ExtensionCommon.jsm

/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
/* vim: set sts=2 sw=2 et tw=80: */
/* 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/. */
"use strict";

/**
 * This module contains utilities and base classes for logic which is
 * common between the parent and child process, and in particular
 * between ExtensionParent.jsm and ExtensionChild.jsm.
 */

/* exported ExtensionCommon */

var EXPORTED_SYMBOLS = ["ExtensionCommon"];

const { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
const { XPCOMUtils } = ChromeUtils.import(
  "resource://gre/modules/XPCOMUtils.jsm"
);

XPCOMUtils.defineLazyGlobalGetters(this, ["fetch"]);

XPCOMUtils.defineLazyModuleGetters(this, {
  AppConstants: "resource://gre/modules/AppConstants.jsm",
  ConsoleAPI: "resource://gre/modules/Console.jsm",
  MessageChannel: "resource://gre/modules/MessageChannel.jsm",
  PrivateBrowsingUtils: "resource://gre/modules/PrivateBrowsingUtils.jsm",
  Schemas: "resource://gre/modules/Schemas.jsm",
  SchemaRoot: "resource://gre/modules/Schemas.jsm",
});

XPCOMUtils.defineLazyServiceGetter(
  this,
  "styleSheetService",
  "@mozilla.org/content/style-sheet-service;1",
  "nsIStyleSheetService"
);

const { ExtensionUtils } = ChromeUtils.import(
  "resource://gre/modules/ExtensionUtils.jsm"
);

var {
  DefaultMap,
  DefaultWeakMap,
  ExtensionError,
  filterStack,
  getInnerWindowID,
  getUniqueId,
  getWinUtils,
} = ExtensionUtils;

function getConsole() {
  return new ConsoleAPI({
    maxLogLevelPref: "extensions.webextensions.log.level",
    prefix: "WebExtensions",
  });
}

XPCOMUtils.defineLazyGetter(this, "console", getConsole);

XPCOMUtils.defineLazyPreferenceGetter(
  this,
  "DELAYED_BG_STARTUP",
  "extensions.webextensions.background-delayed-startup"
);

var ExtensionCommon;

// Run a function and report exceptions.
function runSafeSyncWithoutClone(f, ...args) {
  try {
    return f(...args);
  } catch (e) {
    dump(
      `Extension error: ${e} ${e.fileName} ${
        e.lineNumber
      }\n[[Exception stack\n${filterStack(e)}Current stack\n${filterStack(
        Error()
      )}]]\n`
    );
    Cu.reportError(e);
  }
}

// Return true if the given value is an instance of the given
// native type.
function instanceOf(value, type) {
  return (
    value &&
    typeof value === "object" &&
    ChromeUtils.getClassName(value) === type
  );
}

/**
 * Convert any of several different representations of a date/time to a Date object.
 * Accepts several formats:
 * a Date object, an ISO8601 string, or a number of milliseconds since the epoch as
 * either a number or a string.
 *
 * @param {Date|string|number} date
 *      The date to convert.
 * @returns {Date}
 *      A Date object
 */
function normalizeTime(date) {
  // Of all the formats we accept the "number of milliseconds since the epoch as a string"
  // is an outlier, everything else can just be passed directly to the Date constructor.
  return new Date(
    typeof date == "string" && /^\d+$/.test(date) ? parseInt(date, 10) : date
  );
}

function withHandlingUserInput(window, callable) {
  let handle = getWinUtils(window).setHandlingUserInput(true);
  try {
    return callable();
  } finally {
    handle.destruct();
  }
}

/**
 * Defines a lazy getter for the given property on the given object. The
 * first time the property is accessed, the return value of the getter
 * is defined on the current `this` object with the given property name.
 * Importantly, this means that a lazy getter defined on an object
 * prototype will be invoked separately for each object instance that
 * it's accessed on.
 *
 * @param {object} object
 *        The prototype object on which to define the getter.
 * @param {string|Symbol} prop
 *        The property name for which to define the getter.
 * @param {function} getter
 *        The function to call in order to generate the final property
 *        value.
 */
function defineLazyGetter(object, prop, getter) {
  let redefine = (obj, value) => {
    Object.defineProperty(obj, prop, {
      enumerable: true,
      configurable: true,
      writable: true,
      value,
    });
    return value;
  };

  Object.defineProperty(object, prop, {
    enumerable: true,
    configurable: true,

    get() {
      return redefine(this, getter.call(this));
    },

    set(value) {
      redefine(this, value);
    },
  });
}

function checkLoadURL(url, principal, options) {
  let ssm = Services.scriptSecurityManager;

  let flags = ssm.STANDARD;
  if (!options.allowScript) {
    flags |= ssm.DISALLOW_SCRIPT;
  }
  if (!options.allowInheritsPrincipal) {
    flags |= ssm.DISALLOW_INHERIT_PRINCIPAL;
  }
  if (options.dontReportErrors) {
    flags |= ssm.DONT_REPORT_ERRORS;
  }

  try {
    ssm.checkLoadURIWithPrincipal(principal, Services.io.newURI(url), flags);
  } catch (e) {
    return false;
  }
  return true;
}

function makeWidgetId(id) {
  id = id.toLowerCase();
  // FIXME: This allows for collisions.
  return id.replace(/[^a-z0-9_-]/g, "_");
}

/**
 * A sentinel class to indicate that an array of values should be
 * treated as an array when used as a promise resolution value, but as a
 * spread expression (...args) when passed to a callback.
 */
class SpreadArgs extends Array {
  constructor(args) {
    super();
    this.push(...args);
  }
}

/**
 * Like SpreadArgs, but also indicates that the array values already
 * belong to the target compartment, and should not be cloned before
 * being passed.
 *
 * The `unwrappedValues` property contains an Array object which belongs
 * to the target compartment, and contains the same unwrapped values
 * passed the NoCloneSpreadArgs constructor.
 */
class NoCloneSpreadArgs {
  constructor(args) {
    this.unwrappedValues = args;
  }

  [Symbol.iterator]() {
    return this.unwrappedValues[Symbol.iterator]();
  }
}

const LISTENERS = Symbol("listeners");
const ONCE_MAP = Symbol("onceMap");

class EventEmitter {
  constructor() {
    this[LISTENERS] = new Map();
    this[ONCE_MAP] = new WeakMap();
  }

  /**
   * Checks whether there is some listener for the given event.
   *
   * @param {string} event
   *       The name of the event to listen for.
   * @returns {boolean}
   */
  has(event) {
    return this[LISTENERS].has(event);
  }

  /**
   * Adds the given function as a listener for the given event.
   *
   * The listener function may optionally return a Promise which
   * resolves when it has completed all operations which event
   * dispatchers may need to block on.
   *
   * @param {string} event
   *       The name of the event to listen for.
   * @param {function(string, ...any)} listener
   *        The listener to call when events are emitted.
   */
  on(event, listener) {
    let listeners = this[LISTENERS].get(event);
    if (!listeners) {
      listeners = new Set();
      this[LISTENERS].set(event, listeners);
    }

    listeners.add(listener);
  }

  /**
   * Removes the given function as a listener for the given event.
   *
   * @param {string} event
   *       The name of the event to stop listening for.
   * @param {function(string, ...any)} listener
   *        The listener function to remove.
   */
  off(event, listener) {
    let set = this[LISTENERS].get(event);
    if (set) {
      set.delete(listener);
      set.delete(this[ONCE_MAP].get(listener));
      if (!set.size) {
        this[LISTENERS].delete(event);
      }
    }
  }

