// 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.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.Shared.TestHooks;
 
namespace Roslyn.Utilities;
 
/// <summary>
/// Implements a queue of asynchronously executed tasks.
/// </summary>
internal sealed class TaskQueue
{
    public IAsynchronousOperationListener Listener { get; }
    public TaskScheduler Scheduler { get; }
 
    private readonly object _gate = new();
 
    public TaskQueue(IAsynchronousOperationListener operationListener, TaskScheduler taskScheduler)
    {
        Contract.ThrowIfNull(operationListener);
        Contract.ThrowIfNull(taskScheduler);
 
        Listener = operationListener;
        Scheduler = taskScheduler;
        LastScheduledTask = Task.CompletedTask;
    }
 
    public Task LastScheduledTask { get; private set; }
 
    private IAsyncToken BeginOperation(string taskName)
        => Listener.BeginAsyncOperation(taskName);
 
    private static TTask EndOperation<TTask>(IAsyncToken token, TTask task) where TTask : Task
    {
        // send the notification on operation being complete but do not wait for the notification to be delivered
        _ = task.CompletesAsyncOperation(token);
 
        return task;
    }
 
#pragma warning disable VSTHRD200 // Use "Async" suffix for async methods (Task wrappers, not asynchronous methods)
 
    /// <summary>
    /// Enqueue specified <paramref name="operation"/> and notify <see cref="Listener"/> of its start and completion.
    /// </summary>
    /// <returns>The <see cref="Task"/> that executes the operation.</returns>
    public Task ScheduleTask(string taskName, Action operation, CancellationToken cancellationToken)
        => EndOperation(BeginOperation(taskName), ScheduleTaskInProgress(operation, cancellationToken));
 
    /// <inheritdoc cref="ScheduleTask(string, Action, CancellationToken)"/>
    public Task<T> ScheduleTask<T>(string taskName, Func<T> operation, CancellationToken cancellationToken)
        => EndOperation(BeginOperation(taskName), ScheduleTaskInProgress(operation, cancellationToken));
 
    /// <inheritdoc cref="ScheduleTask(string, Action, CancellationToken)"/>
    public Task ScheduleTask(string taskName, Func<Task> operation, CancellationToken cancellationToken)
        => EndOperation(BeginOperation(taskName), ScheduleTaskInProgress(operation, cancellationToken));
 
    /// <inheritdoc cref="ScheduleTask(string, Action, CancellationToken)"/>
    public Task<T> ScheduleTask<T>(string taskName, Func<Task<T>> operation, CancellationToken cancellationToken)
        => EndOperation(BeginOperation(taskName), ScheduleTaskInProgress(operation, cancellationToken));
 
    /// <summary>
    /// Enqueue specified <paramref name="operation"/>.
    /// Assumes <see cref="Listener"/> has already been notified of its start and will be notified when it completes.
    /// </summary>
    /// <returns>The <see cref="Task"/> that executes the operation.</returns>
    [PerformanceSensitive("https://developercommunity.visualstudio.com/content/problem/854696/changing-target-framework-takes-10-minutes-with-10.html", AllowCaptures = false)]
    private Task ScheduleTaskInProgress(Action operation, CancellationToken cancellationToken)
    {
        lock (_gate)
        {
            var task = LastScheduledTask.SafeContinueWith(_ => operation(), cancellationToken, TaskContinuationOptions.None, Scheduler);
            LastScheduledTask = task;
            return task;
        }
    }
 
    /// <inheritdoc cref="ScheduleTaskInProgress(Action, CancellationToken)"/>
    [PerformanceSensitive("https://developercommunity.visualstudio.com/content/problem/854696/changing-target-framework-takes-10-minutes-with-10.html", AllowCaptures = false)]
    private Task<T> ScheduleTaskInProgress<T>(Func<T> operation, CancellationToken cancellationToken)
    {
        lock (_gate)
        {
            var task = LastScheduledTask.SafeContinueWith(_ => operation(), cancellationToken, TaskContinuationOptions.None, Scheduler);
            LastScheduledTask = task;
            return task;
        }
    }
 
    /// <inheritdoc cref="ScheduleTaskInProgress(Action, CancellationToken)"/>
    [PerformanceSensitive("https://developercommunity.visualstudio.com/content/problem/854696/changing-target-framework-takes-10-minutes-with-10.html", AllowCaptures = false)]
    private Task ScheduleTaskInProgress(Func<Task> operation, CancellationToken cancellationToken)
    {
        lock (_gate)
        {
            var task = LastScheduledTask.SafeContinueWithFromAsync(_ => operation(), cancellationToken, TaskContinuationOptions.None, Scheduler);
            LastScheduledTask = task;
            return task;
        }
    }
 
    /// <inheritdoc cref="ScheduleTaskInProgress(Action, CancellationToken)"/>
    [PerformanceSensitive("https://developercommunity.visualstudio.com/content/problem/854696/changing-target-framework-takes-10-minutes-with-10.html", AllowCaptures = false)]
    private Task<T> ScheduleTaskInProgress<T>(Func<Task<T>> operation, CancellationToken cancellationToken)
    {
        lock (_gate)
        {
            var task = LastScheduledTask.SafeContinueWithFromAsync(_ => operation(), cancellationToken, TaskContinuationOptions.None, Scheduler);
            LastScheduledTask = task;
            return task;
        }
    }
 
#pragma warning restore
}