject(new Error("Record is not an object."));
          }
          if (!Object.prototype.hasOwnProperty.call(record, "id")) {
              return Promise.reject(new Error("Cannot update a record missing id."));
          }
          if (!this.idSchema.validate(record.id)) {
              return Promise.reject(new Error(`Invalid Id: ${record.id}`));
          }
          return this.execute(txn => txn.update(record, options), {
              preloadIds: [record.id],
          });
      }
      /**
       * Like {@link CollectionTransaction#upsert}, but wrapped in its own transaction.
       *
       * @param  {Object} record
       * @return {Promise}
       */
      upsert(record) {
          // Validate the record and its ID, even though this validation is
          // also done in the CollectionTransaction method, because we need
          // to pass the ID to preloadIds.
          if (typeof record !== "object") {
              return Promise.reject(new Error("Record is not an object."));
          }
          if (!Object.prototype.hasOwnProperty.call(record, "id")) {
              return Promise.reject(new Error("Cannot update a record missing id."));
          }
          if (!this.idSchema.validate(record.id)) {
              return Promise.reject(new Error(`Invalid Id: ${record.id}`));
          }
          return this.execute(txn => txn.upsert(record), { preloadIds: [record.id] });
      }
      /**
       * Like {@link CollectionTransaction#get}, but wrapped in its own transaction.
       *
       * Options:
       * - {Boolean} includeDeleted: Include virtually deleted records.
       *
       * @param  {String} id
       * @param  {Object} options
       * @return {Promise}
       */
      get(id, options = { includeDeleted: false }) {
          return this.execute(txn => txn.get(id, options), { preloadIds: [id] });
      }
      /**
       * Like {@link CollectionTransaction#getAny}, but wrapped in its own transaction.
       *
       * @param  {String} id
       * @return {Promise}
       */
      getAny(id) {
          return this.execute(txn => txn.getAny(id), { preloadIds: [id] });
      }
      /**
       * Same as {@link Collection#delete}, but wrapped in its own transaction.
       *
       * Options:
       * - {Boolean} virtual: When set to `true`, doesn't actually delete the record,
       *   update its `_status` attribute to `deleted` instead (default: true)
       *
       * @param  {String} id       The record's Id.
       * @param  {Object} options  The options object.
       * @return {Promise}
       */
      delete(id, options = { virtual: true }) {
          return this.execute(transaction => {
              return transaction.delete(id, options);
          }, { preloadIds: [id] });
      }
      /**
       * Same as {@link Collection#deleteAll}, but wrapped in its own transaction, execulding the parameter.
       *
       * @return {Promise}
       */
      async deleteAll() {
          const { data } = await this.list({}, { includeDeleted: false });
          const recordIds = data.map(record => record.id);
          return this.execute(transaction => {
              return transaction.deleteAll(recordIds);
          }, { preloadIds: recordIds });
      }
      /**
       * The same as {@link CollectionTransaction#deleteAny}, but wrapped
       * in its own transaction.
       *
       * @param  {String} id       The record's Id.
       * @return {Promise}
       */
      deleteAny(id) {
          return this.execute(txn => txn.deleteAny(id), { preloadIds: [id] });
      }
      /**
       * Lists records from the local database.
       *
       * Params:
       * - {Object} filters Filter the results (default: `{}`).
       * - {String} order   The order to apply   (default: `-last_modified`).
       *
       * Options:
       * - {Boolean} includeDeleted: Include virtually deleted records.
       *
       * @param  {Object} params  The filters and order to apply to the results.
       * @param  {Object} options The options object.
       * @return {Promise}
       */
      async list(params = {}, options = { includeDeleted: false }) {
          params = Object.assign({ order: "-last_modified", filters: {} }, params);
          const results = await this.db.list(params);
          let data = results;
          if (!options.includeDeleted) {
              data = results.filter(record => record._status !== "deleted");
          }
          return { data, permissions: {} };
      }
      /**
       * Imports remote changes into the local database.
       * This method is in charge of detecting the conflicts, and resolve them
       * according to the specified strategy.
       * @param  {SyncResultObject} syncResultObject The sync result object.
       * @param  {Array}            decodedChanges   The list of changes to import in the local database.
       * @param  {String}           strategy         The {@link Collection.strategy} (default: MANUAL)
       * @return {Promise}
       */
      async importChanges(syncResultObject, decodedChanges, strategy = Collection.strategy.MANUAL) {
          // Retrieve records matching change ids.
          try {
              for (let i = 0; i < decodedChanges.length; i += IMPORT_CHUNK_SIZE) {
                  const slice = decodedChanges.slice(i, i + IMPORT_CHUNK_SIZE);
                  const { imports, resolved } = await this.db.execute(transaction => {
                      const imports = slice.map(remote => {
                          // Store remote change into local database.
