refactor: deduplicate hrrr download, simplify radio/mqtt, fix credo/perf issues

- hrrr_client: extract shared fetch_grib_ranges/2 to eliminate ~80% duplicated code
- mqtt: encode_varint/1 uses IO list accumulator instead of O(n^2) binary concat
- commercial: single-pass reduce for aggregate_degradation, remove unused average/1
- scorer: single-pass reduce for safe_avg and build_path_conditions
- terrain_analysis: split 76-line do_analyse/4 into 3 focused functions
- radio: build_position_changes/3 simplified from then-chains to Enum.reduce
- recalibrator_test: fix credo warning (length > 0 -> != [])

lib/microwaveprop/commercial.ex

@@ -102,14 +102,19 @@ defmodule Microwaveprop.Commercial do
   defp aggregate_degradation([]), do: nil
 
   defp aggregate_degradation(list) do
-    baseline_avg = average(Enum.map(list, & &1.baseline_dbm))
-    current_avg = average(Enum.map(list, & &1.current_dbm))
+    {baseline_total, current_total, count} =
+      Enum.reduce(list, {0.0, 0.0, 0}, fn item, {bt, ct, c} ->
+        {bt + item.baseline_dbm, ct + item.current_dbm, c + 1}
+      end)
+
+    baseline_avg = baseline_total / count
+    current_avg = current_total / count
 
     %{
       degradation_db: Float.round(baseline_avg - current_avg, 2),
       baseline_dbm: Float.round(baseline_avg, 2),
       current_dbm: Float.round(current_avg, 2),
-      n_links: length(list)
+      n_links: count
     }
   end
 
@@ -172,9 +177,6 @@ defmodule Microwaveprop.Commercial do
   # which module asked.
   defp haversine_km(lat1, lon1, lat2, lon2), do: Microwaveprop.Radio.haversine_km(lat1, lon1, lat2, lon2)
 
-  defp average([]), do: 0.0
-  defp average(list), do: Enum.sum(list) / length(list)
-
   @spec create_link(map()) :: {:ok, Link.t()} | {:error, Ecto.Changeset.t()}
   def create_link(attrs) do
     %Link{}

lib/microwaveprop/propagation/scorer.ex

@@ -638,8 +638,10 @@ defmodule Microwaveprop.Propagation.Scorer do
 
   defp build_path_conditions(%{temps: temps, dewpoints: dewpoints} = buckets, contact) do
     lon = contact.pos1["lon"] || -97.0
-    avg_temp_c = Enum.sum(temps) / length(temps)
-    avg_dewpoint_c = Enum.sum(dewpoints) / length(dewpoints)
+    {sum_t, count_t} = Enum.reduce(temps, {0, 0}, fn x, {s, c} -> {s + x, c + 1} end)
+    avg_temp_c = sum_t / count_t
+    {sum_d, count_d} = Enum.reduce(dewpoints, {0, 0}, fn x, {s, c} -> {s + x, c + 1} end)
+    avg_dewpoint_c = sum_d / count_d
 
     %{
       abs_humidity: absolute_humidity(avg_temp_c, avg_dewpoint_c),
@@ -661,5 +663,9 @@ defmodule Microwaveprop.Propagation.Scorer do
   end
 
   defp safe_avg([]), do: nil
-  defp safe_avg(list), do: Enum.sum(list) / length(list)
+
+  defp safe_avg(list) do
+    {sum, count} = Enum.reduce(list, {0, 0}, fn x, {s, c} -> {s + x, c + 1} end)
+    sum / count
+  end
 end

lib/microwaveprop/pskr/mqtt.ex

@@ -152,10 +152,16 @@ defmodule Microwaveprop.Pskr.Mqtt do
 
   @doc false
   @spec encode_varint(non_neg_integer()) :: binary()
-  def encode_varint(n) when n in 0..127, do: <<n>>
+  def encode_varint(n) do
+    n
+    |> encode_varint_io([])
+    |> IO.iodata_to_binary()
+  end
 
-  def encode_varint(n) when n <= 268_435_455 do
-    <<(n &&& 0x7F) ||| 0x80>> <> encode_varint(n >>> 7)
+  defp encode_varint_io(n, acc) when n <= 127, do: [acc, <<n>>]
+
+  defp encode_varint_io(n, acc) when n <= 268_435_455 do
+    encode_varint_io(n >>> 7, [acc, <<(n &&& 0x7F) ||| 0x80>>])
   end
 
   @doc false

lib/microwaveprop/radio.ex

@@ -559,11 +559,8 @@ defmodule Microwaveprop.Radio do
   defp compute_distance(_pos1, _pos2, existing_distance), do: existing_distance
 
   defp build_position_changes(contact, pos1, pos2, distance) do
-    %{}
-    |> then(fn c -> if pos1 && is_nil(contact.pos1), do: Map.put(c, :pos1, pos1), else: c end)
-    |> then(fn c -> if pos2 && is_nil(contact.pos2), do: Map.put(c, :pos2, pos2), else: c end)
-    |> then(fn c ->
-      if distance && is_nil(contact.distance_km), do: Map.put(c, :distance_km, distance), else: c
+    Enum.reduce([pos1: pos1, pos2: pos2, distance_km: distance], %{}, fn {key, val}, acc ->
+      if val && is_nil(Map.get(contact, key)), do: Map.put(acc, key, val), else: acc
     end)
   end
 

lib/microwaveprop/terrain/terrain_analysis.ex

@@ -68,63 +68,18 @@ defmodule Microwaveprop.Terrain.TerrainAnalysis do
 
     lambda_m = 0.3 / freq_ghz
     n = length(profile) - 1
+    elev1 = hd(profile).elev + ant_ht_a
+    elev2 = List.last(profile).elev + ant_ht_b
 
