Rebuild CSS values parser to be more standards compliant

CSS values parsing was pretty basic before.  The CSS 2 graamar spec
doesn't actually spell out exactly how quoting should work, but it's
referenced elsewhere in the document, so this commit does its best
to implement quote parsing.  It also implements escaping as per the
spec.

Fixes #165

lib/prawn-svg.rb

@@ -26,6 +26,7 @@
 require 'prawn/svg/css/font_family_parser'
 require 'prawn/svg/css/selector_parser'
 require 'prawn/svg/css/stylesheets'
+require 'prawn/svg/css/values_parser'
 require 'prawn/svg/ttf'
 require 'prawn/svg/font'
 require 'prawn/svg/gradients'

lib/prawn/svg/color.rb

@@ -2,7 +2,7 @@ class Prawn::SVG::Color
   RGB = Struct.new(:value)
   CMYK = Struct.new(:value)
 
-  RGB_DEFAULT_COLOR = RGB.new("000000")
+  RGB_DEFAULT_COLOR = RGB.new('000000')
   CMYK_DEFAULT_COLOR = CMYK.new([0, 0, 0, 100])
 
   HTML_COLORS = {
@@ -155,90 +155,91 @@ class Prawn::SVG::Color
     'yellowgreen' => '9acd32'
   }.freeze
 
-  VALUE_REGEXP = "\s*(-?[0-9.]+%?)\s*"
-  RGB_REGEXP = /\Argb\(#{VALUE_REGEXP},#{VALUE_REGEXP},#{VALUE_REGEXP}\)\z/i
-  CMYK_REGEXP = /\Adevice-cmyk\(#{VALUE_REGEXP},#{VALUE_REGEXP},#{VALUE_REGEXP},#{VALUE_REGEXP}\)\z/i
-  URL_REGEXP = /\Aurl\(([^)]*)\)\z/i
+  class << self
+    def parse(color_string, gradients = nil, color_mode = :rgb)
+      url_specified = false
 
-  def self.parse(color_string, gradients = nil, color_mode = :rgb)
-    url_specified = false
+      values = ::Prawn::SVG::CSS::ValuesParser.parse(color_string)
 
-    components = color_string.to_s.strip.scan(/([^(\s]+(\([^)]*\))?)/)
+      result = values.map do |value|
+        case value
+        in ['rgb', args]
+          hex = (0..2).collect do |n|
+            number = args[n].to_f
+            number *= 2.55 if args[n][-1..] == '%'
+            format('%02x', clamp(number.round, 0, 255))
+          end.join
 
-    result = components.map do |color, *_|
-      if m = color.match(/\A#([0-9a-f])([0-9a-f])([0-9a-f])\z/i)
-        RGB.new("#{m[1] * 2}#{m[2] * 2}#{m[3] * 2}")
+          RGB.new(hex)
 
-      elsif color.match(/\A#[0-9a-f]{6}\z/i)
-        RGB.new(color[1..6])
+        in ['device-cmyk', args]
+          cmyk = (0..3).collect do |n|
+            number = args[n].to_f
+            number *= 100 unless args[n][-1..] == '%'
+            clamp(number, 0, 100)
+          end
 
-      elsif hex = HTML_COLORS[color.downcase]
-        hex_color(hex, color_mode)
+          CMYK.new(cmyk)
 
-      elsif m = color.match(RGB_REGEXP)
-        hex = (1..3).collect do |n|
-          value = m[n].to_f
-          value *= 2.55 if m[n][-1..-1] == '%'
-          "%02x" % clamp(value.round, 0, 255)
-        end.join
+        in ['url', [url]]
+          url_specified = true
+          if url[0] == '#' && gradients && (gradient = gradients[url[1..]])
+            gradient
+          end
 
-        RGB.new(hex)
+        in /\A#([0-9a-f])([0-9a-f])([0-9a-f])\z/i
+          RGB.new("#{$1 * 2}#{$2 * 2}#{$3 * 2}")
 
-      elsif m = color.match(CMYK_REGEXP)
-        cmyk = (1..4).collect do |n|
-          value = m[n].to_f
-          value *= 100 unless m[n][-1..-1] == '%'
-          clamp(value, 0, 100)
-        end
+        in /\A#[0-9a-f]{6}\z/i
+          RGB.new(value[1..])
 
-        CMYK.new(cmyk)
+        in String => color
+          if (hex = HTML_COLORS[color.downcase])
+            hex_color(hex, color_mode)
+          end
 
-      elsif matches = color.match(URL_REGEXP)
-        url_specified = true
-        url = matches[1]
-        if url[0] == "#" && gradients && gradient = gradients[url[1..-1]]
-          gradient
+        else
+          nil
         end
       end
-    end
 
-    # Generally, we default to black if the colour was unparseable.
-    # http://www.w3.org/TR/SVG/painting.html section 11.2 says if a URL was
-    # supplied without a fallback, that's an error.
-    result << default_color(color_mode) unless url_specified
+      # Generally, we default to black if the colour was unparseable.
+      # http://www.w3.org/TR/SVG/painting.html section 11.2 says if a URL was
+      # supplied without a fallback, that's an error.
+      result << default_color(color_mode) unless url_specified
 