                          return importChange(transaction, remote, this.localFields, strategy);
                      });
                      const conflicts = imports
                          .filter(i => i.type === "conflicts")
                          .map(i => i.data);
                      const resolved = this._handleConflicts(transaction, conflicts, strategy);
                      return { imports, resolved };
                  }, { preload: slice.map(record => record.id) });
                  // Lists of created/updated/deleted records
                  imports.forEach(({ type, data }) => syncResultObject.add(type, data));
                  // Automatically resolved conflicts (if not manual)
                  if (resolved.length > 0) {
                      syncResultObject.reset("conflicts").add("resolved", resolved);
                  }
              }
          }
          catch (err) {
              const data = {
                  type: "incoming",
                  message: err.message,
                  stack: err.stack,
              };
              // XXX one error of the whole transaction instead of per atomic op
              syncResultObject.add("errors", data);
          }
          return syncResultObject;
      }
      /**
       * Imports the responses of pushed changes into the local database.
       * Basically it stores the timestamp assigned by the server into the local
       * database.
       * @param  {SyncResultObject} syncResultObject The sync result object.
       * @param  {Array}            toApplyLocally   The list of changes to import in the local database.
       * @param  {Array}            conflicts        The list of conflicts that have to be resolved.
       * @param  {String}           strategy         The {@link Collection.strategy}.
       * @return {Promise}
       */
      async _applyPushedResults(syncResultObject, toApplyLocally, conflicts, strategy = Collection.strategy.MANUAL) {
          const toDeleteLocally = toApplyLocally.filter(r => r.deleted);
          const toUpdateLocally = toApplyLocally.filter(r => !r.deleted);
          const { published, resolved } = await this.db.execute(transaction => {
              const updated = toUpdateLocally.map(record => {
                  const synced = markSynced(record);
                  transaction.update(synced);
                  return synced;
              });
              const deleted = toDeleteLocally.map(record => {
                  transaction.delete(record.id);
                  // Amend result data with the deleted attribute set
                  return { id: record.id, deleted: true };
              });
              const published = updated.concat(deleted);
              // Handle conflicts, if any
              const resolved = this._handleConflicts(transaction, conflicts, strategy);
              return { published, resolved };
          });
          syncResultObject.add("published", published);
          if (resolved.length > 0) {
              syncResultObject
                  .reset("conflicts")
                  .reset("resolved")
                  .add("resolved", resolved);
          }
          return syncResultObject;
      }
      /**
       * Handles synchronization conflicts according to specified strategy.
       *
       * @param  {SyncResultObject} result    The sync result object.
       * @param  {String}           strategy  The {@link Collection.strategy}.
       * @return {Promise<Array<Object>>} The resolved conflicts, as an
       *    array of {accepted, rejected} objects
       */
      _handleConflicts(transaction, conflicts, strategy) {
          if (strategy === Collection.strategy.MANUAL) {
              return [];
          }
          return conflicts.map(conflict => {
              const resolution = strategy === Collection.strategy.CLIENT_WINS
                  ? conflict.local
                  : conflict.remote;
              const rejected = strategy === Collection.strategy.CLIENT_WINS
                  ? conflict.remote
                  : conflict.local;
              let accepted, status, id;
              if (resolution === null) {
                  // We "resolved" with the server-side deletion. Delete locally.
                  // This only happens during SERVER_WINS because the local
                  // version of a record can never be null.
                  // We can get "null" from the remote side if we got a conflict
                  // and there is no remote version available; see kinto-http.js
                  // batch.js:aggregate.
                  transaction.delete(conflict.local.id);
                  accepted = null;
                  // The record was deleted, but that status is "synced" with
                  // the server, so we don't need to push the change.
                  status = "synced";
                  id = conflict.local.id;
              }
              else {
                  const updated = this._resolveRaw(conflict, resolution);
                  transaction.update(updated);
                  accepted = updated;
                  status = updated._status;
                  id = updated.id;
              }
              return { rejected, accepted, id, _status: status };
          });
      }
      /**
       * Execute a bunch of operations in a transaction.
       *
       * This transaction should be atomic -- either all of its operations
       * will succeed, or none will.
       *
       * The argument to this function is itself a function which will be
       * called with a {@link CollectionTransaction}. Collection methods
       * are available on this transaction, but instead of returning
       * promises, they are synchronous. execute() returns a Promise whose
       * value will be the return value of the provided function.
       *
       * Most operations will require access to the record itself, which
       * must be preloaded by passing its ID in the preloadIds option.
       *
       * Options:
       * - {Array} preloadIds: list of IDs to fetch at the beginning of
       *   the transaction
       *
       * @return {Promise} Resolves with the result of the given function
       *    when the transaction commits.
       */
      execute(doOperations, { preloadIds = [] } = {}) {
          for (const id of preloadIds) {
              if (!this.idSchema.validate(id)) {
                  return Promise.reject(Error(`Invalid Id: ${id}`));
              }
          }
          return this.db.execute(transaction => {
              const txn = new CollectionTransaction(this, transaction);
              const result = doOperations(txn);
              txn.emitEvents();
              return result;
          }, { preload: preloadIds });
      }
      /**
       * Resets the local records as if they were never synced; existing records are
       * marked as newly created, deleted records are dropped.
