From 00ed269f6fa98b48249b98362c4ca5cd1505056b Mon Sep 17 00:00:00 2001
From: Ryan <ryan.wang@clickview.com.au>
Date: Mon, 8 Apr 2024 15:19:47 +1000
Subject: [PATCH] add scheduler worker

---
 .../src/ClickView.Extensions.Hosting.csproj   |  3 +-
 .../Hosting/src/Workers/SchedulerWorker.cs    | 84 +++++++++++++++++++
 2 files changed, 86 insertions(+), 1 deletion(-)
 create mode 100644 src/Hosting/Hosting/src/Workers/SchedulerWorker.cs

diff --git a/src/Hosting/Hosting/src/ClickView.Extensions.Hosting.csproj b/src/Hosting/Hosting/src/ClickView.Extensions.Hosting.csproj
index cbb869d..ca2d8b3 100644
--- a/src/Hosting/Hosting/src/ClickView.Extensions.Hosting.csproj
+++ b/src/Hosting/Hosting/src/ClickView.Extensions.Hosting.csproj
@@ -7,8 +7,9 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <PackageReference Include="Cronos" Version="0.8.4" />
     <PackageReference Include="Microsoft.Extensions.Hosting" Version="8.0.0" />
-    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="8.0.0" />
+    <PackageReference Include="Microsoft.Extensions.Logging.Abstractions" Version="8.0.1" />
   </ItemGroup>
 
 </Project>
diff --git a/src/Hosting/Hosting/src/Workers/SchedulerWorker.cs b/src/Hosting/Hosting/src/Workers/SchedulerWorker.cs
new file mode 100644
index 0000000..f6a2510
--- /dev/null
+++ b/src/Hosting/Hosting/src/Workers/SchedulerWorker.cs
@@ -0,0 +1,84 @@
+namespace ClickView.Extensions.Hosting.Workers;
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Cronos;
+using Microsoft.Extensions.Logging;
+
+public abstract class SchedulerWorker : Worker, IDisposable
+{
+    private readonly ILogger _logger;
+    private Timer? _timer;
+    private CancellationTokenSource? _cancellationTokenSource;
+
+    protected abstract string CronSchedule { get; }
+
+    protected SchedulerWorker(ILogger logger) : base(logger)
+    {
+        _logger = logger;
+    }
+
+    protected override Task ExecuteAsync(CancellationToken cancellationToken)
+    {
+        var dueTime = GetNextScheduleDelay();
+        if (!dueTime.HasValue)
+            throw new Exception("Failed to get next schedule");
+
+        _cancellationTokenSource = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+        _timer = new Timer(_ => TimerCallbackAsync(_cancellationTokenSource.Token), null, dueTime.Value, Timeout.InfiniteTimeSpan);
+
+        return Task.CompletedTask;
+    }
+
+    private async void TimerCallbackAsync(CancellationToken cancellationToken)
+    {
+        if (cancellationToken.IsCancellationRequested)
+            return;
+
+        try
+        {
+            await RunAsync(cancellationToken);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Unhandled exception caught in SchedulerWorker ({WorkerName})", Name);
+        }
+        finally
+        {
+            var dueTime = GetNextScheduleDelay();
+            if (dueTime.HasValue)
+            {
+                // Reschedule the timer
+                _timer?.Change(dueTime.Value, Timeout.InfiniteTimeSpan);
+            }
+            else
+            {
+                _logger.LogError("Unable to get the next schedule in SchedulerWorker ({WorkerName})", Name);
+            }
+        }
+    }
+
+    private TimeSpan? GetNextScheduleDelay()
+    {
+        var now = DateTime.UtcNow;
+
+        var cronValue = CronExpression.Parse(CronSchedule);
+        var next = cronValue.GetNextOccurrence(now);
+        if (!next.HasValue)
+            return null;
+
+        return next.Value - now;
+    }
+
+    public void Dispose()
+    {
+        _cancellationTokenSource?.Cancel();
+
+        // Stop the timer
+        _timer?.Change(Timeout.Infinite, 0);
+        _timer?.Dispose();
+    }
+
+    protected abstract Task RunAsync(CancellationToken cancellationToken);
+}