module Rtml::WidgetCore::ClassMethods
  @@gui_enabled_widgets = {}

  def proxy_module
    return @proxy_module if @proxy_module
    @proxy_module = Module.new
    @proxy_module.instance_variable_set("@shared_variables", shared_variables)
    @proxy_module.instance_eval do
      def included(base)
        @shared_variables.each do |sv|
          base.send(:attr_accessor, sv[:name])
        end
      end
    end

    @proxy_module
  end

  # Yields this Widget's GUI configuration to the supplied block, allowing you to set up your Widget to be accessible
  # from the RTML Application Builder. Note that if this method is never called, your Widget will not be available to
  # the GUI.
  def gui
    yield(gui_configuration)
  end

  # Returns the +Rtml::WidgetCore::GuiConfiguration+ instance for this Widget.
  # Shorthand for:
  #   widget.gui_enabled_widgets[widget]
  def gui_configuration
    gui_enabled_widgets[self] ||= Rtml::WidgetCore::GuiConfiguration.new(self)
  end

  ## Returns the array of Widgets that have called the #gui method, thereby marking themselves as accessible to the
  ## RTML Application Builder.
  def gui_enabled_widgets
    @@gui_enabled_widgets
  end

  # Creates a "shared" variable for the parent object with the specified default value, if any. This is much like
  # a class variable, except that it is unique to the parent object in question. Multiple calls to a Widget's
  # entry point will result in multiple Widgets being instantiated. If you use an instance variable to hold data,
  # then that instance variable will be different for every entry point called. However, sometimes you need to share
  # data across multiple instances of the same Widget, but not across *all* instances of the same Widget. For
  # instance, your Widget may want to track references to variables in an individual Screen, but not across multiple
  # Screens. To accomplish this, you essentially need an instance variable for the Screen. The "shared" method
  # manages these variables for you.
  #
  # Examples:
  #   shared :tml_variables
  #   shared :variable_definitions, :variable_declarations
  #   shared :tml_variables => []                          # initializes #tml_variables to [].dup
  def shared(*names)
    names.each do |name|
      if name.kind_of? Hash
        value = name.values.first
        name = name.keys.first.to_s
        shared_variables << { :name => name, :default_value => value }
      else
        name = name.to_s
        shared_variables << { :name => name, :default_value => nil }
      end
      delegate name, "#{name}=", :to => :parent
    end
    reinclude_proxy_module
  end

  # By default, if a Widget's entry point is called with a block argument, it will be passed into the #process method
  # of the entry point's return value. This is called subprocessing -- that is, processing the element to be returned
  # at a lower level. This method disables subprocessing and its related assertions. It's useful, for instance, if you
  # want to manually control how or when the block argument is processed, or if you want to ignore it entirely.
  #
  # If you want to disable subprocessing only under certain conditions, see the instance method of the same name.
  def disable_subprocessing!
    @disable_subprocessing = true
  end

  # Use this to enable subprocessing after it has already been disabled. See #disable_subprocessing!
  def enable_subprocessing!
    @disable_subprocessing = false
  end

  # Returns true if subprocessing has been disabled. See also #disable_subprocessing!
  def subprocessing_disabled?
    @disable_subprocessing ||= false
  end
  alias disable_subprocessing? subprocessing_disabled?

  # Specifies the targets that this Widget will affect. A target can be a name of a model or the name of a TML tag,
  # which matches that model's "name" attribute.
  #
  # Examples:
  #   affects :document, :element, :property # names of models
  #   affects :tml, :head, :screen           # names of TML tags
  #
  def affects(*targets)
    targets.flatten.each do |target|
      target = target.to_s unless target.kind_of?(String)
      unless self.targets.include? target
        self.targets << target
        map = Rtml::Widgets.mapping(target)
        map.proxied_widgets << self
        map.imbue(proxy_module)
      end
    end
  end

  # Goes through each of the targets of this Widget, looks up its mapping in Rtml::Widgets.mapping, and calls
  # proxy_module.append_features(mapping) for each of those mappings.
  def reinclude_proxy_module
    targets.each do |target|
      Rtml::Widgets.mapping(target).imbue(proxy_module)
    end
  end

  # Specifies entry points, which are names of methods that can be called from the targets to invoke this Widget.
  #
  # Examples:
  #   entry_point :screen
  #
  def entry_point(*names)
    names.each do |name|
      name = name.to_s
      unless entry_points.include?(name)
        entry_points << name
        add_entry_point(name)
      end
    end
  end

  # Adds the specified entry point to this Widget's proxy module.
  def add_entry_point(entry_point)
    # This validation doesn't work because it's not this proxy module, it's those of the OTHER Widgets
    # that should be checked. Not sure of the best way to do that yet.
#    if proxy_module.public_instance_methods.include?(entry_point)
#      raise Rtml::Errors::RulesViolationError,
#            "Widget entry point #{entry_point} cannot be defined because it already exists!"
#    end
    entry_point = entry_point.to_s if entry_point.is_a?(Symbol)
    
    enter_from_hash = "#{entry_point}_from_hash"
    ['?','!'].each do |i|
      enter_from_hash = enter_from_hash.gsub(/#{Regexp::escape(i)}/, '') + i if enter_from_hash[i]
    end

    line = __LINE__ + 2
    code = <<-end_code
      def #{entry_point}(*args, &block)               # def screen(*args, &block)
        widget = #{self.name}.new(self)               #   widget = Rtml::Widgets::Screens.new(self)
        r = widget.#{entry_point}(*args, &block)      #   r = widget.screen(*args, &block)

        unless widget.disable_subprocessing? || !block_given?
          unless r.respond_to?(:process)
            raise Rtml::Errors::SubprocessingNotSupported, "Return value \#{r} does not support subprocessing"
          end
          r.process &block
        end
        r
      rescue ArgumentError => ae
        if ae.backtrace[0] =~ /#{Regexp::escape entry_point}/
          raise ArgumentError, ae.message, caller
        else raise ae
        end
      end                                             # end

      # Calls the entry point after reformatting the arguments in hash to fit the entry point's requirements
      # per +Rtml::WidgetCore::GuiConfiguration#construct_arguments+
      #
      # This is primarily for interfacing with the RTML GUI.
      #
      def #{enter_from_hash}(hash, &block)
        arguments = #{self}.gui_configuration.construct_arguments(hash || {})
        self.#{entry_point} *arguments, &block
      end
    end_code
    proxy_module.class_eval code, __FILE__, line
    reinclude_proxy_module
  end

  # Returns true if the specified class is a valid target of this Widget
  def target?(base)
    if base.respond_to?(:name)
      name = base.name.underscore.sub(/^.*\//, '')
      targets.each do |target|
        if base.kind_of?(ActiveRecord::Base) # it's an instance, so we should check the tag name, not the class name
          return true if target == base.name
        else
          return true if target == name
        end
      end
    end
    false
  end
end