  /**
   * Adds the given function as a listener for the given event once.
   *
   * @param {string} event
   *       The name of the event to listen for.
   * @param {function(string, ...any)} listener
   *        The listener to call when events are emitted.
   */
  once(event, listener) {
    let wrapper = (...args) => {
      this.off(event, wrapper);
      this[ONCE_MAP].delete(listener);

      return listener(...args);
    };
    this[ONCE_MAP].set(listener, wrapper);

    this.on(event, wrapper);
  }

  /**
   * Triggers all listeners for the given event. If any listeners return
   * a value, returns a promise which resolves when all returned
   * promises have resolved. Otherwise, returns undefined.
   *
   * @param {string} event
   *       The name of the event to emit.
   * @param {any} args
   *        Arbitrary arguments to pass to the listener functions, after
   *        the event name.
   * @returns {Promise?}
   */
  emit(event, ...args) {
    let listeners = this[LISTENERS].get(event);

    if (listeners) {
      let promises = [];

      for (let listener of listeners) {
        try {
          let result = listener(event, ...args);
          if (result !== undefined) {
            promises.push(result);
          }
        } catch (e) {
          Cu.reportError(e);
        }
      }

      if (promises.length) {
        return Promise.all(promises);
      }
    }
  }
}

/**
 * Base class for WebExtension APIs.  Each API creates a new class
 * that inherits from this class, the derived class is instantiated
 * once for each extension that uses the API.
 */
class ExtensionAPI extends EventEmitter {
  constructor(extension) {
    super();

    this.extension = extension;

    extension.once("shutdown", (what, isAppShutdown) => {
      if (this.onShutdown) {
        this.onShutdown(isAppShutdown);
      }
      this.extension = null;
    });
  }

  destroy() {}

  onManifestEntry(entry) {}

  getAPI(context) {
    throw new Error("Not Implemented");
  }
}

/**
 * A wrapper around a window that returns the window iff the inner window
 * matches the inner window at the construction of this wrapper.
 *
 * This wrapper should not be used after the inner window is destroyed.
 **/
class InnerWindowReference {
  constructor(contentWindow, innerWindowID) {
    this.contentWindow = contentWindow;
    this.innerWindowID = innerWindowID;
    this.needWindowIDCheck = false;

    contentWindow.addEventListener(
      "pagehide",
      this,
      { mozSystemGroup: true },
      false
    );
    contentWindow.addEventListener(
      "pageshow",
      this,
      { mozSystemGroup: true },
      false
    );
  }

  get() {
    // If the pagehide event has fired, the inner window ID needs to be checked,
    // in case the window ref is dereferenced in a pageshow listener (before our
    // pageshow listener was dispatched) or during the unload event.
    if (
      !this.needWindowIDCheck ||
      getInnerWindowID(this.contentWindow) === this.innerWindowID
    ) {
      return this.contentWindow;
    }
    return null;
  }

  invalidate() {
    // If invalidate() is called while the inner window is in the bfcache, then
    // we are unable to remove the event listener, and handleEvent will be
    // called once more if the page is revived from the bfcache.
    if (this.contentWindow && !Cu.isDeadWrapper(this.contentWindow)) {
      this.contentWindow.removeEventListener("pagehide", this, {
        mozSystemGroup: true,
      });
      this.contentWindow.removeEventListener("pageshow", this, {
        mozSystemGroup: true,
      });
    }
    this.contentWindow = null;
    this.needWindowIDCheck = false;
  }

  handleEvent(event) {
    if (this.contentWindow) {
      this.needWindowIDCheck = event.type === "pagehide";
    } else {
      // Remove listener when restoring from the bfcache - see invalidate().
      event.currentTarget.removeEventListener("pagehide", this, {
        mozSystemGroup: true,
      });
      event.currentTarget.removeEventListener("pageshow", this, {
        mozSystemGroup: true,
      });
    }
  }
}

/**
 * This class contains the information we have about an individual
 * extension.  It is never instantiated directly, instead subclasses
 * for each type of process extend this class and add members that are
 * relevant for that process.
 * @abstract
 */
class BaseContext {
  constructor(envType, extension) {
    this.envType = envType;
    this.onClose = new Set();
    this.checkedLastError = false;
    this._lastError = null;
    this.contextId = getUniqueId();
    this.unloaded = false;
    this.extension = extension;
    this.jsonSandbox = null;
    this.active = true;
    this.incognito = null;
    this.messageManager = null;
    this.contentWindow = null;
    this.innerWindowID = 0;

    // These two properties are assigned in ContentScriptContextChild subclass
    // to keep a copy of the content script sandbox Error and Promise globals
    // (which are used by the WebExtensions internals) before any extension
    // content script code had any chance to redefine them.
    this.cloneScopeError = null;
    this.cloneScopePromise = null;
  }

  get Error() {
    // Return the copy stored in the context instance (when the context is an instance of
    // ContentScriptContextChild or the global from extension page window otherwise).
    return this.cloneScopeError || this.cloneScope.Error;
  }

  get Promise() {
    // Return the copy stored in the context instance (when the context is an instance of
    // ContentScriptContextChild or the global from extension page window otherwise).
    return this.cloneScopePromise || this.cloneScope.Promise;
  }

  get privateBrowsingAllowed() {
    return this.extension.privateBrowsingAllowed;
  }

  canAccessWindow(window) {
    return this.extension.canAccessWindow(window);
  }

  openConduit(subject, address) {
    let actor = this.contentWindow.getWindowGlobalChild().getActor("Conduits");
    return actor.openConduit(subject, address);
  }

  setContentWindow(contentWindow) {
    if (!this.canAccessWindow(contentWindow)) {
      throw new Error(
        "BaseContext attempted to load when extension is not allowed due to incognito settings."
      );
    }

    this.innerWindowID = getInnerWindowID(contentWindow);
    this.messageManager = contentWindow.docShell.messageManager;

    if (this.incognito == null) {
      this.incognito = PrivateBrowsingUtils.isContentWindowPrivate(
        contentWindow
      );
    }

    MessageChannel.setupMessageManagers([this.messageManager]);

    let windowRef = new InnerWindowReference(contentWindow, this.innerWindowID);
    Object.defineProperty(this, "active", {
      configurable: true,
      enumerable: true,
      get: () => windowRef.get() !== null,
    });
    Object.defineProperty(this, "contentWindow", {
      configurable: true,
      enumerable: true,
      get: () => windowRef.get(),
    });
    this.callOnClose({
      close: () => {
        // Allow other "close" handlers to use these properties, until the next tick.
        Promise.resolve().then(() => {
          windowRef.invalidate();
          windowRef = null;
          Object.defineProperty(this, "contentWindow", { value: null });
          Object.defineProperty(this, "active", { value: false });
        });
      },
    });
  }

  // All child contexts must implement logActivity.  This is handled if the child
  // context subclasses ExtensionBaseContextChild.  ProxyContextParent overrides
  // this with a noop for parent contexts.
  logActivity(type, name, data) {
    throw new Error(`Not implemented for ${this.envType}`);
  }

  get cloneScope() {
    throw new Error("Not implemented");
  }

  get principal() {
    throw new Error("Not implemented");
  }

  runSafe(callback, ...args) {
    return this.applySafe(callback, args);
  }

  runSafeWithoutClone(callback, ...args) {
    return this.applySafeWithoutClone(callback, args);
  }

  applySafe(callback, args, caller) {
    if (this.unloaded) {
      Cu.reportError("context.runSafe called after context unloaded", caller);
    } else if (!this.active) {
      Cu.reportError(
        "context.runSafe called while context is inactive",
        caller
      );
    } else {
      try {
        let { cloneScope } = this;
        args = args.map(arg => Cu.cloneInto(arg, cloneScope));
      } catch (e) {
        Cu.reportError(e);
        dump(
          `runSafe failure: cloning into ${
            this.cloneScope
          }: ${e}\n\n${filterStack(Error())}`
        );
      }

      return this.applySafeWithoutClone(callback, args, caller);
    }
  }

  applySafeWithoutClone(callback, args, caller) {
    if (this.unloaded) {
      Cu.reportError(
        "context.runSafeWithoutClone called after context unloaded",
        caller
      );
    } else if (!this.active) {
      Cu.reportError(
        "context.runSafeWithoutClone called while context is inactive",
        caller
      );
    } else {
      try {
        return Reflect.apply(callback, null, args);
      } catch (e) {
        dump(
          `Extension error: ${e} ${e.fileName} ${
            e.lineNumber
          }\n[[Exception stack\n${filterStack(e)}Current stack\n${filterStack(
            Error()
          )}]]\n`
        );
        Cu.reportError(e);
      }
    }
  }

  checkLoadURL(url, options = {}) {
    // As an optimization, f the URL starts with the extension's base URL,
    // don't do any further checks. It's always allowed to load it.
    if (url.startsWith(this.extension.baseURL)) {
      return true;
    }

    return checkLoadURL(url, this.principal, options);
  }

  /**
   * Safely call JSON.stringify() on an object that comes from an
   * extension.
   *
   * @param {array<any>} args Arguments for JSON.stringify()
   * @returns {string} The stringified representation of obj
   */
  jsonStringify(...args) {
    if (!this.jsonSandbox) {
      this.jsonSandbox = Cu.Sandbox(this.principal, {
        sameZoneAs: this.cloneScope,
        wantXrays: false,
      });
    }

    return Cu.waiveXrays(this.jsonSandbox.JSON).stringify(...args);
  }

  callOnClose(obj) {
    this.onClose.add(obj);
  }

  forgetOnClose(obj) {
    this.onClose.delete(obj);
  }

  /**
   * A wrapper around MessageChannel.sendMessage which adds the extension ID
   * to the recipient object, and ensures replies are not processed after the
   * context has been unloaded.
   *
   * @param {nsIMessageManager} target
   * @param {string} messageName
   * @param {object} data
   * @param {object} [options]
   * @param {object} [options.sender]
   * @param {object} [options.recipient]
   *
   * @returns {Promise}
   */
  sendMessage(target, messageName, data, options = {}) {
    options.recipient = Object.assign(
      { extensionId: this.extension.id },
      options.recipient
    );
    options.sender = options.sender || {};

    options.sender.extensionId = this.extension.id;
    options.sender.contextId = this.contextId;

    return MessageChannel.sendMessage(target, messageName, data, options);
  }

  get lastError() {
    this.checkedLastError = true;
    return this._lastError;
  }

  set lastError(val) {
    this.checkedLastError = false;
    this._lastError = val;
  }

