add InsinTelemetryDiscoveredPrintersReceiver decorator

Inspectron.Epson/PrintServer/DiscoveredPrintersReceiver/InsinTelemetryDiscoveredPrintersReceiver.cs

@@ -0,0 +1,71 @@
+using Inspectron.Epson;
+using Inspectron.Epson.PrintServer.Telemetry;
+
+namespace EpsonPrintService;
+
+public sealed class InsinTelemetryDiscoveredPrintersReceiver : IDiscoveredPrintersReceiver
+{
+    private readonly IDiscoveredPrintersReceiver _inner;
+    private readonly IInsinTelemetry _telemetry;
+    private readonly HashSet<string> _seenIps = new();
+    private readonly Dictionary<string, bool> _present = new();
+    private readonly object _stateLock = new();
+
+    public InsinTelemetryDiscoveredPrintersReceiver(
+        IDiscoveredPrintersReceiver inner,
+        IInsinTelemetry telemetry)
+    {
+        _inner = inner;
+        _telemetry = telemetry;
+    }
+
+    public async Task OnPrintersDiscoveredAsync(IReadOnlyList<DiscoveredPrinter> printers)
+    {
+        await _inner.OnPrintersDiscoveredAsync(printers);
+
+        List<(string kind, string message)> toEmit;
+        lock (_stateLock)
+        {
+            toEmit = ComputeEvents(printers);
+        }
+
+        foreach (var (kind, message) in toEmit)
+        {
+            try { _telemetry.Emit(kind, message); }
+            catch { /* swallow: telemetry must never break discovery */ }
+        }
+    }
+
+    private List<(string, string)> ComputeEvents(IReadOnlyList<DiscoveredPrinter> printers)
+    {
+        var events = new List<(string, string)>();
+        var currentIps = new HashSet<string>();
+        foreach (var p in printers)
+        {
+            if (string.IsNullOrEmpty(p.IPAddress)) continue;
+            currentIps.Add(p.IPAddress);
+
+            if (_seenIps.Add(p.IPAddress))
+                events.Add((InsinEventKinds.PrinterDiscovered,
+                    InsinMessageFormatter.Format(("printer", p.IPAddress), ("model", p.ModelName))));
+
+            if (!_present.TryGetValue(p.IPAddress, out var wasPresent) || !wasPresent)
+                events.Add((InsinEventKinds.PrinterOnline,
+                    InsinMessageFormatter.Format(("printer", p.IPAddress))));
+
+            _present[p.IPAddress] = true;
+        }
+
+        foreach (var kv in _present.ToList())
+        {
+            if (kv.Value && !currentIps.Contains(kv.Key))
+            {
+                events.Add((InsinEventKinds.PrinterOffline,
+                    InsinMessageFormatter.Format(("printer", kv.Key))));
+                _present[kv.Key] = false;
+            }
+        }
+
+        return events;
+    }
+}