/*
 *  Guacamole - Clientless Remote Desktop
 *  Copyright (C) 2010  Michael Jumper
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

// Guacamole namespace
var Guacamole = Guacamole || {};

/**
 * Abstract ordered drawing surface. Each Layer contains a canvas element and
 * provides simple drawing instructions for drawing to that canvas element,
 * however unlike the canvas element itself, drawing operations on a Layer are
 * guaranteed to run in order, even if such an operation must wait for an image
 * to load before completing.
 * 
 * @constructor
 * 
 * @param {Number} width The width of the Layer, in pixels. The canvas element
 *                       backing this Layer will be given this width.
 *                       
 * @param {Number} height The height of the Layer, in pixels. The canvas element
 *                        backing this Layer will be given this height.
 */
Guacamole.Layer = function(width, height) {

    /**
     * Reference to this Layer.
     * @private
     */
    var layer = this;

    /**
     * The canvas element backing this Layer.
     * @private
     */
    var display = document.createElement("canvas");

    /**
     * The 2D display context of the canvas element backing this Layer.
     * @private
     */
    var displayContext = display.getContext("2d");
    displayContext.save();

    /**
     * The queue of all pending Tasks. Tasks will be run in order, with new
     * tasks added at the end of the queue and old tasks removed from the
     * front of the queue (FIFO).
     * @private
     */
    var tasks = new Array();

    /**
     * Map of all Guacamole channel masks to HTML5 canvas composite operation
     * names. Not all channel mask combinations are currently implemented.
     * @private
     */
    var compositeOperation = {
     /* 0x0 NOT IMPLEMENTED */
        0x1: "destination-in",
        0x2: "destination-out",
     /* 0x3 NOT IMPLEMENTED */
        0x4: "source-in",
     /* 0x5 NOT IMPLEMENTED */
        0x6: "source-atop",
     /* 0x7 NOT IMPLEMENTED */
        0x8: "source-out",
        0x9: "destination-atop",
        0xA: "xor",
        0xB: "destination-over",
        0xC: "copy",
     /* 0xD NOT IMPLEMENTED */
        0xE: "source-over",
        0xF: "lighter"
    };

    /**
     * Resizes the canvas element backing this Layer without testing the
     * new size. This function should only be used internally.
     * 
     * @private
     * @param {Number} newWidth The new width to assign to this Layer.
     * @param {Number} newHeight The new height to assign to this Layer.
     */
    function resize(newWidth, newHeight) {


        // Only preserve old data if width/height are both non-zero
        var oldData = null;
        if (width != 0 && height != 0) {

            // Create canvas and context for holding old data
            oldData = document.createElement("canvas");
            oldData.width = width;
            oldData.height = height;

            var oldDataContext = oldData.getContext("2d");

            // Copy image data from current
            oldDataContext.drawImage(display,
                    0, 0, width, height,
                    0, 0, width, height);

        }

        // Resize canvas
        display.width = newWidth;
        display.height = newHeight;

        // Redraw old data, if any
        if (oldData)
            displayContext.drawImage(oldData, 
                    0, 0, width, height,
                    0, 0, width, height);

        width = newWidth;
        height = newHeight;
    }

    /**
     * Given the X and Y coordinates of the upper-left corner of a rectangle
     * and the rectangle's width and height, resize the backing canvas element
     * as necessary to ensure that the rectangle fits within the canvas
     * element's coordinate space. This function will only make the canvas
     * larger. If the rectangle already fits within the canvas element's
     * coordinate space, the canvas is left unchanged.
     * 
     * @private
     * @param {Number} x The X coordinate of the upper-left corner of the
     *                   rectangle to fit.
     * @param {Number} y The Y coordinate of the upper-left corner of the
     *                   rectangle to fit.
     * @param {Number} w The width of the the rectangle to fit.
     * @param {Number} h The height of the the rectangle to fit.
     */
    function fitRect(x, y, w, h) {
        
        // Calculate bounds
        var opBoundX = w + x;
        var opBoundY = h + y;
        
        // Determine max width
        var resizeWidth;
        if (opBoundX > width)
            resizeWidth = opBoundX;
        else
            resizeWidth = width;

        // Determine max height
        var resizeHeight;
        if (opBoundY > height)
            resizeHeight = opBoundY;
        else
            resizeHeight = height;

        // Resize if necessary
        if (resizeWidth != width || resizeHeight != height)
            resize(resizeWidth, resizeHeight);

    }

    /**
     * A container for an task handler. Each operation which must be ordered
     * is associated with a Task that goes into a task queue. Tasks in this
     * queue are executed in order once their handlers are set, while Tasks 
     * without handlers block themselves and any following Tasks from running.
     *
     * @constructor
     * @private
     * @param {function} taskHandler The function to call when this task 
     *                               runs, if any.
     */
    function Task(taskHandler) {
        
