# encoding: utf-8

# prawn/font/afm.rb : Implements AFM font support for Prawn
#
# Copyright May 2008, Gregory Brown / James Healy.  All Rights Reserved.
#
# This is free software. Please see the LICENSE and COPYING files for details.

require 'prawn/encoding'

module Prawn
  class Font
    class AFM < Font
      BUILT_INS = %w[ Courier Helvetica Times-Roman Symbol ZapfDingbats
                      Courier-Bold Courier-Oblique Courier-BoldOblique
                      Times-Bold Times-Italic Times-BoldItalic
                      Helvetica-Bold Helvetica-Oblique Helvetica-BoldOblique ]

      def unicode?
        false
      end

      def self.metrics_path
        if m = ENV['METRICS']
          @metrics_path ||= m.split(':')
        else
          @metrics_path ||= [
            ".", "/usr/lib/afm",
            "/usr/local/lib/afm",
            "/usr/openwin/lib/fonts/afm",
             Prawn::DATADIR+'/fonts']
        end
      end

      attr_reader :attributes #:nodoc:

      def initialize(document, name, options={}) #:nodoc:
        unless BUILT_INS.include?(name)
          raise Prawn::Errors::UnknownFont, "#{name} is not a known font."
        end

        super

        @@winansi   ||= Prawn::Encoding::WinAnsi.new # parse data/encodings/win_ansi.txt once only
        @@font_data ||= SynchronizedCache.new        # parse each ATM font file once only

        file_name = @name.dup
        file_name << ".afm" unless file_name =~ /\.afm$/
        file_name = file_name[0] == ?/ ? file_name : find_font(file_name)

        font_data = @@font_data[file_name] ||= parse_afm(file_name)
        @glyph_widths    = font_data[:glyph_widths]
        @glyph_table     = font_data[:glyph_table]
        @bounding_boxes  = font_data[:bounding_boxes]
        @kern_pairs      = font_data[:kern_pairs]
        @kern_pair_table = font_data[:kern_pair_table]
        @attributes      = font_data[:attributes]

        @ascender  = @attributes["ascender"].to_i
        @descender = @attributes["descender"].to_i
        @line_gap  = Float(bbox[3] - bbox[1]) - (@ascender - @descender)
      end

      # The font bbox, as an array of integers
      #
      def bbox
        @bbox ||= @attributes['fontbbox'].split(/\s+/).map { |e| Integer(e) }
      end

      # NOTE: String *must* be encoded as WinAnsi
      def compute_width_of(string, options={}) #:nodoc:
        scale = (options[:size] || size) / 1000.0

        if options[:kerning]
          strings, numbers = kern(string).partition { |e| e.is_a?(String) }
          total_kerning_offset = numbers.inject(0.0) { |s,r| s + r }
          (unscaled_width_of(strings.join) - total_kerning_offset) * scale
        else
          unscaled_width_of(string) * scale
        end
      end

      # Returns true if the font has kerning data, false otherwise
      #
      def has_kerning_data?
        @kern_pairs.any?
      end

      # built-in fonts only work with winansi encoding, so translate the
      # string. Changes the encoding in-place, so the argument itself
      # is replaced with a string in WinAnsi encoding.
      #
      def normalize_encoding(text)
        enc = @@winansi
        text.unpack("U*").collect { |i| enc[i] }.pack("C*")
      rescue ArgumentError
        raise Prawn::Errors::IncompatibleStringEncoding,
          "Arguments to text methods must be UTF-8 encoded"
      end

      # Returns the number of characters in +str+ (a WinAnsi-encoded string).
      #
      def character_count(str)
        str.length
      end

