Added a simple ColorSpinPlugin. Fixes to LessEngine.

minor clean up
prevent double evaluation

src/dotless.Core/Engine/LessEngine.cs

@@ -7,6 +7,7 @@ namespace dotless.Core
     using Exceptions;
     using Loggers;
     using Parser.Infrastructure;
+    using Parser.Tree;
 
     public class LessEngine : ILessEngine
     {
@@ -46,7 +47,7 @@ public string TransformToCss(string source, string fileName)
 
                 var env = Env ?? new Env { Compress = Compress };
 
-                tree.Evaluate(env);
+                tree = (Ruleset) tree.Evaluate(env);
 
                 tree = Plugins
                     .Where(p => p.AppliesTo == PluginType.AfterEvaluation)

src/dotless.Core/Parser/Infrastructure/Nodes/Node.cs

@@ -48,12 +48,12 @@ public static bool operator false(Node n)
         /// <summary>
         ///  Copies common properties when evaluating multiple nodes into one
         /// </summary>
-        /// <typeparam name="TN1">Type to return - for convenience</typeparam>
+        /// <typeparam name="T">Type to return - for convenience</typeparam>
         /// <param name="nodes">The nodes this new node is derived from</param>
         /// <returns>The new node</returns>
-		public TN1 ReducedFrom<TN1>(params Node[] nodes) where TN1 : Node
-		{
-            foreach (Node node in nodes)
+        public T ReducedFrom<T>(params Node[] nodes) where T : Node
+        {
+            foreach (var node in nodes)
             {
                 if (node == this)
                 {
@@ -86,9 +86,9 @@ public TN1 ReducedFrom<TN1>(params Node[] nodes) where TN1 : Node
                     }
                 }
             }
-			
-			return (TN1)this;
-		}
+            
+            return (T)this;
+        }
 
         public virtual void AppendCSS(Env env)
         {
@@ -98,13 +98,15 @@ public virtual void AppendCSS(Env env)
             Evaluate(env).AppendCSS(env);
         }
 
-        public virtual string ToCSS(Env env)
-        {
-            env.Output.Push()
-				.Append(this);
-            return env.Output.Pop().ToString();
-        }
-
+        public virtual string ToCSS(Env env)
+        {
+            return env.Output
+                .Push()
+                .Append(this)
+                .Pop()
+                .ToString();
+        }
+
         public virtual Node Evaluate(Env env)
         {
             return this;

src/dotless.Core/Parser/Tree/Root.cs

@@ -40,14 +40,25 @@ public override void AppendCSS(Env env)
 
         public override Node Evaluate(Env env)
         {
-            env = env ?? new Env();
+            if(Evaluated) return this;
 
-            NodeHelper.ExpandNodes<Import>(env, this.Rules);
+            try
+            {
+                env = env ?? new Env();
+
+                NodeHelper.ExpandNodes<Import>(env, Rules);
 
-            Root clone = new Root(new NodeList(Rules), Error, OriginalRuleset).ReducedFrom<Root>(this);
-            clone.EvaluateRules(env);
+                var clone = new Root(new NodeList(Rules), Error, OriginalRuleset).ReducedFrom<Root>(this);
 
-            return clone;
+                clone.EvaluateRules(env);
+                clone.Evaluated = true;
+
+                return clone;
+            }
+            catch (ParsingException e)
+            {
+                throw Error(e);
+            }
         }
     }
 }

src/dotless.Core/Parser/Tree/Ruleset.cs

@@ -11,7 +11,8 @@ namespace dotless.Core.Parser.Tree
     public class Ruleset : Node
     {
         public NodeList<Selector> Selectors { get; set; }
-        public NodeList Rules { get; set; }
+        public NodeList Rules { get; set; }
+        public bool Evaluated { get; protected set; }
 
         /// <summary>
         ///  The original Ruleset this was cloned from during evaluation
@@ -121,26 +122,32 @@ public virtual bool MatchArguments(List<NamedArgument> arguements, Env env)
 
         public override Node Evaluate(Env env)
         {
+            if(Evaluated) return this;
+
             // create a clone so it is non destructive
-            Ruleset clone = new Ruleset(Selectors, new NodeList(Rules), this.OriginalRuleset)
-                .ReducedFrom<Ruleset>(this);
-            clone.EvaluateRules(env);
+            var clone = new Ruleset(Selectors, new NodeList(Rules), OriginalRuleset).ReducedFrom<Ruleset>(this);
+
+            clone.EvaluateRules(env);
+            clone.Evaluated = true;
+
             return clone;
         }
 
+        public override void Accept(IVisitor visitor)
+        {
+            visitor.Visit(Selectors);
+
+            foreach (var rule in Rules)
+            {
+                rule.Accept(visitor);
+            }
+        }
+
         /// <summary>
         ///  Evaluate Rules. Must only be run on a copy of the ruleset otherwise it will
         ///  overwrite defintions that might be required later..
         /// </summary>
         protected void EvaluateRules(Env env)
-
-        public override void Accept(IVisitor visitor)
-        {
-            visitor.Visit(Selectors);
-
-            Rules.ForEach(visitor.Visit);
-        }
-
         {
             env.Frames.Push(this);
 
@@ -157,10 +164,9 @@ public override void Accept(IVisitor visitor)
         public override void AppendCSS(Env env)
         {
             if (!Rules.Any())
-                return;
-
-            ((Ruleset)Evaluate(env))
-                .AppendCSS(env, new Context());
+                return;
+
+            ((Ruleset) Evaluate(env)).AppendCSS(env, new Context());
         }
 