       *
       * A next call to {@link Collection.sync} will thus republish the whole
       * content of the local collection to the server.
       *
       * @return {Promise} Resolves with the number of processed records.
       */
      async resetSyncStatus() {
          const unsynced = await this.list({ filters: { _status: ["deleted", "synced"] }, order: "" }, { includeDeleted: true });
          await this.db.execute(transaction => {
              unsynced.data.forEach(record => {
                  if (record._status === "deleted") {
                      // Garbage collect deleted records.
                      transaction.delete(record.id);
                  }
                  else {
                      // Records that were synced become «created».
                      transaction.update(Object.assign(Object.assign({}, record), { last_modified: undefined, _status: "created" }));
                  }
              });
          });
          this._lastModified = null;
          await this.db.saveLastModified(null);
          return unsynced.data.length;
      }
      /**
       * Returns an object containing two lists:
       *
       * - `toDelete`: unsynced deleted records we can safely delete;
       * - `toSync`: local updates to send to the server.
       *
       * @return {Promise}
       */
      async gatherLocalChanges() {
          const unsynced = await this.list({
              filters: { _status: ["created", "updated"] },
              order: "",
          });
          const deleted = await this.list({ filters: { _status: "deleted" }, order: "" }, { includeDeleted: true });
          return await Promise.all(unsynced.data
              .concat(deleted.data)
              .map(this._encodeRecord.bind(this, "remote")));
      }
      /**
       * Fetch remote changes, import them to the local database, and handle
       * conflicts according to `options.strategy`. Then, updates the passed
       * {@link SyncResultObject} with import results.
       *
       * Options:
       * - {String} strategy: The selected sync strategy.
       * - {String} expectedTimestamp: A timestamp to use as a "cache busting" query parameter.
       * - {Array<String>} exclude: A list of record ids to exclude from pull.
       * - {Object} headers: The HTTP headers to use in the request.
       * - {int} retry: The number of retries to do if the HTTP request fails.
       * - {int} lastModified: The timestamp to use in `?_since` query.
       *
       * @param  {KintoClient.Collection} client           Kinto client Collection instance.
       * @param  {SyncResultObject}       syncResultObject The sync result object.
       * @param  {Object}                 options          The options object.
       * @return {Promise}
       */
      async pullChanges(client, syncResultObject, options = {}) {
          if (!syncResultObject.ok) {
              return syncResultObject;
          }
          const since = this.lastModified
              ? this.lastModified
              : await this.db.getLastModified();
          options = Object.assign({ strategy: Collection.strategy.MANUAL, lastModified: since, headers: {} }, options);
          // Optionally ignore some records when pulling for changes.
          // (avoid redownloading our own changes on last step of #sync())
          let filters;
          if (options.exclude) {
              // Limit the list of excluded records to the first 50 records in order
              // to remain under de-facto URL size limit (~2000 chars).
              // http://stackoverflow.com/questions/417142/what-is-the-maximum-length-of-a-url-in-different-browsers/417184#417184
              const exclude_id = options.exclude
                  .slice(0, 50)
                  .map(r => r.id)
                  .join(",");
              filters = { exclude_id };
          }
          if (options.expectedTimestamp) {
              filters = Object.assign(Object.assign({}, filters), { _expected: options.expectedTimestamp });
          }
          // First fetch remote changes from the server
          const { data, last_modified } = await client.listRecords({
              // Since should be ETag (see https://github.com/Kinto/kinto.js/issues/356)
              since: options.lastModified ? `${options.lastModified}` : undefined,
              headers: options.headers,
              retry: options.retry,
              // Fetch every page by default (FIXME: option to limit pages, see #277)
              pages: Infinity,
              filters,
          });
          // last_modified is the ETag header value (string).
          // For retro-compatibility with first kinto.js versions
          // parse it to integer.
          const unquoted = last_modified ? parseInt(last_modified, 10) : undefined;
          // Check if server was flushed.
          // This is relevant for the Kinto demo server
          // (and thus for many new comers).
          const localSynced = options.lastModified;
          const serverChanged = unquoted > options.lastModified;
          const emptyCollection = data.length === 0;
          if (!options.exclude && localSynced && serverChanged && emptyCollection) {
              const e = new ServerWasFlushedError(localSynced, unquoted, "Server has been flushed. Client Side Timestamp: " +
                  localSynced +
                  " Server Side Timestamp: " +
                  unquoted);
              throw e;
          }
          // Atomic updates are not sensible here because unquoted is not
          // computed as a function of syncResultObject.lastModified.
