/*!
 * by zhangxinxu(.com) 2012-12-27
 * you can visit http://www.zhangxinxu.com/wordpress/?p=3855 to get more infomation
 * under MIT license
*/
var funParabola = function(element, target, options) {
 /*
  * 网页模拟现实需要一个比例尺
  * 如果按照1像素就是1米来算，显然不合适，因为页面动不动就几百像素
  * 页面上，我们放两个物体，200~800像素之间，我们可以映射为现实世界的2米到8米，也就是100:1
  * 不过，本方法没有对此有所体现，因此不必在意
 */
 
 var defaults = {
  speed: 166.67, // 每帧移动的像素大小，每帧（对于大部分显示屏）大约16~17毫秒
  curvature: 0.001, // 实际指焦点到准线的距离，你可以抽象成曲率，这里模拟扔物体的抛物线，因此是开口向下的
  progress: function() {},
  complete: function() {}
 };
 
 var params = {}; options = options || {};
 
 for (var key in defaults) {
  params[key] = options[key] || defaults[key];
 }
 
 var exports = {
  mark: function() { return this; },
  position: function() { return this; },
  move: function() { return this; },
  init: function() { return this; }
 };
 
 /* 确定移动的方式 
  * IE6-IE8 是margin位移
  * IE9+使用transform
 */
 var moveStyle = "margin", testDiv = document.createElement("div");
 if ("oninput" in testDiv) {
  ["", "ms", "webkit"].forEach(function(prefix) {
   var transform = prefix + (prefix? "T": "t") + "ransform";
   if (transform in testDiv.style) {
    moveStyle = transform;
   }
  });  
 }
 
 // 根据两点坐标以及曲率确定运动曲线函数（也就是确定a, b的值）
 /* 公式： y = a*x*x + b*x + c;
 */
 var a = params.curvature, b = 0, c = 0;
 
 // 是否执行运动的标志量
 var flagMove = true;
 
 if (element && target && element.nodeType == 1 && target.nodeType == 1) {
  var rectElement = {}, rectTarget = {};
  
  // 移动元素的中心点位置，目标元素的中心点位置
  var centerElement = {}, centerTarget = {};
  
  // 目标元素的坐标位置
  var coordElement = {}, coordTarget = {};
  
  // 标注当前元素的坐标
  exports.mark = function() {
   if (flagMove == false) return this;
   if (typeof coordElement.x == "undefined") this.position();
   element.setAttribute("data-center", [coordElement.x, coordElement.y].join());
   target.setAttribute("data-center", [coordTarget.x, coordTarget.y].join());
   return this;
  }
  
  exports.position = function() {
   if (flagMove == false) return this;
   
   var scrollLeft = document.documentElement.scrollLeft || document.body.scrollLeft,
    scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
   
   // 初始位置
   if (moveStyle == "margin") {
    element.style.marginLeft = element.style.marginTop = "0px";
   } else {
    element.style[moveStyle] = "translate(0, 0)";
   }
   
   // 四边缘的坐标
   rectElement = element.getBoundingClientRect();
   rectTarget = target.getBoundingClientRect();
   
   // 移动元素的中心点坐标
   centerElement = {
    x: rectElement.left + (rectElement.right - rectElement.left) / 2 + scrollLeft,
    y: rectElement.top + (rectElement.bottom - rectElement.top) / 2 + scrollTop
   };
   
   // 目标元素的中心点位置
   centerTarget = {
    x: rectTarget.left + (rectTarget.right - rectTarget.left) / 2 + scrollLeft,
    y: rectTarget.top + (rectTarget.bottom - rectTarget.top) / 2 + scrollTop  
   };
   
   // 转换成相对坐标位置
   coordElement = {
    x: 0,
    y: 0 
   };
   coordTarget = {
    x: -1 * (centerElement.x - centerTarget.x),
    y: -1 * (centerElement.y - centerTarget.y) 
   };
   
   /*
    * 因为经过(0, 0), 因此c = 0
    * 于是：
    * y = a * x*x + b*x;
    * y1 = a * x1*x1 + b*x1;
    * y2 = a * x2*x2 + b*x2;
    * 利用第二个坐标：
    * b = (y2+ a*x2*x2) / x2
   */
   // 于是
   b = (coordTarget.y - a * coordTarget.x * coordTarget.x) / coordTarget.x; 
   
   return this;
  };  
  
