fix: extract callsigns from MQTT topic when JSON payload omits sc/rc

Some FT8/Q65 multi-decoder spots omit sender/receiver callsigns
from the JSON payload, but the MQTT topic routing path always
carries them in positions 5 (sc) and 6 (rc):

  pskr/filter/v2/<band>/<mode>/<sc>/<rc>/<sl>/<rl>/<sa>/<ra>

Client now extracts callsigns from the topic and threads them
through Aggregator.ingest → Pskr.parse_spot, where they act as
fallback when the JSON sc/rc keys are nil or empty.

JSON payload values still take precedence when present — the topic
is only used as a safety net.

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

lib/microwaveprop/pskr.ex

@@ -73,9 +73,14 @@ defmodule Microwaveprop.Pskr do
   reported (4/6/8/10 chars) and uppercased for consistent storage.
   Returns `{:error, reason}` for any payload missing the fields we
   need — the caller should count and discard.
+
+  Callsigns are taken from the JSON payload (`sc`/`rc` keys).
+  When those keys are absent or empty (common for FT8/Q65 multi-
+  decoder spots), falls back to callsigns extracted from the MQTT
+  topic which always carries them in the routing path.
   """
-  @spec parse_spot(binary()) :: {:ok, spot()} | {:error, term()}
-  def parse_spot(payload) when is_binary(payload) do
+  @spec parse_spot(binary(), keyword()) :: {:ok, spot()} | {:error, term()}
+  def parse_spot(payload, opts \\ []) when is_binary(payload) do
     with {:ok, json} <- Jason.decode(payload),
          {:ok, sender_grid} <- fetch_grid(json, "sl"),
          {:ok, receiver_grid} <- fetch_grid(json, "rl"),
@@ -91,8 +96,12 @@ defmodule Microwaveprop.Pskr do
          transmit_time: transmit_time,
          sender_grid: sender_grid,
          receiver_grid: receiver_grid,
-         sender_callsign: normalize_callsign(Map.get(json, "sc")),
-         receiver_callsign: normalize_callsign(Map.get(json, "rc")),
+         sender_callsign:
+           normalize_callsign(Map.get(json, "sc")) ||
+             normalize_callsign(Keyword.get(opts, :sender_callsign)),
+         receiver_callsign:
+           normalize_callsign(Map.get(json, "rc")) ||
+             normalize_callsign(Keyword.get(opts, :receiver_callsign)),
          sender_country: Map.get(json, "sa"),
          receiver_country: Map.get(json, "ra")
        }}

lib/microwaveprop/pskr/aggregator.ex

@@ -41,10 +41,15 @@ defmodule Microwaveprop.Pskr.Aggregator do
     GenServer.start_link(__MODULE__, opts, name: name)
   end
 
-  @doc "Push one raw MQTT payload (binary JSON) into the accumulator."
-  @spec ingest(GenServer.server(), binary()) :: :ok
-  def ingest(server \\ __MODULE__, payload) when is_binary(payload) do
-    GenServer.cast(server, {:ingest, payload})
+  @doc """
+  Push one raw MQTT payload (binary JSON) into the accumulator.
+
+  `opts` is forwarded to `Pskr.parse_spot/2` for topic-derived
+  fallback values (e.g. callsigns when the JSON payload omits them).
+  """
+  @spec ingest(GenServer.server(), binary(), keyword()) :: :ok
+  def ingest(server \\ __MODULE__, payload, opts \\ []) when is_binary(payload) do
+    GenServer.cast(server, {:ingest, payload, opts})
   end
 
   @doc "Force a synchronous flush. Returns the number of rows written."
@@ -65,8 +70,13 @@ defmodule Microwaveprop.Pskr.Aggregator do
   end
 