          // eslint-disable-next-line require-atomic-updates
          syncResultObject.lastModified = unquoted;
          // Decode incoming changes.
          const decodedChanges = await Promise.all(data.map(change => {
              return this._decodeRecord("remote", change);
          }));
          // Hook receives decoded records.
          const payload = { lastModified: unquoted, changes: decodedChanges };
          const afterHooks = await this.applyHook("incoming-changes", payload);
          // No change, nothing to import.
          if (afterHooks.changes.length > 0) {
              // Reflect these changes locally
              await this.importChanges(syncResultObject, afterHooks.changes, options.strategy);
          }
          return syncResultObject;
      }
      applyHook(hookName, payload) {
          if (typeof this.hooks[hookName] == "undefined") {
              return Promise.resolve(payload);
          }
          return waterfall(this.hooks[hookName].map(hook => {
              return record => {
                  const result = hook(payload, this);
                  const resultThenable = result && typeof result.then === "function";
                  const resultChanges = result && Object.prototype.hasOwnProperty.call(result, "changes");
                  if (!(resultThenable || resultChanges)) {
                      throw new Error(`Invalid return value for hook: ${JSON.stringify(result)} has no 'then()' or 'changes' properties`);
                  }
                  return result;
              };
          }), payload);
      }
      /**
       * Publish local changes to the remote server and updates the passed
       * {@link SyncResultObject} with publication results.
       *
       * Options:
       * - {String} strategy: The selected sync strategy.
       * - {Object} headers: The HTTP headers to use in the request.
       * - {int} retry: The number of retries to do if the HTTP request fails.
       *
       * @param  {KintoClient.Collection} client           Kinto client Collection instance.
       * @param  {SyncResultObject}       syncResultObject The sync result object.
       * @param  {Object}                 changes          The change object.
       * @param  {Array}                  changes.toDelete The list of records to delete.
       * @param  {Array}                  changes.toSync   The list of records to create/update.
       * @param  {Object}                 options          The options object.
       * @return {Promise}
       */
      async pushChanges(client, changes, syncResultObject, options = {}) {
          if (!syncResultObject.ok) {
              return syncResultObject;
          }
          const safe = !options.strategy || options.strategy !== Collection.CLIENT_WINS;
          const toDelete = changes.filter(r => r._status == "deleted");
          const toSync = changes.filter(r => r._status != "deleted");
          // Perform a batch request with every changes.
          const synced = await client.batch(batch => {
              toDelete.forEach(r => {
                  // never published locally deleted records should not be pusblished
                  if (r.last_modified) {
                      batch.deleteRecord(r);
                  }
              });
              toSync.forEach(r => {
                  // Clean local fields (like _status) before sending to server.
                  const published = this.cleanLocalFields(r);
                  if (r._status === "created") {
                      batch.createRecord(published);
                  }
                  else {
                      batch.updateRecord(published);
                  }
              });
          }, {
              headers: options.headers,
              retry: options.retry,
              safe,
              aggregate: true,
          });
          // Store outgoing errors into sync result object
          syncResultObject.add("errors", synced.errors.map(e => (Object.assign(Object.assign({}, e), { type: "outgoing" }))));
          // Store outgoing conflicts into sync result object
          const conflicts = [];
          for (const { type, local, remote } of synced.conflicts) {
              // Note: we ensure that local data are actually available, as they may
              // be missing in the case of a published deletion.
              const safeLocal = (local && local.data) || { id: remote.id };
              const realLocal = await this._decodeRecord("remote", safeLocal);
              // We can get "null" from the remote side if we got a conflict
              // and there is no remote version available; see kinto-http.js
              // batch.js:aggregate.
              const realRemote = remote && (await this._decodeRecord("remote", remote));
              const conflict = { type, local: realLocal, remote: realRemote };
              conflicts.push(conflict);
          }
          syncResultObject.add("conflicts", conflicts);
          // Records that must be deleted are either deletions that were pushed
          // to server (published) or deleted records that were never pushed (skipped).
          const missingRemotely = synced.skipped.map(r => (Object.assign(Object.assign({}, r), { deleted: true })));
          // For created and updated records, the last_modified coming from server
          // will be stored locally.
          // Reflect publication results locally using the response from
          // the batch request.
          const published = synced.published.map(c => c.data);
          const toApplyLocally = published.concat(missingRemotely);
          // Apply the decode transformers, if any
          const decoded = await Promise.all(toApplyLocally.map(record => {
              return this._decodeRecord("remote", record);
          }));
          // We have to update the local records with the responses of the server
          // (eg. last_modified values etc.).
          if (decoded.length > 0 || conflicts.length > 0) {
              await this._applyPushedResults(syncResultObject, decoded, conflicts, options.strategy);
          }
          return syncResultObject;
      }
      /**
       * Return a copy of the specified record without the local fields.
       *
       * @param  {Object} record  A record with potential local fields.
       * @return {Object}
       */
      cleanLocalFields(record) {
          const localKeys = RECORD_FIELDS_TO_CLEAN.concat(this.localFields);
          return omitKeys(record, localKeys);
      }
      /**
       * Resolves a conflict, updating local record according to proposed
       * resolution — keeping remote record `last_modified` value as a reference for
       * further batch sending.
       *
       * @param  {Object} conflict   The conflict object.
       * @param  {Object} resolution The proposed record.