  /**
   * Normalizes the given error object for use by the target scope. If
   * the target is an error object which belongs to that scope, it is
   * returned as-is. If it is an ordinary object with a `message`
   * property, it is converted into an error belonging to the target
   * scope. If it is an Error object which does *not* belong to the
   * clone scope, it is reported, and converted to an unexpected
   * exception error.
   *
   * @param {Error|object} error
   * @param {SavedFrame?} [caller]
   * @returns {Error}
   */
  normalizeError(error, caller) {
    if (error instanceof this.Error) {
      return error;
    }
    let message, fileName;
    if (error && typeof error === "object") {
      const isPlain = ChromeUtils.getClassName(error) === "Object";
      if (isPlain && error.mozWebExtLocation) {
        caller = error.mozWebExtLocation;
      }
      if (isPlain && caller && (error.mozWebExtLocation || !error.fileName)) {
        caller = Cu.cloneInto(caller, this.cloneScope);
        return ChromeUtils.createError(error.message, caller);
      }

      if (
        isPlain ||
        error instanceof ExtensionError ||
        this.principal.subsumes(Cu.getObjectPrincipal(error))
      ) {
        message = error.message;
        fileName = error.fileName;
      }
    }

    if (!message) {
      Cu.reportError(error);
      message = "An unexpected error occurred";
    }
    return new this.Error(message, fileName);
  }

  /**
   * Sets the value of `.lastError` to `error`, calls the given
   * callback, and reports an error if the value has not been checked
   * when the callback returns.
   *
   * @param {object} error An object with a `message` property. May
   *     optionally be an `Error` object belonging to the target scope.
   * @param {SavedFrame?} caller
   *        The optional caller frame which triggered this callback, to be used
   *        in error reporting.
   * @param {function} callback The callback to call.
   * @returns {*} The return value of callback.
   */
  withLastError(error, caller, callback) {
    this.lastError = this.normalizeError(error);
    try {
      return callback();
    } finally {
      if (!this.checkedLastError) {
        Cu.reportError(`Unchecked lastError value: ${this.lastError}`, caller);
      }
      this.lastError = null;
    }
  }

  /**
   * Captures the most recent stack frame which belongs to the extension.
   *
   * @returns {SavedFrame?}
   */
  getCaller() {
    return ChromeUtils.getCallerLocation(this.principal);
  }

  /**
   * Wraps the given promise so it can be safely returned to extension
   * code in this context.
   *
   * If `callback` is provided, however, it is used as a completion
   * function for the promise, and no promise is returned. In this case,
   * the callback is called when the promise resolves or rejects. In the
   * latter case, `lastError` is set to the rejection value, and the
   * callback function must check `browser.runtime.lastError` or
   * `extension.runtime.lastError` in order to prevent it being reported
   * to the console.
   *
   * @param {Promise} promise The promise with which to wrap the
   *     callback. May resolve to a `SpreadArgs` instance, in which case
   *     each element will be used as a separate argument.
   *
   *     Unless the promise object belongs to the cloneScope global, its
   *     resolution value is cloned into cloneScope prior to calling the
   *     `callback` function or resolving the wrapped promise.
   *
   * @param {function} [callback] The callback function to wrap
   *
   * @returns {Promise|undefined} If callback is null, a promise object
   *     belonging to the target scope. Otherwise, undefined.
   */
  wrapPromise(promise, callback = null) {
    let caller = this.getCaller();
    let applySafe = this.applySafe.bind(this);
    if (Cu.getGlobalForObject(promise) === this.cloneScope) {
      applySafe = this.applySafeWithoutClone.bind(this);
    }

    if (callback) {
      promise.then(
        args => {
          if (this.unloaded) {
            Cu.reportError(`Promise resolved after context unloaded\n`, caller);
          } else if (!this.active) {
            Cu.reportError(
              `Promise resolved while context is inactive\n`,
              caller
            );
          } else if (args instanceof NoCloneSpreadArgs) {
            this.applySafeWithoutClone(callback, args.unwrappedValues, caller);
          } else if (args instanceof SpreadArgs) {
            applySafe(callback, args, caller);
          } else {
            applySafe(callback, [args], caller);
          }
        },
        error => {
          this.withLastError(error, caller, () => {
            if (this.unloaded) {
              Cu.reportError(
                `Promise rejected after context unloaded\n`,
                caller
              );
            } else if (!this.active) {
              Cu.reportError(
                `Promise rejected while context is inactive\n`,
                caller
              );
            } else {
              this.applySafeWithoutClone(callback, [], caller);
            }
          });
        }
      );
    } else {
      return new this.Promise((resolve, reject) => {
        promise.then(
          value => {
            if (this.unloaded) {
              Cu.reportError(
                `Promise resolved after context unloaded\n`,
                caller
              );
            } else if (!this.active) {
              Cu.reportError(
                `Promise resolved while context is inactive\n`,
                caller
              );
            } else if (value instanceof NoCloneSpreadArgs) {
              let values = value.unwrappedValues;
              this.applySafeWithoutClone(
                resolve,
                values.length == 1 ? [values[0]] : [values],
                caller
              );
            } else if (value instanceof SpreadArgs) {
              applySafe(resolve, value.length == 1 ? value : [value], caller);
            } else {
              applySafe(resolve, [value], caller);
            }
          },
          value => {
            if (this.unloaded) {
              Cu.reportError(
                `Promise rejected after context unloaded: ${value &&
                  value.message}\n`,
                caller
              );
            } else if (!this.active) {
              Cu.reportError(
                `Promise rejected while context is inactive: ${value &&
                  value.message}\n`,
                caller
              );
            } else {
              this.applySafeWithoutClone(
                reject,
                [this.normalizeError(value, caller)],
                caller
              );
            }
          }
        );
      });
    }
  }

  unload() {
    this.unloaded = true;

    MessageChannel.abortResponses({
      extensionId: this.extension.id,
      contextId: this.contextId,
    });

    for (let obj of this.onClose) {
      obj.close();
    }
    this.onClose.clear();
  }

  /**
   * A simple proxy for unload(), for use with callOnClose().
   */
  close() {
    this.unload();
  }
}

/**
 * An object that runs the implementation of a schema API. Instantiations of
 * this interfaces are used by Schemas.jsm.
 *
 * @interface
 */
class SchemaAPIInterface {
  /**
   * Calls this as a function that returns its return value.
   *
   * @abstract
   * @param {Array} args The parameters for the function.
   * @returns {*} The return value of the invoked function.
   */
  callFunction(args) {
    throw new Error("Not implemented");
  }

  /**
   * Calls this as a function and ignores its return value.
   *
   * @abstract
   * @param {Array} args The parameters for the function.
   */
  callFunctionNoReturn(args) {
    throw new Error("Not implemented");
  }

  /**
   * Calls this as a function that completes asynchronously.
   *
   * @abstract
   * @param {Array} args The parameters for the function.
   * @param {function(*)} [callback] The callback to be called when the function
   *     completes.
   * @param {boolean} [requireUserInput=false] If true, the function should
   *                  fail if the browser is not currently handling user input.
   * @returns {Promise|undefined} Must be void if `callback` is set, and a
   *     promise otherwise. The promise is resolved when the function completes.
   */
  callAsyncFunction(args, callback, requireUserInput = false) {
    throw new Error("Not implemented");
  }

  /**
   * Retrieves the value of this as a property.
   *
   * @abstract
   * @returns {*} The value of the property.
   */
  getProperty() {
    throw new Error("Not implemented");
  }

  /**
   * Assigns the value to this as property.
   *
   * @abstract
   * @param {string} value The new value of the property.
   */
  setProperty(value) {
    throw new Error("Not implemented");
  }

