/** 将base64转换为文件对象

 *  @param {String} base64 base64字符串

 * */

var convertBase64ToBlob = function(base64){

    var base64Arr = base64.split(',');

    var imgtype = '';

    var base64String = '';

    if(base64Arr.length > 1){

        //如果是图片base64，去掉头信息

        base64String = base64Arr[1];

        imgtype = base64Arr[0].substring(base64Arr[0].indexOf(':')+1,base64Arr[0].indexOf(';'));

    }

    // 将base64解码

    var bytes = atob(base64String);

    //var bytes = base64;

    var bytesCode = new ArrayBuffer(bytes.length);

     // 转换为类型化数组

    var byteArray = new Uint8Array(bytesCode);

    // 将base64转换为ascii码

    for (var i = 0; i < bytes.length; i++) {

        byteArray[i] = bytes.charCodeAt(i);

    }

    // 生成Blob对象（文件对象）

    return new Blob( [bytesCode] , {type : imgtype});

};

/** 压缩图片

 * @param {Object} file 上传对象files[0]

 * @param {Object} options 压缩设置对象

 * @param {Function} callback 回调函数

 * @result {Object} 返回blob文件对象

 * */

var compressImg = function(file,options,callback){

    var self = this;

    var imgname = file.name;

    var imgtype = (imgname.substring(imgname.lastIndexOf('.') + 1)).toLowerCase();

    if(imgtype == 'jpg' || imgtype == 'jpeg'){

        imgtype = 'image/jpeg';

    }else{

        imgtype = 'image/png';

    }

    // 用FileReader读取文件

    var reader = new FileReader();

    // 将图片读取为base64

    reader.readAsDataURL(file);

    reader.onload = function(evt){

        var base64 = evt.target.result;

        // 创建图片对象

        var img = new Image();

        // 用图片对象加载读入的base64

        img.src = base64;

        img.onload = function () {

            var that = this,

                canvas = document.createElement('canvas'),

                ctx = canvas.getContext('2d');

            canvas.setAttribute('width', that.width);

            canvas.setAttribute('height', that.height);

            // 将图片画入canvas

            ctx.drawImage(that, 0, 0, that.width, that.height);

            // 压缩到指定体积以下（M）

            if(options.size){

                var scale = 0.9;

                (function f(scale){

                    if(base64.length / 1024 / 1024 > options.size && scale > 0){

                        base64 = canvas.toDataURL(imgtype, scale);

                        scale = scale - 0.1;

                        f(scale);

                    }else{

                        callback(base64);

                    }

                })(scale);

            } else if(options.scale){

                // 按比率压缩

                base64 = canvas.toDataURL(imgtype, options.scale);

                callback(base64);

            }

        }

    }

};

/**

 * 图片预览

 * @param {Object} $fileInput 文件上传file

 * @param {Object} $previewImg 预览图片的image元素

 */

function previewImg($fileInput, $previewImg) {

    $fileInput.onchange = function ($event) {

        var $target = $event.target;

        if ($target.files && $target.files[0]) {

            var reader = new FileReader();

            reader.onload = function(evt){

                $previewImg.src = evt.target.result;

            }

            reader.readAsDataURL($target.files[0]);

        }

    }

}

/**

 * 将图片旋转到正确的角度

 * （解决移动端上传的图片角度不正确的问题）

 * （旋转后返回的是base64，可以参照本目录下的convertBase64ToBlob.js，将base64还原为file input读取得到的文件对象）

 * @param {Dom Object} $fileInput 文件上传输入框

 * @param {Function} callback 旋转完成后的回调函数

 */

function resetImgOrientation($fileInput, callback) {

    // 绑定change事件

    $fileInput.onchange = function ($event) {

        var $target = $event.target;

        if ($target.files && $target.files[0]) {

            // 获取图片旋转角度

            getOrientation($target.files[0], function (orientation) {

                var reader = new FileReader();

                reader.readAsDataURL($target.files[0]);

                reader.onload = function(evt){

                    var base64 = evt.target.result;

                    // 将图片旋转到正确的角度

                    resetOrientation(base64, orientation, function (resultBase64) {

                        callback(resultBase64);

                    });

                }

            });

        }

    }

}

// 获取图片旋转的角度

function getOrientation(file, callback) {

    var reader = new FileReader();

    reader.readAsArrayBuffer(file);

    reader.onload = function(e) {

        var view = new DataView(e.target.result);

        if (view.getUint16(0, false) != 0xFFD8) return callback(-2);

        var length = view.byteLength, offset = 2;

        while (offset < length) {

            var marker = view.getUint16(offset, false);

            offset += 2;

            if (marker == 0xFFE1) {

                if (view.getUint32(offset += 2, false) != 0x45786966) return callback(-1);

                var little = view.getUint16(offset += 6, false) == 0x4949;

                offset += view.getUint32(offset + 4, little);

                var tags = view.getUint16(offset, little);

                offset += 2;

                for (var i = 0; i < tags; i++)

                    if (view.getUint16(offset + (i * 12), little) == 0x0112)

                        return callback(view.getUint16(offset + (i * 12) + 8, little));

            }

            else if ((marker & 0xFF00) != 0xFF00) break;

            else offset += view.getUint16(offset, false);

        }

        return callback(-1);

    };

}

// 将图片旋转到正确的角度

function resetOrientation(srcBase64, srcOrientation, callback) {

    var img = new Image();

    img.onload = function() {

        var width = img.width,

            height = img.height,

            canvas = document.createElement('canvas'),

            ctx = canvas.getContext("2d");

        // set proper canvas dimensions before transform & export

        if ([5,6,7,8].indexOf(srcOrientation) > -1) {

            canvas.width = height;

            canvas.height = width;

        } else {

            canvas.width = width;

            canvas.height = height;

        }

        // transform context before drawing image

        switch (srcOrientation) {

            case 2: ctx.transform(-1, 0, 0, 1, width, 0); break;

            case 3: ctx.transform(-1, 0, 0, -1, width, height ); break;

            case 4: ctx.transform(1, 0, 0, -1, 0, height ); break;

            case 5: ctx.transform(0, 1, 1, 0, 0, 0); break;

            case 6: ctx.transform(0, 1, -1, 0, height , 0); break;

            case 7: ctx.transform(0, -1, -1, 0, height , width); break;

            case 8: ctx.transform(0, -1, 1, 0, 0, width); break;

            default: ctx.transform(1, 0, 0, 1, 0, 0);

        }

        // draw image

        ctx.drawImage(img, 0, 0);

        // export base64

        callback(canvas.toDataURL('image/jpeg'));

    };

    img.src = srcBase64;

};