       * @return {Promise}
       */
      resolve(conflict, resolution) {
          return this.db.execute(transaction => {
              const updated = this._resolveRaw(conflict, resolution);
              transaction.update(updated);
              return { data: updated, permissions: {} };
          });
      }
      /**
       * @private
       */
      _resolveRaw(conflict, resolution) {
          const resolved = Object.assign(Object.assign({}, resolution), {
              // Ensure local record has the latest authoritative timestamp
              last_modified: conflict.remote && conflict.remote.last_modified });
          // If the resolution object is strictly equal to the
          // remote record, then we can mark it as synced locally.
          // Otherwise, mark it as updated (so that the resolution is pushed).
          const synced = deepEqual(resolved, conflict.remote);
          return markStatus(resolved, synced ? "synced" : "updated");
      }
      /**
       * Synchronize remote and local data. The promise will resolve with a
       * {@link SyncResultObject}, though will reject:
       *
       * - if the server is currently backed off;
       * - if the server has been detected flushed.
       *
       * Options:
       * - {Object} headers: HTTP headers to attach to outgoing requests.
       * - {String} expectedTimestamp: A timestamp to use as a "cache busting" query parameter.
       * - {Number} retry: Number of retries when server fails to process the request (default: 1).
       * - {Collection.strategy} strategy: See {@link Collection.strategy}.
       * - {Boolean} ignoreBackoff: Force synchronization even if server is currently
       *   backed off.
       * - {String} bucket: The remove bucket id to use (default: null)
       * - {String} collection: The remove collection id to use (default: null)
       * - {String} remote The remote Kinto server endpoint to use (default: null).
       *
       * @param  {Object} options Options.
       * @return {Promise}
       * @throws {Error} If an invalid remote option is passed.
       */
      async sync(options = {
          strategy: Collection.strategy.MANUAL,
          headers: {},
          retry: 1,
          ignoreBackoff: false,
          bucket: null,
          collection: null,
          remote: null,
          expectedTimestamp: null,
      }) {
          options = Object.assign(Object.assign({}, options), { bucket: options.bucket || this.bucket, collection: options.collection || this.name });
          const previousRemote = this.api.remote;
          if (options.remote) {
              // Note: setting the remote ensures it's valid, throws when invalid.
              this.api.remote = options.remote;
          }
          if (!options.ignoreBackoff && this.api.backoff > 0) {
              const seconds = Math.ceil(this.api.backoff / 1000);
              return Promise.reject(new Error(`Server is asking clients to back off; retry in ${seconds}s or use the ignoreBackoff option.`));
          }
          const client = this.api
              .bucket(options.bucket)
              .collection(options.collection);
          const result = new SyncResultObject();
          try {
              // Fetch collection metadata.
              await this.pullMetadata(client, options);
              // Fetch last changes from the server.
              await this.pullChanges(client, result, options);
              const { lastModified } = result;
              if (options.strategy != Collection.strategy.PULL_ONLY) {
                  // Fetch local changes
                  const toSync = await this.gatherLocalChanges();
                  // Publish local changes and pull local resolutions
                  await this.pushChanges(client, toSync, result, options);
                  // Publish local resolution of push conflicts to server (on CLIENT_WINS)
                  const resolvedUnsynced = result.resolved.filter(r => r._status !== "synced");
                  if (resolvedUnsynced.length > 0) {
                      const resolvedEncoded = await Promise.all(resolvedUnsynced.map(resolution => {
                          let record = resolution.accepted;
                          if (record === null) {
                              record = { id: resolution.id, _status: resolution._status };
                          }
                          return this._encodeRecord("remote", record);
                      }));
                      await this.pushChanges(client, resolvedEncoded, result, options);
                  }
                  // Perform a last pull to catch changes that occured after the last pull,
                  // while local changes were pushed. Do not do it nothing was pushed.
                  if (result.published.length > 0) {
                      // Avoid redownloading our own changes during the last pull.
                      const pullOpts = Object.assign(Object.assign({}, options), { lastModified, exclude: result.published });
                      await this.pullChanges(client, result, pullOpts);
                  }
              }
              // Don't persist lastModified value if any conflict or error occured
              if (result.ok) {
                  // No conflict occured, persist collection's lastModified value
                  this._lastModified = await this.db.saveLastModified(result.lastModified);
              }
          }
          catch (e) {
              this.events.emit("sync:error", Object.assign(Object.assign({}, options), { error: e }));
              throw e;
          }
          finally {
              // Ensure API default remote is reverted if a custom one's been used
              this.api.remote = previousRemote;
          }
          this.events.emit("sync:success", Object.assign(Object.assign({}, options), { result }));
          return result;
      }
      /**
       * Load a list of records already synced with the remote server.
       *
       * The local records which are unsynced or whose timestamp is either missing
       * or superior to those being loaded will be ignored.
       *
       * @deprecated Use {@link importBulk} instead.
       * @param  {Array} records The previously exported list of records to load.
       * @return {Promise} with the effectively imported records.
