Parsing support for :nth-of-type()

lib/oga/css/parser.y

@@ -429,6 +429,40 @@ end
     return node
   end
 
+  ##
+  # Generates the AST for the `nth-of-type` pseudo class.
+  #
+  # @param [AST::Node] arg
+  # @return [AST::Node]
+  #
+  def on_pseudo_class_nth_of_type(arg)
+    position_call = s(:call, 'position')
+
+    # literal 2, 4, etc
+    if int_node?(arg)
+      node = s(:eq, position_call, arg)
+    else
+      step, offset = *arg
+      compare      = step_comparison(step)
+
+      # 2n+2, 2n-4, etc
+      if offset
+        mod_val = step_modulo_value(step)
+        node    = s(
+          :and,
+          s(compare, position_call, offset),
+          s(:eq, s(:mod, s(:sub, position_call, offset), mod_val), s(:int, 0))
+        )
+
+      # 2n, n, -2n
+      else
+        node = s(:eq, s(:mod, position_call, step), s(:int, 0))
+      end
+    end
+
+    return node
+  end
+
   private
 
   ##

spec/oga/css/parser/pseudo_classes/nth_of_type_spec.rb

@@ -0,0 +1,111 @@
+require 'spec_helper'
+
+describe Oga::CSS::Parser do
+  context ':nth-of-type pseudo class' do
+    example 'parse the :nth-of-type(1) pseudo class' do
+      parse_css(':nth-of-type(1)').should == parse_xpath(
+        'descendant-or-self::*[position() = 1]'
+      )
+    end
+
+    example 'parse the :nth-of-type(2n) pseudo class' do
+      parse_css(':nth-of-type(2n)').should == parse_xpath(
+        'descendant-or-self::*[(position() mod 2) = 0]'
+      )
+    end
+
+    example 'parse the :nth-of-type(3n) pseudo class' do
+      parse_css(':nth-of-type(3n)').should == parse_xpath(
+        'descendant-or-self::*[(position() mod 3) = 0]'
+      )
+    end
+
+    example 'parse the :nth-of-type(2n+5) pseudo class' do
+      parse_css(':nth-of-type(2n+5)').should == parse_xpath(
+        'descendant-or-self::*[(position() >= 5) ' \
+          'and (((position() - 5) mod 2) = 0)]'
+      )
+    end
+
+    example 'parse the :nth-of-type(3n+5) pseudo class' do
+      parse_css(':nth-of-type(3n+5)').should == parse_xpath(
+        'descendant-or-self::*[(position() >= 5) ' \
+          'and (((position() - 5) mod 3) = 0)]'
+      )
+    end
+
+    example 'parse the :nth-of-type(2n-5) pseudo class' do
+      parse_css(':nth-of-type(2n-5)').should == parse_xpath(
+        'descendant-or-self::*[(position() >= 1) ' \
+          'and (((position() - 1) mod 2) = 0)]'
+      )
+    end
+
+    example 'parse the :nth-of-type(2n-6) pseudo class' do
+      parse_css(':nth-of-type(2n-6)').should == parse_xpath(
+        'descendant-or-self::*[(position() >= 2) ' \
+          'and (((position() - 2) mod 2) = 0)]'
+      )
+    end
+
+    example 'parse the :nth-of-type(-2n+5) pseudo class' do
+      parse_css(':nth-of-type(-2n+5)').should == parse_xpath(
+        'descendant-or-self::*[(position() <= 5) ' \
+          'and ((position() - 5) mod 2) = 0]'
+      )
+    end
+
+    example 'parse the :nth-of-type(-2n-5) pseudo class' do
+      parse_css(':nth-of-type(-2n-5)').should == parse_xpath(
+        'descendant-or-self::*[(position() <= -1) ' \
+          'and ((position() - -1) mod 2) = 0]'
+      )
+    end
+
+    example 'parse the :nth-of-type(-2n-6) pseudo class' do
+      parse_css(':nth-of-type(-2n-6)').should == parse_xpath(
+        'descendant-or-self::*[(position() <= -2) ' \
+          'and ((position() - -2) mod 2) = 0]'
+      )
+    end
+
+    example 'parse the :nth-of-type(even) pseudo class' do
+      parse_css(':nth-of-type(even)').should == parse_xpath(
+        'descendant-or-self::*[(position() mod 2) = 0]'
+      )
+    end
+
+    example 'parse the :nth-of-type(odd) pseudo class' do
+      parse_css(':nth-of-type(odd)').should == parse_xpath(
+        'descendant-or-self::*[(position() >= 1) ' \
+          'and (((position() - 1) mod 2) = 0)]'
+      )
+    end
+
+    example 'parse the :nth-of-type(n) pseudo class' do
+      parse_css(':nth-of-type(n)').should == parse_xpath(
+        'descendant-or-self::*[(position() mod 1) =0]'
+      )
+    end
+
+    example 'parse the :nth-of-type(n+5) pseudo class' do
+      parse_css(':nth-of-type(n+5)').should == parse_xpath(
+        'descendant-or-self::*[position() >= 5 ' \
+          'and ((position() - 5) mod 1) = 0]'
+      )
+    end
+
+    example 'parse the :nth-of-type(-n) pseudo class' do
+      parse_css(':nth-of-type(-n)').should == parse_xpath(
+        'descendant-or-self::*[(position() mod 1) = 0]'
+      )
+    end
+
+    example 'parse the :nth-of-type(-n+5) pseudo class' do
+      parse_css(':nth-of-type(-n+5)').should == parse_xpath(
+        'descendant-or-self::*[(position() <= 5) ' \
+          'and ((position() - 5) mod 1) = 0]'
+      )
+    end
+  end
+end