  // 按照这个曲线运动
  exports.move = function() {
   // 如果曲线运动还没有结束，不再执行新的运动
   if (flagMove == false) return this;
   
   var startx = 0, rate = coordTarget.x > 0? 1: -1;

   var step = function() {
    // 切线 y'=2ax+b
    var tangent = 2 * a * startx + b; // = y / x
    // y*y + x*x = speed
    // (tangent * x)^2 + x*x = speed
    // x = Math.sqr(speed / (tangent * tangent + 1));
    startx = startx + rate * Math.sqrt(params.speed / (tangent * tangent + 1));
    
    // 防止过界
    if ((rate == 1 && startx > coordTarget.x) || (rate == -1 && startx < coordTarget.x)) {
     startx = coordTarget.x;
    }
    var x = startx, y = a * x * x + b * x;
    
    // 标记当前位置，这里有测试使用的嫌疑，实际使用可以将这一行注释
    element.setAttribute("data-center", [Math.round(x), Math.round(y)].join());
    
    // x, y目前是坐标，需要转换成定位的像素值
    if (moveStyle == "margin") {
     element.style.marginLeft = x + "px";
     element.style.marginTop = y + "px";
    } else {
     element.style[moveStyle] = "translate("+ [x + "px", y + "px"].join() +")";
    }
    
    if (startx !== coordTarget.x) {
     params.progress(x, y);
     window.requestAnimationFrame(step); 
    } else {
     // 运动结束，回调执行
     params.complete();
     flagMove = true; 
    }
   };
   window.requestAnimationFrame(step);
   flagMove = false;
   
   return this;
  };
  
  // 初始化方法
  exports.init = function() {
   this.position().mark().move();
  };
 }
 
 return exports;
};

/*! requestAnimationFrame.js
 * by zhangxinxu 2013-09-30
*/
(function() {
 var lastTime = 0;
 var vendors = ['webkit', 'moz'];
 for(var x = 0; x < vendors.length && !window.requestAnimationFrame; ++x) {
  window.requestAnimationFrame = window[vendors[x] + 'RequestAnimationFrame'];
  window.cancelAnimationFrame = window[vendors[x] + 'CancelAnimationFrame'] || // name has changed in Webkit
          window[vendors[x] + 'CancelRequestAnimationFrame'];
 }

 if (!window.requestAnimationFrame) {
  window.requestAnimationFrame = function(callback, element) {
   var currTime = new Date().getTime();
   var timeToCall = Math.max(0, 16.7 - (currTime - lastTime));
   var id = window.setTimeout(function() {
    callback(currTime + timeToCall);
   }, timeToCall);
   lastTime = currTime + timeToCall;
   return id;
  };
 }
 if (!window.cancelAnimationFrame) {
  window.cancelAnimationFrame = function(id) {
   clearTimeout(id);
  };
 }
}());

/* 元素 */
var element = document.getElementById("element"), 
 target = document.getElementById("target");
// 抛物线元素的的位置标记
var parabola = funParabola(element, target).mark();
// 抛物线运动的触发
document.body.onclick = function() {
 element.style.marginLeft = "0px";
 element.style.marginTop = "0px";
 parabola.init();
};

/* 本demo演示脚本基于ieBetter.js, 项目地址：https://github.com/zhangxinxu/ieBetter.js */

// 元素以及其他一些变量
var eleFlyElement = document.querySelector("#flyItem"), eleShopCart = document.querySelector("#shopCart");
var numberItem = 0;
// 抛物线运动
var myParabola = funParabola(eleFlyElement, eleShopCart, {
 speed: 400,
 curvature: 0.002, 
 complete: function() {
  eleFlyElement.style.visibility = "hidden";
  eleShopCart.querySelector("span").innerHTML = ++numberItem;
 }
});
// 绑定点击事件
if (eleFlyElement && eleShopCart) {
 [].slice.call(document.getElementsByClassName("btnCart")).forEach(function(button) {
  button.addEventListener("click", function() {
   // 滚动大小
   var scrollLeft = document.documentElement.scrollLeft || document.body.scrollLeft || 0,
    scrollTop = document.documentElement.scrollTop || document.body.scrollTop || 0;

   eleFlyElement.style.left = event.clientX + scrollLeft + "px";
   eleFlyElement.style.top = event.clientY + scrollTop + "px";
   eleFlyElement.style.visibility = "visible";
   
   // 需要重定位
   myParabola.position().move(); 
  });
 });
}