  /**
   * Registers a `listener` to this as an event.
   *
   * @abstract
   * @param {function} listener The callback to be called when the event fires.
   * @param {Array} args Extra parameters for EventManager.addListener.
   * @see EventManager.addListener
   */
  addListener(listener, args) {
    throw new Error("Not implemented");
  }

  /**
   * Checks whether `listener` is listening to this as an event.
   *
   * @abstract
   * @param {function} listener The event listener.
   * @returns {boolean} Whether `listener` is registered with this as an event.
   * @see EventManager.hasListener
   */
  hasListener(listener) {
    throw new Error("Not implemented");
  }

  /**
   * Unregisters `listener` from this as an event.
   *
   * @abstract
   * @param {function} listener The event listener.
   * @see EventManager.removeListener
   */
  removeListener(listener) {
    throw new Error("Not implemented");
  }

  /**
   * Revokes the implementation object, and prevents any further method
   * calls from having external effects.
   *
   * @abstract
   */
  revoke() {
    throw new Error("Not implemented");
  }
}

/**
 * An object that runs a locally implemented API.
 */
class LocalAPIImplementation extends SchemaAPIInterface {
  /**
   * Constructs an implementation of the `name` method or property of `pathObj`.
   *
   * @param {object} pathObj The object containing the member with name `name`.
   * @param {string} name The name of the implemented member.
   * @param {BaseContext} context The context in which the schema is injected.
   */
  constructor(pathObj, name, context) {
    super();
    this.pathObj = pathObj;
    this.name = name;
    this.context = context;
  }

  revoke() {
    if (this.pathObj[this.name][Schemas.REVOKE]) {
      this.pathObj[this.name][Schemas.REVOKE]();
    }

    this.pathObj = null;
    this.name = null;
    this.context = null;
  }

  callFunction(args) {
    try {
      return this.pathObj[this.name](...args);
    } catch (e) {
      throw this.context.normalizeError(e);
    }
  }

  callFunctionNoReturn(args) {
    try {
      this.pathObj[this.name](...args);
    } catch (e) {
      throw this.context.normalizeError(e);
    }
  }

  callAsyncFunction(args, callback, requireUserInput) {
    let promise;
    try {
      if (requireUserInput) {
        if (!getWinUtils(this.context.contentWindow).isHandlingUserInput) {
          throw new ExtensionError(
            `${this.name} may only be called from a user input handler`
          );
        }
      }
      promise = this.pathObj[this.name](...args) || Promise.resolve();
    } catch (e) {
      promise = Promise.reject(e);
    }
    return this.context.wrapPromise(promise, callback);
  }

  getProperty() {
    return this.pathObj[this.name];
  }

  setProperty(value) {
    this.pathObj[this.name] = value;
  }

  addListener(listener, args) {
    try {
      this.pathObj[this.name].addListener.call(null, listener, ...args);
    } catch (e) {
      throw this.context.normalizeError(e);
    }
  }

  hasListener(listener) {
    return this.pathObj[this.name].hasListener.call(null, listener);
  }

  removeListener(listener) {
    this.pathObj[this.name].removeListener.call(null, listener);
  }
}

// Recursively copy properties from source to dest.
function deepCopy(dest, source) {
  for (let prop in source) {
    let desc = Object.getOwnPropertyDescriptor(source, prop);
    if (typeof desc.value == "object") {
      if (!(prop in dest)) {
        dest[prop] = {};
      }
      deepCopy(dest[prop], source[prop]);
    } else {
      Object.defineProperty(dest, prop, desc);
    }
  }
}

function getChild(map, key) {
  let child = map.children.get(key);
  if (!child) {
    child = {
      modules: new Set(),
      children: new Map(),
    };

    map.children.set(key, child);
  }
  return child;
}

function getPath(map, path) {
  for (let key of path) {
    map = getChild(map, key);
  }
  return map;
}

function mergePaths(dest, source) {
  for (let name of source.modules) {
    dest.modules.add(name);
  }

  for (let [name, child] of source.children.entries()) {
    mergePaths(getChild(dest, name), child);
  }
}

/**
 * Manages loading and accessing a set of APIs for a specific extension
 * context.
 *
 * @param {BaseContext} context
 *        The context to manage APIs for.
 * @param {SchemaAPIManager} apiManager
 *        The API manager holding the APIs to manage.
 * @param {object} root
 *        The root object into which APIs will be injected.
 */
class CanOfAPIs {
  constructor(context, apiManager, root) {
    this.context = context;
    this.scopeName = context.envType;
    this.apiManager = apiManager;
    this.root = root;

    this.apiPaths = new Map();

    this.apis = new Map();
  }

  /**
   * Synchronously loads and initializes an ExtensionAPI instance.
   *
   * @param {string} name
   *        The name of the API to load.
   */
  loadAPI(name) {
    if (this.apis.has(name)) {
      return;
    }

    let { extension } = this.context;

    let api = this.apiManager.getAPI(name, extension, this.scopeName);
    if (!api) {
      return;
    }

    this.apis.set(name, api);

    deepCopy(this.root, api.getAPI(this.context));
  }

  /**
   * Asynchronously loads and initializes an ExtensionAPI instance.
   *
   * @param {string} name
   *        The name of the API to load.
   */
  async asyncLoadAPI(name) {
    if (this.apis.has(name)) {
      return;
    }

    let { extension } = this.context;
    if (!Schemas.checkPermissions(name, extension)) {
      return;
    }

    let api = await this.apiManager.asyncGetAPI(
      name,
      extension,
      this.scopeName
    );
    // Check again, because async;
    if (this.apis.has(name)) {
      return;
    }

    this.apis.set(name, api);

    deepCopy(this.root, api.getAPI(this.context));
  }

  /**
   * Finds the API at the given path from the root object, and
   * synchronously loads the API that implements it if it has not
   * already been loaded.
   *
   * @param {string} path
   *        The "."-separated path to find.
   * @returns {*}
   */
  findAPIPath(path) {
    if (this.apiPaths.has(path)) {
      return this.apiPaths.get(path);
    }

    let obj = this.root;
    let modules = this.apiManager.modulePaths;

    let parts = path.split(".");
    for (let [i, key] of parts.entries()) {
      if (!obj) {
        return;
      }
      modules = getChild(modules, key);

      for (let name of modules.modules) {
        if (!this.apis.has(name)) {
          this.loadAPI(name);
        }
      }

      if (!(key in obj) && i < parts.length - 1) {
        obj[key] = {};
      }
      obj = obj[key];
    }

    this.apiPaths.set(path, obj);
    return obj;
  }

  /**
   * Finds the API at the given path from the root object, and
   * asynchronously loads the API that implements it if it has not
   * already been loaded.
   *
   * @param {string} path
   *        The "."-separated path to find.
   * @returns {Promise<*>}
   */
  async asyncFindAPIPath(path) {
    if (this.apiPaths.has(path)) {
      return this.apiPaths.get(path);
    }

    let obj = this.root;
    let modules = this.apiManager.modulePaths;

    let parts = path.split(".");
    for (let [i, key] of parts.entries()) {
      if (!obj) {
        return;
      }
      modules = getChild(modules, key);

      for (let name of modules.modules) {
        if (!this.apis.has(name)) {
          await this.asyncLoadAPI(name);
        }
      }

      if (!(key in obj) && i < parts.length - 1) {
        obj[key] = {};
      }

      if (typeof obj[key] === "function") {
        obj = obj[key].bind(obj);
      } else {
        obj = obj[key];
      }
    }

    this.apiPaths.set(path, obj);
    return obj;
  }
}

/**
 * @class APIModule
 * @abstract
 *
 * @property {string} url
 *       The URL of the script which contains the module's
 *       implementation. This script must define a global property
 *       matching the modules name, which must be a class constructor
 *       which inherits from {@link ExtensionAPI}.
 *
 * @property {string} schema
 *       The URL of the JSON schema which describes the module's API.
 *
 * @property {Array<string>} scopes
 *       The list of scope names into which the API may be loaded.
 *
 * @property {Array<string>} manifest
 *       The list of top-level manifest properties which will trigger
 *       the module to be loaded, and its `onManifestEntry` method to be
 *       called.
 *
 * @property {Array<string>} events
 *       The list events which will trigger the module to be loaded, and
 *       its appropriate event handler method to be called. Currently
 *       only accepts "startup".
 *
 * @property {Array<string>} permissions
 *       An optional list of permissions, any of which must be present
 *       in order for the module to load.
 *
 * @property {Array<Array<string>>} paths
 *       A list of paths from the root API object which, when accessed,
 *       will cause the API module to be instantiated and injected.
 */

