/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

/* global define, module, require, exports */

(function (root, factory) {
    if (typeof define === 'function' && define.amd) {
        define([], function () {
            return (nf.Storage = factory());
        });
    } else if (typeof exports === 'object' && typeof module === 'object') {
        module.exports = (nf.Storage = factory());
    } else {
        nf.Storage = factory();
    }
}(this, function () {

    var disconnectionAcknowledged = false;

    // Store items for two days before being eligible for removal.
    var MILLIS_PER_DAY = 86400000;
    var TWO_DAYS = MILLIS_PER_DAY * 2;

    var isUndefined = function (obj) {
        return typeof obj === 'undefined';
    };

    var isNull = function (obj) {
        return obj === null;
    };

    var isDefinedAndNotNull = function (obj) {
        return !isUndefined(obj) && !isNull(obj);
    };

    /**
     * Checks the expiration for the specified entry.
     *
     * @param {object} entry
     * @returns {boolean}
     */
    var checkExpiration = function (entry) {
        if (isDefinedAndNotNull(entry.expires)) {
            // get the expiration
            var expires = new Date(entry.expires);
            var now = new Date();

            // return whether the expiration date has passed
            return expires.valueOf() < now.valueOf();
        } else {
            return false;
        }
    };

    /**
     * Gets an enty for the key. The entry expiration is not checked.
     *
     * @param {string} key
     */
    var getEntry = function (key) {
        try {
            // parse the entry
            var entry = JSON.parse(localStorage.getItem(key));

            // ensure the entry and item are present
            if (isDefinedAndNotNull(entry)) {
                return entry;
            } else {
                return null;
            }
        } catch (e) {
            return null;
        }
    };

    return {
        /**
         * Initializes the storage. Items will be persisted for two days. Once the scripts runs
         * thereafter, all eligible items will be removed. This strategy does not support persistence.
         */
        init: function () {
            for (var i = 0; i < localStorage.length; i++) {
                try {
                    // get the next item
                    var key = localStorage.key(i);

                    // attempt to get the item which will expire if necessary
                    this.getItem(key);
                } catch (e) {
                }
            }
        },

        acknowledgeDisconnection: function () {
            disconnectionAcknowledged = true;
        },

        resetDisconnectionAcknowledgement: function () {
            disconnectionAcknowledged = false;
        },

        isDisconnectionAcknowledged: function () {
            return disconnectionAcknowledged;
        },

        /**
         * Stores the specified item.
         *
         * @param {string} key
         * @param {object} item
         * @param {integer} expires
         */
        setItem: function (key, item, expires) {
            // calculate the expiration
            expires = isDefinedAndNotNull(expires) ? expires : new Date().valueOf() + TWO_DAYS;

            // create the entry
            var entry = {
                expires: expires,
                item: item
            };

            // store the item
            localStorage.setItem(key, JSON.stringify(entry));
        },

        /**
         * Returns whether there is an entry for this key. This will not check the expiration. If
         * the entry is expired, it will return null on a subsequent getItem invocation.
         *
         * @param {string} key
         * @returns {boolean}
         */
        hasItem: function (key) {
            return getEntry(key) !== null;
        },

        /**
         * Gets the item with the specified key. If an item with this key does
         * not exist, null is returned. If an item exists but cannot be parsed
         * or is malformed/unrecognized, null is returned.
         *
         * @param {type} key
         */
        getItem: function (key) {
            var entry = getEntry(key);
            if (entry === null) {
                return null;
            }

            // if the entry is expired, drop it and return null
            if (checkExpiration(entry)) {
                this.removeItem(key);
                return null;
            }

            // if the entry has the specified field return its value
            if (isDefinedAndNotNull(entry['item'])) {
                return entry['item'];
            } else {
                return null;
            }
        },

        /**
         * Gets the expiration for the specified item. This will not check the expiration. If
         * the entry is expired, it will return null on a subsequent getItem invocation.
         *
         * @param {string} key
         * @returns {integer}
         */
        getItemExpiration: function (key) {
            var entry = getEntry(key);
            if (entry === null) {
                return null;
            }

            // if the entry has the specified field return its value
            if (isDefinedAndNotNull(entry['expires'])) {
                return entry['expires'];
            } else {
                return null;
            }
        },

        /**
         * Removes the item with the specified key.
         *
         * @param {type} key
         */
        removeItem: function (key) {
            localStorage.removeItem(key);
        }
    };
}));