      # Perform any changes to the string that need to happen
      # before it is rendered to the canvas. Returns an array of
      # subset "chunks", where each chunk is an array of two elements.
      # The first element is the font subset number, and the second
      # is either a string or an array (for kerned text).
      #
      # For Adobe fonts, there is only ever a single subset, so
      # the first element of the array is "0", and the second is
      # the string itself (or an array, if kerning is performed).
      #
      # The +text+ parameter must be in WinAnsi encoding (cp1252).
      #
      def encode_text(text, options={})
        [[0, options[:kerning] ? kern(text) : text]]
      end

      def glyph_present?(char)
        if char == "_"
          true
        else
          normalize_encoding(char) != "_"
        end
      end

      private

      def register(subset)
        font_dict = {:Type     => :Font,
                     :Subtype  => :Type1,
                     :BaseFont => name.to_sym}

        # Symbolic AFM fonts (Symbol, ZapfDingbats) have their own encodings
        font_dict.merge!(:Encoding => :WinAnsiEncoding) unless symbolic?

        @document.ref!(font_dict)
      end

      def symbolic?
        attributes["characterset"] == "Special"
      end

      def find_font(file)
        self.class.metrics_path.find { |f| File.exist? "#{f}/#{file}" } + "/#{file}"
      rescue NoMethodError
        raise Prawn::Errors::UnknownFont,
          "Couldn't find the font: #{file} in any of:\n" +
           self.class.metrics_path.join("\n")
      end

      def parse_afm(file_name)
        data    = {:glyph_widths => {}, :bounding_boxes => {}, :kern_pairs => {}, :attributes => {}}         
        section = []

        File.foreach(file_name) do |line|
          case line
          when /^Start(\w+)/
            section.push $1
            next
          when /^End(\w+)/
            section.pop
            next
          end

          case section
          when ["FontMetrics", "CharMetrics"]
            next unless line =~ /^CH?\s/

            name                        = line[/\bN\s+(\.?\w+)\s*;/, 1]
            data[:glyph_widths][name]   = line[/\bWX\s+(\d+)\s*;/, 1].to_i
            data[:bounding_boxes][name] = line[/\bB\s+([^;]+);/, 1].to_s.rstrip
          when ["FontMetrics", "KernData", "KernPairs"]
            next unless line =~ /^KPX\s+(\.?\w+)\s+(\.?\w+)\s+(-?\d+)/
            data[:kern_pairs][[$1, $2]] = $3.to_i
          when ["FontMetrics", "KernData", "TrackKern"],
            ["FontMetrics", "Composites"]
            next
          else
            parse_generic_afm_attribute(line, data)
          end
        end
        
        # process data parsed from AFM file to build tables which
        #   will be used when measuring and kerning text
        data[:glyph_table] = (0..255).map do |i|
          data[:glyph_widths][Encoding::WinAnsi::CHARACTERS[i]].to_i
        end

        character_hash = Hash[Encoding::WinAnsi::CHARACTERS.zip((0..Encoding::WinAnsi::CHARACTERS.size).to_a)]
        data[:kern_pair_table] = data[:kern_pairs].inject({}) do |h,p|
          h[p[0].map { |n| character_hash[n] }] = p[1]
          h
        end

        data.each_value { |hash| hash.freeze }
        data.freeze
      end

      def parse_generic_afm_attribute(line, hash)
        line =~ /(^\w+)\s+(.*)/
        key, value = $1.to_s.downcase, $2

        hash[:attributes][key] = hash[:attributes][key] ? Array(hash[:attributes][key]) << value : value
      end

      # converts a string into an array with spacing offsets
      # bewteen characters that need to be kerned
      #
      # String *must* be encoded as WinAnsi
      #
      def kern(string)
        kerned = [[]]
        last_byte = nil

        string.each_byte do |byte|
          if k = last_byte && @kern_pair_table[[last_byte, byte]]
            kerned << -k << [byte]
          else
            kerned.last << byte
          end
          last_byte = byte
        end

        kerned.map { |e|
          e = (Array === e ? e.pack("C*") : e)
          e.respond_to?(:force_encoding) ? e.force_encoding(::Encoding::Windows_1252) : e
        }
      end
      
      private
      
      def unscaled_width_of(string)
        string.bytes.inject(0) do |s,r|
          s + @glyph_table[r]
        end
      end
    end
  end
end