# encoding: utf-8
#
# stamp.rb : Implements a repeatable stamp
#
# Copyright October 2009, Daniel Nelson. All Rights Reserved.
#
# This is free software. Please see the LICENSE and COPYING files for details.
#

module Prawn

  # The Prawn::Stamp module is used to create content that will be
  # included multiple times in a document. Using a stamp has three
  # advantages over creating content anew each time it is placed on
  # the page:
  #   i.   faster document creation
  #   ii.  smaller final document
  #   iii. faster display on subsequent displays of the repeated
  #   element because the viewer application can cache the rendered
  #   results
  #
  # Example:
  #   pdf.create_stamp("my_stamp") {
  #     pdf.fill_circle_at([10, 15], :radius => 5)
  #     pdf.draw_text("hello world", :at => [20, 10])
  #   }
  #   pdf.stamp("my_stamp")
  #
  module Stamp

    # Renders the stamp named <tt>name</tt> to the page
    # raises <tt>Prawn::Errors::InvalidName</tt> if name.empty?
    # raises <tt>Prawn::Errors::UndefinedObjectName</tt> if no stamp
    # has been created with this name
    #
    # Example:
    #   pdf.create_stamp("my_stamp") {
    #     pdf.fill_circle_at([10, 15], :radius => 5)
    #     pdf.text("hello world", :at => [20, 10])
    #   }
    #   pdf.stamp("my_stamp")
    #
    def stamp(name)
      dictionary_name, dictionary = stamp_dictionary(name)
      add_content "/#{dictionary_name} Do"
      state.page.xobjects.merge!(dictionary_name => dictionary)
    end

    # Renders the stamp named <tt>name</tt> at a position offset from
    # the initial coords at which the elements of the stamp was
    # created
    #
    # Example:
    #   pdf.create_stamp("circle") do
    #     pdf.fill_circle_at([0, 0], :radius => 25)
    #   end
    #   # draws a circle at 100, 100
    #   pdf.stamp_at("circle", [100, 100])
    #
    # See stamp() for exceptions that might be raised
    #
    def stamp_at(name, point)
      translate(point[0], point[1]) { stamp(name) }
    end

    # Creates a re-usable stamp named <tt>name</tt>
    #
    # raises <tt>Prawn::Errors::NameTaken</tt> if a stamp already
    # exists in this document with this name
    # raises <tt>Prawn::Errors::InvalidName</tt> if name.empty?
    #
    # Example:
    #   pdf.create_stamp("my_stamp") {
    #     pdf.fill_circle_at([10, 15], :radius => 5)
    #     pdf.draw_text("hello world", :at => [20, 10])
    #   }
    #
    def create_stamp(name, &block)
      dictionary = create_stamp_dictionary(name)

      state.page.stamp_stream(dictionary, &block)
    end
    
    private

    def stamp_dictionary_registry
      @stamp_dictionary_registry ||= {}
    end

    def next_stamp_dictionary_id
      stamp_dictionary_registry.length + 1
    end

    def stamp_dictionary(name)
      raise Prawn::Errors::InvalidName if name.empty?
      if stamp_dictionary_registry[name].nil?
        raise Prawn::Errors::UndefinedObjectName
      end

      dict = stamp_dictionary_registry[name]

      dictionary_name = dict[:stamp_dictionary_name]
      dictionary = dict[:stamp_dictionary]
      [dictionary_name, dictionary]
    end

    def create_stamp_dictionary(name)
      raise Prawn::Errors::InvalidName if name.empty?
      raise Prawn::Errors::NameTaken unless stamp_dictionary_registry[name].nil?
      # BBox origin is the lower left margin of the page, so we need
      # it to be the full dimension of the page, or else things that
      # should appear near the top or right margin are invisible
      dictionary = ref!(:Type    => :XObject,
                        :Subtype => :Form,
                        :BBox    => [0, 0,
                                     state.page.dimensions[2], state.page.dimensions[3]])

      dictionary_name = "Stamp#{next_stamp_dictionary_id}"

      stamp_dictionary_registry[name] = { :stamp_dictionary_name => dictionary_name,
                                          :stamp_dictionary      => dictionary }
      dictionary
    end

  end
end