fix: replace duplicate spatial registrations

lib/aprsme/spatial_pubsub.ex

@@ -85,14 +85,17 @@ defmodule Aprsme.SpatialPubSub do
     # Create a unique topic for this client
     topic = "spatial:#{client_id}"
 
+    state = replace_existing_client(state, client_id)
+
     # Monitor the client process
-    Process.monitor(pid)
+    ref = Process.monitor(pid)
 
     # Update client info
     client_info = %{
       bounds: normalize_bounds(bounds),
       topic: topic,
-      pid: pid
+      pid: pid,
+      monitor_ref: ref
     }
 
     # Update spatial index
@@ -353,6 +356,14 @@ defmodule Aprsme.SpatialPubSub do
       nil ->
         state
 
+      %{bounds: bounds, monitor_ref: ref} ->
+        Process.demonitor(ref, [:flush])
+
+        state
+        |> remove_from_spatial_index(client_id, bounds)
+        |> update_in([:clients], &Map.delete(&1, client_id))
+        |> update_in([:stats, :clients_count], &max(0, &1 - 1))
+
       %{bounds: bounds} ->
         state
         |> remove_from_spatial_index(client_id, bounds)
@@ -361,6 +372,13 @@ defmodule Aprsme.SpatialPubSub do
     end
   end
 
+  defp replace_existing_client(state, client_id) do
+    case Map.get(state.clients, client_id) do
+      nil -> state
+      _client_info -> remove_client(state, client_id)
+    end
+  end
+
   defp calculate_avg_clients_per_cell(spatial_index) do
     non_nil_cells =
       spatial_index

test/aprsme/spatial_pubsub_test.exs

@@ -34,6 +34,28 @@ defmodule Aprsme.SpatialPubSubTest do
 
       SpatialPubSub.unregister_client(client_id)
     end
+
+    test "re-registering an existing client replaces the old viewport without inflating counts" do
+      client_id = "test_reregister_#{:rand.uniform(100_000)}"
+      bounds_1 = %{north: 41.0, south: 40.0, east: -73.0, west: -74.0}
+      bounds_2 = %{north: 36.0, south: 35.0, east: -79.0, west: -80.0}
+
+      before_stats = SpatialPubSub.get_stats()
+
+      assert {:ok, _topic} = SpatialPubSub.register_viewport(client_id, bounds_1)
+      mid_stats = SpatialPubSub.get_stats()
+      assert mid_stats.clients_count == before_stats.clients_count + 1
+
+      assert {:ok, _topic} = SpatialPubSub.register_viewport(client_id, bounds_2)
+      after_stats = SpatialPubSub.get_stats()
+
+      assert after_stats.clients_count == before_stats.clients_count + 1
+
+      state = :sys.get_state(SpatialPubSub)
+      assert state.clients[client_id].bounds == bounds_2
+
+      SpatialPubSub.unregister_client(client_id)
+    end
   end
 
   describe "duplicate packet prevention" do