// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
using System;
using System.Composition;
using System.Diagnostics;
using System.Reflection.PortableExecutable;
using System.Text;
using ICSharpCode.Decompiler;
using ICSharpCode.Decompiler.CSharp;
using ICSharpCode.Decompiler.CSharp.Transforms;
using ICSharpCode.Decompiler.Metadata;
using ICSharpCode.Decompiler.TypeSystem;
using Microsoft.CodeAnalysis.DecompiledSource;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Text;
 
namespace Microsoft.CodeAnalysis.CSharp.DecompiledSource
{
    [ExportLanguageService(typeof(IDecompilationService), LanguageNames.CSharp), Shared]
    internal class CSharpDecompilationService : IDecompilationService
    {
        private static readonly FileVersionInfo s_decompilerVersion = FileVersionInfo.GetVersionInfo(typeof(CSharpDecompiler).Assembly.Location);
 
        [ImportingConstructor]
        [Obsolete(MefConstruction.ImportingConstructorMessage, error: true)]
        public CSharpDecompilationService()
        {
        }
 
        public FileVersionInfo GetDecompilerVersion()
        {
            return s_decompilerVersion;
        }
 
        public Document? PerformDecompilation(Document document, string fullName, Compilation compilation, MetadataReference? metadataReference, string? assemblyLocation)
        {
            var logger = new StringBuilder();
            var resolver = new AssemblyResolver(compilation, logger);
 
            // Load the assembly.
            PEFile? file = null;
            if (metadataReference is not null)
                file = resolver.TryResolve(metadataReference, PEStreamOptions.PrefetchEntireImage);
 
            if (file is null && assemblyLocation is not null)
                file = new PEFile(assemblyLocation, PEStreamOptions.PrefetchEntireImage);
 
            if (file is null)
                return null;
 
            using (file)
            {
                // Initialize a decompiler with default settings.
                var decompiler = new CSharpDecompiler(file, resolver, new DecompilerSettings());
                // Escape invalid identifiers to prevent Roslyn from failing to parse the generated code.
                // (This happens for example, when there is compiler-generated code that is not yet recognized/transformed by the decompiler.)
                decompiler.AstTransforms.Add(new EscapeInvalidIdentifiers());
 
                var fullTypeName = new FullTypeName(fullName);
 
                // ILSpy only allows decompiling a type that comes from the 'Main Module'.  They will throw on anything
                // else.  Prevent this by doing this quick check corresponding to:
                // https://github.com/icsharpcode/ILSpy/blob/4ebe075e5859939463ae420446f024f10c3bf077/ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs#L978
                var type = decompiler.TypeSystem.MainModule.GetTypeDefinition(fullTypeName);
                if (type is null)
                    return null;
 
                // Try to decompile; if an exception is thrown the caller will handle it
                var text = decompiler.DecompileTypeAsString(fullTypeName);
 
                text += "#if false // " + FeaturesResources.Decompilation_log + Environment.NewLine;
                text += logger.ToString();
                text += "#endif" + Environment.NewLine;
 
                return document.WithText(SourceText.From(text, encoding: null, checksumAlgorithm: SourceHashAlgorithms.Default));
            }
        }
    }
}