Quelle prefs.js Sprache: JAVA

/* 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";

const EventEmitter = require("resource://devtools/shared/event-emitter.js");

/**
* Shortcuts for lazily accessing and setting various preferences.
* Usage:
*   let prefs = new Prefs("root.path.to.branch", {
*     myIntPref: ["Int", "leaf.path.to.my-int-pref"],
*     myCharPref: ["Char", "leaf.path.to.my-char-pref"],
*     myJsonPref: ["Json", "leaf.path.to.my-json-pref"],
*     myFloatPref: ["Float", "leaf.path.to.my-float-pref"]
*     ...
*   });
*
* Get/set:
*   prefs.myCharPref = "foo";
*   let aux = prefs.myCharPref;
*
* Observe:
*   prefs.registerObserver();
*   prefs.on("pref-changed", (prefValue) => {
*     ...
*   });
*
* @param string prefsRoot
*        The root path to the required preferences branch.
* @param object prefsBlueprint
*        An object containing { accessorName: [prefType, prefName] } keys.
*/
function PrefsHelper(prefsRoot = "", prefsBlueprint = {}) {
  EventEmitter.decorate(this);

  const cache = new Map();

  for (const accessorName in prefsBlueprint) {
    const [prefType, prefName, fallbackValue] = prefsBlueprint[accessorName];
    map(
      this,
      cache,
      accessorName,
      prefType,
      prefsRoot,
      prefName,
      fallbackValue
    );
  }

  const observer = makeObserver(this, cache, prefsRoot, prefsBlueprint);
  this.registerObserver = () => observer.register();
  this.unregisterObserver = () => observer.unregister();
}

/**
* Helper method for getting a pref value.
*
* @param Map cache
* @param string prefType
* @param string prefsRoot
* @param string prefName
* @param string|int|boolean fallbackValue
* @return any
*/
function get(cache, prefType, prefsRoot, prefName, fallbackValue) {
  const cachedPref = cache.get(prefName);
  if (cachedPref !== undefined) {
    return cachedPref;
  }
  const value = Services.prefs["get" + prefType + "Pref"](
    [prefsRoot, prefName].join("."),
    fallbackValue
  );
  cache.set(prefName, value);
  return value;
}

/**
* Helper method for setting a pref value.
*
* @param Map cache
* @param string prefType
* @param string prefsRoot
* @param string prefName
* @param any value
*/
function set(cache, prefType, prefsRoot, prefName, value) {
  Services.prefs["set" + prefType + "Pref"](
    [prefsRoot, prefName].join("."),
    value
  );
  cache.set(prefName, value);
}

/**
* Maps a property name to a pref, defining lazy getters and setters.
* Supported types are "Bool", "Char", "Int", "Float" (sugar around "Char"
* type and casting), and "Json" (which is basically just sugar for "Char"
* using the standard JSON serializer).
*
* @param PrefsHelper self
* @param Map cache
* @param string accessorName
* @param string prefType
* @param string prefsRoot
* @param string prefName
* @param string|int|boolean fallbackValue
* @param array serializer [optional]
*/
function map(
  self,
  cache,
  accessorName,
  prefType,
  prefsRoot,
  prefName,
  fallbackValue,
  serializer = { in: e => e, out: e => e }
) {
  if (prefName in self) {
    throw new Error(
      `Can't use ${prefName} because it overrides a property` +
        "on the instance."
    );
  }
  if (prefType == "Json") {
    map(
      self,
      cache,
      accessorName,
      "String",
      prefsRoot,
      prefName,
      fallbackValue,
      {
        in: JSON.parse,
        out: JSON.stringify,
      }
    );
    return;
  }
  if (prefType == "Float") {
    map(self, cache, accessorName, "Char", prefsRoot, prefName, fallbackValue, {
      in: Number.parseFloat,
      out: n => n + "",
    });
    return;
  }

  Object.defineProperty(self, accessorName, {
    get: () =>
      serializer.in(get(cache, prefType, prefsRoot, prefName, fallbackValue)),
    set: e => {
      set(cache, prefType, prefsRoot, prefName, serializer.out(e));
    },
  });
}

/**
* Finds the accessor for the provided pref, based on the blueprint object
* used in the constructor.
*
* @param PrefsHelper self
* @param object prefsBlueprint
* @return string
*/
function accessorNameForPref(somePrefName, prefsBlueprint) {
  for (const accessorName in prefsBlueprint) {
    const [, prefName] = prefsBlueprint[accessorName];
    if (somePrefName == prefName) {
      return accessorName;
    }
  }
  return "";
}

/**
* Creates a pref observer for `self`.
*
* @param PrefsHelper self
* @param Map cache
* @param string prefsRoot
* @param object prefsBlueprint
* @return object
*/
function makeObserver(self, cache, prefsRoot, prefsBlueprint) {
  return {
    register() {
      this._branch = Services.prefs.getBranch(prefsRoot + ".");
      this._branch.addObserver("", this);
    },
    unregister() {
      this._branch.removeObserver("", this);
    },
    observe(subject, topic, prefName) {
      // If this particular pref isn't handled by the blueprint object,
      // even though it's in the specified branch, ignore it.
      const accessorName = accessorNameForPref(prefName, prefsBlueprint);
      if (!(accessorName in self)) {
        return;
      }
      cache.delete(prefName);
      self.emit("pref-changed", accessorName, self[accessorName]);
    },
  };
}

exports.PrefsHelper = PrefsHelper;

/**
* A PreferenceObserver observes a pref branch for pref changes.
* It emits an event for each preference change.
*/
class PrefObserver extends EventEmitter {
  constructor(branchName) {
    super();

    this.#branchName = branchName;
    this.#branch = Services.prefs.getBranch(branchName);
    this.#branch.addObserver("", this);
  }

  #branchName;
  #branch;

  observe(subject, topic, data) {
    if (topic == "nsPref:changed") {
      this.emit(this.#branchName + data);
    }
  }

  destroy() {
    this.#branch.removeObserver("", this);
  }
}

exports.PrefObserver = PrefObserver;

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