/* SPDX-License-Identifier: Apache-2.0
*
* The OpenSearch Contributors require contributions made to
* this file be licensed under the Apache-2.0 license or a
* compatible open source license.
*/
/*
* Modifications Copyright OpenSearch Contributors. See
* GitHub history for details.
*
*  Licensed to Elasticsearch B.V. under one or more contributor
*  license agreements. See the NOTICE file distributed with
*  this work for additional information regarding copyright
*  ownership. Elasticsearch B.V. licenses this file to you under
*  the Apache License, Version 2.0 (the "License"); you may
*  not use this file except in compliance with the License.
*  You may obtain a copy of the License at
*
* 	http://www.apache.org/licenses/LICENSE-2.0
*
*  Unless required by applicable law or agreed to in writing,
*  software distributed under the License is distributed on an
*  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
*  KIND, either express or implied.  See the License for the
*  specific language governing permissions and limitations
*  under the License.
*/

using System;
using System.Text;

namespace OpenSearch.Net.Extensions
{
	/// <summary>Provide a cached reusable instance of stringbuilder per thread.</summary>
	internal static class StringBuilderCache
	{
		private const int DefaultCapacity = 16; // == StringBuilder.DefaultCapacity

		// The value 360 was chosen in discussion with performance experts as a compromise between using
		// as little memory per thread as possible and still covering a large part of short-lived
		// StringBuilder creations on the startup path of VS designers.
		private const int MaxBuilderSize = 360;

		// WARNING: We allow diagnostic tools to directly inspect this member (t_cachedInstance).
		// See https://github.com/dotnet/corert/blob/master/Documentation/design-docs/diagnostics/diagnostics-tools-contract.md for more details.
		// Please do not change the type, the name, or the semantic usage of this member without understanding the implication for tools.
		// Get in touch with the diagnostics team if you have questions.
		[ThreadStatic]
		private static StringBuilder _cachedInstance;

		/// <summary>Get a StringBuilder for the specified capacity.</summary>
		/// <remarks>If a StringBuilder of an appropriate size is cached, it will be returned and the cache emptied.</remarks>
		public static StringBuilder Acquire(int capacity = DefaultCapacity)
		{
			if (capacity <= MaxBuilderSize)
			{
				var sb = _cachedInstance;
				if (sb != null)
				{
					// Avoid stringbuilder block fragmentation by getting a new StringBuilder
					// when the requested size is larger than the current capacity
					if (capacity <= sb.Capacity)
					{
						_cachedInstance = null;
						sb.Clear();
						return sb;
					}
				}
			}

			return new StringBuilder(capacity);
		}

		/// <summary>Place the specified builder in the cache if it is not too big.</summary>
		public static void Release(StringBuilder sb)
		{
			if (sb.Capacity <= MaxBuilderSize) _cachedInstance = sb;
		}

		/// <summary>ToString() the stringbuilder, Release it to the cache, and return the resulting string.</summary>
		public static string GetStringAndRelease(StringBuilder sb)
		{
			var result = sb.ToString();
			Release(sb);
			return result;
		}
	}
}