require 'active_support/core_ext/module/attr_internal'

module AbstractController
  class Error < StandardError; end

  class DoubleRenderError < Error
    DEFAULT_MESSAGE = "Render and/or redirect were called multiple times in this action. Please note that you may only call render OR redirect, and at most once per action. Also note that neither redirect nor render terminate execution of the action, so if you want to exit an action after redirecting, you need to do something like \"redirect_to(...) and return\"."

    def initialize(message = nil)
      super(message || DEFAULT_MESSAGE)
    end
  end

  class Base
    attr_internal :response_body
    attr_internal :action_name

    class << self
      attr_reader :abstract
      alias_method :abstract?, :abstract

      # Define a controller as abstract. See internal_methods for more
      # details.
      def abstract!
        @abstract = true
      end

      def inherited(klass)
        ::AbstractController::Base.descendants << klass.to_s
        super
      end

      # A list of all descendents of AbstractController::Base. This is
      # useful for initializers which need to add behavior to all controllers.
      def descendants
        @descendants ||= []
      end

      # A list of all internal methods for a controller. This finds the first
      # abstract superclass of a controller, and gets a list of all public
      # instance methods on that abstract class. Public instance methods of
      # a controller would normally be considered action methods, so we
      # are removing those methods on classes declared as abstract
      # (ActionController::Http and ActionController::Base are defined
      # as abstract)
      def internal_methods
        controller = self
        controller = controller.superclass until controller.abstract?
        controller.public_instance_methods(true)
      end

      # The list of hidden actions to an empty Array. Defaults to an
      # empty Array. This can be modified by other modules or subclasses
      # to specify particular actions as hidden.
      #
      # ==== Returns
      # Array[String]:: An array of method names that should not be
      #                 considered actions.
      def hidden_actions
        []
      end

      # A list of method names that should be considered actions. This
      # includes all public instance methods on a controller, less
      # any internal methods (see #internal_methods), adding back in
      # any methods that are internal, but still exist on the class
      # itself. Finally, #hidden_actions are removed.
      #
      # ==== Returns
      # Array[String]:: A list of all methods that should be considered
      #                 actions.
      def action_methods
        @action_methods ||=
          # All public instance methods of this class, including ancestors
          public_instance_methods(true).map { |m| m.to_s }.to_set -
          # Except for public instance methods of Base and its ancestors
          internal_methods.map { |m| m.to_s } +
          # Be sure to include shadowed public instance methods of this class
          public_instance_methods(false).map { |m| m.to_s } -
          # And always exclude explicitly hidden actions
          hidden_actions
      end
    end

    abstract!

    # Calls the action going through the entire action dispatch stack.
    # 
    # The actual method that is called is determined by calling
    # #method_for_action. If no method can handle the action, then an
    # ActionNotFound error is raised.
    #
    # ==== Returns
    # self
    def process(action)
      @_action_name = action_name = action.to_s

      unless action_name = method_for_action(action_name)
        raise ActionNotFound, "The action '#{action}' could not be found"
      end

      process_action(action_name)
      self
    end

  private
    # See AbstractController::Base.action_methods
    def action_methods
      self.class.action_methods
    end

    # Returns true if the name can be considered an action. This can
    # be overridden in subclasses to modify the semantics of what
    # can be considered an action.
    #
    # ==== Parameters
    # name<String>:: The name of an action to be tested
    #
    # ==== Returns
    # TrueClass, FalseClass
    def action_method?(name)
      action_methods.include?(name)
    end

    # Call the action. Override this in a subclass to modify the
    # behavior around processing an action. This, and not #process,
    # is the intended way to override action dispatching.
    def process_action(method_name)
      send_action(method_name)
    end

    # Actually call the method associated with the action. Override
    # this method if you wish to change how action methods are called,
    # not to add additional behavior around it. For example, you would
    # override #send_action if you want to inject arguments into the
    # method.
    alias send_action send

    # If the action name was not found, but a method called "action_missing"
    # was found, #method_for_action will return "_handle_action_missing".
    # This method calls #action_missing with the current action name.
    def _handle_action_missing
      action_missing(@_action_name)
    end

    # Takes an action name and returns the name of the method that will
    # handle the action. In normal cases, this method returns the same
    # name as it receives. By default, if #method_for_action receives
    # a name that is not an action, it will look for an #action_missing
    # method and return "_handle_action_missing" if one is found.
    #
    # Subclasses may override this method to add additional conditions
    # that should be considered an action. For instance, an HTTP controller
    # with a template matching the action name is considered to exist.
    #
    # If you override this method to handle additional cases, you may
    # also provide a method (like _handle_method_missing) to handle
    # the case.
    #
    # If none of these conditions are true, and method_for_action
    # returns nil, an ActionNotFound exception will be raised.
    #
    # ==== Parameters
    # action_name<String>:: An action name to find a method name for
    #
    # ==== Returns
    # String:: The name of the method that handles the action
    # nil::    No method name could be found. Raise ActionNotFound.
    def method_for_action(action_name)
      if action_method?(action_name) then action_name
      elsif respond_to?(:action_missing, true) then "_handle_action_missing"
      end
    end
  end
end