define(['./requestAnimationFrame'], function () {
    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: 0.005,  // 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
            minScale: 0.5,
            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;

                    // x, y目前是坐标，需要转换成定位的像素值

                    //运动过程中，缩小球的大小
                    var scale = 1 - (1 - params.minScale) * (x / coordTarget.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());
                    if (moveStyle == "margin") {
                        element.style.marginLeft = x + "px";
                        element.style.marginTop = y + "px";
                        $(element).children().css({
                            width: $(element).width() * scale,
                            height: $(element).height() * scale
                        });
                    } else {

                        element.style[moveStyle] = "translate(" + [x + "px", y + "px"].join() + ") scale(" + scale + ")";
                    }

                    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 () {
                element.style.marginLeft = "0px";
                element.style.marginTop = "0px";
                this.position().mark().move();
            };
        }

        return exports;
    };
    // 这是很简单的拖拽方法
    funParabola.funDrag = function (element, callback) {
        callback = callback || function () {
            };
        var params = {
            left: 0,
            top: 0,
            currentX: 0,
            currentY: 0,
            flag: false
        };
        //获取相关CSS属性
        var getCss = function (o, key) {
            return o.currentStyle ? o.currentStyle[key] : document.defaultView.getComputedStyle(o, false)[key];
        };

        //拖拽的实现
        if (getCss(element, "left") !== "auto") {
            params.left = getCss(element, "left");
        }
        if (getCss(element, "top") !== "auto") {
            params.top = getCss(element, "top");
        }
        //o是移动对象
        element.onmousedown = function (event) {
            params.flag = true;
            event = event || window.event;
            params.currentX = event.clientX;
            params.currentY = event.clientY;
        };
        document.onmouseup = function () {
            params.flag = false;
            if (getCss(element, "left") !== "auto") {
                params.left = getCss(element, "left");
            }
            if (getCss(element, "top") !== "auto") {
                params.top = getCss(element, "top");
            }
            callback();
        };
        document.onmousemove = function (event) {
            event = event || window.event;
            if (params.flag) {
                var nowX = event.clientX, nowY = event.clientY;
                var disX = nowX - params.currentX, disY = nowY - params.currentY;
                element.style.left = parseInt(params.left) + disX + "px";
                element.style.top = parseInt(params.top) + disY + "px";
            }
        }
    };
    return funParabola;
});