/**
 * Infinite Ajax Scroll v2.2.0
 * A jQuery plugin for infinite scrolling
 * http://infiniteajaxscroll.com
 *
 * Commercial use requires one-time purchase of a commercial license
 * http://infiniteajaxscroll.com/docs/license.html
 *
 * Non-commercial use is licensed under the MIT License
 *
 * Copyright 2014 Webcreate (Jeroen Fiege)
 */

(function ($) {

    'use strict';

    var UNDETERMINED_SCROLLOFFSET = -1;

    var IAS = function ($element, options) {
        this.itemsContainerSelector = options.container;
        this.itemSelector = options.item;
        this.nextSelector = options.next;
        this.paginationSelector = options.pagination;
        this.$scrollContainer = $element;
        this.$container = (window === $element.get(0) ? $(document) : $element);
        this.defaultDelay = options.delay;
        this.negativeMargin = options.negativeMargin;
        this.nextUrl = null;
        this.isBound = false;
        this.isPaused = false;
        this.listeners = {
            next: new IASCallbacks(),
            load: new IASCallbacks(),
            loaded: new IASCallbacks(),
            render: new IASCallbacks(),
            rendered: new IASCallbacks(),
            scroll: new IASCallbacks(),
            noneLeft: new IASCallbacks(),
            ready: new IASCallbacks()
        };
        this.extensions = [];

        /**
         * Scroll event handler
         *
         * Note: calls to this functions should be throttled
         *
         * @private
         */
        this.scrollHandler = function () {
            // the throttle method can call the scrollHandler even thought we have called unbind()
            if (!this.isBound || this.isPaused) {
                return;
            }

            var currentScrollOffset = this.getCurrentScrollOffset(this.$scrollContainer),
                    scrollThreshold = this.getScrollThreshold()
                    ;

            // invalid scrollThreshold. The DOM might not have loaded yet...
            if (UNDETERMINED_SCROLLOFFSET == scrollThreshold) {
                return;
            }

            this.fire('scroll', [currentScrollOffset, scrollThreshold]);

            if (currentScrollOffset >= scrollThreshold) {
                this.next();
            }
        };

        /**
         * Returns the items container currently in the DOM
         *
         * @private
         * @returns {object}
         */
        this.getItemsContainer = function () {
            return $(this.itemsContainerSelector);
        };

        /**
         * Returns the last item currently in the DOM
         *
         * @private
         * @returns {object}
         */
        this.getLastItem = function () {
            return $(this.itemSelector, this.getItemsContainer().get(0)).last();
        };

        /**
         * Returns the first item currently in the DOM
         *
         * @private
         * @returns {object}
         */
        this.getFirstItem = function () {
            return $(this.itemSelector, this.getItemsContainer().get(0)).first();
        };

        /**
         * Returns scroll threshold. This threshold marks the line from where
         * IAS should start loading the next page.
         *
         * @private
         * @param negativeMargin defaults to {this.negativeMargin}
         * @return {number}
         */
        this.getScrollThreshold = function (negativeMargin) {
            var $lastElement;

            negativeMargin = negativeMargin || this.negativeMargin;
            negativeMargin = (negativeMargin >= 0 ? negativeMargin * -1 : negativeMargin);

            $lastElement = this.getLastItem();

            // if the don't have a last element, the DOM might not have been loaded,
            // or the selector is invalid
            if (0 === $lastElement.length) {
                return UNDETERMINED_SCROLLOFFSET;
            }

            return ($lastElement.offset().top + $lastElement.height() + negativeMargin);
        };

        /**
         * Returns current scroll offset for the given scroll container
         *
         * @private
         * @param $container
         * @returns {number}
         */
        this.getCurrentScrollOffset = function ($container) {
            var scrollTop = 0,
                    containerHeight = $container.height();

            if (window === $container.get(0)) {
                scrollTop = $container.scrollTop();
            } else {
                scrollTop = $container.offset().top;
            }

            // compensate for iPhone
            if (navigator.platform.indexOf("iPhone") != -1 || navigator.platform.indexOf("iPod") != -1) {
                containerHeight += 80;
            }

            return (scrollTop + containerHeight);
        };

        /**
         * Returns the url for the next page
         *
         * @private
         */
        this.getNextUrl = function (container) {
            container = container || this.$container;

            // always take the last matching item
            return $(this.nextSelector, container).last().attr('href');
        };

