// ==UserScript==
// @name         图片压缩
// @namespace    http://tampermonkey.net/
// @version      0.2
// @description  select img to zip!
// @author       Paul
// @match        *://www.baidu.com
// @require      https://cdnjs.cloudflare.com/ajax/libs/jquery/2.2.4/jquery.js
// @require      https://cdnjs.cloudflare.com/ajax/libs/layer/2.3/layer.js
// @grant        GM_addStyle
// @run-at       document-end
// @downloadURL none
// ==/UserScript==

(function() {
    'use strict';
    ({
        $container: null,
        reader: null,
        img:null
        , addCss: function () {
            $(document.head).append('<link rel="stylesheet" type="text/css" href="https://cdnjs.cloudflare.com/ajax/libs/layer/2.3/skin/layer.css"/>')
            GM_addStyle('.btnContainer{ position:absolute;left:50%;top:50%;transform:translate(-50%,-50%);width:60px;height:35px;line-height:35px; }\
                         .btnContainer .ubtn{ display:block; text-align:center;width:100%;height:100%;background-color:#38f;color:#fff; }\
                         .btnContainer .ufile{display:block; position:absolute;top:0;left:0;width:100%;height:100%;opacity:0; }\
                         .maxImg{ max-height:100%;max-width:100%; }');
        }
        , createBtn: function () {
            var htmlStr = '<div class="btnContainer"><span class="ubtn">选择图片</span><input type="file" class="ufile" /></div>';
            this.addCss();
            this.$container = $(htmlStr);
            this.$container.appendTo($('body'));
            this.addEvent();
        }
        , addEvent: function () {
            var that = this;
            var canvas = document.createElement('canvas');
            var context = canvas.getContext('2d');
            this.img.onload = function () {
                // 图片原始尺寸
                var originWidth = this.width;
                var originHeight = this.height;
                // 最大尺寸限制，可通过国设置宽高来实现图片压缩程度
                var maxWidth = 800,
                    maxHeight = 800;
                // 目标尺寸
                var targetWidth = originWidth,
                    targetHeight = originHeight;
                // 图片尺寸超过400x400的限制
                if (originWidth > maxWidth || originHeight > maxHeight) {
                    if (originWidth / originHeight > maxWidth / maxHeight) {
                        // 更宽，按照宽度限定尺寸
                        targetWidth = maxWidth;
                        targetHeight = Math.round(maxWidth * (originHeight / originWidth));
                    } else {
                        targetHeight = maxHeight;
                        targetWidth = Math.round(maxHeight * (originWidth / originHeight));
                    }
                }
                // canvas对图片进行缩放
                canvas.width = targetWidth;
                canvas.height = targetHeight;
                // 清除画布
                context.clearRect(0, 0, targetWidth, targetHeight);
                // 图片压缩
                context.drawImage(that.img, 0, 0, targetWidth, targetHeight);
                /*第一个参数是创建的img对象；第二个参数是左上角坐标，后面两个是画布区域宽高*/
                //压缩后的图片base64 url
                /*canvas.toDataURL(mimeType, qualityArgument),mimeType 默认值是'image/jpeg';
                 * qualityArgument表示导出的图片质量，只要导出为jpg和webp格式的时候此参数才有效果，默认值是0.92*/
                var newUrl = canvas.toDataURL('image/jpeg', 0.80);//base64 格式
                //console.log(canvas.toDataURL('image/jpeg', 0.92));
                layer.open({
                    type: 1,
                    title: '压缩后图片',
                    content: '<div style="height:300px;widht:500px;"><img src="' + newUrl + '" class="maxImg" /></div>',
                    success: function () {
                        layer.msg('在图片上右键，另存为即可');
                    }
                });
            };
            this.reader.onload=function (e) { this.img.src = e.target.result; }.bind(this);
            this.$container.find('input:first').on('change', this.change.bind(this));
        }

        , change: function (e) {
            var file = e.target.files[0];
            if (file.type.indexOf("image") == 0) {
                this.reader.readAsDataURL(file);
            }
        }
        , run: function () {
            this.reader = new FileReader();
            this.img = new Image();
            this.createBtn();
        }
     }).run();
    // Your code here...
})();