        /**
         * The handler this Task is associated with, if any.
         * 
         * @type function
         */
        this.handler = taskHandler;
        
    }

    /**
     * If no tasks are pending or running, run the provided handler immediately,
     * if any. Otherwise, schedule a task to run immediately after all currently
     * running or pending tasks are complete.
     * 
     * @private
     * @param {function} handler The function to call when possible, if any.
     * @returns {Task} The Task created and added to the queue for future
     *                 running, if any, or null if the handler was run
     *                 immediately and no Task needed to be created.
     */
    function scheduleTask(handler) {
        
        // If no pending tasks, just call (if available) and exit
        if (layer.isReady() && handler != null) {
            handler();
            return null;
        }

        // If tasks are pending/executing, schedule a pending task
        // and return a reference to it.
        var task = new Task(handler);
        tasks.push(task);
        return task;
        
    }

    var tasksInProgress = false;

    /**
     * Run any Tasks which were pending but are now ready to run and are not
     * blocked by other Tasks.
     * @private
     */
    function handlePendingTasks() {

        if (tasksInProgress)
            return;

        tasksInProgress = true;

        // Draw all pending tasks.
        var task;
        while ((task = tasks[0]) != null && task.handler) {
            tasks.shift();
            task.handler();
        }

        tasksInProgress = false;

    }

    /**
     * Set to true if this Layer should resize itself to accomodate the
     * dimensions of any drawing operation, and false (the default) otherwise.
     * 
     * Note that setting this property takes effect immediately, and thus may
     * take effect on operations that were started in the past but have not
     * yet completed. If you wish the setting of this flag to only modify
     * future operations, you will need to make the setting of this flag an
     * operation with sync().
     * 
     * @example
     * // Set autosize to true for all future operations
     * layer.sync(function() {
     *     layer.autosize = true;
     * });
     * 
     * @type Boolean
     * @default false
     */
    this.autosize = false;

    /**
     * Returns the canvas element backing this Layer.
     * @returns {Element} The canvas element backing this Layer.
     */
    this.getCanvas = function() {
        return display;
    };

    /**
     * Returns whether this Layer is ready. A Layer is ready if it has no
     * pending operations and no operations in-progress.
     * 
     * @returns {Boolean} true if this Layer is ready, false otherwise.
     */
    this.isReady = function() {
        return tasks.length == 0;
    };

    /**
     * Changes the size of this Layer to the given width and height. Resizing
     * is only attempted if the new size provided is actually different from
     * the current size.
     * 
     * @param {Number} newWidth The new width to assign to this Layer.
     * @param {Number} newHeight The new height to assign to this Layer.
     */
    this.resize = function(newWidth, newHeight) {
        scheduleTask(function() {
            if (newWidth != width || newHeight != height)
                resize(newWidth, newHeight);
        });
    };

    /**
     * Draws the specified image at the given coordinates. The image specified
     * must already be loaded.
     * 
     * @param {Number} x The destination X coordinate.
     * @param {Number} y The destination Y coordinate.
     * @param {Image} image The image to draw. Note that this is an Image
     *                      object - not a URL.
     */
    this.drawImage = function(x, y, image) {
        scheduleTask(function() {
            if (layer.autosize != 0) fitRect(x, y, image.width, image.height);
            displayContext.drawImage(image, x, y);
        });
    };

    /**
     * Draws the image at the specified URL at the given coordinates. The image
     * will be loaded automatically, and this and any future operations will
     * wait for the image to finish loading.
     * 
     * @param {Number} x The destination X coordinate.
     * @param {Number} y The destination Y coordinate.
     * @param {String} url The URL of the image to draw.
     */
    this.draw = function(x, y, url) {
        var task = scheduleTask(null);

        var image = new Image();
        image.onload = function() {

            task.handler = function() {
                if (layer.autosize != 0) fitRect(x, y, image.width, image.height);
                displayContext.drawImage(image, x, y);
            };

            // As this task originally had no handler and may have blocked
            // other tasks, handle any blocked tasks.
            handlePendingTasks();

        };
        image.src = url;

    };

    /**
     * Run an arbitrary function as soon as currently pending operations
     * are complete.
     * 
     * @param {function} handler The function to call once all currently
     *                           pending operations are complete.
     */
    this.sync = function(handler) {
        scheduleTask(handler);
    };

