/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

import { XPCOMUtils } from "resource://gre/modules/XPCOMUtils.sys.mjs";
import { BaseFeature } from "resource:///modules/urlbar/private/BaseFeature.sys.mjs";

const lazy = {};

ChromeUtils.defineESModuleGetters(lazy, {
  EventEmitter: "resource://gre/modules/EventEmitter.sys.mjs",
  TaskQueue: "resource:///modules/UrlbarUtils.sys.mjs",
  UrlbarPrefs: "resource:///modules/UrlbarPrefs.sys.mjs",
});

XPCOMUtils.defineLazyModuleGetters(lazy, {
  RemoteSettings: "resource://services-settings/remote-settings.js",
});

const RS_COLLECTION = "quicksuggest";

// Categories that should show "Firefox Suggest" instead of "Sponsored"
const NONSPONSORED_IAB_CATEGORIES = new Set(["5 - Education"]);

// Default score for remote settings suggestions.
const DEFAULT_SUGGESTION_SCORE = 0.2;

// Entries are added to the `#resultsByKeyword` map in chunks, and each chunk
// will add at most this many entries.
const ADD_RESULTS_CHUNK_SIZE = 1000;

const TELEMETRY_LATENCY = "FX_URLBAR_QUICK_SUGGEST_REMOTE_SETTINGS_LATENCY_MS";

/**
 * Fetches the suggestions data from RemoteSettings and builds the structures
 * to provide suggestions for UrlbarProviderQuickSuggest.
 */
export class RemoteSettingsClient extends BaseFeature {
  /**
   * @returns {number}
   *   The default score for remote settings suggestions, a value in the range
   *   [0, 1]. All suggestions require a score that can be used for comparison,
   *   so if a remote settings suggestion does not have one, it's assigned this
   *   value.
   */
  static get DEFAULT_SUGGESTION_SCORE() {
    return DEFAULT_SUGGESTION_SCORE;
  }

  constructor() {
    super();
    this.#taskQueue = new lazy.TaskQueue();
    this.#emitter = new lazy.EventEmitter();
  }

  get shouldEnable() {
    return (
      lazy.UrlbarPrefs.get("suggest.quicksuggest.nonsponsored") ||
      lazy.UrlbarPrefs.get("suggest.quicksuggest.sponsored")
    );
  }

  get enablingPreferences() {
    return [
      "suggest.quicksuggest.nonsponsored",
      "suggest.quicksuggest.sponsored",
    ];
  }

  /**
   * @returns {EventEmitter}
   *   The client will emit events on this object.
   */
  get emitter() {
    return this.#emitter;
  }

  /**
   * @returns {Promise}
   *   Resolves when any ongoing updates to the suggestions data are done.
   */
  get readyPromise() {
    return this.#taskQueue.emptyPromise;
  }

  /**
   * @returns {object}
   *   Global quick suggest configuration stored in remote settings. When the
   *   config changes the `emitter` property will emit a "config-set" event. The
   *   config is an object that looks like this:
   *
   *   {
   *     best_match: {
   *       min_search_string_length,
   *       blocked_suggestion_ids,
   *     },
   *     impression_caps: {
   *       nonsponsored: {
   *         lifetime,
   *         custom: [
   *           { interval_s, max_count },
   *         ],
   *       },
   *       sponsored: {
   *         lifetime,
   *         custom: [
   *           { interval_s, max_count },
   *         ],
   *       },
   *     },
   *   }
   */
  get config() {
    return this.#config;
  }

  enable(enabled) {
    this.#queueSettingsSetup(enabled);
  }

  /**
   * Fetches remote settings suggestions.
   *
   * @param {string} searchString
   *   The search string.
   * @returns {Array}
   *   The remote settings suggestions. If there are no matches, an empty array
   *   is returned.
   */
  async fetch(searchString) {
    let suggestions;
    let stopwatchInstance = {};
    TelemetryStopwatch.start(TELEMETRY_LATENCY, stopwatchInstance);
    try {
      suggestions = await this.#fetchHelper(searchString);
      TelemetryStopwatch.finish(TELEMETRY_LATENCY, stopwatchInstance);
    } catch (error) {
      TelemetryStopwatch.cancel(TELEMETRY_LATENCY, stopwatchInstance);
      this.logger.error("Error fetching suggestions: " + error);
    }

    return suggestions || [];
  }

  /**
   * Helper for `fetch()` that actually looks up the matching suggestions.
   *
   * @param {string} phrase
   *   The search string.
   * @returns {Array}
   *   The matched suggestion objects. If there are no matches, an empty array
   *   is returned.
   */
  async #fetchHelper(phrase) {
    this.logger.info("Handling query: " + JSON.stringify(phrase));

    phrase = phrase.toLowerCase();
    let object = this.#resultsByKeyword.get(phrase);
    if (!object) {
      return [];
    }

