refactor: FP patterns in packets_live/callsign_view

- mount: extract subscribe_if_connected/2, split assign_valid/assign_invalid
  to eliminate inline if/else for validation + subscription logic.

- enrich_packet_with_device_identifier: extract resolve_canonical_identifier/1
  as multi-clause function (binary guard + catch-all) instead of nested if.

- update_packet_lists: cond → multi-clause do_update/4 with guards.
  Three explicit paths: at-cap no-stored, at-cap with-stored, under-cap.

- get_timestamp_microseconds: case → multi-clause (%DateTime{}, binary,
  catch-all) for cleaner dispatch.

lib/aprsme_web/live/packets_live/callsign_view.ex

@@ -13,42 +13,43 @@ defmodule AprsmeWeb.PacketsLive.CallsignView do
 
   @impl true
   def mount(%{"callsign" => callsign}, _session, socket) do
-    # Validate and normalize callsign
-    normalized_callsign = Callsign.normalize(callsign)
+    normalized = Callsign.normalize(callsign)
 
-    if Callsign.valid?(normalized_callsign) do
-      # Subscribe to live packet updates for this callsign only
-      _ =
-        if connected?(socket) do
-          Phoenix.PubSub.subscribe(Aprsme.PubSub, "packets:#{normalized_callsign}")
-        end
-
-      # Get stored packets for this callsign (up to 100)
-      stored_packets = get_stored_packets(normalized_callsign, 100)
-      all_packets = stored_packets
-
-      socket =
-        socket
-        |> assign(:callsign, normalized_callsign)
-        |> assign(:packets, stored_packets)
-        |> assign(:live_packets, [])
-        |> assign(:all_packets, all_packets)
-        |> assign(:error, nil)
-
-      {:ok, socket}
+    if Callsign.valid?(normalized) do
+      socket = subscribe_if_connected(socket, normalized)
+      stored = get_stored_packets(normalized, 100)
+      {:ok, assign_valid(socket, normalized, stored)}
     else
-      socket =
-        socket
-        |> assign(:callsign, normalized_callsign)
-        |> assign(:packets, [])
-        |> assign(:live_packets, [])
-        |> assign(:all_packets, [])
-        |> assign(:error, "Invalid callsign format")
-
-      {:ok, socket}
+      {:ok, assign_invalid(socket, normalized)}
     end
   end
 
+  defp subscribe_if_connected(socket, callsign) do
+    if connected?(socket) do
+      Phoenix.PubSub.subscribe(Aprsme.PubSub, "packets:#{callsign}")
+    end
+
+    socket
+  end
+
+  defp assign_valid(socket, callsign, stored) do
+    socket
+    |> assign(:callsign, callsign)
+    |> assign(:packets, stored)
+    |> assign(:live_packets, [])
+    |> assign(:all_packets, stored)
+    |> assign(:error, nil)
+  end
+
+  defp assign_invalid(socket, callsign) do
+    socket
+    |> assign(:callsign, callsign)
+    |> assign(:packets, [])
+    |> assign(:live_packets, [])
+    |> assign(:all_packets, [])
+    |> assign(:error, "Invalid callsign format")
+  end
+
   @impl true
   def handle_info({:postgres_packet, payload}, socket) do
     SharedPacketHandler.handle_packet_update(payload, socket,
@@ -60,7 +61,6 @@ defmodule AprsmeWeb.PacketsLive.CallsignView do
   def handle_info(_message, socket), do: {:noreply, socket}
 
   defp process_matching_packet(enriched_payload, socket) do
-    # Device identifier enrichment specific to this module
     enriched_payload = enrich_packet_with_device_identifier(enriched_payload)
 
     current_live = socket.assigns.live_packets
@@ -69,13 +69,11 @@ defmodule AprsmeWeb.PacketsLive.CallsignView do
     {updated_stored, updated_live} = update_packet_lists(current_stored, current_live, enriched_payload)
     all_packets = get_all_packets_list(updated_stored, updated_live)
 
