module Nifty
  module KeyValueStore
    module ModelExtension

      def self.included(base)
        base.extend ClassMethods
      end

      module ClassMethods
        def key_value_stores
          @key_value_stores ||= []
        end
  
        def key_value_store(*names)
          
          unless self.reflect_on_all_associations(:has_many).map(&:name).include?(:nifty_key_value_pairs)
            has_many :nifty_key_value_pairs, :as => :parent, :dependent => :destroy, :class_name => 'Nifty::KeyValueStore::KeyValuePair'
            after_save :save_custom_values_to_db
          end
          
          names.each do |name|
            key_value_stores << name
      
            # Getter
            define_method name do
              if value = instance_variable_get("@#{name}")
                value
              else
                instance_variable_set "@#{name}", get_custom_values_for(name)
              end
            end
      
            # JSON Getter
            define_method "#{name}_json" do
              send(name).to_json
            end
      
            # Setter
            define_method "#{name}=" do |value|
              instance_variable_set("@#{name}", value)
            end
      
            # JSON Setter
            define_method "#{name}_json=" do |value|
              send("#{name}=", JSON.parse(value))
            end
      
          end
        end
      end

      # Get the values for a given group as a hash from the database without caching
      def get_custom_values_for(group)
        nifty_key_value_pairs.where(:group => group).inject({}) do |hash, value|
          hash[value.name] = value.value
          hash
        end
      end

      # Save all custom values in the appropriate methods to the 
      def save_custom_values_to_db
        # get the existing joins ready
        existing_joins = self.nifty_key_value_pairs
        # go through all groups
        self.class.key_value_stores.each do |group|
          db_values     = get_custom_values_for(group)
          local_values  = self.send(group).delete_if { |k,v| v.blank? }
    
          # remove any keys which no longer exist
          keys_to_remove = db_values.keys - local_values.keys
          self.nifty_key_value_pairs.where(:group => group, :name => keys_to_remove).destroy_all unless keys_to_remove.empty?
    
          # add/update all remaining keys
          local_values.each do |key, value|
            if existing_join = existing_joins.select { |j| j.group == group.to_s && j.name == key}.first
              existing_join.value = value
              existing_join.save
            else
              self.nifty_key_value_pairs.create(:group => group, :name => key, :value => value)
            end
          end
        end
      end

    end
  end
end