-    first = hd(profile)
-    last = List.last(profile)
-    elev1 = first.elev + ant_ht_a
-    elev2 = last.elev + ant_ht_b
-
-    # Build effective profile with earth curvature correction
-    points =
-      profile
-      |> Enum.with_index()
-      |> Enum.map(fn {p, i} ->
-        frac = i / n
-        d1_m = frac * dist_km * 1000
-        d2_m = (1 - frac) * dist_km * 1000
-
-        beam = beam_height(frac, elev1, elev2)
-        bulge = earth_bulge(frac, dist_km, k)
-        eff_terrain = p.elev + bulge
-        r1 = fresnel_radius(d1_m, d2_m, lambda_m)
-        clearance = beam - eff_terrain
-        f1_clear = if r1 > 0, do: clearance - r1, else: clearance
-
-        is_endpoint = i == 0 or i == n
-
-        %{
-          lat: p.lat,
-          lon: p.lon,
-          d: p.d,
-          elev: p.elev,
-          dist_km: p.dist_km,
-          idx: i,
-          beam: beam,
-          eff_terrain: eff_terrain,
-          bulge: bulge,
-          r1: r1,
-          d1_m: d1_m,
-          d2_m: d2_m,
-          clearance: clearance,
-          f1_clear: f1_clear,
-          obstructed: not is_endpoint and clearance < 0,
-          fresnel_penetrated: not is_endpoint and r1 > 0 and f1_clear < 0 and clearance >= 0
-        }
-      end)
-
+    points = build_analysis_points(profile, n, dist_km, lambda_m, k, elev1, elev2)
     interior = Enum.slice(points, 1..-2//1)
+
     obstructed = Enum.filter(interior, & &1.obstructed)
     fresnel_hit = Enum.filter(interior, & &1.fresnel_penetrated)
-
-    # Deygout diffraction: compute loss across all interior points
     diffraction_db = deygout_diffraction(interior, lambda_m)
-
     verdict = classify_verdict(diffraction_db, obstructed, fresnel_hit)
 
-    elev_vals = Enum.map(profile, & &1.elev)
-    clearance_vals = Enum.map(interior, & &1.clearance)
-    max_elevation_m = Enum.max(elev_vals, fn -> 0.0 end)
-    min_clearance_m = if clearance_vals == [], do: 999.0, else: Enum.min(clearance_vals)
+    {max_elevation_m, min_clearance_m} = compute_terrain_summary(profile, interior)
 
     %{
       points: points,
@@ -138,6 +93,56 @@ defmodule Microwaveprop.Terrain.TerrainAnalysis do
     }
   end
 
+  defp build_analysis_points(profile, n, dist_km, lambda_m, k, elev1, elev2) do
+    profile
+    |> Enum.with_index()
+    |> Enum.map(fn {p, i} ->
+      frac = i / n
+      d1_m = frac * dist_km * 1000
+      d2_m = (1 - frac) * dist_km * 1000
+
+      beam = beam_height(frac, elev1, elev2)
+      bulge = earth_bulge(frac, dist_km, k)
+      r1 = fresnel_radius(d1_m, d2_m, lambda_m)
+      clearance = beam - (p.elev + bulge)
+
+      is_endpoint = i == 0 or i == n
+
+      f1_clear = if r1 > 0, do: clearance - r1, else: clearance
+
+      %{
+        lat: p.lat,
+        lon: p.lon,
+        d: p.d,
+        elev: p.elev,
+        dist_km: p.dist_km,
+        idx: i,
+        beam: beam,
+        eff_terrain: p.elev + bulge,
+        bulge: bulge,
+        r1: r1,
+        d1_m: d1_m,
+        d2_m: d2_m,
+        clearance: clearance,
+        f1_clear: f1_clear,
+        obstructed: not is_endpoint and clearance < 0,
+        fresnel_penetrated: not is_endpoint and r1 > 0 and f1_clear < 0 and clearance >= 0
+      }
+    end)
+  end
+
+  defp compute_terrain_summary(profile, interior) do
+    max_elevation_m = Enum.reduce(profile, 0.0, fn p, acc -> max(p.elev, acc) end)
+
+    min_clearance_m =
+      case interior do
+        [] -> 999.0
+        _ -> Enum.reduce(interior, :infinity, fn p, acc -> min(p.clearance, acc) end)
+      end
+
+    {max_elevation_m, min_clearance_m}
+  end
+
   @doc "First Fresnel zone radius at a point between two antennas."
   @spec fresnel_radius(number(), number(), number()) :: number()
   def fresnel_radius(d1_m, d2_m, lambda_m) do

