/* eslint-disable */
/**
 * Created by TaoHuang on 2016/10/10.
 */
function dataLazyLoad(doc) {

    // 兼容低版本 IE
    Function.prototype.bind = Function.prototype.bind || function(context) {
            var that = this;
            return function() {
                return that.apply(context, arguments);
            };
        };

    // 工具方法 begin
    var Util = {
        getElementsByClassName: function(cls) {
            if (doc.getElementsByClassName) {
                return doc.getElementsByClassName(cls);
            }

            var o = doc.getElementsByTagName("*"),
                rs = [];

            for (var i = 0, t, len = o.length; i < len; i++) {
                (t = o[i]) && ~t.className.indexOf(cls) && rs.push(t);
            }

            return rs;
        },
        addEvent: function(ele, type, fn) {
            ele.attachEvent ? ele.attachEvent("on" + type, fn) : ele.addEventListener(type, fn, false);
        },
        removeEvent: function(ele, type, fn) {
            ele.detachEvent ? ele.detachEvent("on" + type, fn) : ele.removeEventListener(type, fn, false);
        },
        getPos: function(ele) {
            var pos = {
                x: 0,
                y: 0
            };

            while (ele.offsetParent) {
                pos.x += ele.offsetLeft;
                pos.y += ele.offsetTop;
                ele = ele.offsetParent;
            }

            return pos;
        },
        getViewport: function() {
            var html = doc.documentElement;

            return {
                w: !window.innerWidth ? html.clientHeight : window.innerWidth,
                h: !window.innerHeight ? html.clientHeight : window.innerHeight
            };
        },
        getScrollHeight: function() {
            html = doc.documentElement, bd = doc.body;
            return Math.max(window.pageYOffset || 0, html.scrollTop, bd.scrollTop);
        },
        getEleSize: function(ele) {
            return {
                w: ele.offsetWidth,
                h: ele.offsetHeight
            };
        }
    };
    // 工具方法 end

    return {
        threshold: 0,  // {number} 阈值，预加载高度，单位(px)
        els: null,  // {Array} 延迟加载元素集合(数组)
        fn: null,   // {Function} scroll、resize、touchmove 所绑定方法，即为 pollTextareas()

        evalScripts: function(code) {
            var head = doc.getElementsByClassName("yoho-footer")[0],
                js = doc.createElement("script");

            js.text = code;
            head.appendChild(js, head.firstChild);
            head.removeChild(js);
        },

        evalStyles: function(code) {
            var head = doc.getElementsByTagName("head")[0],
                css = doc.createElement("style");

            css.type = "text/css";

            try {
                css.appendChild(doc.createTextNode(code));
            } catch (e) {
                css.styleSheet.cssText = code;
            }

            head.appendChild(css);
        },

        extractCode: function(str, isStyle) {
            var cata = isStyle ? "style" : "script",
                scriptFragment = "<" + cata + "[^>]*>([\\S\\s]*?)</" + cata + "\\s*>",
                matchAll = new RegExp(scriptFragment, "img"),
                matchOne = new RegExp(scriptFragment, "im"),
                matchResults = str.match(matchAll) || [],
                ret = [];

            for (var i = 0, len = matchResults.length; i < len; i++) {
                var temp = (matchResults[i].match(matchOne) || ["", ""])[1];
                temp && ret.push(temp);
            }
            return ret;
        },

        decodeHTML: function(str) {
            return str.replace(/</g, "<").replace(/>/g, ">").replace(/&/g, "&")
                .replace(/&lt;/g, '<').replace(/&gt;/g, '>');
        },

        insert: function(ele) {
            var parent = ele.parentNode,
                txt = this.decodeHTML(ele.innerHTML),
                matchStyles = this.extractCode(txt, true),
                matchScripts = this.extractCode(txt);

            parent.innerHTML = txt
                .replace(new RegExp("<script[^>]*>([\\S\\s]*?)</script\\s*>", "img"), "")
                .replace(new RegExp("<style[^>]*>([\\S\\s]*?)</style\\s*>", "img"), "");

            if (matchStyles.length) {
                for (var i = matchStyles.length; i--;) {
                    this.evalStyles(matchStyles[i]);
                }
            }


            // 如果延迟部分需要做 loading 效果
            parent.className = parent.className.replace("loading", "");

            if (matchScripts.length) {
                for (var i = 0, len = matchScripts.length; i < len; i++) {
                    this.evalScripts(matchScripts[i]);
                }
            }
        },

        inView: function(ele) {
            var top = Util.getPos(ele).y
                , viewVal = Util.getViewport().h
                , scrollVal = Util.getScrollHeight()
                , eleHeight = Util.getEleSize(ele).h;

            if (top >= scrollVal - eleHeight - this.threshold && top <= scrollVal + viewVal + this.threshold) {
                return true;
            }

            return false;
        },

        pollTextareas: function() {
            // 需延迟加载的元素已经全部加载完
            if (!this.els.length) {
                Util.removeEvent(window, "scroll", this.fn);
                Util.removeEvent(window, "resize", this.fn);
                Util.removeEvent(doc.body, "touchMove", this.fn);
                return;
            }

            // 判断是否需要加载
            for (var i = this.els.length; i--;) {
                var ele = this.els[i];

                if (!this.inView(ele)) {
                    continue;
                }

                this.insert(ele);
                this.els.splice(i, 1);
            }
        },

        init: function(config) {
            var cls = config.cls;
            this.threshold = config.threshold ? config.threshold : 0;

            this.els = Array.prototype.slice.call(Util.getElementsByClassName(cls));
            this.fn = this.pollTextareas.bind(this);

            this.fn();
            Util.addEvent(window, "scroll", this.fn);
            Util.addEvent(window, "resize", this.fn);
            Util.addEvent(doc.body, "touchMove", this.fn);
        }
    };
}

module.exports = dataLazyLoad;

/**
 * demo
 * datalazyload.init({
 *     cls: "datalazyload",    // 需要延迟加载的类，即 textarea 的类名
 *     threshold: 100          // 距离底部多高，进行延迟加载的阈值
 * });
 */