/* 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/>. */

// @flow

import { asyncStorage } from "devtools-modules";

/*
 * asyncStoreHelper wraps asyncStorage so that it is easy to define project
 * specific properties. It is similar to PrefsHelper.
 *
 * e.g.
 *   const asyncStore = asyncStoreHelper("r", {a: "_a"})
 *   asyncStore.a         // => asyncStorage.getItem("r._a")
 *   asyncStore.a = 2     // => asyncStorage.setItem("r._a", 2)
 */
export function asyncStoreHelper(root: string, mappings: Object) {
  let store: any = {};

  function getMappingKey(key) {
    return Array.isArray(mappings[key]) ? mappings[key][0] : mappings[key];
  }

  function getMappingDefaultValue(key) {
    return Array.isArray(mappings[key]) ? mappings[key][1] : null;
  }

  Object.keys(mappings).map(key =>
    Object.defineProperty(store, key, {
      async get() {
        const value = await asyncStorage.getItem(
          `${root}.${getMappingKey(key)}`
        );
        return value || getMappingDefaultValue(key);
      },
      set(value) {
        return asyncStorage.setItem(`${root}.${getMappingKey(key)}`, value);
      }
    })
  );

  store = new Proxy(store, {
    set: function(target, property, value, receiver) {
      if (!mappings.hasOwnProperty(property)) {
        throw new Error(`AsyncStore: ${property} is not defined in mappings`);
      }

      Reflect.set(...arguments);
      return true;
    }
  });

  return (store: { [$Keys<typeof mappings>]: any });
}