From a81e55e3484f8ba6cabe4005a6c0b45a08685154 Mon Sep 17 00:00:00 2001
From: Graham McIntire <graham@mcintire.me>
Date: Tue, 21 Apr 2026 09:16:01 -0500
Subject: [PATCH] refactor(propagation): drop ShadowComparator (Phase 1 only)
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Phase 2 cutover completed in 65693ed — Rust prop-grid-rs owns
f01-f18 production writes and the shadow path has been dead
for weeks. No callers in lib/, test/, or mix tasks.
---
 .../propagation/shadow_comparator.ex          | 119 ------------------
 1 file changed, 119 deletions(-)
 delete mode 100644 lib/microwaveprop/propagation/shadow_comparator.ex

diff --git a/lib/microwaveprop/propagation/shadow_comparator.ex b/lib/microwaveprop/propagation/shadow_comparator.ex
deleted file mode 100644
index 39ee2d0d..00000000
--- a/lib/microwaveprop/propagation/shadow_comparator.ex
+++ /dev/null
@@ -1,119 +0,0 @@
-defmodule Microwaveprop.Propagation.ShadowComparator do
-  @moduledoc """
-  Shadow-mode validator for the Rust `prop-grid-rs` port.
-
-  During Phase 1 shadow mode the Rust worker writes score-grid files to
-  `/data/scores_shadow/<band>/<iso>.ntms` while Elixir keeps writing to
-  `/data/scores/`. This module compares the two files and logs the
-  per-band delta distribution so drift is visible before cutover.
-
-  Callable from IEx on demand or from a one-shot Mix task; not started
-  in the supervision tree (this is temporary instrumentation).
-  """
-
-  alias Microwaveprop.Propagation.ScoresFile
-
-  require Logger
-
-  @default_prod_dir "/data/scores"
-  @default_shadow_dir "/data/scores_shadow"
-
-  @type diff :: %{
-          band_mhz: non_neg_integer(),
-          valid_time: DateTime.t(),
-          total_cells: non_neg_integer(),
-          matching_cells: non_neg_integer(),
-          missing_shadow_cells: non_neg_integer(),
-          max_abs_delta: non_neg_integer(),
-          mean_abs_delta: float()
-        }
-
-  @spec compare(non_neg_integer(), DateTime.t(), keyword()) ::
-          {:ok, diff()} | {:error, term()}
-  def compare(band_mhz, %DateTime{} = valid_time, opts \\ []) do
-    prod_dir = Keyword.get(opts, :prod_dir, @default_prod_dir)
-    shadow_dir = Keyword.get(opts, :shadow_dir, @default_shadow_dir)
-
-    with {:ok, prod} <- read_file(prod_dir, band_mhz, valid_time),
-         {:ok, shadow} <- read_file(shadow_dir, band_mhz, valid_time) do
-      {:ok, diff_payloads(band_mhz, valid_time, prod, shadow)}
-    end
-  end
-
-  defp read_file(dir, band_mhz, valid_time) do
-    path = band_mhz |> ScoresFile.path_for(valid_time) |> swap_base(dir)
-
-    case File.read(path) do
-      {:ok, binary} -> decode_scores_file(binary)
-      {:error, reason} -> {:error, {:read, path, reason}}
-    end
-  end
-
-  defp swap_base(path, new_base) do
-    suffix = Path.relative_to(path, ScoresFile.base_dir())
-    Path.join(new_base, suffix)
-  end
-
-  # Inline parse of the v1 scores-file on-disk format so this module
-  # doesn't reach into `ScoresFile`'s private `decode/1`. The format is
-  # documented in `ScoresFile`'s moduledoc; only the body size and
-  # dimensions matter for a diff, so we intentionally keep this minimal.
-  # The literal "NTMS" magic is the file-header marker already on disk.
-  defp decode_scores_file(
-         <<"NTMS", 1::unsigned-8, _band_mhz::unsigned-little-32, _valid_time_unix::signed-little-64,
-           _lat_min::float-little-32, _lon_min::float-little-32, _step::float-little-32, n_rows::unsigned-little-16,
-           n_cols::unsigned-little-16, body::binary>>
-       ) do
-    expected = n_rows * n_cols
-
-    if byte_size(body) == expected do
-      {:ok, %{n_rows: n_rows, n_cols: n_cols, scores: body}}
-    else
-      {:error, :invalid_format}
-    end
-  end
-
-  defp decode_scores_file(_), do: {:error, :invalid_format}
-
-  defp diff_payloads(band_mhz, valid_time, prod, shadow) do
-    %{scores: p_body, n_cols: n_cols, n_rows: n_rows} = prod
-    %{scores: s_body} = shadow
-
-    {total, matching, missing, max_abs, sum_abs} =
-      for row <- 0..(n_rows - 1),
-          col <- 0..(n_cols - 1),
-          reduce: {0, 0, 0, 0, 0} do
-        {t, m, miss, max_d, sum_d} ->
-          idx = row * n_cols + col
-          p = :binary.at(p_body, idx)
-          s = :binary.at(s_body, idx)
-
-          cond do
-            p == 255 and s == 255 ->
-              {t, m, miss, max_d, sum_d}
-
-            p != 255 and s == 255 ->
-              {t + 1, m, miss + 1, max_d, sum_d}
-
-            p == s ->
-              {t + 1, m + 1, miss, max_d, sum_d}
-
-            true ->
-              d = abs(p - s)
-              {t + 1, m, miss, max(max_d, d), sum_d + d}
-          end
-      end
-
-    mean = if total > 0, do: sum_abs / total, else: 0.0
-
-    %{
-      band_mhz: band_mhz,
-      valid_time: valid_time,
-      total_cells: total,
-      matching_cells: matching,
-      missing_shadow_cells: missing,
-      max_abs_delta: max_abs,
-      mean_abs_delta: mean
-    }
-  end
-end