#coding: utf-8
=begin
  字段映射，业务字段-数据库字段对应

  TODO: 
  将不需进行字段装换的功能玻璃出来
=end
require 'fileutils'
module Ns
  module FieldMapping
    def self.included(base)
      base.extend(ClassMethods)
    end

    #在将model转成json数据时会自动调用该方法
    def as_json(options={})
      #获取数据库属性数据
      #TODO 想到的一个改进点：数据库查的时候根据mapping来选字段，而非全查出来，影响效率，影响较大，先不改！
      default_attrs = self.class.buz_hashize(self.attributes)
      #支持自定义方法的传入 20111118 for gao
      add_virtual_buz_attributes!(default_attrs) 
    end

    # 将对象转成json数据时，允许添加额外的属性字段，但并不存入数据库
    def add_virtual_buz_attributes!(db_buz_attrs = {})
      the_mapping = self.class.mapping
      #获取非数据库属性，称为业务虚拟属性
      delta_attrs = the_mapping.keys - db_buz_attrs.keys
      delta_attrs.each do |key|
        method_name = the_mapping[key]
        db_buz_attrs[key] = if self.respond_to?(method_name)
          self.send(method_name)
        else
          self.class.get_map_value(key, nil)#给出默认实现
        end
      end
      db_buz_attrs
    end

    def update_from_buz(params={})
      update_attributes(self.class.db_hashize(params))
    end
    
    module ClassMethods
      #Fix a bug on 20111117 by shang, this override the original method name
      def __model_clazz_name
        self.name.underscore
      end
      def model_key
        "#{__model_clazz_name}_mapping"
      end

      def mapping
        GlobalConst.send(model_key)
      end

      def get_map_value(k, value)
        #raise "Not implemented!"
        #提供默认处理 #TODO 根据数据类型做些更好的转换
        case k
        when :created_at, :updated_at
          value.try(:to_s, :db)
        else
          value
        end
      end
      
      #辅助方法
      def new_from_buz(params = {})
        new(db_hashize(params))
      end
      def create_from_buz(params = {})
        create(db_hashize(params))
      end
      
      #生成field mapping，dump到指定的yaml文件中
      def dump_mapping(attr_prefix = nil, force = false, with_timestamp = false)
        file = nil
        if defined?(Rails)
          tstamp = with_timestamp ? ".#{Time.now.to_i}" : ""
          file = "#{Rails.root}/#{GlobalConst::APP_CODE_HASHES}mappings/#{model_key}.yml#{tstamp}"
          path = File.dirname(file)
          FileUtils.mkpath(path) unless File.directory?(path)
          existed = File.exists?(file)
          if existed
            puts "Warning: #{file} has existed! check it!"
          end
          if !existed || force
            #获取数据库字段列表，屏蔽掉自动维护的created_at/updated_at，也可在生成的文件中配上
            #20111203 讨论后打开此屏蔽 #.delete_if{|k| k =~ /^created_at|updated_at$/}
            keys = new.attributes.symbolize_keys.keys
            h = keys.inject({}) do |r, k|
              #移除掉表前缀
              rm_prefix = attr_prefix.nil? ? "#{__model_clazz_name}_" : attr_prefix
              new_key = k.to_s.sub(rm_prefix, '').to_sym
              r[new_key] = k 
              r
            end
            FileUtils.rm_f(file) if existed
            File.open(file, 'w+') do |f|
              f.puts "#==本文件由Nsp生成#于{Time.now.to_s(:db)}，可根据规则编辑"
              f.puts YAML.dump(model_key.to_sym=>h)
            end
          end
          file
        end
      end

      #TODO
      def dump_field_map(force=true)
        puts "==Warning: please use dump_mapping instead, this will be removed..."
        dump_mapping(nil, true)
      end
     
      #业务层到数据层字段参数转换并做一定值处理
      def db_hashize(params = {})
        new_params = params.symbolize_keys
        common_keys = new_params.keys & mapping.keys
        common_keys.inject({}) do |result, key|
          result[mapping[key]] = get_map_value(key, new_params[key])
          result
        end
      end
   
      #将数据层表示转成业务层表示
      def buz_hashize(attrs = {})
        #return {} if attrs.blank?
        #获取默认初始值
        attrs = new.attributes if attrs.blank?
        new_attrs = attrs.symbolize_keys
        invert_maps = mapping.invert_data
        common_db_attrs = new_attrs.keys & invert_maps.keys
        common_db_attrs.inject({}) do |result, attr| 
          buz_field = invert_maps[attr]
          result[buz_field] = get_map_value(buz_field, new_attrs[attr])
          result
        end
      end
    end
  end
end