prop/test/microwaveprop/weather/gefs_client_test.exs

defmodule Microwaveprop.Weather.GefsClientTest do
  use ExUnit.Case, async: true
  use ExUnitProperties

  alias Microwaveprop.Weather.GefsClient

  describe "nearest_run/1" do
    test "rounds down to the same 6-hour cycle within the cycle window" do
      assert GefsClient.nearest_run(~U[2026-04-18 13:30:00Z]) == ~U[2026-04-18 12:00:00Z]
    end

    test "snaps to 00Z when given 02:15" do
      assert GefsClient.nearest_run(~U[2026-04-18 02:15:00Z]) == ~U[2026-04-18 00:00:00Z]
    end

    test "snaps to 18Z when given 23:59" do
      assert GefsClient.nearest_run(~U[2026-04-18 23:59:00Z]) == ~U[2026-04-18 18:00:00Z]
    end

    test "is a no-op when already on a cycle boundary" do
      assert GefsClient.nearest_run(~U[2026-04-18 06:00:00Z]) == ~U[2026-04-18 06:00:00Z]
    end
  end

  describe "ensmean_url/3" do
    test "builds a pgrb2ap5 ensemble-mean URL for a run + forecast hour" do
      url = GefsClient.ensmean_url(~D[2026-04-18], 12, 24)

      assert url ==
               "https://nomads.ncep.noaa.gov/pub/data/nccf/com/gens/prod/gefs.20260418/12/atmos/pgrb2ap5/geavg.t12z.pgrb2a.0p50.f024"
    end

    test "pads forecast hour to three digits" do
      url = GefsClient.ensmean_url(~D[2026-04-18], 0, 6)
      assert String.ends_with?(url, "geavg.t00z.pgrb2a.0p50.f006")
    end

    test "handles 240-hour forecast horizon" do
      url = GefsClient.ensmean_url(~D[2026-04-18], 12, 240)
      assert String.ends_with?(url, "geavg.t12z.pgrb2a.0p50.f240")
    end

    test "pads single-digit runs" do
      url = GefsClient.ensmean_url(~D[2026-04-18], 6, 24)
      assert String.contains?(url, "/06/atmos/")
      assert String.contains?(url, "geavg.t06z.")
    end
  end

  describe "idx_url/1" do
    test "appends .idx to the GRIB2 URL" do
      base = GefsClient.ensmean_url(~D[2026-04-18], 12, 24)
      assert GefsClient.idx_url(base) == base <> ".idx"
    end
  end

  describe "forecast_hours/0" do
    test "returns 3-hourly hours out to 240 then 6-hourly to 384" do
      hours = GefsClient.forecast_hours()
      assert Enum.take(hours, 4) == [0, 3, 6, 9]
      assert 240 in hours
      assert 246 in hours
      assert 384 in hours
      assert List.last(hours) == 384
      refute 243 in hours
    end
  end

  describe "surface_messages/0" do
    test "lists the variables the scorer needs from the pgrb2a file" do
      msgs = GefsClient.surface_messages()

      vars = Enum.map(msgs, & &1.var)
      assert "TMP" in vars
      assert "RH" in vars
      assert "PRES" in vars
      assert "PWAT" in vars
      assert "UGRD" in vars
      assert "VGRD" in vars
      assert "TCDC" in vars
      assert "APCP" in vars
    end

    test "2m TMP and RH use the '2 m above ground' level string" do
      msgs = GefsClient.surface_messages()

      assert %{var: "TMP", level: "2 m above ground"} in msgs
      assert %{var: "RH", level: "2 m above ground"} in msgs
    end

    test "10m winds use the '10 m above ground' level string" do
      msgs = GefsClient.surface_messages()

      assert %{var: "UGRD", level: "10 m above ground"} in msgs
      assert %{var: "VGRD", level: "10 m above ground"} in msgs
    end
  end

  describe "build_profile/1" do
    @raw %{
      "TMP:2 m above ground" => 293.15,
      "RH:2 m above ground" => 50.0,
      "PRES:surface" => 101_325.0,
      "PWAT:entire atmosphere (considered as a single layer)" => 25.4,
      "UGRD:10 m above ground" => 3.0,
      "VGRD:10 m above ground" => -1.5,
      "TCDC:entire atmosphere" => 62.0,
      "APCP:surface" => 0.0,
      "TMP:1000 mb" => 293.15,
      "RH:1000 mb" => 50.0,
      "HGT:1000 mb" => 110.0,
      "TMP:925 mb" => 288.15,
      "RH:925 mb" => 40.0,
      "HGT:925 mb" => 780.0
    }

    test "converts surface TMP from Kelvin to Celsius" do
      p = GefsClient.build_profile(@raw)
      assert_in_delta p.surface_temp_c, 20.0, 0.01
    end

    test "converts surface PRES from Pa to mb" do
      p = GefsClient.build_profile(@raw)
      assert_in_delta p.surface_pressure_mb, 1013.25, 0.1
    end