/**
 * This object loads the ext-*.js scripts that define the extension API.
 *
 * This class instance is shared with the scripts that it loads, so that the
 * ext-*.js scripts and the instantiator can communicate with each other.
 */
class SchemaAPIManager extends EventEmitter {
  /**
   * @param {string} processType
   *     "main" - The main, one and only chrome browser process.
   *     "addon" - An addon process.
   *     "content" - A content process.
   *     "devtools" - A devtools process.
   * @param {SchemaRoot} schema
   */
  constructor(processType, schema) {
    super();
    this.processType = processType;
    this.global = null;
    if (schema) {
      this.schema = schema;
    }

    this.modules = new Map();
    this.modulePaths = { children: new Map(), modules: new Set() };
    this.manifestKeys = new Map();
    this.eventModules = new DefaultMap(() => new Set());
    this.settingsModules = new Set();

    this._modulesJSONLoaded = false;

    this.schemaURLs = new Map();

    this.apis = new DefaultWeakMap(() => new Map());

    this._scriptScopes = [];
  }

  onStartup(extension) {
    let promises = [];
    for (let apiName of this.eventModules.get("startup")) {
      promises.push(
        extension.apiManager.asyncGetAPI(apiName, extension).then(api => {
          if (api) {
            api.onStartup();
          }
        })
      );
    }

    return Promise.all(promises);
  }

  async loadModuleJSON(urls) {
    let promises = urls.map(url => fetch(url).then(resp => resp.json()));

    return this.initModuleJSON(await Promise.all(promises));
  }

  initModuleJSON(blobs) {
    for (let json of blobs) {
      this.registerModules(json);
    }

    this._modulesJSONLoaded = true;

    return new StructuredCloneHolder({
      modules: this.modules,
      modulePaths: this.modulePaths,
      manifestKeys: this.manifestKeys,
      eventModules: this.eventModules,
      settingsModules: this.settingsModules,
      schemaURLs: this.schemaURLs,
    });
  }

  initModuleData(moduleData) {
    if (!this._modulesJSONLoaded) {
      let data = moduleData.deserialize({}, true);

      this.modules = data.modules;
      this.modulePaths = data.modulePaths;
      this.manifestKeys = data.manifestKeys;
      this.eventModules = new DefaultMap(() => new Set(), data.eventModules);
      this.settingsModules = new Set(data.settingsModules);
      this.schemaURLs = data.schemaURLs;
    }

    this._modulesJSONLoaded = true;
  }

  /**
   * Registers a set of ExtensionAPI modules to be lazily loaded and
   * managed by this manager.
   *
   * @param {object} obj
   *        An object containing property for eacy API module to be
   *        registered. Each value should be an object implementing the
   *        APIModule interface.
   */
  registerModules(obj) {
    for (let [name, details] of Object.entries(obj)) {
      details.namespaceName = name;

      if (this.modules.has(name)) {
        throw new Error(`Module '${name}' already registered`);
      }
      this.modules.set(name, details);

      if (details.schema) {
        let content =
          details.scopes &&
          (details.scopes.includes("content_parent") ||
            details.scopes.includes("content_child"));
        this.schemaURLs.set(details.schema, { content });
      }

      for (let event of details.events || []) {
        this.eventModules.get(event).add(name);
      }

      if (details.settings) {
        this.settingsModules.add(name);
      }

      for (let key of details.manifest || []) {
        if (this.manifestKeys.has(key)) {
          throw new Error(
            `Manifest key '${key}' already registered by '${this.manifestKeys.get(
              key
            )}'`
          );
        }

        this.manifestKeys.set(key, name);
      }

      for (let path of details.paths || []) {
        getPath(this.modulePaths, path).modules.add(name);
      }
    }
  }

  /**
   * Emits an `onManifestEntry` event for the top-level manifest entry
   * on all relevant {@link ExtensionAPI} instances for the given
   * extension.
   *
   * The API modules will be synchronously loaded if they have not been
   * loaded already.
   *
   * @param {Extension} extension
   *        The extension for which to emit the events.
   * @param {string} entry
   *        The name of the top-level manifest entry.
   *
   * @returns {*}
   */
  emitManifestEntry(extension, entry) {
    let apiName = this.manifestKeys.get(entry);
    if (apiName) {
      let api = extension.apiManager.getAPI(apiName, extension);
      return api.onManifestEntry(entry);
    }
  }
  /**
   * Emits an `onManifestEntry` event for the top-level manifest entry
   * on all relevant {@link ExtensionAPI} instances for the given
   * extension.
   *
   * The API modules will be asynchronously loaded if they have not been
   * loaded already.
   *
   * @param {Extension} extension
   *        The extension for which to emit the events.
   * @param {string} entry
   *        The name of the top-level manifest entry.
   *
   * @returns {Promise<*>}
   */
  async asyncEmitManifestEntry(extension, entry) {
    let apiName = this.manifestKeys.get(entry);
    if (apiName) {
      let api = await extension.apiManager.asyncGetAPI(apiName, extension);
      return api.onManifestEntry(entry);
    }
  }

  /**
   * Returns the {@link ExtensionAPI} instance for the given API module,
   * for the given extension, in the given scope, synchronously loading
   * and instantiating it if necessary.
   *
   * @param {string} name
   *        The name of the API module to load.
   * @param {Extension} extension
   *        The extension for which to load the API.
   * @param {string} [scope = null]
   *        The scope type for which to retrieve the API, or null if not
   *        being retrieved for a particular scope.
   *
   * @returns {ExtensionAPI?}
   */
  getAPI(name, extension, scope = null) {
    if (!this._checkGetAPI(name, extension, scope)) {
      return;
    }

    let apis = this.apis.get(extension);
    if (apis.has(name)) {
      return apis.get(name);
    }

    let module = this.loadModule(name);

    let api = new module(extension);
    apis.set(name, api);
    return api;
  }
  /**
   * Returns the {@link ExtensionAPI} instance for the given API module,
   * for the given extension, in the given scope, asynchronously loading
   * and instantiating it if necessary.
   *
   * @param {string} name
   *        The name of the API module to load.
   * @param {Extension} extension
   *        The extension for which to load the API.
   * @param {string} [scope = null]
   *        The scope type for which to retrieve the API, or null if not
   *        being retrieved for a particular scope.
   *
   * @returns {Promise<ExtensionAPI>?}
   */
  async asyncGetAPI(name, extension, scope = null) {
    if (!this._checkGetAPI(name, extension, scope)) {
      return;
    }

    let apis = this.apis.get(extension);
    if (apis.has(name)) {
      return apis.get(name);
    }

    let module = await this.asyncLoadModule(name);

    // Check again, because async.
    if (apis.has(name)) {
      return apis.get(name);
    }

    let api = new module(extension);
    apis.set(name, api);
    return api;
  }

  /**
   * Synchronously loads an API module, if not already loaded, and
   * returns its ExtensionAPI constructor.
   *
   * @param {string} name
   *        The name of the module to load.
   *
   * @returns {class}
   */
  loadModule(name) {
    let module = this.modules.get(name);
    if (module.loaded) {
      return this.global[name];
    }

    this._checkLoadModule(module, name);

    this.initGlobal();

    Services.scriptloader.loadSubScript(module.url, this.global);

    module.loaded = true;

    return this.global[name];
  }
  /**
   * aSynchronously loads an API module, if not already loaded, and
   * returns its ExtensionAPI constructor.
   *
   * @param {string} name
   *        The name of the module to load.
   *
   * @returns {Promise<class>}
   */
  asyncLoadModule(name) {
    let module = this.modules.get(name);
    if (module.loaded) {
      return Promise.resolve(this.global[name]);
    }
    if (module.asyncLoaded) {
      return module.asyncLoaded;
    }

    this._checkLoadModule(module, name);

    module.asyncLoaded = ChromeUtils.compileScript(module.url).then(script => {
      this.initGlobal();
      script.executeInGlobal(this.global);

      module.loaded = true;

      return this.global[name];
    });

    return module.asyncLoaded;
  }

  asyncLoadSettingsModules() {
    return Promise.all(
      Array.from(this.settingsModules).map(apiName =>
        this.asyncLoadModule(apiName)
      )
    );
  }

  getModule(name) {
    return this.modules.get(name);
  }

  /**
   * Checks whether the given API module may be loaded for the given
   * extension, in the given scope.
   *
   * @param {string} name
   *        The name of the API module to check.
   * @param {Extension} extension
   *        The extension for which to check the API.
   * @param {string} [scope = null]
   *        The scope type for which to check the API, or null if not
   *        being checked for a particular scope.
   *
   * @returns {boolean}
   *        Whether the module may be loaded.
   */
  _checkGetAPI(name, extension, scope = null) {
    let module = this.getModule(name);

    if (
      module.permissions &&
      !module.permissions.some(perm => extension.hasPermission(perm))
    ) {
      return false;
    }

    if (!scope) {
      return true;
    }

    if (!module.scopes.includes(scope)) {
      return false;
    }

    if (!Schemas.checkPermissions(module.namespaceName, extension)) {
      return false;
    }

    return true;
  }

  _checkLoadModule(module, name) {
    if (!module) {
      throw new Error(`Module '${name}' does not exist`);
    }
    if (module.asyncLoaded) {
      throw new Error(`Module '${name}' currently being lazily loaded`);
    }
    if (this.global && this.global[name]) {
      throw new Error(
        `Module '${name}' conflicts with existing global property`
      );
    }
  }

