public async Task StartAsync()

in src/WebJobs.Extensions/Extensions/Timers/Listener/TimerListener.cs [93:164]
51 lines of code
7 McCabe index (conditional complexity)

        public async Task StartAsync(CancellationToken cancellationToken)
        {
            ThrowIfDisposed();

            if (_timer != null && _timer.Enabled)
            {
                throw new InvalidOperationException("The listener has already been started.");
            }

            // if schedule monitoring is enabled, record (or initialize)
            // the current schedule status
            bool isPastDue = false;

            // we use DateTimeOffset.Now rather than DateTimeOffset.UtcNow to allow the local machine to set the time zone. In Azure this will be
            // UTC by default, but can be configured to use any time zone if it makes scheduling easier.
            DateTimeOffset now = DateTimeOffset.Now;

            Logger.ScheduleAndTimeZone(_logger, _functionLogName, _schedule, TimeZoneInfo.Local.DisplayName);

            if (ScheduleMonitor != null)
            {
                // check to see if we've missed an occurrence since we last started.
                // If we have, invoke it immediately.
                ScheduleStatus = await ScheduleMonitor.GetSafeStatusAsync(_timerLookupName);

                Logger.InitialStatus(_logger, _functionLogName, ScheduleStatus?.Last.ToString("o"), ScheduleStatus?.Next.ToString("o"), ScheduleStatus?.LastUpdated.ToString("o"));
                TimeSpan pastDueDuration = await ScheduleMonitor.CheckPastDueAsync(_timerLookupName, now, _schedule, ScheduleStatus);
                isPastDue = pastDueDuration != TimeSpan.Zero;
            }

            if (ScheduleStatus == null)
            {
                // no schedule status has been stored yet, so initialize
                ScheduleStatus = new ScheduleStatus
                {
                    Last = ScheduleMonitor.DefaultDateTime,
                    Next = _schedule.GetNextOccurrence(now.LocalDateTime),
                    LastUpdated = ScheduleMonitor.DefaultDateTime
                };
            }

            // log the next several occurrences to console for visibility
            string nextOccurrences = TimerInfo.FormatNextOccurrences(_schedule, 5);
            Logger.NextOccurrences(_logger, _functionLogName, _schedule, nextOccurrences);

            if (isPastDue)
            {
                // when we're past due, so we schedule an immediate invocation
                StartupInvocation = new StartupInvocationContext
                {
                    IsPastDue = true,
                    OriginalSchedule = ScheduleStatus.Next
                };
                StartTimer(StartupInvocation.Interval);
            }
            else if (_attribute.RunOnStartup)
            {
                // function is marked RunOnStartup, so we schedule an immediate invocation
                StartupInvocation = new StartupInvocationContext
                {
                    RunOnStartup = true
                };
                StartTimer(StartupInvocation.Interval);
            }
            else
            {
                // start the regular schedule
                StartTimer(DateTimeOffset.Now);
            }

            _logger.LogDebug($"Timer listener started ({_functionLogName})");
        }