Backfill missing QSO distances during weather enqueue scan

Adds haversine_km/4 to Radio context and backfill_distances/1 which
calculates distance_km from pos1/pos2 for QSOs missing it. Called
by QsoWeatherEnqueueWorker before enqueueing weather fetches.

lib/microwaveprop/radio.ex

@@ -57,6 +57,42 @@ defmodule Microwaveprop.Radio do
     |> Repo.update_all(set: [weather_queued: true])
   end
 
+  @earth_radius_km 6371.0
+
+  def haversine_km(lat1, lon1, lat2, lon2) do
+    dlat = deg_to_rad(lat2 - lat1)
+    dlon = deg_to_rad(lon2 - lon1)
+    rlat1 = deg_to_rad(lat1)
+    rlat2 = deg_to_rad(lat2)
+
+    a =
+      :math.sin(dlat / 2) ** 2 +
+        :math.cos(rlat1) * :math.cos(rlat2) * :math.sin(dlon / 2) ** 2
+
+    2 * @earth_radius_km * :math.asin(:math.sqrt(a))
+  end
+
+  def backfill_distances(qsos) do
+    Enum.each(qsos, fn qso ->
+      if is_nil(qso.distance_km) && qso.pos1 && qso.pos2 do
+        lat1 = qso.pos1["lat"]
+        lon1 = qso.pos1["lon"] || qso.pos1["lng"]
+        lat2 = qso.pos2["lat"]
+        lon2 = qso.pos2["lon"] || qso.pos2["lng"]
+
+        if lat1 && lon1 && lat2 && lon2 do
+          dist = lat1 |> haversine_km(lon1, lat2, lon2) |> round() |> Decimal.new()
+
+          Qso
+          |> where([q], q.id == ^qso.id)
+          |> Repo.update_all(set: [distance_km: dist])
+        end
+      end
+    end)
+  end
+
+  defp deg_to_rad(deg), do: deg * :math.pi() / 180
+
   def get_qso!(id) do
     Repo.get!(Qso, id)
   end

lib/microwaveprop/workers/qso_weather_enqueue_worker.ex

@@ -14,6 +14,8 @@ defmodule Microwaveprop.Workers.QsoWeatherEnqueueWorker do
     qsos = Radio.unprocessed_qsos()
 
     if qsos != [] do
+      Radio.backfill_distances(qsos)
+
       jobs = build_weather_jobs(qsos)
 
       if jobs != [] do

test/microwaveprop/radio_test.exs

@@ -162,6 +162,48 @@ defmodule Microwaveprop.RadioTest do
     end
   end
 
+  describe "haversine_km/4" do
+    test "calculates distance between two known points" do
+      # Dallas to Austin ~roughly 295 km
+      dist = Radio.haversine_km(32.9, -97.0, 30.3, -97.7)
+      assert_in_delta dist, 295, 5
+    end
+
+    test "returns 0 for same point" do
+      assert Radio.haversine_km(32.9, -97.0, 32.9, -97.0) == 0.0
+    end
+  end
+
+  describe "backfill_distances/1" do
+    test "calculates and stores distance for QSOs missing distance_km" do
+      qso = create_qso(%{distance_km: nil})
+      assert is_nil(qso.distance_km)
+
+      Radio.backfill_distances([qso])
+
+      updated = Repo.get!(Qso, qso.id)
+      assert_in_delta Decimal.to_float(updated.distance_km), 295, 5
+    end
+
+    test "skips QSOs that already have a distance" do
+      qso = create_qso(%{distance_km: Decimal.new("100")})
+
+      Radio.backfill_distances([qso])
+
+      updated = Repo.get!(Qso, qso.id)
+      assert updated.distance_km == Decimal.new("100")
+    end
+
+    test "skips QSOs missing pos2" do
+      qso = create_qso(%{distance_km: nil, pos2: nil})
+
+      Radio.backfill_distances([qso])
+
+      updated = Repo.get!(Qso, qso.id)
+      assert is_nil(updated.distance_km)
+    end
+  end
+
   describe "get_qso!/1" do
     test "returns a QSO by ID" do
       qso = create_qso()

test/microwaveprop/workers/qso_weather_enqueue_worker_test.exs

@@ -147,6 +147,17 @@ defmodule Microwaveprop.Workers.QsoWeatherEnqueueWorkerTest do
       assert :ok = QsoWeatherEnqueueWorker.perform(%Oban.Job{args: %{}})
     end
 
+    test "backfills distance_km for QSOs missing it" do
+      _station = create_asos_station("KDFW", 32.90, -97.04)
+      qso = create_qso(%{distance_km: nil})
+
+      assert :ok = QsoWeatherEnqueueWorker.perform(%Oban.Job{args: %{}})
+
+      updated = Repo.get!(Qso, qso.id)
+      assert updated.distance_km
+      assert_in_delta Decimal.to_float(updated.distance_km), 295, 5
+    end
+
     test "skips QSOs without positions" do
       _station = create_asos_station("KDFW", 32.90, -97.04)
       _qso = create_qso(%{pos1: nil})