prop/test/microwaveprop/propagation/pgrid_test.exs

defmodule Microwaveprop.Propagation.PgridTest do
  @moduledoc """
  The `.pgrid` reader is the Elixir half of a format shared with
  `rust/prop_grid_rs/src/pgrid.rs`. These tests build the binary by hand
  to the documented layout, which is what pins the two implementations
  together — if the Rust writer's header or field ordering drifts, the
  hand-built fixture here still asserts the contract the reader expects.
  """
  # NOT async: the setup swaps `:propagation_scores_dir` in the
  # application env, which is global. Running concurrently with other
  # tests lets them observe this suite's temp directory (and lets them
  # observe each other's), which showed up as cross-suite failures in
  # ImportLive / ContactEdit / MonitorLive as well as flaky failures here.
  use ExUnit.Case, async: false

  alias Microwaveprop.Propagation.Pgrid
  alias Microwaveprop.Propagation.ProfilesFile

  @magic "PGRD"
  @version 1
  @field_name_len 32

  @scalar_fields ~w(
    surface_temp_c surface_dewpoint_c surface_pressure_mb hpbl_m pwat_mm
    wind_u wind_v cloud_cover_pct precip_mm native_min_gradient
    best_duct_freq_ghz max_duct_thickness_m duct_count
    nexrad_max_reflectivity_dbz commercial_degradation_db
    commercial_baseline_dbm commercial_current_dbm commercial_n_links
    surface_refractivity min_refractivity_gradient
  )

  @levels [1000, 925, 850]

  setup do
    dir = Path.join(System.tmp_dir!(), "pgrid_test_#{System.unique_integer([:positive])}")
    File.mkdir_p!(Path.join(dir, "profiles"))
    prev = Application.get_env(:microwaveprop, :propagation_scores_dir)
    Application.put_env(:microwaveprop, :propagation_scores_dir, dir)

    on_exit(fn ->
      if prev,
        do: Application.put_env(:microwaveprop, :propagation_scores_dir, prev),
        else: Application.delete_env(:microwaveprop, :propagation_scores_dir)

      File.rm_rf(dir)
    end)

    {:ok, dir: dir}
  end

  defp field_names do
    @scalar_fields ++
      Enum.flat_map(@levels, fn p -> ["hght_m_#{p}mb", "tmpc_#{p}mb", "dwpc_#{p}mb"] end)
  end

  defp nan, do: <<0, 0, 192, 127>>

  # Build a .pgrid byte-for-byte per the documented layout. `cells` is a
  # map of cell_index => %{field_name => value}; everything else is NaN.
  defp build(valid_time, opts, cells) do
    names = field_names()
    n_fields = length(names)
    n_rows = Keyword.fetch!(opts, :n_rows)
    n_cols = Keyword.fetch!(opts, :n_cols)

    table =
      names
      |> Enum.map(fn n -> n <> String.duplicate(<<0>>, @field_name_len - byte_size(n)) end)
      |> IO.iodata_to_binary()

    body =
      for cell <- 0..(n_rows * n_cols - 1), name <- names, into: <<>> do
        case cells |> Map.get(cell, %{}) |> Map.get(name) do
          nil -> nan()
          v -> <<v::float-little-32>>
        end
      end

    flags = if opts[:hrdps], do: 1, else: 0
    unix = DateTime.to_unix(valid_time)
    lat_start = Keyword.fetch!(opts, :lat_start)
    lon_start = Keyword.fetch!(opts, :lon_start)

    header =
      @magic <>
        <<@version, flags, n_fields::little-16, unix::little-signed-64, lat_start::little-float-64,
          lon_start::little-float-64, 0.125::little-float-64, 0.125::little-float-64, n_rows::little-16,
          n_cols::little-16>>

    header <> table <> body
  end

  defp write!(valid_time, opts, cells) do
    path = Pgrid.path_for(valid_time)
    File.mkdir_p!(Path.dirname(path))
    File.write!(path, build(valid_time, opts, cells))
    path
  end

  defp vt, do: ~U[2026-04-19 14:00:00Z]

  defp grid_opts, do: [n_rows: 2, n_cols: 3, lat_start: 32.0, lon_start: -97.0]

