/* 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.Collections.Generic;
using System.Collections.ObjectModel;
using System.Threading;

namespace OpenSearch.Net.Diagnostics
{
	/// <summary>
	/// Retrieves Statistics for thread pools
	/// </summary>
	public class ThreadPoolStats
	{
		private static readonly string WorkerThreads = "Worker";
		private static readonly string CompletionPortThreads = "IOCP";

		/// <summary>
		/// Retrieve thread pool statistics
		/// </summary>
		public static ReadOnlyDictionary<string, ThreadPoolStatistics> GetStats()
		{
			var dictionary = new Dictionary<string, ThreadPoolStatistics>(2);
			ThreadPool.GetMaxThreads(out var maxWorkerThreads, out var maxIoThreads);
			ThreadPool.GetAvailableThreads(out var freeWorkerThreads, out var freeIoThreads);
			ThreadPool.GetMinThreads(out var minWorkerThreads, out var minIoThreads);
			var busyIoThreads = maxIoThreads - freeIoThreads;
			var busyWorkerThreads = maxWorkerThreads - freeWorkerThreads;

			dictionary.Add(WorkerThreads, new ThreadPoolStatistics(minWorkerThreads, maxWorkerThreads, busyWorkerThreads, freeWorkerThreads));
			dictionary.Add(CompletionPortThreads, new ThreadPoolStatistics(minIoThreads, maxIoThreads, busyIoThreads, freeIoThreads));
			return new ReadOnlyDictionary<string, ThreadPoolStatistics>(dictionary);
		}
	}

	/// <summary>
	/// Statistics for a thread pool
	/// </summary>
	public class ThreadPoolStatistics
	{
		public ThreadPoolStatistics(int min, int max, int busy, int free)
		{
			Min = min;
			Max = max;
			Busy = busy;
			Free = free;
		}

		/// <summary>The difference between the maximum number of thread pool threads returned by
		/// <see cref="Max"/>, and the number currently free.
		/// </summary>
		public int Busy { get; }

		/// <summary>The difference between the maximum number of thread pool threads returned by
		/// <see cref="Max"/>, and the number currently active.
		/// </summary>
		public int Free { get; }

		/// <summary>
		/// The number of requests to the thread pool that can be active concurrently. All requests above that number remain queued until
		/// thread pool threads become available.
		/// </summary>
		public int Max { get; }

		/// <summary>
		/// The minimum number of threads the thread pool creates on demand, as new requests are made, before switching to an algorithm for
		/// managing thread creation and destruction.
		/// </summary>
		public int Min { get; }
	}
}