    test "derives surface dewpoint from RH via Magnus" do
      p = GefsClient.build_profile(@raw)
      assert_in_delta p.surface_dewpoint_c, 9.27, 0.3
    end

    test "carries PWAT, winds, cloud cover, precip through untouched" do
      p = GefsClient.build_profile(@raw)
      assert p.pwat_mm == 25.4
      assert p.wind_u == 3.0
      assert p.wind_v == -1.5
      assert p.cloud_cover_pct == 62.0
      assert p.precip_mm == 0.0
    end

    test "builds a pressure-level profile with Td derived from RH at each level" do
      p = GefsClient.build_profile(@raw)
      assert length(p.profile) == 2

      l1000 = Enum.find(p.profile, &(&1["pres"] == 1000.0))
      assert_in_delta l1000["tmpc"], 20.0, 0.01
      assert_in_delta l1000["dwpc"], 9.27, 0.3
      assert l1000["hght"] == 110.0

      l925 = Enum.find(p.profile, &(&1["pres"] == 925.0))
      assert_in_delta l925["tmpc"], 15.0, 0.01
      assert l925["dwpc"] < l925["tmpc"]
    end

    test "falls back to the lowest pressure-level values when surface fields are missing" do
      raw = %{
        "TMP:1000 mb" => 293.15,
        "RH:1000 mb" => 60.0,
        "HGT:1000 mb" => 100.0
      }

      p = GefsClient.build_profile(raw)
      assert_in_delta p.surface_temp_c, 20.0, 0.01
      assert is_float(p.surface_dewpoint_c)
      assert p.surface_pressure_mb == nil
    end

    test "skips pressure levels that lack TMP or HGT" do
      raw =
        Map.drop(@raw, [
          "TMP:925 mb",
          "RH:925 mb",
          "HGT:925 mb"
        ])

      p = GefsClient.build_profile(raw)
      pressures = Enum.map(p.profile, & &1["pres"])
      assert 1000.0 in pressures
      refute 925.0 in pressures
    end
  end

  describe "dewpoint_from_rh/2" do
    test "returns the input temperature when RH is 100%" do
      # At saturation, Td == T. Magnus returns T exactly.
      assert_in_delta GefsClient.dewpoint_from_rh(20.0, 100.0), 20.0, 0.05
    end

    test "returns a cooler dewpoint than temperature when RH is below saturation" do
      td = GefsClient.dewpoint_from_rh(25.0, 50.0)
      assert td < 25.0
      # Tables put Td(25 °C, 50% RH) at ~13.9 °C. Allow ±0.5 °C slack.
      assert_in_delta td, 13.9, 0.5
    end

    test "handles very dry air without crashing" do
      td = GefsClient.dewpoint_from_rh(30.0, 5.0)
      assert is_float(td)
      assert td < 0.0
    end

    test "clamps RH<=0 to a very-dry fallback rather than returning NaN/Inf" do
      td = GefsClient.dewpoint_from_rh(10.0, 0.0)
      assert is_float(td)
      assert td < -30.0
    end

    property "Td is never greater than T (physics floor)" do
      check all(
              temp_c <- float(min: -40.0, max: 50.0),
              rh_pct <- float(min: 0.01, max: 100.0)
            ) do
        td = GefsClient.dewpoint_from_rh(temp_c, rh_pct)
        # Magnus formula: at RH=100 Td≈T; below saturation Td < T.
        # Allow 1.0 °C slack for the Magnus approximation near
        # saturation at the extremes of the temperature range.
        assert td <= temp_c + 1.0
      end
    end

    property "Td increases monotonically with RH at fixed T" do
      check all(
              temp_c <- float(min: -20.0, max: 40.0),
              rh_low <- float(min: 1.0, max: 50.0),
              rh_delta <- float(min: 1.0, max: 50.0)
            ) do
        rh_high = min(rh_low + rh_delta, 100.0)
        td_low = GefsClient.dewpoint_from_rh(temp_c, rh_low)
        td_high = GefsClient.dewpoint_from_rh(temp_c, rh_high)

        assert td_low <= td_high
      end
    end

    property "is always finite for any positive RH in [0.01, 100]" do
      check all(
              temp_c <- float(min: -50.0, max: 60.0),
              rh_pct <- float(min: 0.01, max: 100.0)
            ) do
        td = GefsClient.dewpoint_from_rh(temp_c, rh_pct)
        assert is_float(td)
        # The bound checks also screen out NaN and ±Inf since both
        # `NaN < 1000.0` and `NaN > -1000.0` return false in Elixir.
        assert td > -1000.0
        assert td < 1000.0
      end
    end
  end

  describe "fetch_grid_profiles/3 error paths" do
    test "idx HTTP 500 returns {:error, _} with status in the message" do
      Req.Test.stub(GefsClient, fn conn ->
        Plug.Conn.send_resp(conn, 500, "boom")
      end)

