var DDSPEED = 10;
var DDTIMER = 15;
//此段代码并不影响程序的运行速度
// 处理鼠标动作的主函数 //
function ddMenu(id, d) {
	var h = document.getElementById(id + "-dh");
	var c = document.getElementById(id + "-dc");
	clearInterval(c.timer);
	if (d == 1) {
		clearTimeout(h.timer);
		if (c.maxh && c.maxh <= c.offsetHeight) {
			return;
		} else {
			if (!c.maxh) {
				c.style.display = "block";
				c.style.height = "auto";
				c.maxh = c.offsetHeight;
				c.style.height = "0px";
			}
		}
		c.timer = setInterval(function () {
			ddSlide(c, 1);
		}, DDTIMER);
	} else {
		h.timer = setTimeout(function () {
			ddCollapse(c);
		}, 50);
	}
}

// 回缩菜单 //
function ddCollapse(c) {
	c.timer = setInterval(function () {
		ddSlide(c, -1);
	}, DDTIMER);
}

// 如果有用户将鼠标放置在菜单上则取消回溯 //
function cancelHide(id) {
	var h = document.getElementById(id + "-dh");
	var c = document.getElementById(id + "-dc");
	clearTimeout(h.timer);
	clearInterval(c.timer);
	if (c.offsetHeight < c.maxh) {
		c.timer = setInterval(function () {
			ddSlide(c, 1);
		}, DDTIMER);
	}
}

// 展开/回缩菜单，并设置透明度 //
function ddSlide(c, d) {
	var currh = c.offsetHeight;
	var dist;
	if (d == 1) {
		dist = (Math.round((c.maxh - currh) / DDSPEED));
	} else {
		dist = (Math.round(currh / DDSPEED));
	}
	if (dist <= 1 && d == 1) {
		dist = 1;
	}
	c.style.height = currh + (dist * d) + "px";
	c.style.opacity = currh / c.maxh;
	c.style.filter = "alpha(opacity=" + (currh * 100 / c.maxh) + ")";
	if ((currh < 2 && d != 1) || (currh > (c.maxh - 2) && d == 1)) {
		clearInterval(c.timer);
	}
}
function menuFix() {
	var sfEls = document.getElementById("nav").getElementsByTagName("li");
	for (var i = 0; i < sfEls.length; i++) {
		sfEls[i].onmouseover = function () {
			this.className += (this.className.length > 0 ? " " : "") + "sfhover";
		};
		sfEls[i].onMouseDown = function () {
			this.className += (this.className.length > 0 ? " " : "") + "sfhover";
		};
		sfEls[i].onMouseUp = function () {
			this.className += (this.className.length > 0 ? " " : "") + "sfhover";
		};
		sfEls[i].onmouseout = function () {
			this.className = this.className.replace(new RegExp("( ?|^)sfhover\\b"), "");
		};
	}
}
window.onload = menuFix;