lib/microwaveprop/weather/hrrr_client.ex

@@ -134,10 +134,9 @@ defmodule Microwaveprop.Weather.HrrrClient do
 
         {:ok, profiles}
 
-      {:error, reason} = error ->
+      {:error, _reason} = error ->
         # Drain the pressure task so it doesn't leak past this scope.
         _ = Task.await(prs_task, 20 * 60 * 1000)
-        _ = reason
         error
     end
   end
@@ -540,46 +539,11 @@ defmodule Microwaveprop.Weather.HrrrClient do
   def download_grib_ranges_to_file(_url, [], _dest_path), do: :ok
 
   def download_grib_ranges_to_file(url, ranges, dest_path) do
-    # Fetch ranges concurrently — Range requests against the HRRR
-    # mirror are independent and typically complete in ~200-500ms each
-    # when sequential. With 40+ ranges per native-duct fetch, serial
-    # download dominated the per-forecast-hour wall time. 8-way
-    # parallelism drops a 20s download to ~3s while still respecting
-    # the mirror's modest connection concurrency. Routed through the
-    # partitioned Task.Supervisor to avoid contention when the hourly
-    # PropagationGridWorker fetches f00-f18 alongside recalibrator/GEFS.
-    merged = merge_ranges(ranges)
-    supervisor = {:via, PartitionSupervisor, {Microwaveprop.TaskSupervisor, self()}}
+    case fetch_grib_ranges(url, ranges) do
+      {:error, _} = error ->
+        error
 
-    results =
-      supervisor
-      |> Task.Supervisor.async_stream_nolink(
-        merged,
-        fn {start, stop} ->
-          case Req.get(url, [{:headers, [{"Range", "bytes=#{start}-#{stop}"}]} | req_options()]) do
-            {:ok, %{status: 206, body: body}} -> {:ok, start, body}
-            {:ok, %{status: status}} -> {:error, "HRRR grib HTTP #{status}"}
-            {:error, reason} -> {:error, reason}
-          end
-        end,
-        max_concurrency: 8,
-        timeout: 120_000
-      )
-      |> Enum.map(fn
-        {:ok, result} ->
-          result
-
-        {:exit, reason} ->
-          Logger.error("HRRR grib range download crashed (to_file): url=#{url} reason=#{inspect(reason)}")
-
-          {:error, reason}
-      end)
-
-    case Enum.find(results, &match?({:error, _}, &1)) do
-      {:error, reason} ->
-        {:error, reason}
-
-      nil ->
+      {:ok, results} ->
         file = File.open!(dest_path, [:write, :binary])
 
         try do
@@ -595,13 +559,25 @@ defmodule Microwaveprop.Weather.HrrrClient do
   end
 
   defp download_grib_ranges_remote(url, ranges) do
-    # Merge adjacent/overlapping ranges to reduce HTTP requests
+    case fetch_grib_ranges(url, ranges) do
+      {:error, _} = error ->
+        error
+
+      {:ok, results} ->
+        binary =
+          results
+          |> Enum.sort_by(fn {:ok, offset, _} -> offset end)
+          |> Enum.map(fn {:ok, _, body} -> body end)
+          |> IO.iodata_to_binary()
+
+        {:ok, binary}
+    end
+  end
+
+  defp fetch_grib_ranges(url, ranges) do
     merged = merge_ranges(ranges)
     supervisor = {:via, PartitionSupervisor, {Microwaveprop.TaskSupervisor, self()}}
 
-    # Download ranges in parallel, routed through the partitioned
-    # Task.Supervisor so concurrent f00-f18 fetches do not serialize on
-    # a single supervisor PID.
     results =
       supervisor
       |> Task.Supervisor.async_stream_nolink(
@@ -622,23 +598,13 @@ defmodule Microwaveprop.Weather.HrrrClient do
 
         {:exit, reason} ->
           Logger.error("HRRR grib range download crashed: url=#{url} reason=#{inspect(reason)}")
-
           {:error, reason}
       end)
 
-    # Sort by offset and concatenate
-    case Enum.find(results, &match?({:error, _}, &1)) do
-      {:error, reason} ->
-        {:error, reason}
-
-      nil ->
-        binary =
-          results
-          |> Enum.sort_by(fn {:ok, offset, _} -> offset end)
-          |> Enum.map(fn {:ok, _, body} -> body end)
-          |> IO.iodata_to_binary()
-
-        {:ok, binary}
+    if error = Enum.find(results, &match?({:error, _}, &1)) do
+      error
+    else
+      {:ok, results}
     end
   end
 

test/microwaveprop/pskr/recalibrator_test.exs

@@ -74,7 +74,7 @@ defmodule Microwaveprop.Pskr.RecalibratorTest do
       assert run.avg_spots_per_sample > 0
 
       bins = Repo.all(from(fb in FeatureBin, where: fb.run_id == ^run.id))
-      assert length(bins) > 0
+      assert bins != []
 
       # Every bin row should reference the run, target this band, and
       # carry non-negative stats.