/*
 * JavaScript Load Image iOS scaling fixes 1.0
 * https://github.com/blueimp/JavaScript-Load-Image
 *
 * Copyright 2013, Sebastian Tschan
 * https://blueimp.net
 *
 * iOS image scaling fixes based on
 * https://github.com/stomita/ios-imagefile-megapixel
 *
 * Licensed under the MIT license:
 * http://www.opensource.org/licenses/MIT
 */

/*jslint nomen: true, bitwise: true */
/*global define, window, document */

(function (factory) {
    'use strict';
    if (typeof define === 'function' && define.amd) {
        // Register as an anonymous AMD module:
        define(['load-image'], factory);
    } else {
        // Browser globals:
        factory(window.loadImage);
    }
}(function (loadImage) {
    'use strict';

    // Only apply fixes on the iOS platform:
    if (!window.navigator || !window.navigator.platform ||
             !(/iP(hone|od|ad)/).test(window.navigator.platform)) {
        return;
    }

    var originalRenderMethod = loadImage.renderImageToCanvas;

    // Detects subsampling in JPEG images:
    loadImage.detectSubsampling = function (img) {
        var canvas,
            context;
        if (img.width * img.height > 1024 * 1024) { // only consider mexapixel images
            canvas = document.createElement('canvas');
            canvas.width = canvas.height = 1;
            context = canvas.getContext('2d');
            context.drawImage(img, -img.width + 1, 0);
            // subsampled image becomes half smaller in rendering size.
            // check alpha channel value to confirm image is covering edge pixel or not.
            // if alpha value is 0 image is not covering, hence subsampled.
            return context.getImageData(0, 0, 1, 1).data[3] === 0;
        }
        return false;
    };

    // Detects vertical squash in JPEG images:
    loadImage.detectVerticalSquash = function (img, correctedHeight) {
        var canvas = document.createElement('canvas'),
            context = canvas.getContext('2d'),
            data,
            sy,
            ey,
            py,
            alpha;
        canvas.width = 1;
        canvas.height = correctedHeight;
        context.drawImage(img, 0, 0);
        data = context.getImageData(0, 0, 1, correctedHeight).data;
        // search image edge pixel position in case it is squashed vertically:
        sy = 0;
        ey = correctedHeight;
        py = correctedHeight;
        while (py > sy) {
            alpha = data[(py - 1) * 4 + 3];
            if (alpha === 0) {
                ey = py;
            } else {
                sy = py;
            }
            py = (ey + sy) >> 1;
        }
        return (py / correctedHeight) || 1;
    };

    // Renders image to canvas while working around iOS image scaling bugs:
    // https://github.com/blueimp/JavaScript-Load-Image/issues/13
    loadImage.renderImageToCanvas = function (
        canvas,
        img,
        sourceX,
        sourceY,
        sourceWidth,
        sourceHeight,
        destX,
        destY,
        destWidth,
        destHeight
    ) {
        if (img._type === 'image/jpeg') {
            var context = canvas.getContext('2d'),
                tmpCanvas = document.createElement('canvas'),
                tileSize = 1024,
                tmpContext = tmpCanvas.getContext('2d'),
                subSampled,
                vertSquashRatio,
                tileX,
                tileY;
            tmpCanvas.width = tileSize;
            tmpCanvas.height = tileSize;
            context.save();
            subSampled = loadImage.detectSubsampling(img);
            if (subSampled) {
                sourceWidth /= 2;
                sourceHeight /= 2;
            }
            vertSquashRatio = loadImage.detectVerticalSquash(img, sourceHeight);
            if (subSampled && vertSquashRatio !== 1) {
                destWidth = Math.ceil(tileSize * destWidth / sourceWidth);
                destHeight = Math.ceil(
                    tileSize * destHeight / sourceHeight / vertSquashRatio
                );
                destY = 0;
                tileY = 0;
                while (tileY < sourceHeight) {
                    destX = 0;
                    tileX = 0;
                    while (tileX < sourceWidth) {
                        tmpContext.clearRect(0, 0, tileSize, tileSize);
                        tmpContext.drawImage(
                            img,
                            sourceX,
                            sourceY,
                            sourceWidth,
                            sourceHeight,
                            -tileX,
                            -tileY,
                            sourceWidth,
                            sourceHeight
                        );
                        context.drawImage(
                            tmpCanvas,
                            0,
                            0,
                            tileSize,
                            tileSize,
                            destX,
                            destY,
                            destWidth,
                            destHeight
                        );
                        tileX += tileSize;
                        destX += destWidth;
                    }
                    tileY += tileSize;
                    destY += destHeight;
                }
                context.restore();
                return canvas;
            }
        }
        return originalRenderMethod(
            canvas,
            img,
            sourceX,
            sourceY,
            sourceWidth,
            sourceHeight,
            destX,
            destY,
            destWidth,
            destHeight
        );
    };

}));