module AbstractController
  module Layouts
    extend ActiveSupport::Concern

    include Renderer

    included do
      extlib_inheritable_accessor(:_layout_conditions) { Hash.new }
    end

    module ClassMethods
      def inherited(klass)
        super
        klass._write_layout_method
      end

      # Specify the layout to use for this class.
      #
      # If the specified layout is a:
      # String:: the String is the template name
      # Symbol:: call the method specified by the symbol, which will return
      #   the template name
      # false::  There is no layout
      # true::   raise an ArgumentError
      #
      # ==== Parameters
      # layout<String, Symbol, false)>:: The layout to use.
      #
      # ==== Options (conditions)
      # :only<#to_s, Array[#to_s]>:: A list of actions to apply this layout to.
      # :except<#to_s, Array[#to_s]>:: Apply this layout to all actions but this one
      def layout(layout, conditions = {})
        conditions.each {|k, v| conditions[k] = Array(v).map {|a| a.to_s} }
        self._layout_conditions = conditions

        @_layout = layout || false # Converts nil to false
        _write_layout_method
      end

      # If no layout is supplied, look for a template named the return
      # value of this method.
      #
      # ==== Returns
      # String:: A template name
      def _implied_layout_name
        name.underscore
      end

      # Takes the specified layout and creates a _layout method to be called
      # by _default_layout
      #
      # If there is no explicit layout specified:
      # If a layout is found in the view paths with the controller's
      # name, return that string. Otherwise, use the superclass'
      # layout (which might also be implied)
      def _write_layout_method
        case @_layout
        when String
          self.class_eval %{def _layout(details) #{@_layout.inspect} end}
        when Symbol
          self.class_eval <<-ruby_eval, __FILE__, __LINE__ + 1
            def _layout(details)
              #{@_layout}.tap do |layout|
                unless layout.is_a?(String) || !layout
                  raise ArgumentError, "Your layout method :#{@_layout} returned \#{layout}. It " \
                    "should have returned a String, false, or nil"
                end
              end
            end
          ruby_eval
        when false
          self.class_eval %{def _layout(details) end}
        when true
          raise ArgumentError, "Layouts must be specified as a String, Symbol, false, or nil"
        when nil
          self.class_eval <<-ruby_eval, __FILE__, __LINE__ + 1
            def _layout(details)
              if view_paths.find_by_parts?("#{_implied_layout_name}", details, "layouts")
                "#{_implied_layout_name}"
              else
                super
              end
            end
          ruby_eval
        end
        self.class_eval { private :_layout }
      end
    end

  private
    # This will be overwritten by _write_layout_method
    def _layout(details) end

    # Determine the layout for a given name and details.
    #
    # ==== Parameters
    # name<String>:: The name of the template
    # details<Hash{Symbol => Object}>:: A list of details to restrict
    #   the lookup to. By default, layout lookup is limited to the
    #   formats specified for the current request.
    def _layout_for_name(name, details = {:formats => formats})
      name && _find_by_parts(name, details)
    end

    # Take in the name and details and find a Template.
    #
    # ==== Parameters
    # name<String>:: The name of the template to retrieve
    # details<Hash>:: A list of details to restrict the search by. This
    #   might include details like the format or locale of the template.
    #
    # ==== Returns
    # Template:: A template object matching the name and details
    def _find_by_parts(name, details)
      # TODO: Make prefix actually part of details in ViewPath#find_by_parts
      prefix = details.key?(:prefix) ? details.delete(:prefix) : "layouts"
      view_paths.find_by_parts(name, details, prefix)
    end

    # Returns the default layout for this controller and a given set of details. 
    # Optionally raises an exception if the layout could not be found.
    #
    # ==== Parameters
    # details<Hash>:: A list of details to restrict the search by. This
    #   might include details like the format or locale of the template.
    # require_layout<Boolean>:: If this is true, raise an ArgumentError
    #   with details about the fact that the exception could not be
    #   found (defaults to false)
    #
    # ==== Returns
    # Template:: The template object for the default layout (or nil)
    def _default_layout(details, require_layout = false)
      if require_layout && _action_has_layout? && !_layout(details)
        raise ArgumentError,
          "There was no default layout for #{self.class} in #{view_paths.inspect}"
      end

      begin
        _layout_for_name(_layout(details), details) if _action_has_layout?
      rescue NameError => e
        raise NoMethodError,
          "You specified #{@_layout.inspect} as the layout, but no such method was found"
      end
    end

    # Determines whether the current action has a layout by checking the
    # action name against the :only and :except conditions set on the
    # layout.
    #
    # ==== Returns
    # Boolean:: True if the action has a layout, false otherwise.
    def _action_has_layout?
      conditions = _layout_conditions
      if only = conditions[:only]
        only.include?(action_name)
      elsif except = conditions[:except]
        !except.include?(action_name)
      else
        true
      end
    end
  end
end