  defp full_cell do
    %{
      "surface_temp_c" => 22.5,
      "surface_dewpoint_c" => 17.0,
      "surface_pressure_mb" => 1013.2,
      "hpbl_m" => 1500.0,
      "pwat_mm" => 30.0,
      "wind_u" => 3.0,
      "wind_v" => 4.0,
      "cloud_cover_pct" => 20.0,
      "precip_mm" => 0.5,
      "duct_count" => 2.0,
      "best_duct_freq_ghz" => 18.4,
      "surface_refractivity" => 320.0,
      "min_refractivity_gradient" => -150.0,
      "hght_m_1000mb" => 100.0,
      "tmpc_1000mb" => 21.0,
      "dwpc_1000mb" => 16.0,
      "hght_m_850mb" => 1500.0,
      "tmpc_850mb" => 12.75,
      "dwpc_850mb" => 7.0
    }
  end

  describe "read_point/3" do
    test "returns the cell's scalars with atom keys" do
      write!(vt(), grid_opts(), %{0 => full_cell()})

      profile = Pgrid.read_point(vt(), 32.0, -97.0)

      assert profile.surface_temp_c == 22.5
      assert profile.surface_dewpoint_c == 17.0
      # `.pgrid` stores f32, so values that aren't exactly representable
      # come back with ~7 significant digits (1013.2 -> 1013.2000122).
      # The source GRIB2 data is f32 anyway, and HRRR surface pressure is
      # good to ~0.1 mb, so this is below the noise floor of the input.
      assert_in_delta profile.surface_pressure_mb, 1013.2, 0.001
      assert profile.hpbl_m == 1500.0
      assert profile.pwat_mm == 30.0
      assert profile.wind_u == 3.0
      assert profile.cloud_cover_pct == 20.0
      assert profile.surface_refractivity == 320.0
      assert profile.min_refractivity_gradient == -150.0
    end

    test "duct_count comes back as an integer, matching the msgpack shape" do
      write!(vt(), grid_opts(), %{0 => full_cell()})
      assert Pgrid.read_point(vt(), 32.0, -97.0).duct_count === 2
    end

    test "rebuilds the pressure-level profile list, skipping absent levels" do
      write!(vt(), grid_opts(), %{0 => full_cell()})

      profile = Pgrid.read_point(vt(), 32.0, -97.0)

      # 925 mb was never written, so it must not appear.
      assert [l1000, l850] = profile.profile
      assert l1000.pres_mb == 1000.0
      assert l1000.hght_m == 100.0
      assert l1000.tmpc == 21.0
      assert l1000.dwpc == 16.0
      assert l850.pres_mb == 850.0
      assert l850.tmpc == 12.75
    end

    test "a level with height and temperature but no dewpoint omits :dwpc" do
      cell = Map.drop(full_cell(), ["dwpc_1000mb", "hght_m_850mb", "tmpc_850mb", "dwpc_850mb"])
      write!(vt(), grid_opts(), %{0 => cell})

      assert [level] = Pgrid.read_point(vt(), 32.0, -97.0).profile
      assert level.tmpc == 21.0
      refute Map.has_key?(level, :dwpc)
    end

    test "NaN fields are absent rather than surfacing as NaN" do
      # Only surface temp written; everything else is the NaN sentinel.
      write!(vt(), grid_opts(), %{0 => %{"surface_temp_c" => 10.0}})

      profile = Pgrid.read_point(vt(), 32.0, -97.0)

      assert profile.surface_temp_c == 10.0
      refute Map.has_key?(profile, :pwat_mm)
      refute Map.has_key?(profile, :hpbl_m)
      refute Map.has_key?(profile, :profile)
    end

    test "reconstructs the nested commercial_link_degradation map" do
      cell =
        Map.merge(full_cell(), %{
          "commercial_degradation_db" => 6.5,
          "commercial_baseline_dbm" => -45.0,
          "commercial_current_dbm" => -51.5,
          "commercial_n_links" => 3.0
        })

      write!(vt(), grid_opts(), %{0 => cell})

      assert %{
               degradation_db: 6.5,
               baseline_dbm: -45.0,
               current_dbm: -51.5,
               n_links: 3
             } = Pgrid.read_point(vt(), 32.0, -97.0).commercial_link_degradation
    end

    test "commercial_* fields are not surfaced at the top level" do
      write!(vt(), grid_opts(), %{0 => full_cell()})
      profile = Pgrid.read_point(vt(), 32.0, -97.0)
      refute Map.has_key?(profile, :commercial_degradation_db)
      refute Map.has_key?(profile, :commercial_link_degradation)
    end

    test "addresses the correct cell for a non-origin coordinate" do
      # cell 4 => row 1, col 1 => lat 32.125, lon -96.875
      write!(vt(), grid_opts(), %{4 => %{"surface_temp_c" => 99.0}})