         /// <summary>

src/dotless.Core/Plugins/ColorSpinPlugin.cs

@@ -0,0 +1,40 @@
+namespace dotless.Core.Plugins
+{
+    using System;
+    using Parser.Infrastructure.Nodes;
+    using Parser.Tree;
+    using Utils;
+
+    public class ColorSpinPlugin : VisitorPlugin
+    {
+        public double Spin { get; set; }
+
+        public ColorSpinPlugin(double spin)
+        {
+            Spin = spin;
+        }
+
+        public override PluginType AppliesTo
+        {
+            get { return PluginType.AfterEvaluation; }
+        }
+
+        public override bool Execute(Node node)
+        {
+            if(node is Color)
+            {
+                var color = node as Color;
+
+                var hslColor = HslColor.FromRgbColor(color);
+                hslColor.Hue += Spin/360.0d;
+                var newColor = hslColor.ToRgbColor();
+
+                color.R = newColor.R;
+                color.G = newColor.G;
+                color.B = newColor.B;
+            }
+
+            return true;
+        }
+    }
+}

src/dotless.Core/dotless.Core.csproj

@@ -99,6 +99,7 @@
     <Compile Include="Parser\Tree\KeyFrame.cs" />
     <Compile Include="Parser\Tree\Script.cs" />
     <Compile Include="Parser\Tree\Root.cs" />
+    <Compile Include="Plugins\ColorSpinPlugin.cs" />
     <Compile Include="Plugins\IPlugin.cs" />
     <Compile Include="Plugins\IVisitor.cs" />
     <Compile Include="Plugins\VisitorPlugin.cs" />

src/dotless.Test/Plugins/ColorSpinPluginFixture.cs

@@ -0,0 +1,38 @@
+namespace dotless.Test.Plugins
+{
+    using System.Collections.Generic;
+    using System.Linq;
+    using Core.Parser.Infrastructure;
+    using Core.Parser.Infrastructure.Nodes;
+    using Core.Parser.Tree;
+    using Core.Plugins;
+    using NUnit.Framework;
+
+    public class ColorSpinPluginFixture : SpecFixtureBase
+    {
+        protected List<Color> Colors;
+        protected Ruleset Tree { get; set; }
+        protected ColorSpinPlugin Plugin { get; set; }
+
+        [SetUp]
+        public void Setup()
+        {
+            Plugins.Clear();
+            Plugins.Add(new ColorSpinPlugin(60));
+        }
+
+        [Test]
+        public void ColorIsRotated60Degrees()
+        {
+            AssertExpression("#646400", "#640000");
+            AssertExpression("#00c8c8", "#00c800");
+        }
+
+        [Test]
+        public void ExpressionIsRotatedAfterEvaluation()
+        {
+            AssertExpression("#00c864", "#640000 + #00c800");
+        }
+
+    }
+}

src/dotless.Test/SpecFixtureBase.cs

@@ -6,15 +6,18 @@
     using Core.Parser;
     using System.Collections.Generic;
     using System.Linq;
-    using Core.Parser.Infrastructure;
+    using Core.Parser.Infrastructure;
+    using Core.Parser.Tree;
+    using Core.Plugins;
     using Core.Stylizers;
     using NUnit.Framework;
 
     public class SpecFixtureBase
     {
         protected Func<IStylizer> DefaultStylizer;
         protected Func<Parser> DefaultParser;
-        protected Func<Env> DefaultEnv;
+        protected Func<Env> DefaultEnv;
+        protected List<IPlugin> Plugins { get; set; }
         protected int Optimisation { get; set; }
 
         [SetUp]
@@ -24,6 +27,7 @@ public void SetupParser()
             DefaultStylizer = () => new PlainStylizer();
             DefaultParser = () => new Parser(Optimisation, DefaultStylizer(), new Importer());
             DefaultEnv = () => new Env();
+            Plugins = new List<IPlugin>();
         }
 
         protected void AssertLess(string input, string expected)
@@ -137,8 +141,21 @@ public string Evaluate(string input)
 
         public string Evaluate(string input, Parser parser)
         {
-            var tree = parser.Parse(input.Trim(), null);
-            return tree.ToCSS(DefaultEnv());
+            var tree = parser.Parse(input.Trim(), null);
+
+            var env = DefaultEnv();
+
+            tree = Plugins
+                .Where(p => p.AppliesTo == PluginType.BeforeEvaluation)
+                .Aggregate(tree, (current, plugin) => plugin.Apply(current));
+
+            tree = (Ruleset) tree.Evaluate(env);
+
+            tree = Plugins
+                .Where(p => p.AppliesTo == PluginType.AfterEvaluation)
+                .Aggregate(tree, (current, plugin) => plugin.Apply(current));
+
+            return tree.ToCSS(env);
         }
     }
 }

src/dotless.Test/dotless.Test.csproj

@@ -82,6 +82,7 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="Plugins\ColorSpinPluginFixture.cs" />
     <Compile Include="Specs\Compression\ColorsFixture.cs" />
     <Compile Include="Specs\Compression\CommentsFixture.cs" />
     <Compile Include="CompressedSpecFixtureBase.cs" />
@@ -169,6 +170,7 @@
       <Install>true</Install>
     </BootstrapperPackage>
   </ItemGroup>
+  <ItemGroup />
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.