        /**
         * Loads a page url
         *
         * @param url
         * @param callback
         * @param delay
         * @returns {object}        jsXhr object
         */
        this.load = function (url, callback, delay) {
            var self = this,
                    $itemContainer,
                    items = [],
                    timeStart = +new Date(),
                    timeDiff;

            delay = delay || this.defaultDelay;

            var loadEvent = {
                url: url
            };

            self.fire('load', [loadEvent]);

            return $.get(loadEvent.url, null, $.proxy(function (data) {
                $itemContainer = $(this.itemsContainerSelector, data).eq(0);
                if (0 === $itemContainer.length) {
                    $itemContainer = $(data).filter(this.itemsContainerSelector).eq(0);
                }

                if ($itemContainer) {
                    $itemContainer.find(this.itemSelector).each(function () {
                        items.push(this);
                    });
                }

                self.fire('loaded', [data, items]);

                if (callback) {
                    timeDiff = +new Date() - timeStart;
                    if (timeDiff < delay) {
                        setTimeout(function () {
                            callback.call(self, data, items);
                        }, delay - timeDiff);
                    } else {
                        callback.call(self, data, items);
                    }
                }
            }, self), 'html');
        };

        /**
         * Renders items
         *
         * @param callback
         * @param items
         */
        this.render = function (items, callback) {
            var self = this,
                    $lastItem = this.getLastItem(),
                    count = 0;

            var promise = this.fire('render', [items]);

            promise.done(function () {
                $(items).hide(); // at first, hide it so we can fade it in later

                $lastItem.after(items);

                $(items).fadeIn(400, function () {
                    // complete callback get fired for each item,
                    // only act on the last item
                    if (++count < items.length) {
                        return;
                    }

                    self.fire('rendered', [items]);

                    if (callback) {
                        callback();
                    }
                });
            });
        };

        /**
         * Hides the pagination
         */
        this.hidePagination = function () {
            if (this.paginationSelector) {
                $(this.paginationSelector, this.$container).hide();
            }
        };

        /**
         * Restores the pagination
         */
        this.restorePagination = function () {
            if (this.paginationSelector) {
                $(this.paginationSelector, this.$container).show();
            }
        };

        /**
         * Throttles a method
         *
         * Adopted from Ben Alman's jQuery throttle / debounce plugin
         *
         * @param callback
         * @param delay
         * @return {object}
         */
        this.throttle = function (callback, delay) {
            var lastExecutionTime = 0,
                    wrapper,
                    timerId
                    ;

            wrapper = function () {
                var that = this,
                        args = arguments,
                        diff = +new Date() - lastExecutionTime;

                function execute() {
                    lastExecutionTime = +new Date();
                    callback.apply(that, args);
                }

                if (!timerId) {
                    execute();
                } else {
                    clearTimeout(timerId);
                }

                if (diff > delay) {
                    execute();
                } else {
                    timerId = setTimeout(execute, delay);
                }
            };

            if ($.guid) {
                wrapper.guid = callback.guid = callback.guid || $.guid++;
            }

            return wrapper;
        };

        /**
         * Fires an event with the ability to cancel further processing. This
         * can be achieved by returning false in a listener.
         *
         * @param event
         * @param args
         * @returns {*}
         */
        this.fire = function (event, args) {
            return this.listeners[event].fireWith(this, args);
        };

        /**
         * Pauses the scroll handler
         *
         * Note: internal use only, if you need to pause IAS use `unbind` method.
         *
         * @private
         */
        this.pause = function () {
            this.isPaused = true;
        };

        /**
         * Resumes the scroll handler
         *
         * Note: internal use only, if you need to resume IAS use `bind` method.
         *
         * @private
         */
        this.resume = function () {
            this.isPaused = false;
        };

        return this;
    };

    /**
     * Initialize IAS
     *
     * Note: Should be called when the document is ready
     *
     * @public
     */
    IAS.prototype.initialize = function () {
        var supportsOnScroll = (!!('onscroll' in this.$scrollContainer.get(0))),
                currentScrollOffset = this.getCurrentScrollOffset(this.$scrollContainer),
                scrollThreshold = this.getScrollThreshold();

        // bail out when the browser doesn't support the scroll event
        if (!supportsOnScroll) {
            return false;
        }

        this.hidePagination();
        this.bind();

        this.fire('ready');

        this.nextUrl = this.getNextUrl();

        // start loading next page if content is shorter than page fold
        if (currentScrollOffset >= scrollThreshold) {
            this.next();
        }

        return this;
    };

    /**
     * Reinitializes IAS, for example after an ajax page update
     *
     * @public
     */
    IAS.prototype.reinitialize = function () {
        this.unbind();
        this.initialize();
    };

