// 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.Collections;
using System.Collections.Generic;
using System.Collections.Immutable;
using Microsoft.VisualStudio.Composition;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.Host.Mef;
 
/// <summary>
/// Provides host services imported via VS MEF.
/// </summary>
internal sealed class VisualStudioMefHostServices : HostServices, IMefHostExportProvider
{
    // the export provider for the MEF composition
    private readonly ExportProvider _exportProvider;
 
    // accumulated cache for exports
    private ImmutableDictionary<ExportKey, IEnumerable> _exportsMap
        = ImmutableDictionary<ExportKey, IEnumerable>.Empty;
 
    private VisualStudioMefHostServices(ExportProvider exportProvider)
    {
        Contract.ThrowIfNull(exportProvider);
        _exportProvider = exportProvider;
    }
 
    public static VisualStudioMefHostServices Create(ExportProvider exportProvider)
        => new(exportProvider);
 
    /// <summary>
    /// Creates a new <see cref="HostWorkspaceServices"/> associated with the specified workspace.
    /// </summary>
    protected internal override HostWorkspaceServices CreateWorkspaceServices(Workspace workspace)
        => new MefWorkspaceServices(this, workspace);
 
    /// <summary>
    /// Gets all the MEF exports of the specified type with the specified metadata.
    /// </summary>
    public IEnumerable<Lazy<TExtension, TMetadata>> GetExports<TExtension, TMetadata>()
    {
        var key = new ExportKey(typeof(TExtension).AssemblyQualifiedName!, typeof(TMetadata).AssemblyQualifiedName!);
        if (!_exportsMap.TryGetValue(key, out var exports))
        {
            exports = ImmutableInterlocked.GetOrAdd(ref _exportsMap, key, _ =>
            {
                return _exportProvider.GetExports<TExtension, TMetadata>().ToImmutableArray();
            });
        }
 
        return (IEnumerable<Lazy<TExtension, TMetadata>>)exports;
    }
 
    /// <summary>
    /// Gets all the MEF exports of the specified type.
    /// </summary>
    public IEnumerable<Lazy<TExtension>> GetExports<TExtension>()
    {
        var key = new ExportKey(typeof(TExtension).AssemblyQualifiedName!, "");
        if (!_exportsMap.TryGetValue(key, out var exports))
        {
            exports = ImmutableInterlocked.GetOrAdd(ref _exportsMap, key, _ =>
                _exportProvider.GetExports<TExtension>().ToImmutableArray());
        }
 
        return (IEnumerable<Lazy<TExtension>>)exports;
    }
 
    private readonly struct ExportKey : IEquatable<ExportKey>
    {
        internal readonly string ExtensionTypeName;
        internal readonly string MetadataTypeName;
 
        public ExportKey(string extensionTypeName, string metadataTypeName)
        {
            ExtensionTypeName = extensionTypeName;
            MetadataTypeName = metadataTypeName;
        }
 
        public bool Equals(ExportKey other)
            => string.Compare(ExtensionTypeName, other.ExtensionTypeName, StringComparison.OrdinalIgnoreCase) == 0 &&
               string.Compare(MetadataTypeName, other.MetadataTypeName, StringComparison.OrdinalIgnoreCase) == 0;
 
        public override bool Equals(object? obj)
            => obj is ExportKey key && Equals(key);
 
        public override int GetHashCode()
            => Hash.Combine(MetadataTypeName.GetHashCode(), ExtensionTypeName.GetHashCode());
    }
}