module HashPersistent
  module Collection
    
    def self.included(base)
      base.extend ClassMethods_Initial
      base.module_eval do
        include HashPersistent::Resource
      end
    end
    
    module ClassMethods_Initial      
      def attach(resource_class, collection_basis)
        raise "You must create a persistent subclass before attaching this collection class. Use HashPersistent::persist_to()" unless included_modules.include?(HashPersistent::Resource::InstanceMethods)
        raise "You can attach this collection class only to a class that has been created with HashPersistent::Resource.persist_to()" unless resource_class.included_modules.include?(HashPersistent::Resource::InstanceMethods)
        raise "Did not find the specified basis attribute (#{collection_basis}) in the given resource class" unless resource_class.instance_methods.include?(collection_basis.to_s)
        
        extend  ClassMethods
        include InstanceMethods

        @collection_basis = collection_basis
        @resource_class = resource_class
        resource_class.on_save do |resource|
          collected_resource_saved(resource)
        end
        
        resource_class.on_delete do |resource|
          collected_resource_deleted(resource)
        end
      end
    end

    module ClassMethods
      attr_reader :resource_class
      
      def collected_resource_saved(resource)
        collection = find(resource.send(@collection_basis))
        unless collection
          collection = new
          collection.collected_keys = []
          collection.key = resource.send(@collection_basis)
        end
        collection.collected_keys << resource.key
        collection.collected_keys.uniq!
        collection.save
      end

      def collected_resource_deleted(resource)
        collection = find(resource.send(@collection_basis))
        collection.collected_keys.delete(resource.key)
        if collection.collected_keys.empty?
          collection.delete
        else
          collection.save
        end
      end
    end
    
    module InstanceMethods
      attr_accessor :collected_keys
    
      def collected_resources
        collected_keys.collect do |key|
          self.class.resource_class.send(:find, key)
        end
      end
    end
  end
end