-    socket =
-      socket
-      |> assign(:packets, updated_stored)
-      |> assign(:live_packets, updated_live)
-      |> assign(:all_packets, all_packets)
-
-    {:noreply, socket}
+    {:noreply,
+     socket
+     |> assign(:packets, updated_stored)
+     |> assign(:live_packets, updated_live)
+     |> assign(:all_packets, all_packets)}
   end
 
   defp enrich_packet_with_device_identifier(sanitized_payload) do
@@ -84,18 +82,18 @@ defmodule AprsmeWeb.PacketsLive.CallsignView do
         Map.get(sanitized_payload, "device_identifier") ||
         DeviceParser.extract_device_identifier(sanitized_payload)
 
-    canonical_identifier =
-      if is_binary(device_identifier) do
-        matched_device = Aprsme.DeviceIdentification.lookup_device_by_identifier(device_identifier)
-        if matched_device, do: matched_device.identifier, else: device_identifier
-      else
-        device_identifier
-      end
-
+    canonical_identifier = resolve_canonical_identifier(device_identifier)
     Map.put(sanitized_payload, :device_identifier, canonical_identifier)
   end
 
-  # Private helper functions
+  defp resolve_canonical_identifier(identifier) when is_binary(identifier) do
+    case Aprsme.DeviceIdentification.lookup_device_by_identifier(identifier) do
+      %{identifier: canonical} -> canonical
+      nil -> identifier
+    end
+  end
+
+  defp resolve_canonical_identifier(identifier), do: identifier
 
   # Get recent packets for this callsign from the database (all packets, not just position)
   # Returns the latest packets regardless of age, filtered by callsign
@@ -133,37 +131,28 @@ defmodule AprsmeWeb.PacketsLive.CallsignView do
     |> Enum.take(100)
   end
 
-  defp get_timestamp_microseconds(packet) do
-    case packet.received_at do
-      %DateTime{} = dt ->
-        DateTime.to_unix(dt, :microsecond)
+  defp get_timestamp_microseconds(%DateTime{} = dt), do: DateTime.to_unix(dt, :microsecond)
 
-      dt when is_binary(dt) ->
-        case DateTime.from_iso8601(dt) do
-          {:ok, parsed_dt, _} -> DateTime.to_unix(parsed_dt, :microsecond)
-          _ -> 0
-        end
-
-      _ ->
-        0
+  defp get_timestamp_microseconds(dt) when is_binary(dt) do
+    case DateTime.from_iso8601(dt) do
+      {:ok, parsed_dt, _} -> DateTime.to_unix(parsed_dt, :microsecond)
+      _ -> 0
     end
   end
 
-  # Helper to update stored and live packet lists, keeping total <= 100
+  defp get_timestamp_microseconds(_), do: 0
+
+  # Helper to update stored and live packet lists, keeping total <= 100.
+  # Dispatches on capacity: at-cap with no stored, at-cap with stored, under-cap.
   defp update_packet_lists(current_stored, current_live, sanitized_payload) do
-    total_count = length(current_live) + length(current_stored)
-
-    cond do
-      total_count >= 100 and current_stored == [] ->
-        live_without_oldest = Enum.drop(current_live, -1)
-        {current_stored, [sanitized_payload | live_without_oldest]}
-
-      total_count >= 100 ->
-        stored_without_oldest = Enum.drop(current_stored, -1)
-        {stored_without_oldest, [sanitized_payload | current_live]}
-
-      true ->
-        {current_stored, [sanitized_payload | current_live]}
-    end
+    total = length(current_live) + length(current_stored)
+    do_update(total, current_stored, current_live, sanitized_payload)
   end
+
+  defp do_update(total, [], current_live, payload) when total >= 100, do: {[], [payload | Enum.drop(current_live, -1)]}
+
+  defp do_update(total, current_stored, current_live, payload) when total >= 100,
+    do: {Enum.drop(current_stored, -1), [payload | current_live]}
+
+  defp do_update(_total, current_stored, current_live, payload), do: {current_stored, [payload | current_live]}
 end