require 'glimmer/data_binding/observable'
require 'glimmer/data_binding/observer'

module Glimmer
  module DataBinding
    class ModelBinding
      include Observable
      include Observer

      attr_reader :binding_options

      def initialize(base_model, property_name_expression, binding_options = nil)
        @base_model = base_model
        @property_name_expression = property_name_expression
        @binding_options = binding_options || {}
        if computed?
          @computed_model_bindings = computed_by.map do |computed_by_property_expression|
            self.class.new(base_model, computed_by_property_expression)
          end
        end
      end

      def model
        nested_property? ? nested_model : base_model
      end

      # e.g. person.address.state returns [person, person.address]
      def nested_models
        @nested_models = [base_model]
        model_property_names.reduce(base_model) do |reduced_model, nested_model_property_name|
          if reduced_model.nil?
            nil
          else
            invoke_property_reader(reduced_model, nested_model_property_name).tap do |new_reduced_model|
              @nested_models << new_reduced_model
            end
          end
        end
        @nested_models
      end

      def nested_model
        nested_models.last
      end

      def base_model
        @base_model
      end

      def property_name
        nested_property? ? nested_property_name : property_name_expression
      end

      def convert_on_read(value)
        apply_converter(@binding_options[:on_read], value)
      end

      def convert_on_write(value)
        apply_converter(@binding_options[:on_write], value)
      end

      def apply_converter(converter, value)
        if converter.nil?
          value
        elsif converter.is_a?(String) || converter.is_a?(Symbol)
          if value.respond_to?(converter)
            value.send(converter)
          else
            raise Glimmer::Error, "Unsupported bind converter: #{converter.inspect}"
          end
        elsif converter.respond_to?(:call, value)
          converter.call(value)
        else
          raise Glimmer::Error, "Unsupported bind converter: #{converter.inspect}"
        end
      end

      # All nested property names
      # e.g. property name expression "address.state" gives ['address', 'state']
      # If there are any indexed property names, this returns indexes as properties.
      # e.g. property name expression "addresses[1].state" gives ['addresses', '[1]', 'state']
      def nested_property_names
        @nested_property_names ||= property_name_expression.split(".").map {|pne| pne.match(/([^\[]+)(\[[^\]]+\])?/).to_a.drop(1)}.flatten.compact
      end

      # Final nested property name
      # e.g. property name expression "address.state" gives :state
      def nested_property_name
        nested_property_names.last
      end

      # Model representing nested property names
      # e.g. property name expression "address.state" gives [:address]
      def model_property_names
        nested_property_names[0...-1]
      end

      def nested_property?
        property_name_expression.match(/[.\[]/)
      end

      def property_name_expression
        @property_name_expression
      end

      def computed?
        !computed_by.empty?
      end

      def computed_by
        [@binding_options[:computed_by]].flatten.compact
      end

      def nested_property_observers_for(observer)
        @nested_property_observers_collection ||= {}
        unless @nested_property_observers_collection.has_key?(observer)
          @nested_property_observers_collection[observer] = nested_property_names.reduce({}) do |output, property_name|
            output.merge(
              property_name => Observer.proc do |new_value|
                # Ensure reattaching observers when a higher level nested property is updated (e.g. person.address changes reattaches person.address.street observer)
                add_observer(observer)
                observer.call(evaluate_property)
              end
            )
          end
        end
        @nested_property_observers_collection[observer]
      end

      def add_observer(observer)
        if computed?
          add_computed_observers(observer)
        elsif nested_property?
          add_nested_observers(observer)
        else
          model_binding_observer = Observer.proc do |new_value|
            observer.call(evaluate_property)
          end
          observer_registration = model_binding_observer.observe(model, property_name)
          my_registration = observer.registration_for(self)
          observer.add_dependent(my_registration => observer_registration)
        end
      end

      def remove_observer(observer)
        if computed?
          @computed_model_bindings.each do |computed_model_binding|
            computed_observer_for(observer).unobserve(computed_model_binding)
          end
          @computed_observer_collection.delete(observer)
        elsif nested_property?
          nested_property_observers_for(observer).clear
        else
          observer.unobserve(model, property_name)
        end
      end

      def computed_observer_for(observer)
        @computed_observer_collection ||= {}
        unless @computed_observer_collection.has_key?(observer)
          @computed_observer_collection[observer] = Observer.proc do |new_value|
            observer.call(evaluate_property)
          end
        end
        @computed_observer_collection[observer]
      end

      def add_computed_observers(observer)
        @computed_model_bindings.each do |computed_model_binding|
          observer_registration = computed_observer_for(observer).observe(computed_model_binding)
          my_registration = observer.registration_for(self)
          observer.add_dependent(my_registration => observer_registration)
        end
      end

      def add_nested_observers(observer)
        nested_property_observers = nested_property_observers_for(observer)
        nested_models.zip(nested_property_names).each_with_index do |zip, i|
          model, property_name = zip
          nested_property_observer = nested_property_observers[property_name]
          previous_index = i - 1
          parent_model = previous_index.negative? ? self : nested_models[previous_index]
          parent_property_name = previous_index.negative? ? nil : nested_property_names[previous_index]
          parent_observer = previous_index.negative? ? observer : nested_property_observers[parent_property_name]
          parent_property_name = nil if parent_property_name.to_s.start_with?('[')
          unless model.nil?
            if property_indexed?(property_name)
              # TODO figure out a way to deal with this more uniformly
              observer_registration = nested_property_observer.observe(model)
            else
              observer_registration = nested_property_observer.observe(model, property_name)
            end
            parent_registration = parent_observer.registration_for(parent_model, parent_property_name)
            parent_observer.add_dependent(parent_registration => observer_registration)
          end
        end
      end

      def call(value)
        return if model.nil?
        converted_value = value
        invoke_property_writer(model, "#{property_name}=", converted_value) unless evaluate_property == converted_value
      end

      def evaluate_property
        unless model.nil?
          value = invoke_property_reader(model, property_name)
          convert_on_read(value)        
        end
      end

      def evaluate_options_property
        model.send(options_property_name) unless model.nil?
      end

      def options_property_name
        self.property_name + "_options"
      end

      def property_indexed?(property_expression)
        property_expression.to_s.start_with?('[')
      end

      def invoke_property_reader(object, property_expression)
        if property_indexed?(property_expression)
          property_method = '[]'
          property_argument = property_expression[1...-1]
          property_argument = property_argument.to_i if property_argument.match(/\d+/)
          object.send(property_method, property_argument)
        else
          object.send(property_expression)
        end
      end

      def invoke_property_writer(object, property_expression, value)
        value = convert_on_write(value)
        if property_indexed?(property_expression)
          property_method = '[]='
          property_argument = property_expression[1...-2]
          property_argument = property_argument.to_i if property_argument.match(/\d+/)
          object.send(property_method, property_argument, value)
        else
          object.send(property_expression, value)
        end
      end
    end
  end
end