  /**
   * Create a global object that is used as the shared global for all ext-*.js
   * scripts that are loaded via `loadScript`.
   *
   * @returns {object} A sandbox that is used as the global by `loadScript`.
   */
  _createExtGlobal() {
    let global = Cu.Sandbox(
      Services.scriptSecurityManager.getSystemPrincipal(),
      {
        wantXrays: false,
        wantGlobalProperties: ["ChromeUtils"],
        sandboxName: `Namespace of ext-*.js scripts for ${
          this.processType
        } (from: resource://gre/modules/ExtensionCommon.jsm)`,
      }
    );

    Object.assign(global, {
      Cc,
      ChromeWorker,
      Ci,
      Cr,
      Cu,
      ExtensionAPI,
      ExtensionCommon,
      MatchGlob,
      MatchPattern,
      MatchPatternSet,
      StructuredCloneHolder,
      XPCOMUtils,
      extensions: this,
      global,
    });

    ChromeUtils.import("resource://gre/modules/AppConstants.jsm", global);

    XPCOMUtils.defineLazyGetter(global, "console", getConsole);

    XPCOMUtils.defineLazyModuleGetters(global, {
      ExtensionUtils: "resource://gre/modules/ExtensionUtils.jsm",
      XPCOMUtils: "resource://gre/modules/XPCOMUtils.jsm",
    });

    return global;
  }

  initGlobal() {
    if (!this.global) {
      this.global = this._createExtGlobal();
    }
  }

  /**
   * Load an ext-*.js script. The script runs in its own scope, if it wishes to
   * share state with another script it can assign to the `global` variable. If
   * it wishes to communicate with this API manager, use `extensions`.
   *
   * @param {string} scriptUrl The URL of the ext-*.js script.
   */
  loadScript(scriptUrl) {
    // Create the object in the context of the sandbox so that the script runs
    // in the sandbox's context instead of here.
    let scope = Cu.createObjectIn(this.global);

    Services.scriptloader.loadSubScript(scriptUrl, scope);

    // Save the scope to avoid it being garbage collected.
    this._scriptScopes.push(scope);
  }
}

class LazyAPIManager extends SchemaAPIManager {
  constructor(processType, moduleData, schemaURLs) {
    super(processType);

    this.initialized = false;

    this.initModuleData(moduleData);

    this.schemaURLs = schemaURLs;
  }
}

defineLazyGetter(LazyAPIManager.prototype, "schema", function() {
  let root = new SchemaRoot(Schemas.rootSchema, this.schemaURLs);
  root.parseSchemas();
  return root;
});

class MultiAPIManager extends SchemaAPIManager {
  constructor(processType, children) {
    super(processType);

    this.initialized = false;

    this.children = children;
  }

  async lazyInit() {
    if (!this.initialized) {
      this.initialized = true;

      for (let child of this.children) {
        if (child.lazyInit) {
          let res = child.lazyInit();
          if (res && typeof res.then === "function") {
            await res;
          }
        }

        mergePaths(this.modulePaths, child.modulePaths);
      }
    }
  }

  onStartup(extension) {
    return Promise.all(this.children.map(child => child.onStartup(extension)));
  }

  getModule(name) {
    for (let child of this.children) {
      if (child.modules.has(name)) {
        return child.modules.get(name);
      }
    }
  }

  loadModule(name) {
    for (let child of this.children) {
      if (child.modules.has(name)) {
        return child.loadModule(name);
      }
    }
  }

  asyncLoadModule(name) {
    for (let child of this.children) {
      if (child.modules.has(name)) {
        return child.asyncLoadModule(name);
      }
    }
  }
}

defineLazyGetter(MultiAPIManager.prototype, "schema", function() {
  let bases = this.children.map(child => child.schema);

  // All API manager schema roots should derive from the global schema root,
  // so it doesn't need its own entry.
  if (bases[bases.length - 1] === Schemas) {
    bases.pop();
  }

  if (bases.length === 1) {
    bases = bases[0];
  }
  return new SchemaRoot(bases, new Map());
});

function LocaleData(data) {
  this.defaultLocale = data.defaultLocale;
  this.selectedLocale = data.selectedLocale;
  this.locales = data.locales || new Map();
  this.warnedMissingKeys = new Set();

  // Map(locale-name -> Map(message-key -> localized-string))
  //
  // Contains a key for each loaded locale, each of which is a
  // Map of message keys to their localized strings.
  this.messages = data.messages || new Map();

  if (data.builtinMessages) {
    this.messages.set(this.BUILTIN, data.builtinMessages);
  }
}

LocaleData.prototype = {
  // Representation of the object to send to content processes. This
  // should include anything the content process might need.
  serialize() {
    return {
      defaultLocale: this.defaultLocale,
      selectedLocale: this.selectedLocale,
      messages: this.messages,
      locales: this.locales,
    };
  },

  BUILTIN: "@@BUILTIN_MESSAGES",

  has(locale) {
    return this.messages.has(locale);
  },

  // https://developer.chrome.com/extensions/i18n
  localizeMessage(message, substitutions = [], options = {}) {
    let defaultOptions = {
      defaultValue: "",
      cloneScope: null,
    };

    let locales = this.availableLocales;
    if (options.locale) {
      locales = new Set(
        [this.BUILTIN, options.locale, this.defaultLocale].filter(locale =>
          this.messages.has(locale)
        )
      );
    }

    options = Object.assign(defaultOptions, options);

    // Message names are case-insensitive, so normalize them to lower-case.
    message = message.toLowerCase();
    for (let locale of locales) {
      let messages = this.messages.get(locale);
      if (messages.has(message)) {
        let str = messages.get(message);

        if (!str.includes("$")) {
          return str;
        }

        if (!Array.isArray(substitutions)) {
          substitutions = [substitutions];
        }

        let replacer = (matched, index, dollarSigns) => {
          if (index) {
            // This is not quite Chrome-compatible. Chrome consumes any number
            // of digits following the $, but only accepts 9 substitutions. We
            // accept any number of substitutions.
            index = parseInt(index, 10) - 1;
            return index in substitutions ? substitutions[index] : "";
          }
          // For any series of contiguous `$`s, the first is dropped, and
          // the rest remain in the output string.
          return dollarSigns;
        };
        return str.replace(/\$(?:([1-9]\d*)|(\$+))/g, replacer);
      }
    }

    // Check for certain pre-defined messages.
    if (message == "@@ui_locale") {
      return this.uiLocale;
    } else if (message.startsWith("@@bidi_")) {
      let rtl = Services.locale.isAppLocaleRTL;

      if (message == "@@bidi_dir") {
        return rtl ? "rtl" : "ltr";
      } else if (message == "@@bidi_reversed_dir") {
        return rtl ? "ltr" : "rtl";
      } else if (message == "@@bidi_start_edge") {
        return rtl ? "right" : "left";
      } else if (message == "@@bidi_end_edge") {
        return rtl ? "left" : "right";
      }
    }

    if (!this.warnedMissingKeys.has(message)) {
      let error = `Unknown localization message ${message}`;
      if (options.cloneScope) {
        error = new options.cloneScope.Error(error);
      }
      Cu.reportError(error);
      this.warnedMissingKeys.add(message);
    }
    return options.defaultValue;
  },

  // Localize a string, replacing all |__MSG_(.*)__| tokens with the
  // matching string from the current locale, as determined by
  // |this.selectedLocale|.
  //
  // This may not be called before calling either |initLocale| or
  // |initAllLocales|.
  localize(str, locale = this.selectedLocale) {
    if (!str) {
      return str;
    }

    return str.replace(/__MSG_([A-Za-z0-9@_]+?)__/g, (matched, message) => {
      return this.localizeMessage(message, [], {
        locale,
        defaultValue: matched,
      });
    });
  },