       */
      async loadDump(records) {
          return this.importBulk(records);
      }
      /**
       * Load a list of records already synced with the remote server.
       *
       * The local records which are unsynced or whose timestamp is either missing
       * or superior to those being loaded will be ignored.
       *
       * @param  {Array} records The previously exported list of records to load.
       * @return {Promise} with the effectively imported records.
       */
      async importBulk(records) {
          if (!Array.isArray(records)) {
              throw new Error("Records is not an array.");
          }
          for (const record of records) {
              if (!Object.prototype.hasOwnProperty.call(record, "id") ||
                  !this.idSchema.validate(record.id)) {
                  throw new Error("Record has invalid ID: " + JSON.stringify(record));
              }
              if (!record.last_modified) {
                  throw new Error("Record has no last_modified value: " + JSON.stringify(record));
              }
          }
          // Fetch all existing records from local database,
          // and skip those who are newer or not marked as synced.
          // XXX filter by status / ids in records
          const { data } = await this.list({}, { includeDeleted: true });
          const existingById = data.reduce((acc, record) => {
              acc[record.id] = record;
              return acc;
          }, {});
          const newRecords = records.filter(record => {
              const localRecord = existingById[record.id];
              const shouldKeep =
              // No local record with this id.
              localRecord === undefined ||
                  // Or local record is synced
                  (localRecord._status === "synced" &&
                      // And was synced from server
                      localRecord.last_modified !== undefined &&
                      // And is older than imported one.
                      record.last_modified > localRecord.last_modified);
              return shouldKeep;
          });
          return await this.db.importBulk(newRecords.map(markSynced));
      }
      async pullMetadata(client, options = {}) {
          const { expectedTimestamp, headers } = options;
          const query = expectedTimestamp
              ? { query: { _expected: expectedTimestamp } }
              : undefined;
          const metadata = await client.getData(Object.assign(Object.assign({}, query), { headers }));
          return this.db.saveMetadata(metadata);
      }
      async metadata() {
          return this.db.getMetadata();
      }
  }
  /**
   * A Collection-oriented wrapper for an adapter's transaction.
   *
   * This defines the high-level functions available on a collection.
   * The collection itself offers functions of the same name. These will
   * perform just one operation in its own transaction.
   */
  class CollectionTransaction {
      constructor(collection, adapterTransaction) {
          this.collection = collection;
          this.adapterTransaction = adapterTransaction;
          this._events = [];
      }
      _queueEvent(action, payload) {
          this._events.push({ action, payload });
      }
      /**
       * Emit queued events, to be called once every transaction operations have
       * been executed successfully.
       */
      emitEvents() {
          for (const { action, payload } of this._events) {
              this.collection.events.emit(action, payload);
          }
          if (this._events.length > 0) {
              const targets = this._events.map(({ action, payload }) => (Object.assign({ action }, payload)));
              this.collection.events.emit("change", { targets });
          }
          this._events = [];
      }
      /**
       * Retrieve a record by its id from the local database, or
       * undefined if none exists.
       *
       * This will also return virtually deleted records.
       *
       * @param  {String} id
       * @return {Object}
       */
      getAny(id) {
          const record = this.adapterTransaction.get(id);
          return { data: record, permissions: {} };
      }
      /**
       * Retrieve a record by its id from the local database.
       *
       * Options:
       * - {Boolean} includeDeleted: Include virtually deleted records.
       *
       * @param  {String} id
       * @param  {Object} options
       * @return {Object}
       */
      get(id, options = { includeDeleted: false }) {
          const res = this.getAny(id);
          if (!res.data ||
              (!options.includeDeleted && res.data._status === "deleted")) {
              throw new Error(`Record with id=${id} not found.`);
          }
          return res;
      }
      /**
       * Deletes a record from the local database.
       *
       * Options:
       * - {Boolean} virtual: When set to `true`, doesn't actually delete the record,
       *   update its `_status` attribute to `deleted` instead (default: true)
       *
       * @param  {String} id       The record's Id.
       * @param  {Object} options  The options object.
       * @return {Object}
       */
      delete(id, options = { virtual: true }) {
          // Ensure the record actually exists.
          const existing = this.adapterTransaction.get(id);
          const alreadyDeleted = existing && existing._status == "deleted";
          if (!existing || (alreadyDeleted && options.virtual)) {
              throw new Error(`Record with id=${id} not found.`);
          }
          // Virtual updates status.
          if (options.virtual) {
              this.adapterTransaction.update(markDeleted(existing));
          }
          else {
              // Delete for real.
              this.adapterTransaction.delete(id);
          }
          this._queueEvent("delete", { data: existing });
          return { data: existing, permissions: {} };
      }
      /**
       * Soft delete all records from the local database.
       *
       * @param  {Array} ids        Array of non-deleted Record Ids.
       * @return {Object}
       */
      deleteAll(ids) {
          const existingRecords = [];
          ids.forEach(id => {
              existingRecords.push(this.adapterTransaction.get(id));
              this.delete(id);
          });
          this._queueEvent("deleteAll", { data: existingRecords });
          return { data: existingRecords, permissions: {} };
      }
      /**
       * Deletes a record from the local database, if any exists.
