sharee.bike-App/SharedBusinessLogic/ViewModel/PollingUpdateTaskManager.cs

using System;
using System.Threading.Tasks;
using Serilog;
using ShareeBike.Settings;

namespace ShareeBike.ViewModel
{
	/// <summary>
	/// Performs a periodic update.
	/// </summary>
	public class PollingUpdateTaskManager : IPollingUpdateTaskManager
	{
		/// <summary> Action which performs an update.</summary>
		private Action UpdateAction { get; }

		/// <summary> Reference on the current polling task</summary>
		private PollingUpdateTask UpdateTask { get; set; }

		/// <summary>
		/// Gets or sets polling parameters.
		/// </summary>
		private PollingParameters PollingParameters { get; set; }

		/// <summary> Prevents an invalid instance to be created. </summary>
		private PollingUpdateTaskManager()
		{ }

		/// <summary>Constructs a update manager object. </summary>
		/// <param name="p_oGetChildName">Name of the child class. For logging purposes.</param>
		/// <param name="updateAction"></param>
		public PollingUpdateTaskManager(
			Action updateAction)
		{
			UpdateAction = updateAction ?? throw new ArgumentException(
				$"Can not construct {GetType().Name}- obect. Argument {nameof(updateAction)} must not be null.");
		}

		/// <summary>
		/// Invoked when page is shown. 
		/// Actuates and awaits the first update process and starts a task wich actuate the subseqent update tasks.
		/// </summary>
		/// <param name="pollingParameters">Parametes holding polling period, if null last parameters are used if available.</param>
		public async Task StartAsync(PollingParameters pollingParameters = null)
		{
			if (UpdateTask != null)
			{
				Log.Error($"Call to stop periodic update task missed in context {GetType().Name} at {DateTime.Now}.");

				// Call of StopUpdatePeriodically missed. 
				// Terminate running polling update task before starting a new one
				await UpdateTask.Terminate();
			}

			if (pollingParameters != null)
			{
				// Backup polling parameter for purposee of restart.
				PollingParameters = pollingParameters;
			}

			if (PollingParameters == null)
			{
				// No polling parameters avaialable.
				Log.Error($"Can not start polling. No parameters available.");
				return;
			}


			if (!PollingParameters.IsActivated)
			{
				// Automatic supdate is switched off.
				Log.ForContext<PollingUpdateTask>().Debug($"Automatic update is off, context {GetType().Name} at {DateTime.Now}.");
				return;
			}

			UpdateTask = new PollingUpdateTask(
				UpdateAction,
				PollingParameters.Periode);
		}

		/// <summary>
		/// Invoked when pages is closed/ hidden. 
		/// Stops update process.
		/// </summary>
		public async Task StopAsync()
		{
			if (UpdateTask == null)
			{
				// Nothing to do if there is no update task pending.
				return;
			}

			await UpdateTask.Terminate();

			UpdateTask = null;
		}
	}
}