#nullable enable
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Mono.Cecil;
using Mono.Cecil.Cil;
using Unity.CompilationPipeline.Common.Diagnostics;
using Unity.CompilationPipeline.Common.ILPostProcessing;

namespace ShrinkEventBus.CodeGen
{
    public sealed class EventBusILPostProcessor : ILPostProcessor
    {
        public override ILPostProcessor GetInstance() => this;

        public override bool WillProcess(ICompiledAssembly compiledAssembly)
        {
#if SHRINK_EVENTBUS_HAS_SHARED_CODEGEN
            // The shared processor owns event weaving when its package is installed.
            return false;
#else
            return compiledAssembly.Name != "ShrinkEventBus.Runtime" &&
                   compiledAssembly.References.Any(path =>
                       Path.GetFileNameWithoutExtension(path) == "ShrinkEventBus.Runtime");
#endif
        }

        public override ILPostProcessResult Process(ICompiledAssembly compiledAssembly)
        {
            var diagnostics = new List<DiagnosticMessage>();
#if !SHRINK_EVENTBUS_HAS_SHARED_CODEGEN
            if (!WillProcess(compiledAssembly))
                return new ILPostProcessResult(compiledAssembly.InMemoryAssembly, diagnostics);
            try
            {
                using var resolver = new PostProcessorAssemblyResolver(compiledAssembly);
                using var pe = new MemoryStream(compiledAssembly.InMemoryAssembly.PeData);
                var pdbData = compiledAssembly.InMemoryAssembly.PdbData;
                var hasSymbols = pdbData != null && pdbData.Length > 0;
                using var pdb = hasSymbols ? new MemoryStream(pdbData!) : null;
                using var assembly = AssemblyDefinition.ReadAssembly(pe, new ReaderParameters
                {
                    AssemblyResolver = resolver,
                    ReadingMode = ReadingMode.Immediate,
                    ReflectionImporterProvider = new PostProcessorReflectionImporterProvider(),
                    ReadSymbols = hasSymbols,
                    SymbolStream = pdb,
                    SymbolReaderProvider = hasSymbols ? new PortablePdbReaderProvider() : null
                });
                resolver.AddAssemblyDefinitionBeingOperatedOn(assembly);
                if (assembly.Name.HasPublicKey)
                    throw new InvalidOperationException("Signed assemblies cannot be woven by the standalone EventBus processor.");
                if (!EventBusAssemblyWeaver.Weave(assembly.MainModule))
                    return new ILPostProcessResult(compiledAssembly.InMemoryAssembly, diagnostics);
                using var outputPe = new MemoryStream();
                using var outputPdb = new MemoryStream();
                assembly.Write(outputPe, new WriterParameters
                {
                    WriteSymbols = hasSymbols,
                    SymbolStream = hasSymbols ? outputPdb : null,
                    SymbolWriterProvider = hasSymbols ? new PortablePdbWriterProvider() : null
                });
                return new ILPostProcessResult(new InMemoryAssembly(outputPe.ToArray(),
                    hasSymbols ? outputPdb.ToArray() : Array.Empty<byte>()), diagnostics);
            }
            catch (Exception exception)
            {
                diagnostics.Add(new DiagnosticMessage
                {
                    DiagnosticType = DiagnosticType.Error,
                    MessageData = $"[ShrinkEventBus.CodeGen] {exception.Message}"
                });
            }
#endif
            return new ILPostProcessResult(compiledAssembly.InMemoryAssembly, diagnostics);
        }
    }
}