/*
 * 1. 取得 body 节点
 * 2. 递归子节点类名对象
 *        如果支持 jQuery：可以用 $('body *') 获取 body 下所有子节点
 * 3. 以类名出现次数为索引做成对象，并且初始化 长度为3 的数组
 * 4. 替换取前三
 *         数组中存在该类名，替换该类名
 *         否则，替换数组中最小值
 * 5. 结果
 *         resultCount 使用次数数组
 *         resultName  对应类名数组
 */

(function() {
    classObj = {};
    resultCount = [];
    resultName = [];

    function getAllClass() {
        var bodyList;

        bodyList = Array.prototype.slice.call(document.getElementsByTagName('body'));
        bodyList.forEach(function(ele) {
            nodeRecursion(ele);
        });
        console.log(resultCount, resultName);
    }

    function nodeRecursion(element) {
        var childNode,
            count = 1;

        if (element.className) {
            element.classList.forEach(function(className) {
                if (classObj[className]) {
                    count = ++classObj[className];
                    maxCount(count, className);
                } else {
                    classObj[className] = 1;
                    if (resultCount.length < 3) {
                        resultCount.push(1);
                        resultName.push(className);
                    }
                }
            });
        }

        if (element.childNodes.length > 0) {
            childNode = Array.prototype.slice.call(element.childNodes);
            childNode.forEach(function(ele) {
                return nodeRecursion(ele);
            });
        }
        return classObj;
    }

    function maxCount (count, className) {
        var min = resultCount[0],
            len = resultCount.length,
            i,
            idx,
            index = 0;
        for (i = 0; i < len; i++) {
            if (resultCount[i] < min) {
                min = resultCount[i];
                index = i;
            }
        }

        idx = resultName.indexOf(className);
        if (idx == -1) {
            if (min < count) {
                resultCount[index] = count;
                resultName[index] = className;
            }
        } else {
            resultCount[idx] = count;
            resultName[idx] = className;
        }

    }

    getAllClass();

})();