/* 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/. */

/**
 * We just started (we haven't written anything to disk yet) from
 * `Paths.clean`. The backup directory may not exist.
 */
const STATE_CLEAN = "clean";
/**
 * We know that `Paths.recovery` is good, either because we just read
 * it (we haven't written anything to disk yet) or because have
 * already written once to `Paths.recovery` during this session.
 * `Paths.clean` is absent or invalid. The backup directory exists.
 */
const STATE_RECOVERY = "recovery";
/**
 * We just started from `Paths.upgradeBackup` (we haven't written
 * anything to disk yet). Both `Paths.clean`, `Paths.recovery` and
 * `Paths.recoveryBackup` are absent or invalid. The backup directory
 * exists.
 */
const STATE_UPGRADE_BACKUP = "upgradeBackup";
/**
 * We just started without a valid session store file (we haven't
 * written anything to disk yet). The backup directory may not exist.
 */
const STATE_EMPTY = "empty";

var sessionFileIOMutex = Promise.resolve();
// Ensure that we don't do concurrent I/O on the same file.
// Example usage:
// const unlock = await lockIOWithMutex();
// try {
//   ... (Do I/O work here.)
// } finally { unlock(); }
function lockIOWithMutex() {
  // Return a Promise that resolves when the mutex is free.
  return new Promise(unlock => {
    // Overwrite the mutex variable with a chained-on, new Promise. The Promise
    // we returned to the caller can be called to resolve that new Promise
    // and unlock the mutex.
    sessionFileIOMutex = sessionFileIOMutex.then(() => {
      return new Promise(unlock);
    });
  });
}

/**
 * Interface dedicated to handling I/O for Session Store.
 */
export const SessionWriter = {
  init(origin, useOldExtension, paths, prefs = {}) {
    return SessionWriterInternal.init(origin, useOldExtension, paths, prefs);
  },

  /**
   * Write the contents of the session file.
   * @param state - May get changed on shutdown.
   */
  async write(state, options = {}) {
    const unlock = await lockIOWithMutex();
    try {
      return await SessionWriterInternal.write(state, options);
    } finally {
      unlock();
    }
  },

  async wipe() {
    const unlock = await lockIOWithMutex();
    try {
      return await SessionWriterInternal.wipe();
    } finally {
      unlock();
    }
  },
};

const SessionWriterInternal = {
  // Path to the files used by the SessionWriter
  Paths: null,

  /**
   * The current state of the session file, as one of the following strings:
   * - "empty" if we have started without any sessionstore;
   * - one of "clean", "recovery", "recoveryBackup", "cleanBackup",
   *   "upgradeBackup" if we have started by loading the corresponding file.
   */
  state: null,

  /**
   * A flag that indicates we loaded a session file with the deprecated .js extension.
   */
  useOldExtension: false,

  /**
   * Number of old upgrade backups that are being kept
   */
  maxUpgradeBackups: null,

  /**
   * Initialize (or reinitialize) the writer.
   *
   * @param {string} origin Which of sessionstore.js or its backups
   *   was used. One of the `STATE_*` constants defined above.
   * @param {boolean} a flag indicate whether we loaded a session file with ext .js
   * @param {object} paths The paths at which to find the various files.
   * @param {object} prefs The preferences the writer needs to know.
   */
  init(origin, useOldExtension, paths, prefs) {
    if (!(origin in paths || origin == STATE_EMPTY)) {
      throw new TypeError("Invalid origin: " + origin);
    }

    // Check that all required preference values were passed.
    for (let pref of [
      "maxUpgradeBackups",
      "maxSerializeBack",
      "maxSerializeForward",
    ]) {
      if (!prefs.hasOwnProperty(pref)) {
        throw new TypeError(`Missing preference value for ${pref}`);
      }
    }

    this.useOldExtension = useOldExtension;
    this.state = origin;
    this.Paths = paths;
    this.maxUpgradeBackups = prefs.maxUpgradeBackups;
    this.maxSerializeBack = prefs.maxSerializeBack;
    this.maxSerializeForward = prefs.maxSerializeForward;
    this.upgradeBackupNeeded = paths.nextUpgradeBackup != paths.upgradeBackup;
    return { result: true };
  },

