// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System;
using System.Collections.Concurrent;
using System.Diagnostics;

namespace System.Reflection.Runtime.Dispensers
{
    //
    // This dispenser stores every instance permanently.
    //
    internal sealed class DispenserThatAlwaysReuses<K, V> : Dispenser<K, V>
        where K : IEquatable<K>
        where V : class
    {
        public DispenserThatAlwaysReuses(Func<K, V> factory)
        {
            _concurrentUnifier = new FactoryConcurrentUnifier(factory);
        }

        public sealed override V GetOrAdd(K key)
        {
            return _concurrentUnifier.GetOrAdd(key);
        }

        private sealed class FactoryConcurrentUnifier : ConcurrentUnifier<K, V>
        {
            public FactoryConcurrentUnifier(Func<K, V> factory)
            {
                _factory = factory;
            }

            protected sealed override V Factory(K key)
            {
                return _factory(key);
            }

            private readonly Func<K, V> _factory;
        }

        private readonly FactoryConcurrentUnifier _concurrentUnifier;
    }
}