# encoding: ASCII-8BIT
# images.rb : Implements PDF image embedding
#
# Copyright April 2008, James Healy, Gregory Brown.  All Rights Reserved.
#
# This is free software. Please see the LICENSE and COPYING files for details.

require 'digest/sha1'

module Prawn

  module Images

    # add the image at filename to the current page. Currently only
    # JPG and PNG files are supported.
    #
    # Arguments:
    # <tt>filename</tt>:: the path to the file to be embedded
    #
    # Options:
    # <tt>:at</tt>:: the location of the top left corner of the image.
    # <tt>:position</tt>::  One of (:left, :center, :right) or an x-offset
    # <tt>:height</tt>:: the height of the image [actual height of the image]
    # <tt>:width</tt>:: the width of the image [actual width of the image]
    # <tt>:scale</tt>:: scale the dimensions of the image proportionally      
    # 
    #   Prawn::Document.generate("image2.pdf", :page_layout => :landscape) do     
    #     pigs = "#{Prawn::BASEDIR}/data/images/pigs.jpg" 
    #     image pigs, :at => [50,450], :width => 450                                      
    #
    #     dice = "#{Prawn::BASEDIR}/data/images/dice.png"
    #     image dice, :at => [50, 450], :scale => 0.75 
    #   end   
    #
    # If only one of :width / :height are provided, the image will be scaled
    # proportionally.  When both are provided, the image will be stretched to 
    # fit the dimensions without maintaining the aspect ratio.
    #
    def image(filename, options={})     
      Prawn.verify_options [:at,:position, :height, :width, :scale], options
      raise ArgumentError, "#{filename} not found" unless File.file?(filename)  
      
      image_content =  File.read_binary(filename)
      
      image_sha1 = Digest::SHA1.hexdigest(image_content)

      # register the fact that the current page uses images
      proc_set :ImageC

      # if this image has already been embedded, just reuse it
      image_obj = image_registry[image_sha1]

      if image_registry[image_sha1]
        info = image_registry[image_sha1][:info]
        image_obj = image_registry[image_sha1][:obj]
      else
        # build the image object and embed the raw data
        image_obj = case detect_image_format(image_content)
        when :jpg then
          info = Prawn::Images::JPG.new(image_content)
          build_jpg_object(image_content, info)
        when :png then
          info = Prawn::Images::PNG.new(image_content)
          build_png_object(image_content, info)
        end
        image_registry[image_sha1] = {:obj => image_obj, :info => info}
      end

      # find where the image will be placed and how big it will be  
      w,h = calc_image_dimensions(info, options)
      if options[:at]       
        x,y = translate(options[:at]) 
      else                  
        x,y = image_position(w,h,options) 
        move_text_position h   
      end

      # add a reference to the image object to the current page
      # resource list and give it a label
      label = "I#{next_image_id}"
      page_xobjects.merge!( label => image_obj )

      # add the image to the current page
      instruct = "\nq\n%.3f 0 0 %.3f %.3f %.3f cm\n/%s Do\nQ"
      add_content instruct % [ w, h, x, y - h, label ]
    end

    private   
    
    def image_position(w,h,options)
      options[:position] ||= :left
      x = case options[:position] 
      when :left
        bounds.absolute_left
      when :center
        bounds.absolute_left + (bounds.width - w) / 2.0 
      when :right
        bounds.absolute_right - w
      when Numeric
        options[:position] + bounds.absolute_left
      end       
      
      return [x,y]
    end

    def build_jpg_object(data, jpg) 
      color_space = case jpg.channels
      when 1
        :DeviceGray
      when 4
        :DeviceCMYK
      else
        :DeviceRGB
      end
      obj = ref(:Type       => :XObject,
          :Subtype          => :Image,
          :Filter           => :DCTDecode,
          :ColorSpace       => color_space,
          :BitsPerComponent => jpg.bits,
          :Width            => jpg.width,
          :Height           => jpg.height,
          :Length           => data.size ) 
      obj << data
      return obj
    end

    def build_png_object(data, png)

      if png.compression_method != 0
        raise ArgumentError, 'PNG uses an unsupported compression method'
      end

      if png.filter_method != 0
        raise ArgumentError, 'PNG uses an unsupported filter method'
      end

      if png.interlace_method != 0
        raise ArgumentError, 'PNG uses unsupported interlace method'
      end

      if png.bits > 8
        raise ArgumentError, 'PNG uses more than 8 bits'
      end
      
      case png.pixel_bytes
      when 1
        color = :DeviceGray
      when 3
        color = :DeviceRGB
      end

