require 'set'

require_relative 'observable'

module Glimmer
  module DataBinding
    # TODO prefix utility methods with double-underscore
    module ObservableArray
      include Observable

      def add_observer(observer, element_properties=nil)
        return observer if has_observer?(observer) && element_properties.nil?
        property_observer_list << observer
        [element_properties].flatten.compact.each do |property|
          each do |element|
            observer.observe(element, property)
          end
        end
        observer
      end

      def remove_observer(observer, element_properties=nil)
        property_observer_list.delete(observer)
        [element_properties].flatten.compact.each do |property|
          each do |element|
            observer.unobserve(element, property)
          end
        end
        observer
      end

      def has_observer?(observer)
        property_observer_list.include?(observer)
      end

      def property_observer_list
        @property_observer_list ||= Set.new
      end

      def notify_observers
        property_observer_list.each {|observer| observer.call}
      end

      def self.extend_object(array)
        # TODO consider alias_method, and define_method instead

        array.instance_eval("alias __original_add <<")
        array.instance_eval <<-end_eval, __FILE__, __LINE__
        def <<(value)
          self.__original_add(value)
          notify_observers
        end
        end_eval

        array.instance_eval("alias __original_set_value []=")
        array.instance_eval <<-end_eval, __FILE__, __LINE__
        def []=(index, value)
          old_value = self[index]
          unregister_dependent_observers(old_value)
          self.__original_set_value(index, value)
          notify_observers
        end
        end_eval

        array.instance_eval("alias __original_delete delete")
        array.instance_eval <<-end_eval, __FILE__, __LINE__
        def delete(value)
          unregister_dependent_observers(value)
          self.__original_delete(value)
          notify_observers
        end
        end_eval

        array.instance_eval("alias __original_delete_at delete_at")
        array.instance_eval <<-end_eval, __FILE__, __LINE__
        def delete_at(index)
          old_value = self[index]
          unregister_dependent_observers(old_value)
          self.__original_delete_at(index)
          notify_observers
        end
        end_eval

        array.instance_eval("alias __original_clear clear")
        array.instance_eval <<-end_eval, __FILE__, __LINE__
        def clear
          each do |old_value|
            unregister_dependent_observers(old_value)
          end
          self.__original_clear
          notify_observers
        end
        end_eval

        super
      end

      def unregister_dependent_observers(old_value)
        # TODO look into optimizing this
        return unless old_value.is_a?(ObservableModel) || old_value.is_a?(ObservableArray)
        property_observer_list.each do |observer|
          observer.unregister_dependents_with_observable(observer.registration_for(self), old_value)
        end
      end
    end
  end
end