  // Validates the contents of a locale JSON file, normalizes the
  // messages into a Map of message key -> localized string pairs.
  addLocale(locale, messages, extension) {
    let result = new Map();

    let isPlainObject = obj =>
      obj &&
      typeof obj === "object" &&
      ChromeUtils.getClassName(obj) === "Object";

    // Chrome does not document the semantics of its localization
    // system very well. It handles replacements by pre-processing
    // messages, replacing |$[a-zA-Z0-9@_]+$| tokens with the value of their
    // replacements. Later, it processes the resulting string for
    // |$[0-9]| replacements.
    //
    // Again, it does not document this, but it accepts any number
    // of sequential |$|s, and replaces them with that number minus
    // 1. It also accepts |$| followed by any number of sequential
    // digits, but refuses to process a localized string which
    // provides more than 9 substitutions.
    if (!isPlainObject(messages)) {
      extension.packagingError(`Invalid locale data for ${locale}`);
      return result;
    }

    for (let key of Object.keys(messages)) {
      let msg = messages[key];

      if (!isPlainObject(msg) || typeof msg.message != "string") {
        extension.packagingError(
          `Invalid locale message data for ${locale}, message ${JSON.stringify(
            key
          )}`
        );
        continue;
      }

      // Substitutions are case-insensitive, so normalize all of their names
      // to lower-case.
      let placeholders = new Map();
      if ("placeholders" in msg && isPlainObject(msg.placeholders)) {
        for (let key of Object.keys(msg.placeholders)) {
          placeholders.set(key.toLowerCase(), msg.placeholders[key]);
        }
      }

      let replacer = (match, name) => {
        let replacement = placeholders.get(name.toLowerCase());
        if (isPlainObject(replacement) && "content" in replacement) {
          return replacement.content;
        }
        return "";
      };

      let value = msg.message.replace(/\$([A-Za-z0-9@_]+)\$/g, replacer);

      // Message names are also case-insensitive, so normalize them to lower-case.
      result.set(key.toLowerCase(), value);
    }

    this.messages.set(locale, result);
    return result;
  },

  get acceptLanguages() {
    let result = Services.prefs.getComplexValue(
      "intl.accept_languages",
      Ci.nsIPrefLocalizedString
    ).data;
    return result.split(/\s*,\s*/g);
  },

  get uiLocale() {
    return Services.locale.appLocaleAsBCP47;
  },
};

defineLazyGetter(LocaleData.prototype, "availableLocales", function() {
  return new Set(
    [this.BUILTIN, this.selectedLocale, this.defaultLocale].filter(locale =>
      this.messages.has(locale)
    )
  );
});

/**
 * This is a generic class for managing event listeners.
 *
 * @example
 * new EventManager({
 *   context,
 *   name: "api.subAPI",
 *   register:  fire => {
 *     let listener = (...) => {
 *       // Fire any listeners registered with addListener.
 *       fire.async(arg1, arg2);
 *     };
 *     // Register the listener.
 *     SomehowRegisterListener(listener);
 *     return () => {
 *       // Return a way to unregister the listener.
 *       SomehowUnregisterListener(listener);
 *     };
 *   }
 * }).api()
 *
 * The result is an object with addListener, removeListener, and
 * hasListener methods. `context` is an add-on scope (either an
 * ExtensionContext in the chrome process or ExtensionContext in a
 * content process).
 */
class EventManager {
  /*
   * @param {object} params
   *        Parameters that control this EventManager.
   * @param {BaseContext} params.context
   *        An object representing the extension instance using this event.
   * @param {string} params.name
   *        A name used only for debugging.
   * @param {functon} params.register
   *        A function called whenever a new listener is added.
   * @param {boolean} [params.inputHandling=false]
   *        If true, the "handling user input" flag is set while handlers
   *        for this event are executing.
   * @param {object} [params.persistent]
   *        Details for persistent event listeners
   * @param {string} params.persistent.module
   *        The name of the module in which this event is defined.
   * @param {string} params.persistent.event
   *        The name of this event.
   */
  constructor(params) {
    let {
      context,
      name,
      register,
      inputHandling = false,
      persistent = null,
    } = params;
    this.context = context;
    this.name = name;
    this.register = register;
    this.inputHandling = inputHandling;
    this.persistent = persistent;

    // Don't bother with persistent event handling if delayed background
    // startup is not enabled.
    if (!DELAYED_BG_STARTUP) {
      this.persistent = null;
    }

    this.unregister = new Map();
    this.remove = new Map();

    if (this.persistent) {
      if (this.context.viewType !== "background") {
        this.persistent = null;
      }
      if (AppConstants.DEBUG) {
        if (this.context.envType !== "addon_parent") {
          throw new Error(
            "Persistent event managers can only be created for addon_parent"
          );
        }
        if (!this.persistent.module || !this.persistent.event) {
          throw new Error(
            "Persistent event manager must specify module and event"
          );
        }
      }
    }
  }

  /*
   * Information about listeners to persistent events is associated with
   * the extension to which they belong.  Any extension thas has such
   * listeners has a property called `persistentListeners` that is a
   * 3-level Map.  The first 2 keys are the module name (e.g., webRequest)
   * and the name of the event within the module (e.g., onBeforeRequest).
   * The third level of the map is used to track multiple listeners for
   * the same event, these listeners are distinguished by the extra arguments
   * passed to addListener().  For quick lookups, the key to the third Map
   * is the result of calling uneval() on the array of extra arguments.
   *
   * The value stored in the Map is a plain object with a property called
   * `params` that is the original (ie, not uneval()ed) extra arguments to
   * addListener().  For a primed listener (i.e., the stub listener created
   * during browser startup before the extension background page is started,
   * the object also has a `primed` property that holds the things needed
   * to handle events during startup and eventually connect the listener
   * with a callback registered from the extension.
   *
   * @param {Extension} extension
   * @returns {boolean} True if the extension had any persistent listeners.
   */
  static _initPersistentListeners(extension) {
    if (extension.persistentListeners) {
      return false;
    }

    let listeners = new DefaultMap(() => new DefaultMap(() => new Map()));
    extension.persistentListeners = listeners;

    let { persistentListeners } = extension.startupData;
    if (!persistentListeners) {
      return false;
    }

    let found = false;
    for (let [module, entry] of Object.entries(persistentListeners)) {
      for (let [event, paramlists] of Object.entries(entry)) {
        for (let paramlist of paramlists) {
          let key = uneval(paramlist);
          listeners
            .get(module)
            .get(event)
            .set(key, { params: paramlist });
          found = true;
        }
      }
    }
    return found;
  }

  // Extract just the information needed at startup for all persistent
  // listeners, and arrange for it to be saved.  This should be called
  // whenever the set of persistent listeners for an extension changes.
  static _writePersistentListeners(extension) {
    let startupListeners = {};
    for (let [module, moduleEntry] of extension.persistentListeners) {
      startupListeners[module] = {};
      for (let [event, eventEntry] of moduleEntry) {
        startupListeners[module][event] = Array.from(
          eventEntry.values(),
          listener => listener.params
        );
      }
    }

    extension.startupData.persistentListeners = startupListeners;
    extension.saveStartupData();
  }

  // Set up "primed" event listeners for any saved event listeners
  // in an extension's startup data.
  // This function is only called during browser startup, it stores details
  // about all primed listeners in the extension's persistentListeners Map.
  static primeListeners(extension) {
    if (!EventManager._initPersistentListeners(extension)) {
      return;
    }

    let bgStartupPromise = new Promise(resolve => {
      function resolveBgPromise(type) {
        extension.off("startup", resolveBgPromise);
        extension.off("background-page-aborted", resolveBgPromise);
        extension.off("shutdown", resolveBgPromise);
        resolve();
      }
      extension.on("startup", resolveBgPromise);
      extension.on("background-page-aborted", resolveBgPromise);
      extension.on("shutdown", resolveBgPromise);
    });

    for (let [module, moduleEntry] of extension.persistentListeners) {
      let api = extension.apiManager.getAPI(module, extension, "addon_parent");
      for (let [event, eventEntry] of moduleEntry) {
        for (let listener of eventEntry.values()) {
          let primed = { pendingEvents: [] };
          listener.primed = primed;

          let wakeup = () => {
            extension.emit("background-page-event");
            return bgStartupPromise;
          };

          let fireEvent = (...args) =>
            new Promise((resolve, reject) => {
              if (!listener.primed) {
                reject(new Error("primed listener not re-registered"));
                return;
              }
              primed.pendingEvents.push({ args, resolve, reject });
              extension.emit("background-page-event");
            });

          let fire = {
            wakeup,
            sync: fireEvent,
            async: fireEvent,
          };

          let { unregister, convert } = api.primeListener(
            extension,
            event,
            fire,
            listener.params
          );
          Object.assign(primed, { unregister, convert });
        }
      }
    }
  }