       * Otherwise, do nothing.
       *
       * @param  {String} id       The record's Id.
       * @return {Object}
       */
      deleteAny(id) {
          const existing = this.adapterTransaction.get(id);
          if (existing) {
              this.adapterTransaction.update(markDeleted(existing));
              this._queueEvent("delete", { data: existing });
          }
          return { data: Object.assign({ id }, existing), deleted: !!existing, permissions: {} };
      }
      /**
       * Adds a record to the local database, asserting that none
       * already exist with this ID.
       *
       * @param  {Object} record, which must contain an ID
       * @return {Object}
       */
      create(record) {
          if (typeof record !== "object") {
              throw new Error("Record is not an object.");
          }
          if (!Object.prototype.hasOwnProperty.call(record, "id")) {
              throw new Error("Cannot create a record missing id");
          }
          if (!this.collection.idSchema.validate(record.id)) {
              throw new Error(`Invalid Id: ${record.id}`);
          }
          this.adapterTransaction.create(record);
          this._queueEvent("create", { data: record });
          return { data: record, permissions: {} };
      }
      /**
       * Updates a record from the local database.
       *
       * Options:
       * - {Boolean} synced: Sets record status to "synced" (default: false)
       * - {Boolean} patch:  Extends the existing record instead of overwriting it
       *   (default: false)
       *
       * @param  {Object} record
       * @param  {Object} options
       * @return {Object}
       */
      update(record, options = { synced: false, patch: false }) {
          if (typeof record !== "object") {
              throw new Error("Record is not an object.");
          }
          if (!Object.prototype.hasOwnProperty.call(record, "id")) {
              throw new Error("Cannot update a record missing id.");
          }
          if (!this.collection.idSchema.validate(record.id)) {
              throw new Error(`Invalid Id: ${record.id}`);
          }
          const oldRecord = this.adapterTransaction.get(record.id);
          if (!oldRecord) {
              throw new Error(`Record with id=${record.id} not found.`);
          }
          const newRecord = options.patch ? Object.assign(Object.assign({}, oldRecord), record) : record;
          const updated = this._updateRaw(oldRecord, newRecord, options);
          this.adapterTransaction.update(updated);
          this._queueEvent("update", { data: updated, oldRecord });
          return { data: updated, oldRecord, permissions: {} };
      }
      /**
       * Lower-level primitive for updating a record while respecting
       * _status and last_modified.
       *
       * @param  {Object} oldRecord: the record retrieved from the DB
       * @param  {Object} newRecord: the record to replace it with
       * @return {Object}
       */
      _updateRaw(oldRecord, newRecord, { synced = false } = {}) {
          const updated = Object.assign({}, newRecord);
          // Make sure to never loose the existing timestamp.
          if (oldRecord && oldRecord.last_modified && !updated.last_modified) {
              updated.last_modified = oldRecord.last_modified;
          }
          // If only local fields have changed, then keep record as synced.
          // If status is created, keep record as created.
          // If status is deleted, mark as updated.
          const isIdentical = oldRecord &&
              recordsEqual(oldRecord, updated, this.collection.localFields);
          const keepSynced = isIdentical && oldRecord._status == "synced";
          const neverSynced = !oldRecord || (oldRecord && oldRecord._status == "created");
          const newStatus = keepSynced || synced ? "synced" : neverSynced ? "created" : "updated";
          return markStatus(updated, newStatus);
      }
      /**
       * Upsert a record into the local database.
       *
       * This record must have an ID.
       *
       * If a record with this ID already exists, it will be replaced.
       * Otherwise, this record will be inserted.
       *
       * @param  {Object} record
       * @return {Object}
       */
      upsert(record) {
          if (typeof record !== "object") {
              throw new Error("Record is not an object.");
          }
          if (!Object.prototype.hasOwnProperty.call(record, "id")) {
              throw new Error("Cannot update a record missing id.");
          }
          if (!this.collection.idSchema.validate(record.id)) {
              throw new Error(`Invalid Id: ${record.id}`);
          }
          let oldRecord = this.adapterTransaction.get(record.id);
          const updated = this._updateRaw(oldRecord, record);
          this.adapterTransaction.update(updated);
          // Don't return deleted records -- pretend they are gone
          if (oldRecord && oldRecord._status == "deleted") {
              oldRecord = undefined;
          }
          if (oldRecord) {
              this._queueEvent("update", { data: updated, oldRecord });
          }
          else {
              this._queueEvent("create", { data: updated });
          }
          return { data: updated, oldRecord, permissions: {} };
      }
  }

  const DEFAULT_BUCKET_NAME = "default";
  const DEFAULT_REMOTE = "http://localhost:8888/v1";
  const DEFAULT_RETRY = 1;
  /**
   * KintoBase class.
   */
  class KintoBase {
      /**
       * Provides a public access to the base adapter class. Users can create a
       * custom DB adapter by extending {@link BaseAdapter}.
