/**
 * jQuery多级联动菜单
 * 
 * Author:  ZhouFan <happyeddie@gmail.com>
 * 
 */

 function LinkageSelect(options) {

  var bindEls = new Array();
  var items = {};
  
  // 默认参数
  var settings = {
    data    : {},
    file    : null,
    root    : '0',
    ajax    : null,
    timeout   : 30,
    method    : 'post',
    field_name  : null,
    auto    : false
  };
  
  // 自定义参数
  if(options) {  
    jQuery.extend(settings, options);
  }
  
  items = settings.data;
  
  /**
   * 绑定元素
   * @param {Object} element
   * @param {Object} value
   */
   function _bind(element , value) {

    // 对象关联的key
    var key = bindEls.length ?
    bindEls[bindEls.length - 1].key + ',' + bindEls[bindEls.length - 1].value :
    settings.root;
    
    // 将绑定的元素放入数组
    bindEls.push({
      element : element,
      key   : key,
      value : value
    });
    
    var item_count  = 0;
    for (var i in items) {
      item_count++;
    }
    
    // 查找自身id
    for (var el_id in bindEls) {
      if (bindEls[el_id].element == element) {
        var self_id = parseInt(el_id);
      }
    }
    
    for(var el_id in bindEls){
      // 为所有前面的对象增加onchange事件，onchange时，清空自身
      if (el_id < self_id){
        bindEls[el_id].element.change(function() {
          _fill(element);
        })
      }
    }
    
    // 为上一级对象增加onchange事件，以刷新自身列表
    if (self_id > 0) {
      bindEls[self_id-1].element.change(function() {
        _fill(element , bindEls[self_id].key);
      });
    }
    
    element.change(function() {
      var self_key = bindEls[self_id-1]?bindEls[self_id].key + ',' + $(this).val():'0,' + $(this).val();
      if (typeof bindEls[self_id+1] != 'undefined') {
        bindEls[self_id+1].key  = self_key;
      }
      
      // 自动填入所选值
      if (settings.field_name) {
        $(settings.field_name).val($(this).val());
      }
      
      if (settings.auto) {
        if (typeof bindEls[self_id+1] == 'undefined') {
          _find(self_key , function(key , json) {
            if (json) {
              var el  = $('<select></select>');
              element.after(el);
              _bind(el , '');
              _fill(bindEls[self_id+1].element , key , json);
            }
          });
        }
      }
    })
    _fill(element , key , value);
    
  }
  
  /**
   * 填充option
   * @param {Object} element
   * @param {Object} key
   * @param {Object} value
   */
   function _fill(element , key , value) {

    element.empty();

    var sid = element.attr("id"), option;
    switch (sid) {
      case 'province':
        option = '<option value="">省份</option>';
        break;
      case 'city':
        option = '<option value="">城市</option>';
        break;
      case 'district':
        option = '<option value="">区/县</option>';
        break;
      default:
        option = '<option value="">请选择</option>';
    }
    element.append(option);
    
    var json  = _find(key , function() {
      _fill(element , key , value);
    });
    
    if (!json) {
      if (settings.auto)
        element.hide();
      return false;
    }
    element.show();
    var index = 1;
    var selected_index  = 0;
    for(var opt_value in json) {
      var opt_title = json[opt_value];
      var selected  = '';
      if (opt_value == value) {
        selected_index  = index;
        selected    = 'selected';
      }
      var option  = $('<option value="' + opt_value + '" ' + selected + '>' + opt_title + '</option>');
      element.append(option);
      index++;
    }
    
    if (element[0]) {
      //IE6
      setTimeout(function(){
        element[0].options[selected_index].selected = true;
      }, 0);
      // 让FF选中默认项
      element[0].selectedIndex  = 0;
      element.attr('selectedIndex' , selected_index);
    }
    //element.width(element.width());
  }
  
  /** * 查找元素 * @param {Object} key */
  function _find(key , callback) {
    if (typeof key == 'undefined') {  // 若未定义key
      return null;
    } else if (key[key.length-1] == ',') {  // 若key以','结尾，肯定是取不到值
    return null
  } else if(typeof(items[key]) == "undefined") {

      // 计算items元素个数
      var item_count  = 0;
      for (var i in items) {
        item_count++;
        break;
      }
      
      if (settings.ajax) {
        $.getJSON(settings.ajax , {key:key} , function(json) {
          items[key] = json;
          callback(key , json);
        })
      } else if(settings.file && item_count == 0) {
        $.getJSON(settings.file , function(json) {
          items = json;
          callback(key , json);
        })
      }
    }
    
    return items[key];
  }
  
  /**
   * 获取对象
   * @param {Object} element
   */
   function _getEl(element) {
    if (typeof element == 'string') {
      return $(element);
    } else {
      return element;
    }
  }
  
  
  return {

    // 绑定元素
    bind  : function(element , value) {
      if (typeof element != 'object')
        element = _getEl(element);
      value = value?value:'';
      
      _bind(element , value);
      
    }
  }
  
}