   @impl true
+  # Accept both old (2-tuple) and new (3-tuple with opts) ingest messages.
   def handle_cast({:ingest, payload}, state) do
-    case Pskr.parse_spot(payload) do
+    handle_cast({:ingest, payload, []}, state)
+  end
+
+  def handle_cast({:ingest, payload, opts}, state) do
+    case Pskr.parse_spot(payload, opts) do
       {:ok, spot} ->
         key = Pskr.path_key(spot)
         rows = Map.update(state.rows, key, Pskr.merge_spot(nil, spot), &Pskr.merge_spot(&1, spot))

lib/microwaveprop/pskr/client.ex

@@ -248,12 +248,30 @@ defmodule Microwaveprop.Pskr.Client do
   # etc. before the spots ever reach us.
   defp topic_for(band), do: "pskr/filter/v2/#{band}/+/+/+/+/+/#{@us_dxcc}/#{@us_dxcc}"
 
+  # Extract sender/receiver callsigns from a received topic.
+  # Topic format: pskr/filter/v2/<band>/<mode>/<sc>/<rc>/<sl>/<rl>/<sa>/<ra>
+  # Some FT8/Q65 multi-decoder spots omit `sc`/`rc` from the JSON
+  # payload; the topic always carries them in the routing path.
+  defp topic_callsigns(topic) do
+    case String.split(topic, "/") do
+      ["pskr", "filter", "v2", _band, _mode, sc, rc | _rest] ->
+        opts = []
+        opts = if sc != "+" and sc != "", do: Keyword.put(opts, :sender_callsign, sc), else: opts
+        opts = if rc != "+" and rc != "", do: Keyword.put(opts, :receiver_callsign, rc), else: opts
+        opts
+
+      _ ->
+        []
+    end
+  end
+
   # ---------- Inbound dispatch ----------
 
   defp process_buffer(state) do
     case Mqtt.parse(state.buffer) do
-      {:ok, {:publish, _topic, payload}, rest} ->
-        Aggregator.ingest(state.aggregator, payload)
+      {:ok, {:publish, topic, payload}, rest} ->
+        opts = topic_callsigns(topic)
+        Aggregator.ingest(state.aggregator, payload, opts)
         process_buffer(%{state | buffer: rest, received: state.received + 1})
 
       {:ok, {:suback, _id, results}, rest} ->

test/microwaveprop/pskr_test.exs

@@ -231,5 +231,37 @@ defmodule Microwaveprop.PskrTest do
       assert acc.sender_callsigns == ["K5ABC"]
       assert acc.receiver_callsigns == ["K7XYZ"]
     end
+
+    test "falls back to topic-derived callsign when JSON payload omits sc/rc" do
+      # FT8/Q65 multi-decoder spots sometimes lack sc/rc in the JSON
+      # payload, but the MQTT topic always carries them.
+      payload = @sample |> Map.drop(["sc", "rc"]) |> Jason.encode!()
+      opts = [sender_callsign: "K5TOPIC", receiver_callsign: "K7TOPIC"]
+
+      {:ok, spot} = Pskr.parse_spot(payload, opts)
+
+      assert spot.sender_callsign == "K5TOPIC"
+      assert spot.receiver_callsign == "K7TOPIC"
+    end
+
+    test "prefers JSON callsign over topic fallback when both present" do
+      payload = Jason.encode!(@sample)
+      opts = [sender_callsign: "K5TOPIC", receiver_callsign: "K7TOPIC"]
+
+      {:ok, spot} = Pskr.parse_spot(payload, opts)
+
+      assert spot.sender_callsign == "K5ABC"
+      assert spot.receiver_callsign == "K7XYZ"
+    end
+
+    test "topic fallback with nil/empty JSON callsign prefers topic" do
+      payload = @sample |> Map.put("sc", "") |> Jason.encode!()
+      opts = [sender_callsign: "K5TOPIC"]
+
+      {:ok, spot} = Pskr.parse_spot(payload, opts)
+
+      assert spot.sender_callsign == "K5TOPIC"
+      assert spot.receiver_callsign == "K7XYZ"
+    end
   end
 end