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module ActionController #:nodoc:
  # The flash provides a way to pass temporary objects between actions. Anything you place in the flash will be exposed
  # to the very next action and then cleared out. This is a great way of doing notices and alerts, such as a create action
  # that sets <tt>flash[:notice] = "Successfully created"</tt> before redirecting to a display action that can then expose
  # the flash to its template. Actually, that exposure is automatically done. Example:
  #
  # class WeblogController < ActionController::Base
  # def create
  # # save post
  # flash[:notice] = "Successfully created post"
  # redirect_to :action => "display", :params => { :id => post.id }
  # end
  #
  # def display
  # # doesn't need to assign the flash notice to the template, that's done automatically
  # end
  # end
  #
  # display.rhtml
  # <% if @flash[:notice] %><div class="notice"><%= @flash[:notice] %></div><% end %>
  #
  # This example just places a string in the flash, but you can put any object in there. And of course, you can put as many
  # as you like at a time too. Just remember: They'll be gone by the time the next action has been performed.
  #
  # See docs on the FlashHash class for more details about the flash.
  module Flash
    def self.included(base)
      base.send :include, InstanceMethods

      base.class_eval do
        alias_method :process_cleanup_without_flash, :process_cleanup
        alias_method :process_cleanup, :process_cleanup_with_flash
      end
    end
    
    
    class FlashNow #:nodoc:
      def initialize flash
        @flash = flash
      end
      
      def []=(k, v)
        @flash[k] = v
        @flash.discard(k)
        v
      end
      
      def [](k)
        @flash[k]
      end
    end
    
    class FlashHash < Hash
      def initialize #:nodoc:
        super
        @used = {}
      end
      
      def []=(k, v) #:nodoc:
        keep(k)
        super
      end
      
      def update(h) #:nodoc:
        h.keys.each{ |k| discard(k) }
        super
      end
      
      alias :merge! :update
      
      def replace(h) #:nodoc:
        @used = {}
        super
      end
    
      # Sets a flash that will not be available to the next action, only to the current.
      #
      # flash.now[:message] = "Hello current action"
      #
      # This method enables you to use the flash as a central messaging system in your app.
      # When you need to pass an object to the next action, you use the standard flash assign (<tt>[]=</tt>).
      # When you need to pass an object to the current action, you use <tt>now</tt>, and your object will
      # vanish when the current action is done.
      #
      # Entries set via <tt>now</tt> are accessed the same way as standard entries: <tt>flash['my-key']</tt>.
      def now
        FlashNow.new self
      end
    
      # Keeps either the entire current flash or a specific flash entry available for the next action:
      #
      # flash.keep # keeps the entire flash
      # flash.keep(:notice) # keeps only the "notice" entry, the rest of the flash is discarded
      def keep(k=nil)
        use(k, false)
      end
    
      # Marks the entire flash or a single flash entry to be discarded by the end of the current action
      #
      # flash.keep # keep entire flash available for the next action
      # flash.discard(:warning) # discard the "warning" entry (it'll still be available for the current action)
      def discard(k=nil)
        use(k)
      end
    
      # Mark for removal entries that were kept, and delete unkept ones.
      #
      # This method is called automatically by filters, so you generally don't need to care about it.
      def sweep #:nodoc:
        keys.each do |k|
          unless @used[k]
            use(k)
          else
            delete(k)
            @used.delete(k)
          end
        end
        (@used.keys - keys).each{|k| @used.delete k } # clean up after keys that could have been left over by calling reject! or shift on the flash
      end
    
      private
        # Used internally by the <tt>keep</tt> and <tt>discard</tt> methods
        # use() # marks the entire flash as used
        # use('msg') # marks the "msg" entry as used
        # use(nil, false) # marks the entire flash as unused (keeps it around for one more action)
        # use('msg', false) # marks the "msg" entry as unused (keeps it around for one more action)
        def use(k=nil, v=true)
          unless k.nil?
            @used[k] = v
          else
            keys.each{|key| use key, v }
          end
        end
    end

    module InstanceMethods
      def process_cleanup_with_flash
        process_cleanup_without_flash
        flash.sweep
      end
      
      protected
        # Access the contents of the flash. Use <tt>flash["notice"]</tt> to read a notice you put there or
        # <tt>flash["notice"] = "hello"</tt> to put a new one.
        # Note that if sessions are disabled only flash.now will work.
        def flash #:doc:
          @flash ||=
            if @parent_controller
              @parent_controller.flash
            elsif @session.is_a?(Hash)
              # @session is a Hash, if sessions are disabled
              # we don't put the flash in the session in this case
              FlashHash.new
            else
              # otherwise, @session is a CGI::Session or a TestSession
              # so make sure it gets retrieved from/saved to session storage after request processing
              @session["flash"] ||= FlashHash.new
            end
        end

        # deprecated. use <tt>flash.keep</tt> instead
        def keep_flash #:doc:
          warn 'keep_flash is deprecated; use flash.keep instead.'
          flash.keep
        end
    end
  end
end
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