/**
 * Lightbox library created by binarity s.r.o.
 * www.binarity.cz
 * version 1.0.0
 *
 * Vanilla JavaScript lightbox plugin.
 *
 * Can use custom invoker passed as first argument or uses a default one - .b-lightbox.
 * This allows to have more lightbox instances on one site to categorize items.
 *
 * Default behaviour:
 *      - Hides on escape keydown event - settable (options.allow_escape).
 *      - Hides on background click - settable (options.allow_backgroundclick).
 *      - Hide button in top right corner - settable (options.close_text).
 *      - Allows usage of arrow keys (left/right) to navigate through images - settable (option.allow_arrows).
 *
 * @param options
 * @param autorun
 * @constructor
 */
function BLightBox(options, autorun) {
    // Instance and instance variables.
    var BLightBox               = this,
        escape_key_allowed      = (!(options !== undefined && options.allow_escape === false)),
        hide_on_holder_allowed  = (!(options !== undefined && options.allow_backgroundclick === false)),
        arrows_allowed  = (!(options !== undefined && options.allow_arrows === false)),
        close_text  = (options !== undefined && options.close_text !== undefined) ? options.close_text : 'Close',

        // DOM
        lightbox_holder         = document.createElement('div'),
        invoker_string          = (options !== undefined && options.invoker !== undefined) ? options.invoker : '.b-lightbox',
        invokers                = document.querySelectorAll(invoker_string),
        invokers_length         = invokers.length,
        lightbox_image          = document.createElement('img'),
        close_label             = document.createElement('a'),
        previous_button         = document.createElement('a'),
        next_button             = document.createElement('a'),
        lightbox_label          = document.createElement('span');

    // BLightBox DOM default settings.
    lightbox_holder.className = 'b-lightbox-holder';
    lightbox_image.className = 'b-lightbox-image';
    close_label.className = 'b-lightbox-close-button';
    close_label.textContent = close_text;
    previous_button.className = 'b-lightbox-direction previous';
    previous_button.innerHTML = '‹';
    next_button.className = 'b-lightbox-direction next';
    next_button.innerHTML = '›';
    lightbox_label.className = 'b-lightbox-label';

    /**
     * Show new image according to data-newindex attribute on directional button
     */
    this.loadNewImage = function(event) {
        event.stopPropagation();
        var index = event.target.getAttribute('data-newindex'),
            label = invokers[index].getAttribute('data-label');

        if(invokers[index]) {
            lightbox_image.style.display = 'none';
            this.decideFromLoad(invokers[index]);
            lightbox_image.style.display = 'block';
            if(label != '') {
                lightbox_label.innerHTML = label;
            }
        }

        this.lightboxImageCenter(label != ''); // Center image.

        // Change indexes to be opened.
        previous_button.setAttribute('data-newindex', this.getPreviousIndex(index));
        next_button.setAttribute('data-newindex', this.getNextIndex(index));
    };

    /**
     * Returns first next index possible, or return very first index to allow rotation.
     * @param index
     * @returns {number}
     */
    this.getNextIndex = function(index) {
        // Skip to last image if we are on the first.
        return (index == invokers_length - 1) ? 0 : parseInt(index) + 1;
    };

    /**
     * Returns first previous index possible, or returns last array index to allow rotation.
     * @param index
     * @returns {number}
     */
    this.getPreviousIndex = function(index) {
        // Skip to last image if we are on the first.
        return (index == 0) ? invokers_length - 1 : index - 1;
    };

    /**
     *  Reset ivokers_length variable for re-use.
     */
    this.resetInvokersLength = function() {
        invokers_length = invokers.length;
    };

    /**
     * Provides code for closing a lightbox and hiding images.
     */
    this.listenActionClose = function(event) {
        lightbox_holder.style.display = 'none';
        lightbox_image.style.display = 'none';
    };

    /**
     * Adds src to lightbox image from element's style background-image.
     * Removes url() par of the string.
     * @param el
     */
    this.loadImageFromBackgroundImage = function(el) {
        lightbox_image.src = el.style.backgroundImage.replace(/url\("?(.*[^"])"?\)/, '$1');
    };

    /**
     * Adds src to lightbox image from element's child img tag.
     * @param el
     */
    this.loadImageFromChildImg = function(el) {
        var img = el.querySelector('img');
        if(img) {
            lightbox_image.src = img.src;
        }
    };

    /**
     * Move lightbox image to the center of screen.
     */
    this.lightboxImageCenter = function(bool_label) {
        // Image
        lightbox_image.style.left = ((lightbox_holder.offsetWidth - lightbox_image.offsetWidth) / 2) + 'px';
        lightbox_image.style.top = ((lightbox_holder.offsetHeight - lightbox_image.offsetHeight) / 2) + 'px';