    /**
     * Copy a rectangle of image data from one Layer to this Layer. This
     * operation will copy exactly the image data that will be drawn once all
     * operations of the source Layer that were pending at the time this
     * function was called are complete. This operation will not alter the
     * size of the source Layer even if its autosize property is set to true.
     * 
     * @param {Guacamole.Layer} srcLayer The Layer to copy image data from.
     * @param {Number} srcx The X coordinate of the upper-left corner of the
     *                      rectangle within the source Layer's coordinate
     *                      space to copy data from.
     * @param {Number} srcy The Y coordinate of the upper-left corner of the
     *                      rectangle within the source Layer's coordinate
     *                      space to copy data from.
     * @param {Number} srcw The width of the rectangle within the source Layer's
     *                      coordinate space to copy data from.
     * @param {Number} srch The height of the rectangle within the source
     *                      Layer's coordinate space to copy data from.
     * @param {Number} x The destination X coordinate.
     * @param {Number} y The destination Y coordinate.
     */
    this.copyRect = function(srcLayer, srcx, srcy, srcw, srch, x, y) {

        function doCopyRect() {
            if (layer.autosize != 0) fitRect(x, y, srcw, srch);
            displayContext.drawImage(srcLayer.getCanvas(), srcx, srcy, srcw, srch, x, y, srcw, srch);
        }

        // If we ARE the source layer, no need to sync.
        // Syncing would result in deadlock.
        if (layer === srcLayer)
            scheduleTask(doCopyRect);

        // Otherwise synchronize copy operation with source layer
        else {
            var task = scheduleTask(null);
            srcLayer.sync(function() {
                
                task.handler = doCopyRect;

                // As this task originally had no handler and may have blocked
                // other tasks, handle any blocked tasks.
                handlePendingTasks();

            });
        }

    };

    /**
     * Clear the specified rectangle of image data.
     * 
     * @param {Number} x The X coordinate of the upper-left corner of the
     *                   rectangle to clear.
     * @param {Number} y The Y coordinate of the upper-left corner of the
     *                   rectangle to clear.
     * @param {Number} w The width of the rectangle to clear.
     * @param {Number} h The height of the rectangle to clear.
     */
    this.clearRect = function(x, y, w, h) {
        scheduleTask(function() {
            if (layer.autosize != 0) fitRect(x, y, w, h);
            displayContext.clearRect(x, y, w, h);
        });
    };

    /**
     * Fill the specified rectangle of image data with the specified color.
     * 
     * @param {Number} x The X coordinate of the upper-left corner of the
     *                   rectangle to draw.
     * @param {Number} y The Y coordinate of the upper-left corner of the
     *                   rectangle to draw.
     * @param {Number} w The width of the rectangle to draw.
     * @param {Number} h The height of the rectangle to draw.
     * @param {Number} r The red component of the color of the rectangle.
     * @param {Number} g The green component of the color of the rectangle.
     * @param {Number} b The blue component of the color of the rectangle.
     * @param {Number} a The alpha component of the color of the rectangle.
     */
    this.drawRect = function(x, y, w, h, r, g, b, a) {
        scheduleTask(function() {
            if (layer.autosize != 0) fitRect(x, y, w, h);
            displayContext.fillStyle = "rgba("
                        + r + "," + g + "," + b + "," + a / 255 + ")";
            displayContext.fillRect(x, y, w, h);
        });
    };

    /**
     * Clip all future drawing operations by the specified rectangle.
     * 
     * @param {Number} x The X coordinate of the upper-left corner of the
     *                   rectangle to use for the clipping region.
     * @param {Number} y The Y coordinate of the upper-left corner of the
     *                   rectangle to use for the clipping region.
     * @param {Number} w The width of the rectangle to use for the clipping region.
     * @param {Number} h The height of the rectangle to use for the clipping region.
     */
    this.clipRect = function(x, y, w, h) {
        scheduleTask(function() {

            // Clear any current clipping region
            displayContext.restore();
            displayContext.save();

            if (layer.autosize != 0) fitRect(x, y, w, h);

            // Set new clipping region
            displayContext.beginPath();
            displayContext.rect(x, y, w, h);
            displayContext.clip();

        });
    };

    /**
     * Provides the given filtering function with a writable snapshot of
     * image data and the current width and height of the Layer.
     * 
     * @param {function} filter A function which accepts an array of image
     *                          data (as returned by the canvas element's
     *                          display context's getImageData() function),
     *                          the width of the Layer, and the height of the
     *                          Layer as parameters, in that order. This
     *                          function must accomplish its filtering by
     *                          modifying the given image data array directly.
     */
    this.filter = function(filter) {
        scheduleTask(function() {
            var imageData = displayContext.getImageData(0, 0, width, height);
            filter(imageData.data, width, height);
            displayContext.putImageData(imageData, 0, 0);
        });
    };

    /**
     * Sets the channel mask for future operations on this Layer. The channel
     * mask is a Guacamole-specific compositing operation identifier with a
     * single bit representing each of four channels (in order): source image
     * where destination transparent, source where destination opaque,
     * destination where source transparent, and destination where source
     * opaque.
     * 
     * @param {Number} mask The channel mask for future operations on this
     *                      Layer.
     */
    this.setChannelMask = function(mask) {
        scheduleTask(function() {
            displayContext.globalCompositeOperation = compositeOperation[mask];
        });
    };

    // Initialize canvas dimensions
    display.width = width;
    display.height = height;

};