/*****************************************************************************
 * Open MCT Web, Copyright (c) 2014-2015, United States Government
 * as represented by the Administrator of the National Aeronautics and Space
 * Administration. All rights reserved.
 *
 * Open MCT Web is 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.
 *
 * Open MCT Web includes source code licensed under additional open source
 * licenses. See the Open Source Licenses file (LICENSES.md) included with
 * this source code distribution or the Licensing information page available
 * at runtime from the About dialog for additional information.
 *****************************************************************************/
/*global define,Promise*/

/**
 * Module defining BundleLoader.js. Created by vwoeltje on 10/31/14.
 */
define(
    ['../Constants', './Bundle'],
    function (Constants, Bundle) {
        "use strict";

        var INVALID_ARGUMENT_MESSAGE = "Malformed loadBundles argument; " +
            "expected string or array",
            BAD_CONTENTS_PREFIX = "Invalid bundle contents for ",
            LOAD_ERROR_PREFIX = "Failed to load bundle ";

        /**
         * Loads bundle definitions and wraps them in interfaces which are
         * useful to the framework. This provides the base information which
         * will be used by later phases of framework layer initialization.
         *
         * @memberof platform/framework
         * @constructor
         * @param $http Angular's HTTP requester
         * @param $log Angular's logging service
         */
        function BundleLoader($http, $log, legacyRegistry) {
            this.$http = $http;
            this.$log = $log;
            this.legacyRegistry = legacyRegistry;
        }

        /**
         * Load a group of bundles, to be used to constitute the
         * application by later framework initialization phases.
         *
         * @param {string|string[]} an array of bundle names to load, or
         *        the name of a JSON file containing that array
         * @returns {Promise.<Bundle[]>} a promise for the loaded bundles
         */
        BundleLoader.prototype.loadBundles = function (bundles) {
            var $http = this.$http,
                $log = this.$log,
                legacyRegistry = this.legacyRegistry;

            // Utility function; load contents of JSON file using $http
            function getJSON(file) {
                return $http.get(file).then(function (response) {
                    return response.data;
                });
            }

            // Remove bundles which failed to load properly.
            // These should have been logged when loaded by
            // loadBundleDefinition, so at this point they are safe
            // to discard.
            function filterBundles(array) {
                return array.filter(function (x) { return x !== undefined; });
            }

            // Load a definition for a bundle
            function loadBundleDefinition(bundlePath) {
                return getJSON(bundlePath + "/" + Constants.BUNDLE_FILE).then(
                    function (x) {
                        if (x === null || typeof x !== 'object') {
                            $log.warn(BAD_CONTENTS_PREFIX + bundlePath);
                            return undefined;
                        }
                        return x;
                    },
                    function () {
                        $log.warn(LOAD_ERROR_PREFIX + bundlePath);
                        return undefined;
                    }
                );
            }

            // Load an individual bundle, as a Bundle object.
            // Returns undefined if the definition could not be loaded.
            function loadBundle(bundlePath) {
                if (legacyRegistry.contains(bundlePath)) {
                    return Promise.resolve(new Bundle(
                        bundlePath,
                        legacyRegistry.get(bundlePath)
                    ));
                }

                return loadBundleDefinition(bundlePath).then(function (definition) {
                    return definition && (new Bundle(bundlePath, definition));
                });
            }

            // Used to filter out redundant bundles
            function unique(element, index, array) {
                return array.indexOf(element) === index;
            }

            // Load all named bundles from the array, returned as an array
            // of Bundle objects.
            function loadBundlesFromArray(bundleArray) {
                var bundlePromises = legacyRegistry.list()
                    .concat(bundleArray)
                    .filter(unique)
                    .map(loadBundle);

                return Promise.all(bundlePromises)
                    .then(filterBundles);
            }

            // Load all bundles named in the referenced file. The file is
            // presumed to be a JSON file
            function loadBundlesFromFile(listFile) {
                function handleError(err) {
                    $log.info([
                        "No external bundles loaded;",
                        "could not load bundle listing in",
                        listFile,
                        "due to error",
                        err.status,
                        err.statusText
                    ].join(' '));
                    return loadBundlesFromArray([]);
                }

                return getJSON(listFile)
                    .then(loadBundlesFromArray, handleError);
            }

            return Array.isArray(bundles) ? loadBundlesFromArray(bundles) :
                    (typeof bundles === 'string') ? loadBundlesFromFile(bundles) :
                            Promise.reject(new Error(INVALID_ARGUMENT_MESSAGE));
        };

        return BundleLoader;
    }
);