        // Image label.
        if(bool_label === true) {
            lightbox_label.style.width = lightbox_image.offsetWidth + 'px';
            lightbox_label.style.left = ((lightbox_holder.offsetWidth - lightbox_image.offsetWidth) / 2) + 'px';
            lightbox_label.style.display = 'block';
            lightbox_label.style.top = (lightbox_image.offsetTop + lightbox_image.offsetHeight - lightbox_label.offsetHeight) + 'px';
        }
    };

    /**
     * Returns index in invokers array or false on unsuccessful attempt to find the element.
     * @param el
     * @returns {*}
     */
    this.getIndexInInvokers = function(el) {
        var inv_length = invokers_length;
        while(inv_length--) {
            if(invokers[inv_length].isEqualNode(el)) {
                return inv_length;
            }
        }
        return false;
    };

    /**
     * This method decides from where to load src attribute into lightbox_image.
     * @param el
     */
    this.decideFromLoad = function(el) {
        // Decide from which source to get image url.
        if(el.hasAttribute('data-background')) {
            this.loadImageFromBackgroundImage(el);
        } else if(el.hasAttribute('data-img')) {
            this.loadImageFromChildImg(el);
        }

        lightbox_label.style.display = 'none';
        lightbox_label.innerHTML = '';
    };

    /**
     * Provides code for opening a lightbox and displaying images.
     */
    this.listenActionOpen = function(el, app, event) {
        var label = el.getAttribute('data-label');

        event.stopPropagation();
        event.preventDefault(); // If element is a-tag, prevent from href requesting.

        app.decideFromLoad(el); // Load image into lightbox_image.

        // Change indexes to be opened.
        previous_button.setAttribute('data-newindex', app.getPreviousIndex(app.getIndexInInvokers(el)));
        next_button.setAttribute('data-newindex', app.getNextIndex(app.getIndexInInvokers(el)));

        // Show lightbox and image.
        lightbox_holder.style.display = 'block';
        lightbox_image.style.display = 'block';
        if(label != '') {
            lightbox_label.innerHTML = label;
        }

        // Center lightbox within the screen.
        app.lightboxImageCenter(label != '');
    };

    /**
     * Add lightbox closing method listener to given element.
     * @param el
     */
    this.addCloseListenerFor = function(el) {
        el.addEventListener('click', this.listenActionClose.bind(this));
    };

    /**
     * Add lightbox opening method listener to given element.
     * @param el
     */
    this.addOpenListenerFor = function(el) {
        var app = this;
        el.addEventListener('click', app.listenActionOpen.bind(app, el, this), true);
    };

    /**
     * Initializes all possible listeners at once on class instance creation.
     */
    this.initiateListeners = function() {
        // Open Listeners.
        while(invokers_length--) {
            this.addOpenListenerFor(invokers[invokers_length]);
        }
        this.resetInvokersLength();

        // Close Listeners.
        // On background click.
        if(hide_on_holder_allowed){
            this.addCloseListenerFor(lightbox_holder);
        }
        // On escape key hit, if requested.
        if(escape_key_allowed) {
            window.addEventListener('keydown', function (event) {
                if(event.keyCode === 27) {
                    BLightBox.listenActionClose();
                }
            });
        }

        // Directional buttons.
        previous_button.addEventListener('click',this.loadNewImage.bind(this));
        next_button.addEventListener('click',this.loadNewImage.bind(this));
        // Allow directing with arrows when enabled.
        if(arrows_allowed) {
            window.addEventListener('keydown', function arrowDirections(event) {
                if(event.keyCode === 37) {
                    previous_button.click();
                } else if(event.keyCode === 39) {
                    next_button.click();
                }
            });
        }
    };

    /**
     * Initialization method that starts BLightBox instance.
     * @returns {*}
     */
    this.init = function() {
        // Append lightbox background.
        document.body.appendChild(lightbox_holder);
        lightbox_holder.appendChild(previous_button);
        lightbox_holder.appendChild(lightbox_image);
        lightbox_holder.appendChild(next_button);
        lightbox_holder.appendChild(close_label);
        lightbox_holder.appendChild(lightbox_label);
        // Add event listeners for invokers.
        this.initiateListeners();

        // Auto centering on window.resize;
        window.addEventListener('resize', function() {
            BLightBox.lightboxImageCenter();
        });

        return BLightBox;
    };

    // If autorun is requested, create instance.
    if(autorun !== undefined && autorun === true) {
        return this.init();
    } else {
        return this;
    }
}