prop/test/microwaveprop/weather/nexrad_client_test.exs

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

  alias Microwaveprop.Weather.NexradClient

  describe "round_to_5min/1" do
    test "rounds down to nearest 5-minute boundary" do
      dt = ~U[2022-08-20 14:07:32Z]
      assert NexradClient.round_to_5min(dt) == ~U[2022-08-20 14:05:00Z]
    end

    test "already on a 5-minute boundary stays unchanged" do
      dt = ~U[2022-08-20 14:10:00Z]
      assert NexradClient.round_to_5min(dt) == ~U[2022-08-20 14:10:00Z]
    end

    test "59 minutes rounds down to 55" do
      dt = ~U[2022-08-20 14:59:59Z]
      assert NexradClient.round_to_5min(dt) == ~U[2022-08-20 14:55:00Z]
    end
  end

  describe "frame_url/1" do
    test "builds correct IEM n0q URL from datetime" do
      dt = ~U[2022-08-20 14:05:00Z]
      url = NexradClient.frame_url(dt)

      assert url ==
               "https://mesonet.agron.iastate.edu/archive/data/2022/08/20/GIS/uscomp/n0q_202208201405.png"
    end

    test "pads single-digit month and day" do
      dt = ~U[2022-01-05 03:00:00Z]
      url = NexradClient.frame_url(dt)

      assert url ==
               "https://mesonet.agron.iastate.edu/archive/data/2022/01/05/GIS/uscomp/n0q_202201050300.png"
    end
  end

  describe "latlon_to_pixel/2" do
    test "converts coordinates to pixel positions" do
      # Top-left corner: lat=50, lon=-126
      {x, y} = NexradClient.latlon_to_pixel(50.0, -126.0)
      assert x == 0
      assert y == 0
    end

    test "bottom-right corner" do
      # lon = -65 -> x = (-65 - -126) / 0.005 = 61 / 0.005 = 12200
      # lat = 23 -> y = (50 - 23) / 0.005 = 27 / 0.005 = 5400
      {x, y} = NexradClient.latlon_to_pixel(23.0, -65.0)
      assert x == 12_200
      assert y == 5400
    end

    test "DFW area" do
      # DFW: lat ~32.9, lon ~-97.0
      {x, y} = NexradClient.latlon_to_pixel(32.9, -97.0)

      # x = (-97 - -126) / 0.005 = 29 / 0.005 = 5800
      assert x == 5800
      # y = (50 - 32.9) / 0.005 = 17.1 / 0.005 = 3420
      assert y == 3420
    end
  end

  describe "extract_box/4" do
    test "extracts stats from a box of pixel values" do
      # Create a simple 100x100 image (all zeros except a small region)
      width = 100
      height = 100
      pixels = :binary.copy(<<0>>, width * height)

      # Put some non-zero values around pixel (50, 50) - a 5x5 block
      pixels =
        Enum.reduce(48..52, pixels, fn y, acc ->
          Enum.reduce(48..52, acc, fn x, inner_acc ->
            offset = y * width + x
            <<pre::binary-size(offset), _::8, post::binary>> = inner_acc
            <<pre::binary, 120::8, post::binary>>
          end)
        end)

      result = NexradClient.extract_box(pixels, width, 50, 50, 5)

      assert result.pixel_count == 25
      assert result.max_reflectivity_dbz > 0
      assert result.mean_reflectivity_dbz > 0
      assert result.texture_variance == 0.0
    end

    test "returns zeros for an empty box" do
      width = 100
      height = 100
      pixels = :binary.copy(<<0>>, width * height)

      result = NexradClient.extract_box(pixels, width, 50, 50, 5)

      assert result.pixel_count == 0
      assert result.mean_reflectivity_dbz == 0.0
      assert result.max_reflectivity_dbz == 0.0
      assert result.texture_variance == 0.0
    end

    test "computes texture variance for mixed values" do
      width = 100
      height = 100
      pixels = :binary.copy(<<0>>, width * height)

      # Place alternating values: half 100, half 200
      pixels =
        Enum.reduce(48..52, pixels, fn y, acc ->
          Enum.reduce(48..52, acc, fn x, inner_acc ->
            offset = y * width + x
            value = if rem(x + y, 2) == 0, do: 100, else: 200
            <<pre::binary-size(offset), _::8, post::binary>> = inner_acc
            <<pre::binary, value::8, post::binary>>
          end)
        end)

      result = NexradClient.extract_box(pixels, width, 50, 50, 5)

      assert result.pixel_count == 25
      # Variance should be non-zero since we have mixed values
      assert result.texture_variance > 0.0
    end

    test "handles box at image boundary by clamping" do
      width = 100
      height = 100
      pixels = :binary.copy(<<50>>, width * height)

      # Corner case: near edge
      result = NexradClient.extract_box(pixels, width, 2, 2, 25)

      # Should not crash; pixel_count depends on how many pixels are in bounds
      assert result.pixel_count > 0
    end
  end

  describe "pixel_to_dbz/1" do
    test "value 0 maps to 0 (no echo)" do
      assert NexradClient.pixel_to_dbz(0) == 0.0
    end

    test "value 255 maps to approximately 95 dBZ" do
      dbz = NexradClient.pixel_to_dbz(255)
      assert_in_delta dbz, 95.0, 1.0
    end

    test "mid-range value produces reasonable dBZ" do
      dbz = NexradClient.pixel_to_dbz(128)
      assert dbz > 0.0
      assert dbz < 95.0
    end
  end
end