// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using Microsoft.CodeAnalysis;
using Microsoft.Dnx.Compilation.CSharp;
using Microsoft.Extensions.CompilationAbstractions;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using Microsoft.Extensions.PlatformAbstractions;

namespace Microsoft.AspNet.Mvc.Razor.Compilation
{
    /// <summary>
    /// A type that uses Roslyn to compile C# content and <see cref="ILibraryExporter"/> to find out references.
    /// </summary>
    public class DefaultRoslynCompilationService : RoslynCompilationService
    {
        private readonly IApplicationEnvironment _environment;
        private readonly ILibraryExporter _libraryExporter;

        /// <summary>
        /// Initalizes a new instance of the <see cref="DefaultRoslynCompilationService"/> class.
        /// </summary>
        /// <param name="environment">The environment for the executing application.</param>
        /// <param name="libraryExporter">The library manager that provides export and reference information.</param>
        /// <param name="host">The <see cref="IMvcRazorHost"/> that was used to generate the code.</param>
        /// <param name="optionsAccessor">Accessor to <see cref="RazorViewEngineOptions"/>.</param>
        /// <param name="fileProviderAccessor">The <see cref="IRazorViewEngineFileProviderAccessor"/>.</param>
        /// <param name="loggerFactory">The <see cref="ILoggerFactory"/>.</param>
        public DefaultRoslynCompilationService(IApplicationEnvironment environment,
            ILibraryExporter libraryExporter,
            IMvcRazorHost host,
            IOptions<RazorViewEngineOptions> optionsAccessor,
            IRazorViewEngineFileProviderAccessor fileProviderAccessor,
            ILoggerFactory loggerFactory)
            : base(environment, host, optionsAccessor, fileProviderAccessor, loggerFactory)
        {
            _environment = environment;
            _libraryExporter = libraryExporter;
        }

        protected override List<MetadataReference> GetApplicationReferences()
        {
            var references = new List<MetadataReference>();

            // Get the MetadataReference for the executing application. If it's a Roslyn reference,
            // we can copy the references created when compiling the application to the Razor page being compiled.
            // This avoids performing expensive calls to MetadataReference.CreateFromImage.
            var libraryExport = _libraryExporter.GetExport(_environment.ApplicationName);
            if (libraryExport?.MetadataReferences != null && libraryExport.MetadataReferences.Count > 0)
            {
                Debug.Assert(libraryExport.MetadataReferences.Count == 1,
                    "Expected 1 MetadataReferences, found " + libraryExport.MetadataReferences.Count);
                var roslynReference = libraryExport.MetadataReferences[0] as IRoslynMetadataReference;
                var compilationReference = roslynReference?.MetadataReference as CompilationReference;
                if (compilationReference != null)
                {
                    references.AddRange(compilationReference.Compilation.References);
                    references.Add(roslynReference.MetadataReference);
                    return references;
                }
            }

            var export = _libraryExporter.GetAllExports(_environment.ApplicationName);
            if (export != null)
            {
                foreach (var metadataReference in export.MetadataReferences)
                {
                    // Taken from https://github.com/aspnet/KRuntime/blob/757ba9bfdf80bd6277e715d6375969a7f44370ee/src/...
                    // Microsoft.Extensions.Runtime.Roslyn/RoslynCompiler.cs#L164
                    // We don't want to take a dependency on the Roslyn bit directly since it pulls in more dependencies
                    // than the view engine needs (Microsoft.Extensions.Runtime) for example
                    references.Add(ConvertMetadataReference(metadataReference));
                }
            }

            return references;
        }

        private MetadataReference ConvertMetadataReference(IMetadataReference metadataReference)
        {
            var roslynReference = metadataReference as IRoslynMetadataReference;

            if (roslynReference != null)
            {
                return roslynReference.MetadataReference;
            }

            var embeddedReference = metadataReference as IMetadataEmbeddedReference;

            if (embeddedReference != null)
            {
                return MetadataReference.CreateFromImage(embeddedReference.Contents);
            }

            var fileMetadataReference = metadataReference as IMetadataFileReference;

            if (fileMetadataReference != null)
            {
                return CreateMetadataFileReference(fileMetadataReference.Path);
            }

            var projectReference = metadataReference as IMetadataProjectReference;
            if (projectReference != null)
            {
                using (var ms = new MemoryStream())
                {
                    projectReference.EmitReferenceAssembly(ms);

                    return MetadataReference.CreateFromImage(ms.ToArray());
                }
            }

            throw new NotSupportedException();
        }
    }
}