defmodule Microwaveprop.Propagation.GridTest do
  use ExUnit.Case, async: true

  alias Microwaveprop.Propagation.Grid

  describe "conus_points/0" do
    test "generates grid at 0.125 degree resolution" do
      points = Grid.conus_points()
      assert length(points) > 5000
      assert length(points) < 100_000
    end

    test "all points within CONUS bounds" do
      Enum.each(Grid.conus_points(), fn {lat, lon} ->
        assert lat >= 25.0 and lat <= 50.0
        assert lon >= -125.0 and lon <= -66.0
      end)
    end

    test "points are on 0.125 degree grid" do
      Enum.each(Grid.conus_points(), fn {lat, lon} ->
        assert Float.round(lat * 8, 0) == lat * 8
        assert Float.round(lon * 8, 0) == lon * 8
      end)
    end

    test "first point is at SW corner" do
      [{lat, lon} | _] = Grid.conus_points()
      assert lat == 25.0
      assert lon == -125.0
    end

    test "last point is at NE corner" do
      points = Grid.conus_points()
      {lat, lon} = List.last(points)
      assert lat == 50.0
      assert lon == -66.0
    end
  end

  describe "step/0" do
    test "returns 0.125" do
      assert Grid.step() == 0.125
    end
  end

  describe "bounds/0" do
    test "returns CONUS bounding box" do
      bounds = Grid.bounds()
      assert bounds.lat_min == 25.0
      assert bounds.lat_max == 50.0
      assert bounds.lon_min == -125.0
      assert bounds.lon_max == -66.0
    end
  end

  describe "wgrib2_grid_spec/0" do
    test "lon_start / lat_start match the bounding box SW corner" do
      spec = Grid.wgrib2_grid_spec()
      assert spec.lon_start == -125.0
      assert spec.lat_start == 25.0
    end

    test "grid step matches Grid.step/0 on both axes" do
      spec = Grid.wgrib2_grid_spec()
      assert spec.lon_step == Grid.step()
      assert spec.lat_step == Grid.step()
    end

    test "lon_count and lat_count span the full CONUS box inclusive" do
      spec = Grid.wgrib2_grid_spec()
      # (lon_max - lon_min) / step + 1 = (-66 - -125) / 0.125 + 1 = 473
      assert spec.lon_count == 473
      # (lat_max - lat_min) / step + 1 = (50 - 25) / 0.125 + 1 = 201
      assert spec.lat_count == 201
    end

    test "total cells in wgrib2_grid_spec matches conus_points length" do
      spec = Grid.wgrib2_grid_spec()
      points = Grid.conus_points()
      assert length(points) == spec.lon_count * spec.lat_count
    end
  end
end