      assert {:error, msg} = GefsClient.fetch_grid_profiles(~D[2026-04-18], 12, 24)
      assert is_binary(msg)
      assert msg =~ "HTTP 500"
    end

    test "idx HTTP 404 returns {:error, _}" do
      Req.Test.stub(GefsClient, fn conn ->
        Plug.Conn.send_resp(conn, 404, "not found")
      end)

      assert {:error, msg} = GefsClient.fetch_grid_profiles(~D[2026-04-18], 12, 24)
      assert msg =~ "HTTP 404"
    end

    test "idx transport timeout returns {:error, _}" do
      Req.Test.stub(GefsClient, fn conn ->
        Req.Test.transport_error(conn, :timeout)
      end)

      assert {:error, reason} = GefsClient.fetch_grid_profiles(~D[2026-04-18], 12, 24)
      assert reason
    end

    test "malformed idx body is parsed as empty and surfaces a wgrib2/extraction error rather than raising" do
      # Non-idx-looking body causes HrrrClient.parse_idx to return [],
      # then byte_ranges_for_messages -> [], then download_grib_ranges
      # returns {:ok, <<>>}, and wgrib2 extraction fails on empty input.
      # The important invariant is that the pipeline surfaces an error
      # tuple — it must not raise.
      Req.Test.stub(GefsClient, fn conn ->
        Plug.Conn.send_resp(conn, 200, "<html>not idx</html>")
      end)

      result = GefsClient.fetch_grid_profiles(~D[2026-04-18], 12, 24)
      assert match?({:error, _}, result) or match?({:ok, _}, result)
    end
  end

  describe "ensmean_url/3 round-trip property" do
    property "date, run hour and forecast hour all appear in the built URL" do
      check all(
              year <- integer(2022..2030),
              month <- integer(1..12),
              day <- integer(1..28),
              run_hour <- member_of([0, 6, 12, 18]),
              forecast_hour <- integer(0..384)
            ) do
        {:ok, date} = Date.new(year, month, day)
        url = GefsClient.ensmean_url(date, run_hour, forecast_hour)

        date_str =
          [year, month, day]
          |> Enum.zip([4, 2, 2])
          |> Enum.map_join(fn {n, w} -> n |> Integer.to_string() |> String.pad_leading(w, "0") end)

        hh = run_hour |> Integer.to_string() |> String.pad_leading(2, "0")
        fff = forecast_hour |> Integer.to_string() |> String.pad_leading(3, "0")

        assert String.contains?(url, "gefs.#{date_str}")
        assert String.contains?(url, "/#{hh}/atmos/pgrb2ap5/")
        assert String.contains?(url, "geavg.t#{hh}z.pgrb2a.0p50.f#{fff}")
      end
    end
  end

  describe "nearest_run/1 property" do
    property "is idempotent and output hour is in {0, 6, 12, 18}" do
      check all(
              year <- integer(2020..2030),
              month <- integer(1..12),
              day <- integer(1..28),
              hour <- integer(0..23),
              minute <- integer(0..59),
              second <- integer(0..59)
            ) do
        dt = %DateTime{
          year: year,
          month: month,
          day: day,
          hour: hour,
          minute: minute,
          second: second,
          microsecond: {0, 0},
          std_offset: 0,
          utc_offset: 0,
          zone_abbr: "UTC",
          time_zone: "Etc/UTC"
        }

        once = GefsClient.nearest_run(dt)
        twice = GefsClient.nearest_run(once)

        assert DateTime.compare(once, twice) == :eq
        assert once.hour in [0, 6, 12, 18]
        assert once.minute == 0
        assert once.second == 0
      end
    end
  end

  describe "dewpoint_from_rh/2 edge cases" do
    test "handles 0% RH by clamping to a small positive value" do
      result = GefsClient.dewpoint_from_rh(25.0, 0.0)
      assert is_float(result)
      assert result < 25.0
    end

    test "100% RH at 25°C returns ~25°C dewpoint" do
      result = GefsClient.dewpoint_from_rh(25.0, 100.0)
      assert_in_delta result, 25.0, 0.5
    end

    test "50% RH at 25°C returns dewpoint below 25°C" do
      result = GefsClient.dewpoint_from_rh(25.0, 50.0)
      assert result < 25.0
      assert result > 10.0
    end
  end

  describe "fetch_grid_profiles/3 with injected http_get" do
    setup do
      prev = Application.get_env(:microwaveprop, :gefs_http_get)

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

      :ok
    end

    test "returns error when idx fetch fails" do
      Application.put_env(:microwaveprop, :gefs_http_get, fn _url, _opts ->
        {:error, :timeout}
      end)

      assert {:error, _} = GefsClient.fetch_grid_profiles(~D[2026-04-18], 12, 0)
    end

    test "returns error when idx returns non-200" do
      Application.put_env(:microwaveprop, :gefs_http_get, fn _url, _opts ->
        {:ok, %{status: 404}}
      end)

      assert {:error, _} = GefsClient.fetch_grid_profiles(~D[2026-04-18], 12, 0)
    end
  end
end