// Copyright 1998-2015 Epic Games, Inc. All Rights Reserved.

using System;
using System.Collections.Generic;
using System.IO;
using System.CodeDom.Compiler;
using Microsoft.CSharp;
using System.Reflection;
using System.Diagnostics;

namespace UnrealBuildTool
{
	public class DynamicCompilation
	{
		/// File information for UnrealBuildTool.exe, cached at program start
		private static FileInfo UBTExecutableFileInfo = new FileInfo( Utils.GetExecutingAssemblyLocation() );

		/*
		 * Checks to see if the assembly needs compilation
		 */
		private static bool RequiresCompilation( List<string> SourceFileNames, string AssemblySourceListFilePath, string OutputAssemblyPath )
		{
			if ( UnrealBuildTool.RunningRocket() && ProjectFileGenerator.bGenerateProjectFiles )
			{
				// @todo rocket Do we need a better way to determine if project generation rules modules need to be compiled?
				return true;
			}

			// Check to see if we already have a compiled assembly file on disk
			FileInfo OutputAssemblyInfo = new FileInfo( OutputAssemblyPath );
			if( OutputAssemblyInfo.Exists )
			{
				// Check the time stamp of the UnrealBuildTool.exe file.  If Unreal Build Tool was compiled more
				// recently than the dynamically-compiled assembly, then we'll always recompile it.  This is
				// because Unreal Build Tool's code may have changed in such a way that invalidate these
				// previously-compiled assembly files.
				if( UBTExecutableFileInfo.LastWriteTimeUtc > OutputAssemblyInfo.LastWriteTimeUtc )
				{
					// UnrealBuildTool.exe has been recompiled more recently than our cached assemblies
					Log.TraceVerbose( "UnrealBuildTool.exe has been recompiled more recently than " + OutputAssemblyInfo.Name );

					return true;
				}
				else						  
				{
					// Make sure we have a manifest of source files used to compile the output assembly.  If it doesn't exist
					// for some reason (not an expected case) then we'll need to recompile.
					var AssemblySourceListFile = new FileInfo( AssemblySourceListFilePath );
					if( !AssemblySourceListFile.Exists )
					{
						return true;
					}
					else
					{
						// Make sure the source files we're compiling are the same as the source files that were compiled
						// for the assembly that we want to load
						var ExistingAssemblySourceFileNames = new List<string>();
						{
							using( var Reader = AssemblySourceListFile.OpenRead() )
							{
								using( var TextReader = new StreamReader( Reader ) )
								{
									for( var ExistingSourceFileName = TextReader.ReadLine(); ExistingSourceFileName != null; ExistingSourceFileName = TextReader.ReadLine() )
									{
										ExistingAssemblySourceFileNames.Add( ExistingSourceFileName );

										// Was the existing assembly compiled with a source file that we aren't interested in?  If so, then it needs to be recompiled.
										if( !SourceFileNames.Contains( ExistingSourceFileName ) )
										{
											return true;
										}
									}
								}
							}
						}

						// Test against source file time stamps
						foreach( var SourceFileName in SourceFileNames )
						{
							// Was the existing assembly compiled without this source file?  If so, then we definitely need to recompile it!
							if( !ExistingAssemblySourceFileNames.Contains( SourceFileName ) )
							{
								return true;
							}

							var SourceFileInfo = new FileInfo( Path.GetFullPath( SourceFileName ) );

							// Check to see if the source file exists
							if( !SourceFileInfo.Exists )
							{
								throw new BuildException( "Could not locate source file for dynamic compilation: {0}", SourceFileName );
							}

							// Ignore temp files
							if( !SourceFileInfo.Extension.Equals( ".tmp", StringComparison.CurrentCultureIgnoreCase ) )
							{
								// Check to see if the source file is newer than the compiled assembly file.  We don't want to
								// bother recompiling it if it hasn't changed.
								if( SourceFileInfo.LastWriteTimeUtc > OutputAssemblyInfo.LastWriteTimeUtc )
								{
									// Source file has changed since we last compiled the assembly, so we'll need to recompile it now!
									Log.TraceVerbose( SourceFileInfo.Name + " has been modified more recently than " + OutputAssemblyInfo.Name );

									return true;
								}
							}
						}
					}
				}
			}
			else
			{
				// File doesn't exist, so we'll definitely have to compile it!
				Log.TraceVerbose( OutputAssemblyInfo.Name + " doesn't exist yet" );
				return true;
			}

			return false;
		}

		/*
		 * Compiles an assembly from source files
		 */
		private static Assembly CompileAssembly(string OutputAssemblyPath, List<string> SourceFileNames, List<string> ReferencedAssembies, List<string> PreprocessorDefines = null, bool TreatWarningsAsErrors = false)
		{
			var TemporaryFiles = new TempFileCollection();