  // Remove a primed listener for the given event (with the given extra
  // addListener arguments).  This ordinarily happens as a side effect of
  // calling addListener(), but APIs that need special handling (e.g.,
  // runtime.onConnect and onMessage which don't have EventManagers in the
  // parent process) can use this directly.
  static clearOnePrimedListener(extension, module, event, args = []) {
    let key = uneval(args);
    let listener = extension.persistentListeners
      .get(module)
      .get(event)
      .get(key);
    if (listener.primed) {
      listener.primed = null;
    }
  }

  // Remove any primed listeners that were not re-registered.
  // This function is called after the background page has started.
  // The removed listeners are removed from the set of saved listeners, unless
  // `clearPersistent` is false. If false, the listeners are cleared from
  // memory, but not removed from the extension's startup data.
  static clearPrimedListeners(extension, clearPersistent = true) {
    for (let [module, moduleEntry] of extension.persistentListeners) {
      for (let [event, listeners] of moduleEntry) {
        for (let [key, listener] of listeners) {
          let { primed } = listener;
          if (!primed) {
            continue;
          }
          listener.primed = null;

          for (let evt of primed.pendingEvents) {
            evt.reject(new Error("listener not re-registered"));
          }

          if (clearPersistent) {
            EventManager.clearPersistentListener(extension, module, event, key);
          }
          primed.unregister();
        }
      }
    }
  }

  // Record the fact that there is a listener for the given event in
  // the given extension.  `args` is an Array containing any extra
  // arguments that were passed to addListener().
  static savePersistentListener(extension, module, event, args = []) {
    EventManager._initPersistentListeners(extension);
    let key = uneval(args);
    extension.persistentListeners
      .get(module)
      .get(event)
      .set(key, { params: args });
    EventManager._writePersistentListeners(extension);
  }

  // Remove the record for the given event listener from the extension's
  // startup data.  `key` must be a string, the result of calling uneval()
  // on the array of extra arguments originally passed to addListener().
  static clearPersistentListener(extension, module, event, key = uneval([])) {
    let listeners = extension.persistentListeners.get(module).get(event);
    listeners.delete(key);

    if (listeners.size == 0) {
      let moduleEntry = extension.persistentListeners.get(module);
      moduleEntry.delete(event);
      if (moduleEntry.size == 0) {
        extension.persistentListeners.delete(module);
      }
    }

    EventManager._writePersistentListeners(extension);
  }

  addListener(callback, ...args) {
    if (this.unregister.has(callback)) {
      return;
    }
    this.context.logActivity("api_call", `${this.name}.addListener`, { args });

    let shouldFire = () => {
      if (this.context.unloaded) {
        dump(`${this.name} event fired after context unloaded.\n`);
      } else if (!this.context.active) {
        dump(`${this.name} event fired while context is inactive.\n`);
      } else if (this.unregister.has(callback)) {
        return true;
      }
      return false;
    };

    let fire = {
      sync: (...args) => {
        if (shouldFire()) {
          let result = this.context.applySafe(callback, args);
          this.context.logActivity("api_event", this.name, { args, result });
          return result;
        }
      },
      async: (...args) => {
        return Promise.resolve().then(() => {
          if (shouldFire()) {
            let result = this.context.applySafe(callback, args);
            this.context.logActivity("api_event", this.name, { args, result });
            return result;
          }
        });
      },
      raw: (...args) => {
        if (!shouldFire()) {
          throw new Error("Called raw() on unloaded/inactive context");
        }
        let result = Reflect.apply(callback, null, args);
        this.context.logActivity("api_event", this.name, { args, result });
        return result;
      },
      asyncWithoutClone: (...args) => {
        return Promise.resolve().then(() => {
          if (shouldFire()) {
            let result = this.context.applySafeWithoutClone(callback, args);
            this.context.logActivity("api_event", this.name, { args, result });
            return result;
          }
        });
      },
    };

    let { extension } = this.context;

    let unregister = null;
    let recordStartupData = false;

    // If this is a persistent event, check for a listener that was already
    // created during startup.  If there is one, use it and don't create a
    // new one.
    if (this.persistent) {
      recordStartupData = true;
      let { module, event } = this.persistent;

      let key = uneval(args);
      EventManager._initPersistentListeners(extension);
      let listener = extension.persistentListeners
        .get(module)
        .get(event)
        .get(key);

      if (listener) {
        // If extensions.webextensions.background-delayed-startup is disabled,
        // we can have stored info here but no primed listener.  This check
        // can be removed if/when we make delayed background startup the only
        // supported setting.
        let { primed } = listener;
        if (primed) {
          listener.primed = null;

          primed.convert(fire, this.context);
          unregister = primed.unregister;

          for (let evt of primed.pendingEvents) {
            evt.resolve(fire.async(...evt.args));
          }
        }

        recordStartupData = false;
        this.remove.set(callback, () => {
          EventManager.clearPersistentListener(
            extension,
            module,
            event,
            uneval(args)
          );
        });
      }
    }

    if (!unregister) {
      unregister = this.register(fire, ...args);
    }

    this.unregister.set(callback, unregister);
    this.context.callOnClose(this);

    // If this is a new listener for a persistent event, record
    // the details for subsequent startups.
    if (recordStartupData) {
      let { module, event } = this.persistent;
      EventManager.savePersistentListener(extension, module, event, args);
      this.remove.set(callback, () => {
        EventManager.clearPersistentListener(
          extension,
          module,
          event,
          uneval(args)
        );
      });
    }
  }

  removeListener(callback, clearPersistentListener = true) {
    if (!this.unregister.has(callback)) {
      return;
    }

    let unregister = this.unregister.get(callback);
    this.unregister.delete(callback);
    try {
      unregister();
    } catch (e) {
      Cu.reportError(e);
    }

    if (clearPersistentListener && this.remove.has(callback)) {
      let cleanup = this.remove.get(callback);
      this.remove.delete(callback);
      cleanup();
    }

    if (this.unregister.size == 0) {
      this.context.forgetOnClose(this);
    }
  }

  hasListener(callback) {
    return this.unregister.has(callback);
  }

  revoke() {
    for (let callback of this.unregister.keys()) {
      this.removeListener(callback, false);
    }
  }

  close() {
    this.revoke();
  }

  api() {
    return {
      addListener: (...args) => this.addListener(...args),
      removeListener: (...args) => this.removeListener(...args),
      hasListener: (...args) => this.hasListener(...args),
      setUserInput: this.inputHandling,
      [Schemas.REVOKE]: () => this.revoke(),
    };
  }
}

// Simple API for event listeners where events never fire.
function ignoreEvent(context, name) {
  return {
    addListener: function(callback) {
      let id = context.extension.id;
      let frame = Components.stack.caller;
      let msg = `In add-on ${id}, attempting to use listener "${name}", which is unimplemented.`;
      let scriptError = Cc["@mozilla.org/scripterror;1"].createInstance(
        Ci.nsIScriptError
      );
      scriptError.init(
        msg,
        frame.filename,
        null,
        frame.lineNumber,
        frame.columnNumber,
        Ci.nsIScriptError.warningFlag,
        "content javascript"
      );
      Services.console.logMessage(scriptError);
    },
    removeListener: function(callback) {},
    hasListener: function(callback) {},
  };
}

const stylesheetMap = new DefaultMap(url => {
  let uri = Services.io.newURI(url);
  return styleSheetService.preloadSheet(uri, styleSheetService.AGENT_SHEET);
});

ExtensionCommon = {
  BaseContext,
  CanOfAPIs,
  EventManager,
  ExtensionAPI,
  EventEmitter,
  LocalAPIImplementation,
  LocaleData,
  NoCloneSpreadArgs,
  SchemaAPIInterface,
  SchemaAPIManager,
  SpreadArgs,
  checkLoadURL,
  defineLazyGetter,
  getConsole,
  ignoreEvent,
  instanceOf,
  makeWidgetId,
  normalizeTime,
  runSafeSyncWithoutClone,
  stylesheetMap,
  withHandlingUserInput,

  MultiAPIManager,
  LazyAPIManager,
};