       *
       * @type {Object}
       */
      static get adapters() {
          return {
              BaseAdapter: BaseAdapter,
          };
      }
      /**
       * Synchronization strategies. Available strategies are:
       *
       * - `MANUAL`: Conflicts will be reported in a dedicated array.
       * - `SERVER_WINS`: Conflicts are resolved using remote data.
       * - `CLIENT_WINS`: Conflicts are resolved using local data.
       *
       * @type {Object}
       */
      static get syncStrategy() {
          return Collection.strategy;
      }
      /**
       * Constructor.
       *
       * Options:
       * - `{String}`       `remote`         The server URL to use.
       * - `{String}`       `bucket`         The collection bucket name.
       * - `{EventEmitter}` `events`         Events handler.
       * - `{BaseAdapter}`  `adapter`        The base DB adapter class.
       * - `{Object}`       `adapterOptions` Options given to the adapter.
       * - `{Object}`       `headers`        The HTTP headers to use.
       * - `{Object}`       `retry`          Number of retries when the server fails to process the request (default: `1`)
       * - `{String}`       `requestMode`    The HTTP CORS mode to use.
       * - `{Number}`       `timeout`        The requests timeout in ms (default: `5000`).
       *
       * @param  {Object} options The options object.
       */
      constructor(options = {}) {
          const defaults = {
              bucket: DEFAULT_BUCKET_NAME,
              remote: DEFAULT_REMOTE,
              retry: DEFAULT_RETRY,
          };
          this._options = Object.assign(Object.assign({}, defaults), options);
          if (!this._options.adapter) {
              throw new Error("No adapter provided");
          }
          this._api = null;
          /**
           * The event emitter instance.
           * @type {EventEmitter}
           */
          this.events = this._options.events;
      }
      /**
       * The kinto HTTP client instance.
       * @type {KintoClient}
       */
      get api() {
          const { events, headers, remote, requestMode, retry, timeout, } = this._options;
          if (!this._api) {
              this._api = new this.ApiClass(remote, {
                  events,
                  headers,
                  requestMode,
                  retry,
                  timeout,
              });
          }
          return this._api;
      }
      /**
       * Creates a {@link Collection} instance. The second (optional) parameter
       * will set collection-level options like e.g. `remoteTransformers`.
       *
       * @param  {String} collName The collection name.
       * @param  {Object} [options={}]                 Extra options or override client's options.
       * @param  {Object} [options.idSchema]           IdSchema instance (default: UUID)
       * @param  {Object} [options.remoteTransformers] Array<RemoteTransformer> (default: `[]`])
       * @param  {Object} [options.hooks]              Array<Hook> (default: `[]`])
       * @param  {Object} [options.localFields]        Array<Field> (default: `[]`])
       * @return {Collection}
       */
      collection(collName, options = {}) {
          if (!collName) {
              throw new Error("missing collection name");
          }
          const { bucket, events, adapter, adapterOptions } = Object.assign(Object.assign({}, this._options), options);
          const { idSchema, remoteTransformers, hooks, localFields } = options;
          return new Collection(bucket, collName, this, {
              events,
              adapter,
              adapterOptions,
              idSchema,
              remoteTransformers,
              hooks,
              localFields,
          });
      }
  }

  /*
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  const { setTimeout, clearTimeout } = ChromeUtils.importESModule("resource://gre/modules/Timer.sys.mjs");
  const { XPCOMUtils } = ChromeUtils.importESModule("resource://gre/modules/XPCOMUtils.sys.mjs");
  XPCOMUtils.defineLazyGlobalGetters(global, ["fetch", "indexedDB"]);
  ChromeUtils.defineESModuleGetters(global, {
      EventEmitter: "resource://gre/modules/EventEmitter.sys.mjs"
  });
  // Use standalone kinto-http module landed in FFx.
  ChromeUtils.defineModuleGetter(global, "KintoHttpClient", "resource://services-common/kinto-http-client.js");
  XPCOMUtils.defineLazyGetter(global, "generateUUID", () => {
      const { generateUUID } = Cc["@mozilla.org/uuid-generator;1"].getService(Ci.nsIUUIDGenerator);
      return generateUUID;
  });
  class Kinto extends KintoBase {
      static get adapters() {
          return {
              BaseAdapter,
              IDB,
          };
      }
      get ApiClass() {
          return KintoHttpClient;
      }
      constructor(options = {}) {
          const events = {};
          EventEmitter.decorate(events);
          const defaults = {
              adapter: IDB,
              events,
          };
          super(Object.assign(Object.assign({}, defaults), options));
      }
      collection(collName, options = {}) {
          const idSchema = {
              validate(id) {
                  return typeof id == "string" && RE_RECORD_ID.test(id);
              },
              generate() {
                  return generateUUID()
                      .toString()
                      .replace(/[{}]/g, "");
              },
          };
          return super.collection(collName, Object.assign({ idSchema }, options));
      }
  }

  return Kinto;

})));