# $Id: filters.rb 68 2007-12-09 07:45:37Z tim_pease $

module Webby
module Filters
   
  class << self
    
    # Register a handler for a filter
    def register( filter, &block )
      handlers[filter.to_s] = block
    end
    
    # Process input through filters
    def process( renderer, page, input )
      # Start a new cursor for this page
      Cursor.new(renderer, page).start_for(input)
    end
    
    # Access a filter handler
    def []( name )
      handlers[name]
    end
      
    #######
    private
    #######

    # The registered filter handlers
    def handlers
      @handlers ||= {}
    end
    
    # Instances of this class handle processing a set of filters
    # for a given renderer and page.
    # Note: The instance is passed as the second argument to filters
    #       that require two parameters and can be used to access 
    #       information on the renderer, page, or filters being
    #       processed.
    class Cursor
      
      attr_reader :renderer, :page, :filters
      def initialize(renderer, page)
        @renderer, @page = renderer, page
        @filters = Array(page.filter)
        @log = Logging::Logger[Webby::Renderer]
        @processed = 0
      end
      
      def start_for(input)
        filters.inject(input) do |result, filter|
          handler = Filters[filter]
          args = [result, self][0, handler.arity]
          handle(filter, handler, *args)
        end
      end
      
      # The list of filters yet to be processed
      def remaining_filters
        filters[@processed..-1]
      end
      
      # The name of the current filter
      def current_filter
        filters[@processed]
      end
      
      #######
      private
      #######

      # Process arguments through a single filter
      def handle(filter, handler, *args)
        result = handler.call(*args)
        @processed += 1
        result
      rescue NameError => e
        @log.fatal "Name error in filter `#{filter}' (missing dependency?): #{e.message}"
        exit 1
      rescue => e
        @log.fatal "Error in filter `#{filter}': #{e.message}"
        exit 1
      end
      
    end  # class Cursor
  end  # class << self
    
end  # module Filters
end  # module Webby

# EOF