// 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.Collections.Generic;
 
namespace Roslyn.Utilities
{
    internal static class IReadOnlyDictionaryExtensions
    {
        public static TValue? GetValueOrDefault<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dictionary, TKey key)
            where TKey : notnull
        {
            if (dictionary.TryGetValue(key, out var value))
            {
                return value;
            }
 
            return default!;
        }
 
        public static IEnumerable<T> GetEnumerableMetadata<T>(this IReadOnlyDictionary<string, object> metadata, string name)
        {
            switch (metadata.GetValueOrDefault(name))
            {
                case IEnumerable<T> enumerable: return enumerable;
                case T s: return SpecializedCollections.SingletonEnumerable(s);
                default: return SpecializedCollections.EmptyEnumerable<T>();
            }
        }
 
        public static IReadOnlyDictionary<TKey, TValue?> AsNullable<TKey, TValue>(this IReadOnlyDictionary<TKey, TValue> dictionary)
            where TKey : notnull
            where TValue : class
        {
            // this is a safe cast, even though the language doesn't allow the interface to be 'out TValue'
            return dictionary!;
        }
    }
}