module ActionDispatch
  class Request
    # 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.
    def flash
      @env['action_dispatch.request.flash_hash'] ||= (session["flash"] || Flash::FlashHash.new)
    end
  end

  # 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] = "Post 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 PostsController < ActionController::Base
  #     def create
  #       # save post
  #       flash[:notice] = "Post successfully created"
  #       redirect_to posts_path(@post)
  #     end
  #
  #     def show
  #       # doesn't need to assign the flash notice to the template, that's done automatically
  #     end
  #   end
  #
  #   show.html.erb
  #     <% if flash[:notice] %>
  #       <div class="notice"><%= flash[:notice] %></div>
  #     <% end %>
  #
  # Since the +notice+ and +alert+ keys are a common idiom, convenience accessors are available:
  #
  #   flash.alert = "You must be logged in"
  #   flash.notice = "Post successfully created"
  #
  # 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.
  class Flash
    class FlashNow #:nodoc:
      def initialize(flash)
        @flash = flash
        @closed = false
      end

      attr_reader :closed
      alias :closed? :closed
      def close!; @closed = true end

      def []=(k, v)
        raise ClosedError, "Cannot modify flash because it was closed. This means it was already streamed back to the client or converted to HTTP headers." if closed?
        @flash[k] = v
        @flash.discard(k)
        v
      end

      def [](k)
        @flash[k]
      end

      # Convenience accessor for flash.now[:alert]=
      def alert=(message)
        self[:alert] = message
      end

      # Convenience accessor for flash.now[:notice]=
      def notice=(message)
        self[:notice] = message
      end
    end

    class FlashHash < Hash
      def initialize #:nodoc:
        super
        @used = Set.new
        @closed = false
      end

      attr_reader :closed
      alias :closed? :closed
      def close!; @closed = true end

      def []=(k, v) #:nodoc:
        raise ClosedError, "Cannot modify flash because it was closed. This means it was already streamed back to the client or converted to HTTP headers." if closed?
        keep(k)
        super
      end

      def update(h) #:nodoc:
        h.keys.each { |k| keep(k) }
        super
      end

      alias :merge! :update

      def replace(h) #:nodoc:
        @used = Set.new
        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.discard              # discard the entire flash at the end of the current action
      #     flash.discard(:warning)    # discard only the "warning" entry at the end of 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.include?(k)
            @used << k
          else
            delete(k)
            @used.delete(k)
          end
        end

        # clean up after keys that could have been left over by calling reject! or shift on the flash
        (@used - keys).each{ |k| @used.delete(k) }
      end

      # Convenience accessor for flash[:alert]
      def alert
        self[:alert]
      end

      # Convenience accessor for flash[:alert]=
      def alert=(message)
        self[:alert] = message
      end

      # Convenience accessor for flash[:notice]
      def notice
        self[:notice]
      end

      # Convenience accessor for flash[:notice]=
      def notice=(message)
        self[:notice] = message
      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)
        # Returns the single value for the key you asked to be marked (un)used or the FlashHash itself
        # if no key is passed.
        def use(key = nil, used = true)
          Array(key || keys).each { |k| used ? @used << k : @used.delete(k) }
          return key ? self[key] : self
        end
    end

    def initialize(app)
      @app = app
    end

    def call(env)
      if (session = env['rack.session']) && (flash = session['flash'])
        flash.sweep
      end

      @app.call(env)
    ensure
      session    = env['rack.session'] || {}
      flash_hash = env['action_dispatch.request.flash_hash']

      if flash_hash
       if !flash_hash.empty? || session.key?('flash')
        session["flash"] = flash_hash
       end
       flash_hash.close!
      end

      if session.key?('flash') && session['flash'].empty?
        session.delete('flash')
      end
    end
  end

  class ClosedError < StandardError #:nodoc:
  end
end