Reduce cyclomatic complexity in clustering, encoding, and leader_election

Simplify complex functions to improve readability and maintainability:
- clustering.ex: Convert case statement to map lookup for cluster radii
- encoding.ex: Extract codepoint validation into separate function clauses
- leader_election.ex: Extract PID liveness checking and cleanup logic into helpers

Co-Authored-By: Graham <noreply@anthropic.com>

lib/aprsme/cluster/leader_election.ex

@@ -186,53 +186,53 @@ defmodule Aprsme.Cluster.LeaderElection do
   defp cleanup_stale_registrations do
     case :global.whereis_name(@election_key) do
       :undefined ->
-        # No registration exists
         :ok
 
       pid when is_pid(pid) ->
-        pid_node = node(pid)
-        connected_nodes = [node() | Node.list()]
-
-        # Check if the PID's node is still connected
-        if pid_node in connected_nodes do
-          # Node is connected, try to check if process is alive
-          try do
-            if pid_node == node() do
-              # Local PID - use Process.alive?
-              if Process.alive?(pid) do
-                :ok
-              else
-                Logger.info("Cleaning up stale leader registration for dead local process #{inspect(pid)}")
-                :global.unregister_name(@election_key)
-              end
-            else
-              # Remote PID - use RPC to check if alive
-              case :rpc.call(pid_node, Process, :alive?, [pid]) do
-                true ->
-                  :ok
-
-                false ->
-                  Logger.info("Cleaning up stale leader registration for dead remote process #{inspect(pid)}")
-                  :global.unregister_name(@election_key)
-
-                {:badrpc, _reason} ->
-                  Logger.info("Cleaning up stale leader registration for unreachable process #{inspect(pid)}")
-                  :global.unregister_name(@election_key)
-              end
-            end
-          rescue
-            _error ->
-              Logger.info("Cleaning up stale leader registration for problematic process #{inspect(pid)}")
-              :global.unregister_name(@election_key)
-          end
-        else
-          # Node is disconnected - clean up the registration
-          Logger.info("Cleaning up stale leader registration for disconnected node #{pid_node}")
-          :global.unregister_name(@election_key)
-        end
+        check_and_cleanup_registration(pid)
     end
   end
 
+  defp check_and_cleanup_registration(pid) do
+    pid_node = node(pid)
+    connected_nodes = [node() | Node.list()]
+
+    if pid_node in connected_nodes do
+      check_pid_liveness(pid, pid_node)
+    else
+      cleanup_registration("disconnected node #{pid_node}")
+    end
+  end
+
+  defp check_pid_liveness(pid, pid_node) do
+    if is_pid_alive?(pid, pid_node) do
+      :ok
+    else
+      reason = if pid_node == node(), do: "dead local process", else: "dead remote process"
+      cleanup_registration("#{reason} #{inspect(pid)}")
+    end
+  rescue
+    _error ->
+      cleanup_registration("problematic process #{inspect(pid)}")
+  end
+
+  defp is_pid_alive?(pid, pid_node) when pid_node == node() do
+    Process.alive?(pid)
+  end
+
+  defp is_pid_alive?(pid, pid_node) do
+    if :rpc.call(pid_node, Process, :alive?, [pid]) do
+      true
+    else
+      false
+    end
+  end
+
+  defp cleanup_registration(reason) do
+    Logger.info("Cleaning up stale leader registration for #{reason}")
+    :global.unregister_name(@election_key)
+  end
+
   defp get_cluster_wide_status do
     all_nodes = [node() | Node.list()]
 

lib/aprsme/encoding.ex

@@ -155,25 +155,21 @@ defmodule Aprsme.Encoding do
   @spec valid_grapheme?(String.grapheme()) :: boolean()
   defp valid_grapheme?(grapheme) do
     case String.to_charlist(grapheme) do
-      [cp] ->
-        # Allow tab (0x09), newline (0x0A), carriage return (0x0D)
-        # Remove other control characters
-        case cp do
-          9 -> true
-          10 -> true
-          13 -> true
-          c when c >= 0 and c <= 31 -> false
-          127 -> false
-          c when c >= 128 and c <= 159 -> false
-          _ -> true
-        end
-
-      _ ->
-        # Multi-codepoint grapheme, keep it
-        true
+      [cp] -> valid_codepoint?(cp)
+      _ -> true
     end
   end
 
+  # Allow tab (0x09), newline (0x0A), carriage return (0x0D)
+  # Remove other control characters
+  defp valid_codepoint?(9), do: true
+  defp valid_codepoint?(10), do: true
+  defp valid_codepoint?(13), do: true
+  defp valid_codepoint?(127), do: false
+  defp valid_codepoint?(c) when c >= 0 and c <= 31, do: false
+  defp valid_codepoint?(c) when c >= 128 and c <= 159, do: false
+  defp valid_codepoint?(_), do: true
+
   @spec find_invalid_byte_position(binary()) :: non_neg_integer() | nil
   defp find_invalid_byte_position(input) do
     input

lib/aprsme/packets/clustering.ex

@@ -46,21 +46,24 @@ defmodule Aprsme.Packets.Clustering do
   Calculates the clustering radius in degrees based on zoom level.
   Lower zoom levels get larger radii for more aggressive clustering.
   """
+  # Clustering radius lookup table by zoom level
+  # More aggressive scaling for better separation at higher zooms
+  # Zoom 1: ~5 degrees, Zoom 5: ~0.3 degrees, Zoom 8: ~0.04 degrees
+  @cluster_radii %{
+    1 => 5.0,
+    2 => 2.5,
+    3 => 1.25,
+    4 => 0.625,
+    5 => 0.3125,
+    6 => 0.15625,
+    7 => 0.078125,
+    8 => 0.0390625
+  }
+  @default_radius 0.0390625
+
   @spec calculate_cluster_radius(integer()) :: float()
   def calculate_cluster_radius(zoom) do
-    # More aggressive scaling for better separation at higher zooms
-    # Zoom 1: ~5 degrees, Zoom 5: ~0.3 degrees, Zoom 8: ~0.04 degrees
-    case zoom do
-      1 -> 5.0
-      2 -> 2.5
-      3 -> 1.25
-      4 -> 0.625
-      5 -> 0.3125
-      6 -> 0.15625
-      7 -> 0.078125
-      8 -> 0.0390625
-      _ -> 0.0390625
-    end
+    Map.get(@cluster_radii, zoom, @default_radius)
   end
 
   # Filter packets with valid lat/lon coordinates