using System;
using System.Threading;
using System.Threading.Tasks;

namespace Umbraco.Core.Logging
{
    internal static class LoggingTaskExtension
    {
        /// <summary>
        ///     This task shouldn't be waited on (as it's not guaranteed to run), and you shouldn't wait on the parent task either (because it might throw an
        ///     exception that doesn't get handled). If you want to be waiting on something, use LogErrorsWaitable instead.
        ///
        ///     None of these methods are suitable for tasks that return a value. If you're wanting a result, you should probably be handling
        ///     errors yourself.
        /// </summary>
        public static Task LogErrors(this Task task, Action<string, Exception> logMethod)
        {
            return task.ContinueWith(
                t => LogErrorsInner(t, logMethod),
                CancellationToken.None,
                TaskContinuationOptions.OnlyOnFaulted,
                // Must explicitly specify this, see https://blog.stephencleary.com/2013/10/continuewith-is-dangerous-too.html
                TaskScheduler.Default);
        }

        /// <summary>
        ///     This task can be waited on (as it's guaranteed to run), and you should wait on this rather than the parent task. Because it's
        ///     guaranteed to run, it may be slower than using LogErrors, and you should consider using that method if you don't want to wait.
        ///
        ///     None of these methods are suitable for tasks that return a value. If you're wanting a result, you should probably be handling
        ///     errors yourself.
        /// </summary>
        public static Task LogErrorsWaitable(this Task task, Action<string, Exception> logMethod)
        {
            return task.ContinueWith(
                t => LogErrorsInner(t, logMethod),
                // Must explicitly specify this, see https://blog.stephencleary.com/2013/10/continuewith-is-dangerous-too.html
                TaskScheduler.Default);
        }

        private static void LogErrorsInner(Task task, Action<string, Exception> logAction)
        {
            if (task.Exception != null)
            {
                logAction("Aggregate Exception with " + task.Exception.InnerExceptions.Count + " inner exceptions: ", task.Exception);
                foreach (var innerException in task.Exception.InnerExceptions)
                {
                    logAction("Inner exception from aggregate exception: ", innerException);
                }
            }
        }
    }
}