Add project files.

SyncScheduler.cs

@@ -0,0 +1,73 @@
+using ConnectionsAPI.Events;
+using Cronos;
+using System.Diagnostics.CodeAnalysis;
+
+namespace ConnectionsAPI
+{
+    public class SyncScheduler(ILogger<SyncScheduler> logger, IConfiguration configuration) : BackgroundService
+    {
+        private readonly ILogger<SyncScheduler> _logger = logger;
+        private readonly IConfiguration _configuration = configuration;
+
+        protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+        {
+            // get and parse the cron expression
+            string configCronStr = _configuration.GetValue<string>("Sync:ScheduleCron") ?? string.Empty;
+            if (!TryParseCronExpression(configCronStr, out var cron))
+            {
+                cron = CronExpression.Hourly;
+                _logger.LogWarning("Passed CRON expression was invalid ({configCron}); Defaulting to {newCron}", configCronStr, cron.ToString());
+            }
+            _logger.LogInformation("Starting Sync Scheduler with CRON expression {cron}", cron.ToString());
+
+            // get and parse if immediate execution is wanted
+            bool runImmediately = _configuration.GetValue<bool>("Sync:RunImmediately", false);
+            if (runImmediately)
+            {
+                _logger.LogInformation("Immediate execution enabled; Sending sync command.");
+                await SendSyncEvent(stoppingToken, wait: true);
+            }
+
+            // run the loop for executions
+            while (!stoppingToken.IsCancellationRequested)
+            {
+                // wait for next scheduled run
+                await WaitForNextSchedule(cron, stoppingToken);
+                // run the sync
+                _logger.LogInformation("Sending sync command at: {currentTime}", DateTimeOffset.UtcNow);
+                await SendSyncEvent(stoppingToken, wait: false);
+            }
+        }
+
+        // this method exists because the Cronos TryParse for some reason throws an exception on nulls and empty strings
+        // completely defeating the purpose of the TryParse pattern
+        private static bool TryParseCronExpression(string expression, [NotNullWhen(true)] out CronExpression? cron)
+        {
+            try
+            {
+                cron = CronExpression.Parse(expression);
+                return true;
+            }
+            catch
+            {
+                cron = null;
+                return false;
+            }
+        }
+
+        private static Task SendSyncEvent(CancellationToken stoppingToken, bool wait = false) =>
+            new PuzzleSyncEvent { }.PublishAsync(wait ? Mode.WaitForAll : Mode.WaitForNone, stoppingToken);
+
+        private async Task WaitForNextSchedule(CronExpression cron, CancellationToken ct)
+        {
+            var currentUtcTime = DateTimeOffset.UtcNow.UtcDateTime;
+            var nextOccurrenceTime = cron.GetNextOccurrence(currentUtcTime);
+
+            var delay = nextOccurrenceTime.GetValueOrDefault() - currentUtcTime;
+
+            _logger.LogInformation("Run delayed for {delay}. Next occurrence: {nextOccurrence}; Current time: {currentTime}", delay, nextOccurrenceTime, currentUtcTime);
+
+            await Task.Delay(delay, ct);
+        }
+    }
+}