  /**
   * Write the session to disk.
   * Write the session to disk, performing any necessary backup
   * along the way.
   *
   * @param {object} state The state to write to disk.
   * @param {object} options
   *  - performShutdownCleanup If |true|, we should
   *    perform shutdown-time cleanup to ensure that private data
   *    is not left lying around;
   *  - isFinalWrite If |true|, write to Paths.clean instead of
   *    Paths.recovery
   */
  async write(state, options) {
    let exn;
    let telemetry = {};

    // Cap the number of backward and forward shistory entries on shutdown.
    if (options.isFinalWrite) {
      for (let window of state.windows) {
        for (let tab of window.tabs) {
          let lower = 0;
          let upper = tab.entries.length;

          if (this.maxSerializeBack > -1) {
            lower = Math.max(lower, tab.index - this.maxSerializeBack - 1);
          }
          if (this.maxSerializeForward > -1) {
            upper = Math.min(upper, tab.index + this.maxSerializeForward);
          }

          tab.entries = tab.entries.slice(lower, upper);
          tab.index -= lower;
        }
      }
    }

    try {
      if (this.state == STATE_CLEAN || this.state == STATE_EMPTY) {
        // The backups directory may not exist yet. In all other cases,
        // we have either already read from or already written to this
        // directory, so we are satisfied that it exists.
        await IOUtils.makeDirectory(this.Paths.backups);
      }

      if (this.state == STATE_CLEAN) {
        // Move $Path.clean out of the way, to avoid any ambiguity as
        // to which file is more recent.
        if (!this.useOldExtension) {
          await IOUtils.move(this.Paths.clean, this.Paths.cleanBackup);
        } else {
          // Since we are migrating from .js to .jsonlz4,
          // we need to compress the deprecated $Path.clean
          // and write it to $Path.cleanBackup.
          let oldCleanPath = this.Paths.clean.replace("jsonlz4", "js");
          let d = await IOUtils.read(oldCleanPath);
          await IOUtils.write(this.Paths.cleanBackup, d, { compress: true });
        }
      }

      let startWriteMs = Date.now();
      let fileStat;

      if (options.isFinalWrite) {
        // We are shutting down. At this stage, we know that
        // $Paths.clean is either absent or corrupted. If it was
        // originally present and valid, it has been moved to
        // $Paths.cleanBackup a long time ago. We can therefore write
        // with the guarantees that we erase no important data.
        await IOUtils.writeJSON(this.Paths.clean, state, {
          tmpPath: this.Paths.clean + ".tmp",
          compress: true,
        });
        fileStat = await IOUtils.stat(this.Paths.clean);
      } else if (this.state == STATE_RECOVERY) {
        // At this stage, either $Paths.recovery was written >= 15
        // seconds ago during this session or we have just started
        // from $Paths.recovery left from the previous session. Either
        // way, $Paths.recovery is good. We can move $Path.backup to
        // $Path.recoveryBackup without erasing a good file with a bad
        // file.
        await IOUtils.writeJSON(this.Paths.recovery, state, {
          tmpPath: this.Paths.recovery + ".tmp",
          backupFile: this.Paths.recoveryBackup,
          compress: true,
        });
        fileStat = await IOUtils.stat(this.Paths.recovery);
      } else {
        // In other cases, either $Path.recovery is not necessary, or
        // it doesn't exist or it has been corrupted. Regardless,
        // don't backup $Path.recovery.
        await IOUtils.writeJSON(this.Paths.recovery, state, {
          tmpPath: this.Paths.recovery + ".tmp",
          compress: true,
        });
        fileStat = await IOUtils.stat(this.Paths.recovery);
      }

      telemetry.FX_SESSION_RESTORE_WRITE_FILE_MS = Date.now() - startWriteMs;
      telemetry.FX_SESSION_RESTORE_FILE_SIZE_BYTES = fileStat.size;
    } catch (ex) {
      // Don't throw immediately
      exn = exn || ex;
    }

