CssGenerator.cs

using System.CodeDom;
using System.CodeDom.Compiler;
using System.IO;

using Microsoft.Build.Framework;
using Microsoft.Build.Utilities;
using Microsoft.CSharp;

using Xamarin.Forms.Xaml;

namespace Xamarin.Forms.Build.Tasks
{
	class CssGenerator
	{
		internal CssGenerator()
		{
		}

		public CssGenerator(
			ITaskItem taskItem,
			string language,
			string assemblyName,
			string outputFile,
			TaskLoggingHelper logger)
			: this(
				taskItem.ItemSpec,
				language,
				taskItem.GetMetadata("ManifestResourceName"),
				taskItem.GetMetadata("TargetPath"),
				assemblyName,
				outputFile,
				logger)
		{
		}

		internal static CodeDomProvider Provider = new CSharpCodeProvider();

		public string CssFile { get; }
		public string Language { get; }
		public string ResourceId { get; }
		public string TargetPath { get; }
		public string AssemblyName { get; }
		public string OutputFile { get; }
		public TaskLoggingHelper Logger { get; }

		public CssGenerator(
			string cssFile,
			string language,
			string resourceId,
			string targetPath,
			string assemblyName,
			string outputFile,
			TaskLoggingHelper logger = null)
		{
			CssFile = cssFile;
			Language = language;
			ResourceId = resourceId;
			TargetPath = targetPath;
			AssemblyName = assemblyName;
			OutputFile = outputFile;
			Logger = logger;
		}

		//returns true if a file is generated
		public bool Execute()
		{
			Logger?.LogMessage("Source: {0}", CssFile);
			Logger?.LogMessage(" Language: {0}", Language);
			Logger?.LogMessage(" ResourceID: {0}", ResourceId);
			Logger?.LogMessage(" TargetPath: {0}", TargetPath);
			Logger?.LogMessage(" AssemblyName: {0}", AssemblyName);
			Logger?.LogMessage(" OutputFile {0}", OutputFile);

			GenerateCode();

			return true;
		}

		void GenerateCode()
		{
			//Create the target directory if required
			Directory.CreateDirectory(Path.GetDirectoryName(OutputFile));

			var ccu = new CodeCompileUnit();
			ccu.AssemblyCustomAttributes.Add(
			   new CodeAttributeDeclaration(new CodeTypeReference($"global::{typeof(XamlResourceIdAttribute).FullName}"),
											new CodeAttributeArgument(new CodePrimitiveExpression(ResourceId)),
											new CodeAttributeArgument(new CodePrimitiveExpression(TargetPath)),
											new CodeAttributeArgument(new CodePrimitiveExpression(null))
										   ));

			//write the result
			using (var writer = new StreamWriter(OutputFile))
				Provider.GenerateCodeFromCompileUnit(ccu, writer, new CodeGeneratorOptions());
		}
	}
}