    // `object` will be a single result object if there's only one match or an
    // array of result objects if there's more than one match.
    let results = [object].flat();

    // Start each icon fetch at the same time and wait for them all to finish.
    let icons = await Promise.all(
      results.map(({ icon }) => this.#fetchIcon(icon))
    );

    return results.map(result => ({
      full_keyword: this.getFullKeyword(phrase, result.keywords),
      title: result.title,
      url: result.url,
      click_url: result.click_url,
      impression_url: result.impression_url,
      block_id: result.id,
      advertiser: result.advertiser,
      iab_category: result.iab_category,
      is_sponsored: !NONSPONSORED_IAB_CATEGORIES.has(result.iab_category),
      score:
        typeof result.score == "number"
          ? result.score
          : DEFAULT_SUGGESTION_SCORE,
      source: "remote-settings",
      icon: icons.shift(),
      position: result.position,
    }));
  }

  /**
   * Gets the full keyword (i.e., suggestion) for a result and query.  The data
   * doesn't include full keywords, so we make our own based on the result's
   * keyword phrases and a particular query.  We use two heuristics:
   *
   * (1) Find the first keyword phrase that has more words than the query.  Use
   *     its first `queryWords.length` words as the full keyword.  e.g., if the
   *     query is "moz" and `result.keywords` is ["moz", "mozi", "mozil",
   *     "mozill", "mozilla", "mozilla firefox"], pick "mozilla firefox", pop
   *     off the "firefox" and use "mozilla" as the full keyword.
   * (2) If there isn't any keyword phrase with more words, then pick the
   *     longest phrase.  e.g., pick "mozilla" in the previous example (assuming
   *     the "mozilla firefox" phrase isn't there).  That might be the query
   *     itself.
   *
   * @param {string} query
   *   The query string that matched `result`.
   * @param {Array} keywords
   *   An array of result keywords.
   * @returns {string}
   *   The full keyword.
   */
  getFullKeyword(query, keywords) {
    let longerPhrase;
    let trimmedQuery = query.trim();
    let queryWords = trimmedQuery.split(" ");

    for (let phrase of keywords) {
      if (phrase.startsWith(query)) {
        let trimmedPhrase = phrase.trim();
        let phraseWords = trimmedPhrase.split(" ");
        // As an exception to (1), if the query ends with a space, then look for
        // phrases with one more word so that the suggestion includes a word
        // following the space.
        let extra = query.endsWith(" ") ? 1 : 0;
        let len = queryWords.length + extra;
        if (len < phraseWords.length) {
          // We found a phrase with more words.
          return phraseWords.slice(0, len).join(" ");
        }
        if (
          query.length < phrase.length &&
          (!longerPhrase || longerPhrase.length < trimmedPhrase.length)
        ) {
          // We found a longer phrase with the same number of words.
          longerPhrase = trimmedPhrase;
        }
      }
    }
    return longerPhrase || trimmedQuery;
  }

  /**
   * Queues a task to ensure our remote settings client is initialized or torn
   * down as appropriate.
   *
   * @param {boolean} enabled
   *   Whether the feature should be enabled.
   */
  #queueSettingsSetup(enabled) {
    this.#taskQueue.queue(() => {
      if (enabled && !this.#rs) {
        this.#onSettingsSync = (...args) => this.#queueSettingsSync(...args);
        this.#rs = lazy.RemoteSettings(RS_COLLECTION);
        this.#rs.on("sync", this.#onSettingsSync);
        this.#queueSettingsSync();
      } else if (!enabled && this.#rs) {
        this.#rs.off("sync", this.#onSettingsSync);
        this.#rs = null;
        this.#onSettingsSync = null;
      }
    });
  }

  /**
   * Queues a task to populate the results map from the remote settings data
   * plus any other work that needs to be done on sync.
   *
   * @param {object} [event]
   *   The event object passed to the "sync" event listener if you're calling
   *   this from the listener.
   */
  async #queueSettingsSync(event = null) {
    await this.#taskQueue.queue(async () => {
      if (!this.#rs || this._test_ignoreSettingsSync) {
        return;
      }

