// 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;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Threading;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.Internal.Log
{
    /// <summary>
    /// helper class to aggregate some numeric value log in client side
    /// </summary>
    internal abstract class AbstractLogAggregator<TKey, TValue> : IEnumerable<KeyValuePair<TKey, TValue>>
        where TKey : notnull
        where TValue : class // TValue being constrained to a class will ensure that the ConcurrentDictionaries won't be JITted with structs
    {
        /// <remarks>
        /// The key here is an object even though we will often be putting enums into this map; the problem with the use of enums or other value
        /// types is they prevent the runtime from sharing the same JITted code for each different generic instantiation. In this case,
        /// the cost of boxing is cheaper than the cost of the extra JIT.
        /// </remarks>
        private readonly ConcurrentDictionary<object, TValue> _map = new(concurrencyLevel: 2, capacity: 2);
        private readonly Func<object, TValue> _createCounter;
 
        protected AbstractLogAggregator()
        {
            _createCounter = _ => CreateCounter();
        }
 
        protected abstract TValue CreateCounter();
 
        public bool IsEmpty => _map.IsEmpty;
 
        public void Clear() => _map.Clear();
 
        public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()
            => _map.Select(static kvp => new KeyValuePair<TKey, TValue>((TKey)kvp.Key, kvp.Value)).GetEnumerator();
 
        IEnumerator IEnumerable.GetEnumerator()
            => this.GetEnumerator();
 
        [PerformanceSensitive("https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1279909", AllowCaptures = false)]
        protected TValue GetCounter(TKey key)
            => _map.GetOrAdd((object)key, _createCounter);
 
        protected bool TryGetCounter(TKey key, [MaybeNullWhen(false)] out TValue counter)
        {
            if (_map.TryGetValue((object)key, out counter))
            {
                return true;
            }
 
            return false;
        }
    }
}