      assert Pgrid.read_point(vt(), 32.125, -96.875).surface_temp_c == 99.0
      assert Pgrid.read_point(vt(), 32.0, -97.0) == nil
    end

    test "returns nil outside the grid and for a missing file" do
      write!(vt(), grid_opts(), %{0 => full_cell()})

      assert Pgrid.read_point(vt(), 10.0, -97.0) == nil
      assert Pgrid.read_point(vt(), 32.0, -150.0) == nil
      assert Pgrid.read_point(~U[2026-04-19 15:00:00Z], 32.0, -97.0) == nil
    end

    test "an unpopulated cell reads as nil, not an empty map" do
      write!(vt(), grid_opts(), %{0 => full_cell()})
      assert Pgrid.read_point(vt(), 32.125, -96.875) == nil
    end
  end

  describe "read/1" do
    test "returns only populated cells, keyed by snapped lat/lon" do
      write!(vt(), grid_opts(), %{
        0 => %{"surface_temp_c" => 1.0},
        5 => %{"surface_temp_c" => 2.0}
      })

      assert {:ok, grid} = Pgrid.read(vt())
      assert map_size(grid) == 2
      assert grid[{32.0, -97.0}].surface_temp_c == 1.0
      # cell 5 => row 1, col 2 => lat 32.125, lon -96.75
      assert grid[{32.125, -96.75}].surface_temp_c == 2.0
    end

    test "returns :enoent for a missing file" do
      assert Pgrid.read(vt()) == {:error, :enoent}
    end

    test "rejects a file with the wrong magic" do
      path = Pgrid.path_for(vt())
      File.mkdir_p!(Path.dirname(path))
      bin = build(vt(), grid_opts(), %{0 => full_cell()})
      File.write!(path, "XXXX" <> binary_part(bin, 4, byte_size(bin) - 4))

      assert Pgrid.read(vt()) == {:error, :enoent}
    end
  end

  describe "header" do
    test "carries the hrdps flag and grid geometry" do
      bin = build(vt(), Keyword.put(grid_opts(), :hrdps, true), %{})
      assert {:ok, header} = Pgrid.parse_header(bin)
      assert header.hrdps?
      assert header.valid_time == vt()
      assert header.n_rows == 2
      assert header.n_cols == 3
      assert header.lat_start == 32.0
    end

    test "rejects an unknown version" do
      bin = build(vt(), grid_opts(), %{})
      bumped = binary_part(bin, 0, 4) <> <<99>> <> binary_part(bin, 5, byte_size(bin) - 5)
      assert Pgrid.parse_header(bumped) == :error
    end
  end

  describe "ProfilesFile integration" do
    test "read_point/3 prefers .pgrid and returns the same shape" do
      write!(vt(), grid_opts(), %{0 => full_cell()})

      profile = ProfilesFile.read_point(vt(), 32.0, -97.0)

      assert profile.surface_temp_c == 22.5
      # Same nested shape the `.mp.gz` reader produced, so Skew-T and
      # PathCompute consumers need no change.
      assert [%{pres_mb: 1000.0, tmpc: 21.0}, %{pres_mb: 850.0}] = profile.profile
    end

    test "read_point/3 snaps an off-grid coordinate to the nearest cell" do
      write!(vt(), grid_opts(), %{0 => full_cell()})

      # 31.98 / -96.99 snap to 32.0 / -97.0.
      assert ProfilesFile.read_point(vt(), 31.98, -96.99).surface_temp_c == 22.5
    end

    test "list_valid_times/0 discovers .pgrid files" do
      write!(vt(), grid_opts(), %{0 => full_cell()})
      write!(~U[2026-04-19 15:00:00Z], grid_opts(), %{0 => full_cell()})

      times = ProfilesFile.list_valid_times()

      assert vt() in times
      assert ~U[2026-04-19 15:00:00Z] in times
    end

    test "retain_window/2 prunes .pgrid files outside the window" do
      write!(vt(), grid_opts(), %{0 => full_cell()})
      write!(~U[2026-04-19 20:00:00Z], grid_opts(), %{0 => full_cell()})

      # Keep [14:00, 15:00] — the 20:00 file falls outside.
      assert ProfilesFile.retain_window(vt(), 1) == 1
      assert File.exists?(Pgrid.path_for(vt()))
      refute File.exists?(Pgrid.path_for(~U[2026-04-19 20:00:00Z]))
    end
  end
end