/* Copyright 2017 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
var babel = require('plugin-babel');

var cacheExpiration = 60 /* min */ * 60 * 1000;
var dbVersion = 1;
var dbName = 'babelcache';
var dbCacheTable = 'translated';
var dbPromise;

function getDb() {
  if (!dbPromise) {
    dbPromise = new Promise(function (resolve, reject) {
      var request = indexedDB.open(dbName, dbVersion);
      request.onupgradeneeded = function() {
        var db = request.result;
        db.createObjectStore(dbCacheTable, {keyPath: 'address'});
      };
      request.onsuccess = function() {
        var db = request.result;
        resolve(db);
      };
      request.onerror = function () {
        reject(request.error);
      };
    });
  }
  return dbPromise;
}

function storeCache(address, hashCode, translated, format) {
  return getDb().then(function (db) {
    var tx = db.transaction(dbCacheTable, 'readwrite');
    var store = tx.objectStore(dbCacheTable);
    store.put({
      address: address,
      hashCode: hashCode,
      translated: translated,
      expires: Date.now() + cacheExpiration,
      format: format,
    });
    return new Promise(function (resolve, reject) {
      tx.oncomplete = function () {
        resolve();
      };
    });
  });
}

function loadCache(address, hashCode) {
  return getDb().then(function (db) {
    var tx = db.transaction(dbCacheTable, 'readonly');
    var store = tx.objectStore(dbCacheTable);
    var getAddress = store.get(address);
    return new Promise(function (resolve, reject) {
      tx.oncomplete = function () {
        var found = getAddress.result;
        var isValid = found && found.hashCode === hashCode &&
                      Date.now() < found.expires;
        resolve(isValid ? {
          translated: found.translated,
          format: found.format,
        } : null);
      };
    });
  });
}

var encoder = new TextEncoder('utf-8');
function sha256(str) {
  var buffer = encoder.encode(str);
  return crypto.subtle.digest('SHA-256', buffer).then(function (hash) {
    var data = new Int32Array(hash);
    return data[0].toString(36) + '-' + data[1].toString(36) + '-' +
           data[2].toString(36) + '-' + data[3].toString(36);
  });
}

exports.translate = function (load, opt) {
  var savedHashCode;
  return sha256(load.source).then(function (hashCode) {
    savedHashCode = hashCode;
    return loadCache(load.address, hashCode);
  }).then(function (cache) {
    if (cache) {
      load.metadata.format = cache.format;
      return cache.translated;
    }
    return babel.translate.call(this, load, opt).then(function(translated) {
      return storeCache(load.address, savedHashCode,
                        translated, load.metadata.format).then(function () {
        return translated;
      });
    });
  }.bind(this));
};