// 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.
 
#nullable disable
 
using System;
using System.Composition;
 
namespace Microsoft.CodeAnalysis.Host.Mef
{
    /// <summary>
    /// Use this attribute to declare a <see cref="ILanguageService"/> implementation for inclusion in a MEF-based workspace.
    /// </summary>
    [MetadataAttribute]
    [AttributeUsage(AttributeTargets.Class)]
    public class ExportLanguageServiceAttribute : ExportAttribute
    {
        /// <summary>
        /// The assembly qualified name of the service's type.
        /// </summary>
        public string ServiceType { get; }
 
        /// <summary>
        /// The language that the service is target for; LanguageNames.CSharp, etc.
        /// </summary>
        public string Language { get; }
 
        /// <summary>
        /// The layer that the service is specified for; ServiceLayer.Default, etc.
        /// </summary>
        public string Layer { get; }
 
        /// <summary>
        /// Declares a <see cref="ILanguageService"/> implementation for inclusion in a MEF-based workspace.
        /// </summary>
        /// <param name="type">The type that will be used to retrieve the service from a <see cref="HostLanguageServices"/>.</param>
        /// <param name="language">The language that the service is target for; LanguageNames.CSharp, etc.</param>
        /// <param name="layer">The layer that the service is specified for; ServiceLayer.Default, etc.</param>
        public ExportLanguageServiceAttribute(Type type, string language, string layer = ServiceLayer.Default)
            : base(typeof(ILanguageService))
        {
            if (type == null)
            {
                throw new ArgumentNullException(nameof(type));
            }
 
            this.ServiceType = type.AssemblyQualifiedName;
            this.Language = language ?? throw new ArgumentNullException(nameof(language));
            this.Layer = layer;
        }
    }
}