			// Setup compile parameters
			var CompileParams = new CompilerParameters();
			{
				// Always compile the assembly to a file on disk, so that we can load a cached version later if we have one
				CompileParams.GenerateInMemory = false;

				// This is the full path to the assembly file we're generating
				CompileParams.OutputAssembly = OutputAssemblyPath;

				// We always want to generate a class library, not an executable
				CompileParams.GenerateExecutable = false;

				// Always fail compiles for warnings
				CompileParams.TreatWarningsAsErrors = true;

				// Always generate debug information as it takes minimal time
				CompileParams.IncludeDebugInformation = true;
#if !DEBUG
				// Optimise the managed code in Development
				CompileParams.CompilerOptions += " /optimize";
#endif
				Log.TraceVerbose("Compiling " + OutputAssemblyPath);

				// Keep track of temporary files emitted by the compiler so we can clean them up later
				CompileParams.TempFiles = TemporaryFiles;

				// Warnings as errors if desired
				CompileParams.TreatWarningsAsErrors = TreatWarningsAsErrors;

				// Add assembly references
				{
					if (ReferencedAssembies == null)
					{
						// Always depend on the CLR System assembly
						CompileParams.ReferencedAssemblies.Add("System.dll");
					}
					else
					{
						// Add in the set of passed in referenced assemblies
						CompileParams.ReferencedAssemblies.AddRange(ReferencedAssembies.ToArray());
					}

					// The assembly will depend on this application
					var UnrealBuildToolAssembly = Assembly.GetExecutingAssembly();
					CompileParams.ReferencedAssemblies.Add(UnrealBuildToolAssembly.Location);
				}

				// Add preprocessor definitions
				if (PreprocessorDefines != null && PreprocessorDefines.Count > 0)
				{
					CompileParams.CompilerOptions += " /define:";
					for (int DefinitionIndex = 0; DefinitionIndex < PreprocessorDefines.Count; ++DefinitionIndex)
					{
						if (DefinitionIndex > 0)
						{
							CompileParams.CompilerOptions += ";";
						}
						CompileParams.CompilerOptions += PreprocessorDefines[DefinitionIndex];
					}
				}

				// @todo: Consider embedding resources in generated assembly file (version/copyright/signing)
			}

			// Create the output directory if it doesn't exist already
			DirectoryInfo DirInfo = new DirectoryInfo( Path.GetDirectoryName( OutputAssemblyPath ) );
			if( !DirInfo.Exists )
			{
				try
				{
					DirInfo.Create();
				}
				catch( Exception Ex )
				{
					throw new BuildException( Ex, "Unable to create directory '{0}' for intermediate assemblies (Exception: {1})", OutputAssemblyPath, Ex.Message );
				}
			}

			// Compile the code
			CompilerResults CompileResults;
			try
			{
				// Enable .NET 4.0 as we want modern language features like 'var'
				var ProviderOptions = new Dictionary<string, string>() { { "CompilerVersion", "v4.0" } };
				var Compiler = new CSharpCodeProvider( ProviderOptions );
				CompileResults = Compiler.CompileAssemblyFromFile( CompileParams, SourceFileNames.ToArray() );
			}
			catch( Exception Ex )
			{
				throw new BuildException( Ex, "Failed to launch compiler to compile assembly from source files '{0}' (Exception: {1})", SourceFileNames.ToString(), Ex.Message );
			}

			// Display compilation errors
			if( CompileResults.Errors.Count > 0 )
			{
				Log.TraceInformation("Errors detected while compiling {0}:", OutputAssemblyPath);
				foreach( var CurError in CompileResults.Errors )
				{
					Log.TraceInformation( CurError.ToString() );
				}
				throw new BuildException( "UnrealBuildTool encountered an error while compiling source files" );
			}