      # build the image dict
      obj = ref(:Type             => :XObject,
                :Subtype          => :Image,
                :Height           => png.height,
                :Width            => png.width,
                :BitsPerComponent => png.bits,
                :Length           => png.img_data.size,
                :Filter           => :FlateDecode
                
               )

      unless png.alpha_channel
        obj.data[:DecodeParms] = {:Predictor => 15,
                                  :Colors    => png.pixel_bytes,
                                  :Columns   => png.width}
      end

      # append the actual image data to the object as a stream
      obj << png.img_data
      
      # sort out the colours of the image
      if png.palette.empty?
        obj.data[:ColorSpace] = color
      else
        # embed the colour palette in the PDF as a object stream
        palette_obj = ref(:Length => png.palette.size)
        palette_obj << png.palette

        # build the color space array for the image
        obj.data[:ColorSpace] = [:Indexed, 
                                 :DeviceRGB,
                                 (png.palette.size / 3) -1,
                                 palette_obj]
      end

      # *************************************
      # add transparency data if necessary
      # *************************************

      # For PNG color types 0, 2 and 3, the transparency data is stored in
      # a dedicated PNG chunk, and is exposed via the transparency attribute
      # of the PNG class.
      if png.transparency[:grayscale]
        # Use Color Key Masking (spec section 4.8.5)
        # - An array with N elements, where N is two times the number of color
        #   components.
        val = png.transparency[:grayscale]
        obj.data[:Mask] = [val, val]
      elsif png.transparency[:rgb]
        # Use Color Key Masking (spec section 4.8.5)
        # - An array with N elements, where N is two times the number of color
        #   components.
        rgb = png.transparency[:rgb]
        obj.data[:Mask] = rgb.collect { |val| [val,val] }.flatten
      elsif png.transparency[:indexed]
        # TODO: broken. I was attempting to us Color Key Masking, but I think
        #       we need to construct an SMask i think. Maybe do it inside
        #       the PNG class, and store it in alpha_channel
        #obj.data[:Mask] = png.transparency[:indexed]
      end

      # For PNG color types 4 and 6, the transparency data is stored as a alpha
      # channel mixed in with the main image data. The PNG class seperates
      # it out for us and makes it available via the alpha_channel attribute
      if png.alpha_channel
        smask_obj = ref(:Type             => :XObject,
                        :Subtype          => :Image,
                        :Height           => png.height,
                        :Width            => png.width,
                        :BitsPerComponent => 8,
                        :Length           => png.alpha_channel.size,
                        :Filter           => :FlateDecode,
                        :ColorSpace       => :DeviceGray,
                        :Decode           => [0, 1]
                       )
        smask_obj << png.alpha_channel
        obj.data[:SMask] = smask_obj
      end

      return obj
    end

    def calc_image_dimensions(info, options)
      # TODO: allow the image to be aligned in a box
      w = options[:width] || info.width
      h = options[:height] || info.height

      if options[:width] && !options[:height]
        wp = w / info.width.to_f 
        w = info.width * wp
        h = info.height * wp
      elsif options[:height] && !options[:width]         
        hp = h / info.height.to_f
        w = info.width * hp
        h = info.height * hp   
      elsif options[:scale] 
        w = info.width * options[:scale]
        h = info.height * options[:scale]
      end

      [w,h]
    end

    def detect_image_format(content)
      top = content[0,128]                       

      if top[0, 3] == "\xff\xd8\xff"
        return :jpg
      elsif top[0, 8]  == "\x89PNG\x0d\x0a\x1a\x0a"
        return :png
      else
        raise ArgumentError, "Unsupported Image Type"
      end
    end

    def image_registry
      @image_registry ||= {}
    end

    def next_image_id
      @image_counter ||= 0
      @image_counter += 1
    end
  end
end