// 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.Diagnostics.CodeAnalysis;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis;
 
namespace Roslyn.Utilities
{
    /// <summary>
    /// A class that abstracts the accessing of a value that is guaranteed to be available at some point.
    /// </summary>
    internal abstract class ValueSource<T>
    {
        public abstract bool TryGetValue([MaybeNullWhen(false)] out T value);
        public abstract T GetValue(CancellationToken cancellationToken = default);
        public abstract Task<T> GetValueAsync(CancellationToken cancellationToken = default);
 
        public static ValueSource<T> Constant(T value)
            => new AsyncLazy<T>(value);
    }
 
    internal static class ValueSource
    {
        public static ValueSource<T> Constant<T>(T value)
            => ValueSource<T>.Constant(value);
    }
 
    internal static class ValueSourceExtensions
    {
        internal static T? GetValueOrNull<T>(this Optional<T> optional) where T : class
            => optional.Value;
 
        internal static T GetValueOrDefault<T>(this Optional<T> optional) where T : struct
            => optional.Value;
 
        internal static T? GetValueOrNull<T>(this ValueSource<Optional<T>> optional, CancellationToken cancellationToken = default) where T : class
            => optional.GetValue(cancellationToken).GetValueOrNull();
 
        internal static T GetValueOrDefault<T>(this ValueSource<Optional<T>> optional, CancellationToken cancellationToken = default) where T : struct
            => optional.GetValue(cancellationToken).GetValueOrDefault();
    }
}