// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics.CodeAnalysis;
 
namespace System.ComponentModel.Composition
{
    internal static class MetadataServices
    {
        public static readonly IDictionary<string, object?> EmptyMetadata = new ReadOnlyDictionary<string, object?>(new Dictionary<string, object?>(0));
 
        public static IDictionary<string, object?> AsReadOnly(this IDictionary<string, object?>? metadata)
        {
            if (metadata == null)
            {
                return EmptyMetadata;
            }
 
            if (metadata is ReadOnlyDictionary<string, object?>)
            {
                return metadata;
            }
 
            return new ReadOnlyDictionary<string, object?>(metadata);
        }
 
        public static T? GetValue<T>(this IDictionary<string, object?> metadata, string key)
        {
            ArgumentNullException.ThrowIfNull(metadata);
 
            if (metadata.TryGetValue(key, out object? untypedValue) && untypedValue is T t)
            {
                return t;
            }
 
            return default;
        }
    }
}