    // If necessary, perform an upgrade backup
    let upgradeBackupComplete = false;
    if (
      this.upgradeBackupNeeded &&
      (this.state == STATE_CLEAN || this.state == STATE_UPGRADE_BACKUP)
    ) {
      try {
        // If we loaded from `clean`, the file has since then been renamed to `cleanBackup`.
        let path =
          this.state == STATE_CLEAN
            ? this.Paths.cleanBackup
            : this.Paths.upgradeBackup;
        await IOUtils.copy(path, this.Paths.nextUpgradeBackup);
        this.upgradeBackupNeeded = false;
        upgradeBackupComplete = true;
      } catch (ex) {
        // Don't throw immediately
        exn = exn || ex;
      }

      // Find all backups
      let backups = [];

      try {
        let children = await IOUtils.getChildren(this.Paths.backups);
        backups = children.filter(path =>
          path.startsWith(this.Paths.upgradeBackupPrefix)
        );
      } catch (ex) {
        // Don't throw immediately
        exn = exn || ex;
      }

      // If too many backups exist, delete them
      if (backups.length > this.maxUpgradeBackups) {
        // Use alphanumerical sort since dates are in YYYYMMDDHHMMSS format
        backups.sort();
        // remove backup file if it is among the first (n-maxUpgradeBackups) files
        for (let i = 0; i < backups.length - this.maxUpgradeBackups; i++) {
          try {
            await IOUtils.remove(backups[i]);
          } catch (ex) {
            exn = exn || ex;
          }
        }
      }
    }

    if (options.performShutdownCleanup && !exn) {
      // During shutdown, if auto-restore is disabled, we need to
      // remove possibly sensitive data that has been stored purely
      // for crash recovery. Note that this slightly decreases our
      // ability to recover from OS-level/hardware-level issue.

      // If an exception was raised, we assume that we still need
      // these files.
      await IOUtils.remove(this.Paths.recoveryBackup);
      await IOUtils.remove(this.Paths.recovery);
    }

    this.state = STATE_RECOVERY;

    if (exn) {
      throw exn;
    }

    return {
      result: {
        upgradeBackup: upgradeBackupComplete,
      },
      telemetry,
    };
  },

  /**
   * Wipes all files holding session data from disk.
   */
  async wipe() {
    // Don't stop immediately in case of error.
    let exn = null;

    // Erase main session state file
    try {
      await IOUtils.remove(this.Paths.clean);
      // Remove old extension ones.
      let oldCleanPath = this.Paths.clean.replace("jsonlz4", "js");
      await IOUtils.remove(oldCleanPath, {
        ignoreAbsent: true,
      });
    } catch (ex) {
      // Don't stop immediately.
      exn = exn || ex;
    }

    // Wipe the Session Restore directory
    try {
      await IOUtils.remove(this.Paths.backups, { recursive: true });
    } catch (ex) {
      exn = exn || ex;
    }

    // Wipe legacy Session Restore files from the profile directory
    try {
      await this._wipeFromDir(PathUtils.profileDir, "sessionstore.bak");
    } catch (ex) {
      exn = exn || ex;
    }

    this.state = STATE_EMPTY;
    if (exn) {
      throw exn;
    }

    return { result: true };
  },

  /**
   * Wipe a number of files from a directory.
   *
   * @param {string} path The directory.
   * @param {string} prefix Remove files whose
   * name starts with the prefix.
   */
  async _wipeFromDir(path, prefix) {
    // Sanity check
    if (!prefix) {
      throw new TypeError("Must supply prefix");
    }

    let exn = null;

    let children = await IOUtils.getChildren(path, {
      ignoreAbsent: true,
    });
    for (let entryPath of children) {
      if (!PathUtils.filename(entryPath).startsWith(prefix)) {
        continue;
      }
      try {
        let { type } = await IOUtils.stat(entryPath);
        if (type == "directory") {
          continue;
        }
        await IOUtils.remove(entryPath);
      } catch (ex) {
        // Don't stop immediately
        exn = exn || ex;
      }
    }

    if (exn) {
      throw exn;
    }
  },
};