      // Remove local files of deleted records
      if (event?.data?.deleted) {
        await Promise.all(
          event.data.deleted
            .filter(d => d.attachment)
            .map(entry =>
              Promise.all([
                this.#rs.attachments.deleteDownloaded(entry), // type: data
                this.#rs.attachments.deleteFromDisk(entry), // type: icon
              ])
            )
        );
      }

      let dataType = lazy.UrlbarPrefs.get("quickSuggestRemoteSettingsDataType");
      this.logger.debug("Loading data with type: " + dataType);

      let [configArray, data] = await Promise.all([
        this.#rs.get({ filters: { type: "configuration" } }),
        this.#rs.get({ filters: { type: dataType } }),
        this.#rs
          .get({ filters: { type: "icon" } })
          .then(icons =>
            Promise.all(icons.map(i => this.#rs.attachments.downloadToDisk(i)))
          ),
      ]);

      this.logger.debug("Got configuration: " + JSON.stringify(configArray));
      this.#setConfig(configArray?.[0]?.configuration || {});

      this.#resultsByKeyword.clear();

      this.logger.debug(`Got data with ${data.length} records`);
      for (let record of data) {
        let { buffer } = await this.#rs.attachments.download(record);
        let results = JSON.parse(new TextDecoder("utf-8").decode(buffer));
        this.logger.debug(`Adding ${results.length} results`);
        await this.#addResults(results);
      }
    });
  }

  /**
   * Sets the quick suggest config and emits a "config-set" event.
   *
   * @param {object} config
   *   The config object.
   */
  #setConfig(config) {
    this.#config = config || {};
    this.#emitter.emit("config-set");
  }

  /**
   * Adds a list of result objects to the results map. This method is also used
   * by tests to set up mock suggestions.
   *
   * @param {Array} results
   *   Array of result objects.
   */
  async #addResults(results) {
    // There can be many results, and each result can have many keywords. To
    // avoid blocking the main thread for too long, update the map in chunks,
    // and to avoid blocking the UI and other higher priority work, do each
    // chunk only when the main thread is idle. During each chunk, we'll add at
    // most `_addResultsChunkSize` entries to the map.
    let resultIndex = 0;
    let keywordIndex = 0;

    // Keep adding chunks until all results have been fully added.
    while (resultIndex < results.length) {
      await new Promise(resolve => {
        Services.tm.idleDispatchToMainThread(() => {
          // Keep updating the map until the current chunk is done.
          let indexInChunk = 0;
          while (
            indexInChunk < this._addResultsChunkSize &&
            resultIndex < results.length
          ) {
            let result = results[resultIndex];
            if (keywordIndex == result.keywords.length) {
              resultIndex++;
              keywordIndex = 0;
              continue;
            }
            // If the keyword's only result is `result`, store it directly as
            // the value. Otherwise store an array of results. For details, see
            // the `#resultsByKeyword` comment.
            let keyword = result.keywords[keywordIndex];
            let object = this.#resultsByKeyword.get(keyword);
            if (!object) {
              this.#resultsByKeyword.set(keyword, result);
            } else if (!Array.isArray(object)) {
              this.#resultsByKeyword.set(keyword, [object, result]);
            } else {
              object.push(result);
            }
            keywordIndex++;
            indexInChunk++;
          }

          // The current chunk is done.
          resolve();
        });
      });
    }
  }

  /**
   * Fetch the icon from RemoteSettings attachments.
   *
   * @param {string} path
   *   The icon's remote settings path.
   */
  async #fetchIcon(path) {
    if (!path || !this.#rs) {
      return null;
    }
    let record = (
      await this.#rs.get({
        filters: { id: `icon-${path}` },
      })
    ).pop();
    if (!record) {
      return null;
    }
    return this.#rs.attachments.downloadToDisk(record);
  }

  get _test_rs() {
    return this.#rs;
  }

  get _test_resultsByKeyword() {
    return this.#resultsByKeyword;
  }

  _test_setConfig(config) {
    this.#setConfig(config);
  }

  async _test_addResults(results) {
    await this.#addResults(results);
  }

  // The RemoteSettings client.
  #rs = null;

  // Task queue for serializing access to remote settings and related data.
  // Methods in this class should use this when they need to to modify or access
  // the settings client. It ensures settings accesses are serialized, do not
  // overlap, and happen only one at a time. It also lets clients, especially
  // tests, use this class without having to worry about whether a settings sync
  // or initialization is ongoing; see `readyPromise`.
  #taskQueue = null;

  // Configuration data synced from remote settings. See the `config` getter.
  #config = {};

  // Maps each keyword in the dataset to one or more results for the keyword. If
  // only one result uses a keyword, the keyword's value in the map will be the
  // result object. If more than one result uses the keyword, the value will be
  // an array of the results. The reason for not always using an array is that
  // we expect the vast majority of keywords to be used by only one result, and
  // since there are potentially very many keywords and results and we keep them
  // in memory all the time, we want to save as much memory as possible.
  #resultsByKeyword = new Map();

  // This is only defined as a property so that tests can override it.
  _addResultsChunkSize = ADD_RESULTS_CHUNK_SIZE;

  #onSettingsSync = null;
  #emitter = null;
}