From 484e6bf3e1cb4342c5682557c096d14a666bc7cf Mon Sep 17 00:00:00 2001
From: EugeneTes <meelstorm@gmail.com>
Date: Mon, 23 Feb 2026 16:08:01 +0100
Subject: [PATCH] 1.0.11 discovery retention

---
 EpsonPrintService/EpsonPrintService.csproj    |  2 +-
 .../PrinterDiscoveryBackgroundTask.cs         | 69 +++++++++++++------
 2 files changed, 49 insertions(+), 22 deletions(-)

diff --git a/EpsonPrintService/EpsonPrintService.csproj b/EpsonPrintService/EpsonPrintService.csproj
index 520711e..8e69454 100644
--- a/EpsonPrintService/EpsonPrintService.csproj
+++ b/EpsonPrintService/EpsonPrintService.csproj
@@ -5,7 +5,7 @@
     <TargetFramework>net8.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
-	  <Version>1.0.10</Version>
+	  <Version>1.0.11</Version>
   </PropertyGroup>
 
   <ItemGroup>
diff --git a/EpsonPrintService/PrinterDiscoveryBackgroundTask.cs b/EpsonPrintService/PrinterDiscoveryBackgroundTask.cs
index 50d8744..bed7624 100644
--- a/EpsonPrintService/PrinterDiscoveryBackgroundTask.cs
+++ b/EpsonPrintService/PrinterDiscoveryBackgroundTask.cs
@@ -16,9 +16,11 @@ public class PrinterDiscoveryBackgroundTask
     private readonly PrintServer _printServer;
     private readonly TimeSpan _interval;
     private readonly TimeSpan _discoveryTimeout;
+    private readonly TimeSpan _retentionPeriod;
 
-    private HashSet<string> _lastDiscoveredPrinterIps = new();
-    private List<DiscoveredPrinter> _lastDiscoveredPrinters = new();
+    private readonly Dictionary<string, DateTime> _lastSeenTimes = new();
+    private readonly Dictionary<string, DiscoveredPrinter> _knownPrinters = new();
+    private HashSet<string> _lastEffectiveIps = new();
 
     public PrinterDiscoveryBackgroundTask(
         IDiscoveryService discoveryService,
@@ -32,6 +34,7 @@ public class PrinterDiscoveryBackgroundTask
         _printServer = printServer;
         _interval = TimeSpan.FromSeconds(30);
         _discoveryTimeout = TimeSpan.FromSeconds(3);
+        _retentionPeriod = TimeSpan.FromMinutes(2);
     }
 
     /// <summary>
@@ -69,21 +72,11 @@ public class PrinterDiscoveryBackgroundTask
     private async Task DiscoverAndNotifyAsync()
     {
         List<DiscoveredPrinter> printers;
-        HashSet<string> currentIps;
-        bool configChanged;
 
         await _printServer.EnterDiscoveryLockAsync();
         try
         {
             printers = await _discoveryService.DiscoverPrintersAsync(_discoveryTimeout);
-            currentIps = printers.Select(p => p.IPAddress).ToHashSet();
-            configChanged = HasConfigurationChanged(currentIps);
-
-            if (configChanged)
-            {
-                _lastDiscoveredPrinterIps = currentIps;
-                _lastDiscoveredPrinters = printers;
-            }
         }
         catch (Exception ex)
         {
@@ -95,25 +88,59 @@ public class PrinterDiscoveryBackgroundTask
             _printServer.ExitDiscoveryLock();
         }
 
-        // Register printers AFTER releasing the lock
-        foreach (string currentIp in currentIps)
+        // Update last seen times for discovered printers
+        DateTime now = DateTime.UtcNow;
+        foreach (DiscoveredPrinter printer in printers)
         {
-            _logger.LogDebug("Registering discovered printer with IP: {IP}", currentIp);
-            _printServer.RegisterPrinter(currentIp);
+            _lastSeenTimes[printer.IPAddress] = now;
+            _knownPrinters[printer.IPAddress] = printer;
+        }
+
+        // Remove printers not seen within the retention period
+        List<string> expiredIps = _lastSeenTimes
+            .Where(kvp => now - kvp.Value > _retentionPeriod)
+            .Select(kvp => kvp.Key)
+            .ToList();
+
+        foreach (string expiredIp in expiredIps)
+        {
+            _logger.LogInformation("Printer {IP} not seen for over {Retention}s, removing", expiredIp, _retentionPeriod.TotalSeconds);
+            _lastSeenTimes.Remove(expiredIp);
+            _knownPrinters.Remove(expiredIp);
+        }
+
+        // Compute effective set and detect changes
+        HashSet<string> effectiveIps = _lastSeenTimes.Keys.ToHashSet();
+        bool configChanged = HasConfigurationChanged(effectiveIps);
+
+        // Register newly appeared printers
+        foreach (string ip in effectiveIps.Except(_lastEffectiveIps))
+        {
+            _logger.LogDebug("Registering discovered printer with IP: {IP}", ip);
+            _printServer.RegisterPrinter(ip);
+        }
+
+        // Unregister expired printers
+        foreach (string ip in _lastEffectiveIps.Except(effectiveIps))
+        {
+            _logger.LogDebug("Unregistering expired printer with IP: {IP}", ip);
+            _printServer.UnregisterPrinter(ip);
         }
 
         if (configChanged)
         {
-            _logger.LogInformation("Discovered printer configuration changed: {Count} printer(s)", printers.Count);
-            await _receiver.OnPrintersDiscoveredAsync(printers.AsReadOnly());
+            _lastEffectiveIps = effectiveIps;
+            List<DiscoveredPrinter> effectivePrinters = _knownPrinters.Values.ToList();
+            _logger.LogInformation("Discovered printer configuration changed: {Count} printer(s)", effectivePrinters.Count);
+            await _receiver.OnPrintersDiscoveredAsync(effectivePrinters.AsReadOnly());
         }
     }
 
-    private bool HasConfigurationChanged(HashSet<string> currentIps)
+    private bool HasConfigurationChanged(HashSet<string> effectiveIps)
     {
-        if (currentIps.Count != _lastDiscoveredPrinterIps.Count)
+        if (effectiveIps.Count != _lastEffectiveIps.Count)
             return true;
 
-        return !currentIps.SetEquals(_lastDiscoveredPrinterIps);
+        return !effectiveIps.SetEquals(_lastEffectiveIps);
     }
 }