    /**
     * Binds IAS to DOM events
     *
     * @public
     */
    IAS.prototype.bind = function () {
        if (this.isBound) {
            return;
        }

        this.$scrollContainer.on('scroll', $.proxy(this.throttle(this.scrollHandler, 150), this));

        for (var i = 0, l = this.extensions.length; i < l; i++) {
            this.extensions[i].bind(this);
        }

        this.isBound = true;
        this.resume();
    };

    /**
     * Unbinds IAS to events
     *
     * @public
     */
    IAS.prototype.unbind = function () {
        if (!this.isBound) {
            return;
        }

        this.$scrollContainer.off('scroll', this.scrollHandler);

        // notify extensions about unbinding
        for (var i = 0, l = this.extensions.length; i < l; i++) {
            if (typeof this.extensions[i]['unbind'] != 'undefined') {
                this.extensions[i].unbind(this);
            }
        }

        this.isBound = false;
    };

    /**
     * Destroys IAS instance
     *
     * @public
     */
    IAS.prototype.destroy = function () {
        this.unbind();

        this.$scrollContainer.data('ias', null);
    };

    /**
     * Registers an eventListener
     *
     * Note: chainable
     *
     * @public
     * @returns IAS
     */
    IAS.prototype.on = function (event, callback, priority) {
        if (typeof this.listeners[event] == 'undefined') {
            throw new Error('There is no event called "' + event + '"');
        }

        priority = priority || 0;

        this.listeners[event].add($.proxy(callback, this), priority);

        return this;
    };

    /**
     * Registers an eventListener which only gets
     * fired once.
     *
     * Note: chainable
     *
     * @public
     * @returns IAS
     */
    IAS.prototype.one = function (event, callback) {
        var self = this;

        var remover = function () {
            self.off(event, callback);
            self.off(event, remover);
        };

        this.on(event, callback);
        this.on(event, remover);

        return this;
    };

    /**
     * Removes an eventListener
     *
     * Note: chainable
     *
     * @public
     * @returns IAS
     */
    IAS.prototype.off = function (event, callback) {
        if (typeof this.listeners[event] == 'undefined') {
            throw new Error('There is no event called "' + event + '"');
        }

        this.listeners[event].remove(callback);

        return this;
    };

    /**
     * Load the next page
     *
     * @public
     */
    IAS.prototype.next = function () {
        var url = this.nextUrl,
                self = this;

        this.pause();

        if (!url) {
            this.fire('noneLeft', [this.getLastItem()]);
            this.listeners['noneLeft'].disable(); // disable it so it only fires once

            self.resume();

            return false;
        }

        var promise = this.fire('next', [url]);

        promise.done(function () {
            self.load(url, function (data, items) {
                self.render(items, function () {
                    self.nextUrl = self.getNextUrl(data);

                    self.resume();
                });
            });
        });

        promise.fail(function () {
            self.resume();
        });

        return true;
    };

    /**
     * Adds an extension
     *
     * @public
     */
    IAS.prototype.extension = function (extension) {
        if (typeof extension['bind'] == 'undefined') {
            throw new Error('Extension doesn\'t have required method "bind"');
        }

        if (typeof extension['initialize'] != 'undefined') {
            extension.initialize(this);
        }

        this.extensions.push(extension);

        this.reinitialize();

        return this;
    };

    /**
     * Shortcut. Sets the window as scroll container.
     *
     * @public
     * @param option
     * @returns {*}
     */
    $.ias = function (option) {
        var $window = $(window);

        return $window.ias.apply($window, arguments);
    };

    /**
     * jQuery plugin initialization
     *
     * @public
     * @param option
     * @returns {*} the last IAS instance will be returned
     */
    $.fn.ias = function (option) {
        var args = Array.prototype.slice.call(arguments);
        var retval = this;

        this.each(function () {
            var $this = $(this),
                    instance = $this.data('ias'),
                    options = $.extend({}, $.fn.ias.defaults, $this.data(), typeof option == 'object' && option)
                    ;

            // set a new instance as data
            if (!instance) {
                $this.data('ias', (instance = new IAS($this, options)));

                $(document).ready($.proxy(instance.initialize, instance));
            }

            // when the plugin is called with a method
            if (typeof option === 'string') {
                if (typeof instance[option] !== 'function') {
                    throw new Error('There is no method called "' + option + '"');
                }

                args.shift(); // remove first argument ('option')
                instance[option].apply(instance, args);
            }

            retval = instance;
        });

        return retval;
    };

    /**
     * Plugin defaults
     *
     * @public
     * @type {object}
     */
    $.fn.ias.defaults = {
        item: '.item',
        container: '.listing',
        next: '.next',
        pagination: false,
        delay: 600,
        negativeMargin: 10
    };
})(jQuery);