// 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 [];
        }
    }
 
    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!;
    }
}