-    result.compact
-  end
+      result.compact
+    end
 
-  def self.css_color_to_prawn_color(color)
-    result = parse(color).detect {|result| result.is_a?(RGB) || result.is_a?(CMYK)}
-    result.value if result
-  end
+    def css_color_to_prawn_color(color)
+      parse(color).detect { |value| value.is_a?(RGB) || value.is_a?(CMYK) }&.value
+    end
 
-  protected
+    def default_color(color_mode)
+      color_mode == :cmyk ? CMYK_DEFAULT_COLOR : RGB_DEFAULT_COLOR
+    end
 
-  def self.clamp(value, min_value, max_value)
-    [[value, min_value].max, max_value].min
-  end
+    private
 
-  def self.default_color(color_mode)
-    color_mode == :cmyk ? CMYK_DEFAULT_COLOR : RGB_DEFAULT_COLOR
-  end
+    def clamp(value, min_value, max_value)
+      [[value, min_value].max, max_value].min
+    end
 
-  def self.hex_color(hex, color_mode)
-    if color_mode == :cmyk
-      r, g, b = [hex[0..1], hex[2..3], hex[4..5]].map { |h| h.to_i(16) / 255.0 }
-      k = 1 - [r, g, b].max
-      if k == 1
-        CMYK.new([0, 0, 0, 100])
+    def hex_color(hex, color_mode)
+      if color_mode == :cmyk
+        r, g, b = [hex[0..1], hex[2..3], hex[4..5]].map { |h| h.to_i(16) / 255.0 }
+        k = 1 - [r, g, b].max
+        if k == 1
+          CMYK.new([0, 0, 0, 100])
+        else
+          c = (1 - r - k) / (1 - k)
+          m = (1 - g - k) / (1 - k)
+          y = (1 - b - k) / (1 - k)
+          CMYK.new([c, m, y, k].map { |v| (v * 100).round })
+        end
       else
-        c = (1 - r - k) / (1 - k)
-        m = (1 - g - k) / (1 - k)
-        y = (1 - b - k) / (1 - k)
-        CMYK.new([c, m, y, k].map { |v| (v * 100).round })
+        RGB.new(hex)
       end
-    else
-      RGB.new(hex)
     end
   end
 end

lib/prawn/svg/css/values_parser.rb

@@ -0,0 +1,68 @@
+module Prawn::SVG::CSS
+  class ValuesParser
+    class << self
+      def parse(values)
+        result = []
+
+        while values
+          value, remainder = parse_next(values)
+          break unless value
+
+          result << value
+          values = remainder
+        end
+
+        result
+      end
+
+      private
+
+      def parse_next(values)
+        values = values.strip
+        return if values.empty?
+
+        if (matches = values.match(/\A([a-z-]+)\(\s*(.+)/i))
+          parse_function_call(matches[1].downcase, matches[2])
+        else
+          values.split(/\s+/, 2)
+        end
+      end
+
+      # Note this does not support space-separated arguments.
+      # I don't think CSS 2 has any, but in case it does here is the place to add them.
+      def parse_function_call(name, rest)
+        arguments = []
+        in_quote = nil
+        in_escape = false
+        current = ''
+
+        rest.chars.each.with_index do |char, index|
+          if in_escape
+            current << char
+            in_escape = false
+          elsif %w[" '].include?(char)
+            if in_quote == char
+              in_quote = nil
+            elsif in_quote.nil?
+              in_quote = char
+            else
+              current << char
+            end
+          elsif char == '\\'
+            in_escape = true
+          elsif in_quote.nil? && char == ','
+            arguments << current.strip
+            current = ''
+          elsif in_quote.nil? && char == ')'
+            arguments << current.strip
+            return [[name, arguments], rest[index + 1..]]
+          else
+            current << char
+          end
+        end
+
+        [rest, nil]
+      end
+    end
+  end
+end

lib/prawn/svg/elements/base.rb

@@ -261,10 +261,16 @@ def require_positive_value(*args)
     end
   end
 
-  def extract_element_from_url_id_reference(value, expected_type = nil)
-    matches = value.strip.match(/\Aurl\(\s*#(\S+)\s*\)\z/i) if value
-    element = document.elements_by_id[matches[1]] if matches
-    element if element && (expected_type.nil? || element.name == expected_type)
+  def extract_element_from_url_id_reference(values, expected_type = nil)
+    Prawn::SVG::CSS::ValuesParser.parse(values).detect do |value|
+      case value
+      in ['url', [url]]
+        element = document.elements_by_id[url[1..]] if url.start_with?('#')
+        break element if element && (expected_type.nil? || element.name == expected_type)
+      else
+        nil
+      end
+    end
   end
 
   def href_attribute

spec/prawn/svg/css/values_parser_spec.rb

@@ -0,0 +1,16 @@
+require 'spec_helper'
+
+RSpec.describe Prawn::SVG::CSS::ValuesParser do
+  it 'parses specified values' do
+    values = 'hello world url("#myid") no-quote(very good) escaping(")\\")ok") rgb( 1,4,  5 )'
+
+    expect(described_class.parse(values)).to eq [
+      'hello',
+      'world',
+      ['url', ['#myid']],
+      ['no-quote', ['very good']],
+      ['escaping', [')")ok']],
+      ['rgb', %w[1 4 5]]
+    ]
+  end
+end