// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;

namespace NuGet.Protocol.Plugins
{
    /// <summary>
    /// Plugin multiclient utilities.
    /// </summary>
    public sealed class PluginMulticlientUtilities : IPluginMulticlientUtilities
    {
        private readonly ConcurrentDictionary<string, Lazy<Task>> _actions;

        /// <summary>
        /// Initializes a new <see cref="PluginMulticlientUtilities" /> class.
        /// </summary>
        public PluginMulticlientUtilities()
        {
            _actions = new ConcurrentDictionary<string, Lazy<Task>>();
        }

        /// <summary>
        /// Asynchronously executes a task once per plugin lifetime per key.
        /// </summary>
        /// <param name="key">A key that identifies the task.</param>
        /// <param name="taskFunc">A function that returns a task.</param>
        /// <param name="cancellationToken">A cancellation token.</param>
        /// <returns>A task that represents the asynchronous operation.</returns>
        /// <exception cref="ArgumentException">Thrown if <paramref name="key" />
        /// is either <see langword="null" /> or an empty string.</exception>
        /// <exception cref="ArgumentNullException">Thrown if <paramref name="taskFunc" />
        /// is either <see langword="null" />.</exception>
        /// <exception cref="OperationCanceledException">Thrown if <paramref name="cancellationToken" />
        /// is cancelled.</exception>
        public async Task DoOncePerPluginLifetimeAsync(
            string key,
            Func<Task> taskFunc,
            CancellationToken cancellationToken)
        {
            if (string.IsNullOrEmpty(key))
            {
                throw new ArgumentException(Strings.ArgumentCannotBeNullOrEmpty, nameof(key));
            }

            if (taskFunc == null)
            {
                throw new ArgumentNullException(nameof(taskFunc));
            }

            cancellationToken.ThrowIfCancellationRequested();

            var lazyTask = _actions.GetOrAdd(key, _ => new Lazy<Task>(() => taskFunc()));

            await lazyTask.Value;
        }
    }
}