// 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.Generic;
using Microsoft.CodeAnalysis.PooledObjects;
 
namespace Microsoft.CodeAnalysis
{
    /// <summary>
    /// Shared object pool for roslyn
    /// 
    /// Use this shared pool if only concern is reducing object allocations.
    /// if perf of an object pool itself is also a concern, use ObjectPool directly.
    /// 
    /// For example, if you want to create a million of small objects within a second, 
    /// use the ObjectPool directly. it should have much less overhead than using this.
    /// </summary>
    internal static class SharedPools
    {
        /// <summary>
        /// pool that uses default constructor with 100 elements pooled
        /// </summary>
        public static ObjectPool<T> BigDefault<T>() where T : class, new()
            => DefaultBigPool<T>.Instance;
 
        /// <summary>
        /// pool that uses default constructor with 20 elements pooled
        /// </summary>
        public static ObjectPool<T> Default<T>() where T : class, new()
            => DefaultNormalPool<T>.Instance;
 
        /// <summary>
        /// pool that uses string as key with StringComparer.OrdinalIgnoreCase as key comparer
        /// </summary>
        public static ObjectPool<Dictionary<string, T>> StringIgnoreCaseDictionary<T>()
            => StringIgnoreCaseDictionaryNormalPool<T>.Instance;
 
        /// <summary>
        /// pool that uses string as element with StringComparer.OrdinalIgnoreCase as element comparer
        /// </summary>
        public static readonly ObjectPool<HashSet<string>> StringIgnoreCaseHashSet =
            new(() => new HashSet<string>(StringComparer.OrdinalIgnoreCase), 20);
 
        /// <summary>
        /// pool that uses string as element with StringComparer.Ordinal as element comparer
        /// </summary>
        public static readonly ObjectPool<HashSet<string>> StringHashSet =
            new(() => new HashSet<string>(StringComparer.Ordinal), 20);
 
        /// <summary>
        /// Used to reduce the # of temporary byte[]s created to satisfy serialization and
        /// other I/O requests
        /// </summary>
        public static readonly ObjectPool<byte[]> ByteArray = new(() => new byte[ByteBufferSize], ByteBufferCount);
        public static readonly ObjectPool<char[]> CharArray = new(() => new char[ByteBufferSize], CharBufferCount);
 
        // byte pooled memory : 4K * 512 = 4MB
        public const int ByteBufferSize = 4 * 1024;
        private const int ByteBufferCount = 512;
 
        // char pooled memory : 8K * 5 = 40K
        private const int CharBufferCount = 5;
 
        private static class DefaultBigPool<T> where T : class, new()
        {
            public static readonly ObjectPool<T> Instance = new(() => new T(), 100);
        }
 
        private static class DefaultNormalPool<T> where T : class, new()
        {
            public static readonly ObjectPool<T> Instance = new(() => new T(), 20);
        }
 
        private static class StringIgnoreCaseDictionaryNormalPool<T>
        {
            public static readonly ObjectPool<Dictionary<string, T>> Instance =
                new(() => new Dictionary<string, T>(StringComparer.OrdinalIgnoreCase), 20);
        }
    }
}