Implements border side parsing

Per specs at http://www.w3.org/TR/CSS21/box.html#propdef-border-top and
http://www.w3.org/TR/CSS/

Author: zmoazeni

lib/csscss.rb

@@ -24,4 +24,5 @@
 require "csscss/parser/border_width"
 require "csscss/parser/border_color"
 require "csscss/parser/border_style"
+require "csscss/parser/border_side"
 

lib/csscss/parser/border_side.rb

@@ -0,0 +1,68 @@
+module Csscss
+  module Parser
+    module BorderSide
+      extend Parser::Base
+
+      class Parser < Parslet::Parser
+        include Common
+
+        attr_reader :side
+        def initialize(side)
+          @side = side.to_sym
+        end
+
+        rule(:border_width) { BorderWidth::Parser.new.border_width_side }
+        rule(:border_style) { BorderStyle::Parser.new.border_style_side }
+        rule(:border_color) { BorderColor::Parser.new.border_color_side }
+
+        rule(:border_side) {
+          (
+           symbol("inherit") >> eof  | (
+             border_width.maybe.as(:width) >>
+             border_style.maybe.as(:style) >>
+             border_color.maybe.as(:color)
+            ).as(side)
+          ).as(:border_side)
+        }
+
+        root(:border_side)
+      end
+
+      class Transformer < Parslet::Transform
+        extend Color::Transformer
+
+        class << self
+          def transform_top(context);    transform_side("top", context);    end
+          def transform_right(context);  transform_side("right", context);  end
+          def transform_bottom(context); transform_side("bottom", context); end
+          def transform_left(context);   transform_side("left", context);   end
+
+          def transform_side(side, context)
+            width = context[:width]
+            style = context[:style]
+            color = context[:color]
+
+            [].tap do |declarations|
+              declarations << Declaration.from_parser("border-#{side}-width", width) if width
+              declarations << Declaration.from_parser("border-#{side}-style", style) if style
+              declarations << Declaration.from_parser("border-#{side}-color", color.value) if color
+            end
+          end
+        end
+
+        rule(border_side: simple(:inherit)) {[]}
+
+        [:top, :right, :bottom, :left].each do |side|
+          rule(border_side: {
+            side => {
+              width:simple(:width),
+              style:simple(:style),
+              color:simple(:color)
+            }
+          }, &method("transform_#{side}"))
+        end
+
+      end
+    end
+  end
+end

test/csscss/parser/border_side_test.rb

@@ -0,0 +1,44 @@
+require "test_helper"
+
+module Csscss::Parser
+  module BorderSide
+    describe self do
+      include CommonParserTests
+
+      before do
+        @parser = Parser.new("top")
+      end
+
+      def trans_top(s)
+        Transformer.new.apply(@parser.parse(s))
+      end
+      alias_method :trans, :trans_top
+
+      def trans_bottom(s)
+        Transformer.new.apply(Parser.new("bottom").parse(s))
+      end
+
+      it "converts shorthand rules to longhand" do
+        trans_top("thin").must_equal([
+          dec("border-top-width", "thin")
+        ])
+
+        trans_bottom("rgb(1, 2, 3)").must_equal([
+          dec("border-bottom-color", "rgb(1, 2, 3)")
+        ])
+
+        trans_top("thin solid #fff").must_equal([
+          dec("border-top-width", "thin"),
+          dec("border-top-style", "solid"),
+          dec("border-top-color", "#fff")
+        ])
+
+        trans_bottom("thin solid #fff").must_equal([
+          dec("border-bottom-width", "thin"),
+          dec("border-bottom-style", "solid"),
+          dec("border-bottom-color", "#fff")
+        ])
+      end
+    end
+  end
+end