/* 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
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*  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
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using System;
using System.Runtime.CompilerServices;
using System.Threading.Tasks;

namespace Tests.Framework.EndpointTests.TestState
{
	/// <summary>
	/// Provides support for asynchronous lazy initialization. This type is fully threadsafe.
	/// </summary>
	/// <typeparam name="T">The type of object that is being asynchronously initialized.</typeparam>
	public class AsyncLazy<T>
	{
		/// <summary>
		/// The underlying lazy task.
		/// </summary>
		private readonly Lazy<Task<T>> _instance;

		/// <summary>
		/// Initializes a new instance of the <see cref="AsyncLazy&lt;T&gt;" /> class.
		/// </summary>
		/// <param name="factory">The delegate that is invoked on a background thread to produce the value when it is needed.</param>
		public AsyncLazy(Func<T> factory) => _instance = new Lazy<Task<T>>(() => Task.Run(factory));

		/// <summary>
		/// Initializes a new instance of the <see cref="AsyncLazy&lt;T&gt;" /> class.
		/// </summary>
		/// <param name="factory">The asynchronous delegate that is invoked on a background thread to produce the value when it is needed.</param>
		public AsyncLazy(Func<Task<T>> factory) => _instance = new Lazy<Task<T>>(() => Task.Run(factory));

		/// <summary>
		/// Asynchronous infrastructure support. This method permits instances of <see cref="AsyncLazy&lt;T&gt;" /> to be await'ed.
		/// </summary>
		public TaskAwaiter<T> GetAwaiter() => _instance.Value.GetAwaiter();

		/// <summary>
		/// Starts the asynchronous initialization, if it has not already started.
		/// </summary>
		public void Start()
		{
			var unused = _instance.Value;
		}
	}
}