			// Grab the generated assembly
			Assembly CompiledAssembly = CompileResults.CompiledAssembly;
			if( CompiledAssembly == null )
			{
				throw new BuildException( "UnrealBuildTool was unable to compile an assembly for '{0}'", SourceFileNames.ToString() );
			}

			// Clean up temporary files that the compiler saved
			TemporaryFiles.Delete();

			return CompiledAssembly;
		}

		/// <summary>
		/// Dynamically compiles an assembly for the specified source file and loads that assembly into the application's
		/// current domain.  If an assembly has already been compiled and is not out of date, then it will be loaded and
		/// no compilation is necessary.
		/// </summary>
		/// <param name="SourceFileNames">List of source file name</param>
		/// <param name="OutputAssemblyPath">Full path to the assembly to be created</param>
		/// <returns>The assembly that was loaded</returns>
		public static Assembly CompileAndLoadAssembly(string OutputAssemblyPath, List<string> SourceFileNames, List<string> ReferencedAssembies = null, List<string> PreprocessorDefines = null, bool DoNotCompile = false, bool TreatWarningsAsErrors = false)
		{
			// Load assembly requires absolute paths
			OutputAssemblyPath = Path.GetFullPath( OutputAssemblyPath );

			// Check to see if the resulting assembly is compiled and up to date
			var AssemblySourcesListFilePath = Path.Combine( Path.GetDirectoryName( OutputAssemblyPath ), Path.GetFileNameWithoutExtension( OutputAssemblyPath ) + "SourceFiles.txt" );
			bool bNeedsCompilation = false;
			if (!DoNotCompile)
			{
				bNeedsCompilation = RequiresCompilation(SourceFileNames, AssemblySourcesListFilePath, OutputAssemblyPath);
			}

			// Load the assembly to ensure it is correct
			Assembly CompiledAssembly = null;
			if( !bNeedsCompilation )
			{
				try
				{
					// Load the previously-compiled assembly from disk
					CompiledAssembly = Assembly.LoadFile( OutputAssemblyPath );
				}
				catch( FileLoadException Ex )
				{
					Log.TraceInformation( String.Format( "Unable to load the previously-compiled assembly file '{0}'.  Unreal Build Tool will try to recompile this assembly now.  (Exception: {1})", OutputAssemblyPath, Ex.Message ) );
					bNeedsCompilation = true;
				}
				catch( BadImageFormatException Ex )
				{
					Log.TraceInformation( String.Format( "Compiled assembly file '{0}' appears to be for a newer CLR version or is otherwise invalid.  Unreal Build Tool will try to recompile this assembly now.  (Exception: {1})", OutputAssemblyPath, Ex.Message ) );
					bNeedsCompilation = true;
				}
				catch( Exception Ex )
				{
					throw new BuildException( Ex, "Error while loading previously-compiled assembly file '{0}'.  (Exception: {1})", OutputAssemblyPath, Ex.Message );
				}
			}

			// Compile the assembly if me
			if( bNeedsCompilation )
			{
				CompiledAssembly = CompileAssembly(OutputAssemblyPath, SourceFileNames, ReferencedAssembies, PreprocessorDefines, TreatWarningsAsErrors);

				// Save out a list of all the source files we compiled.  This is so that we can tell if whole files were added or removed
				// since the previous time we compiled the assembly.  In that case, we'll always want to recompile it!
				{
					FileInfo AssemblySourcesListFile = new FileInfo( AssemblySourcesListFilePath );
					using( var Writer = AssemblySourcesListFile.OpenWrite() )
					{
						using( var TextWriter = new StreamWriter( Writer ) )
						{
							SourceFileNames.ForEach( x => TextWriter.WriteLine( x ) );
						}
					}
				}
			}

			// Load the assembly into our app domain
			try
			{
				AppDomain.CurrentDomain.Load( CompiledAssembly.GetName() );
			}
			catch( Exception Ex )
			{
				throw new BuildException( Ex, "Unable to load the compiled build assembly '{0}' into our application's domain.  (Exception: {1})", OutputAssemblyPath, Ex.Message );
			}

			return CompiledAssembly;
		}
	}
}