add InsinTelemetryDiscoveredPrintersReceiver decorator

Inspectron.Epson.Tests/Telemetry/InsinTelemetryDiscoveredPrintersReceiverTests.cs

@@ -0,0 +1,104 @@
+using EpsonPrintService;
+using Inspectron.Epson;
+using Inspectron.Epson.PrintServer.Telemetry;
+
+namespace Inspectron.Epson.Tests.Telemetry;
+
+public class InsinTelemetryDiscoveredPrintersReceiverTests
+{
+    private sealed class RecordingTelemetry : IInsinTelemetry
+    {
+        public List<(string Kind, string Message)> Events { get; } = new();
+        public void Emit(string kind, string message) => Events.Add((kind, message));
+    }
+
+    private sealed class CountingInner : IDiscoveredPrintersReceiver
+    {
+        public int Calls;
+        public Task OnPrintersDiscoveredAsync(IReadOnlyList<DiscoveredPrinter> printers)
+        {
+            Calls++;
+            return Task.CompletedTask;
+        }
+    }
+
+    private static DiscoveredPrinter Printer(string ip, string model = "TM-T30III") =>
+        new() { IPAddress = ip, ModelName = model };
+
+    [Fact]
+    public async Task First_sighting_emits_discovered_and_online()
+    {
+        var telemetry = new RecordingTelemetry();
+        var inner = new CountingInner();
+        var sut = new InsinTelemetryDiscoveredPrintersReceiver(inner, telemetry);
+
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+
+        Assert.Equal(1, inner.Calls);
+        Assert.Collection(telemetry.Events,
+            e => Assert.Equal("printer.discovered", e.Kind),
+            e => Assert.Equal("printer.online",     e.Kind));
+        Assert.Contains("printer=192.168.1.10", telemetry.Events[0].Message);
+        Assert.Contains("model=TM-T30III",      telemetry.Events[0].Message);
+    }
+
+    [Fact]
+    public async Task Repeat_sighting_emits_nothing()
+    {
+        var telemetry = new RecordingTelemetry();
+        var sut = new InsinTelemetryDiscoveredPrintersReceiver(new CountingInner(), telemetry);
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+        telemetry.Events.Clear();
+
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+
+        Assert.Empty(telemetry.Events);
+    }
+
+    [Fact]
+    public async Task Disappearance_emits_offline()
+    {
+        var telemetry = new RecordingTelemetry();
+        var sut = new InsinTelemetryDiscoveredPrintersReceiver(new CountingInner(), telemetry);
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+        telemetry.Events.Clear();
+
+        await sut.OnPrintersDiscoveredAsync(Array.Empty<DiscoveredPrinter>());
+
+        Assert.Single(telemetry.Events);
+        Assert.Equal("printer.offline", telemetry.Events[0].Kind);
+        Assert.Equal("printer=192.168.1.10", telemetry.Events[0].Message);
+    }
+
+    [Fact]
+    public async Task Reappearance_emits_online_only_not_discovered()
+    {
+        var telemetry = new RecordingTelemetry();
+        var sut = new InsinTelemetryDiscoveredPrintersReceiver(new CountingInner(), telemetry);
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+        await sut.OnPrintersDiscoveredAsync(Array.Empty<DiscoveredPrinter>());
+        telemetry.Events.Clear();
+
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+
+        Assert.Single(telemetry.Events);
+        Assert.Equal("printer.online", telemetry.Events[0].Kind);
+    }
+
+    [Fact]
+    public async Task Telemetry_failures_do_not_break_inner()
+    {
+        var telemetry = new ThrowingTelemetry();
+        var inner = new CountingInner();
+        var sut = new InsinTelemetryDiscoveredPrintersReceiver(inner, telemetry);
+
+        await sut.OnPrintersDiscoveredAsync(new[] { Printer("192.168.1.10") });
+
+        Assert.Equal(1, inner.Calls);
+    }
+
+    private sealed class ThrowingTelemetry : IInsinTelemetry
+    {
+        public void Emit(string kind, string message) => throw new InvalidOperationException("boom");
+    }
+}

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;
+    }
+}