defmodule Microwaveprop.Terrain.ViewshedTest do
  use ExUnit.Case, async: true

  alias Microwaveprop.Terrain.Viewshed

  describe "destination_point/4" do
    test "north bearing increases latitude, holds longitude" do
      {lat, lon} = Viewshed.destination_point(32.0, -97.0, 0, 100.0)
      assert_in_delta lat, 32.899, 0.01
      assert_in_delta lon, -97.0, 0.01
    end

    test "east bearing increases longitude, holds latitude" do
      {lat, lon} = Viewshed.destination_point(32.0, -97.0, 90, 100.0)
      assert_in_delta lat, 32.0, 0.01
      assert lon > -97.0
    end

    test "south bearing decreases latitude" do
      {lat, lon} = Viewshed.destination_point(32.0, -97.0, 180, 50.0)
      assert lat < 32.0
      assert_in_delta lon, -97.0, 0.01
    end

    test "zero distance returns origin" do
      {lat, lon} = Viewshed.destination_point(32.0, -97.0, 45, 0.0)
      assert_in_delta lat, 32.0, 0.001
      assert_in_delta lon, -97.0, 0.001
    end
  end

  describe "find_reach_km/2" do
    test "returns max range when no points are obstructed" do
      points = [
        %{obstructed: false, dist_km: 0.0},
        %{obstructed: false, dist_km: 10.0},
        %{obstructed: false, dist_km: 20.0},
        %{obstructed: false, dist_km: 30.0},
        %{obstructed: false, dist_km: 50.0}
      ]

      assert Viewshed.find_reach_km(points, 50.0) == 50.0
    end

    test "returns distance of point before first obstruction" do
      points = [
        %{obstructed: false, dist_km: 0.0},
        %{obstructed: false, dist_km: 10.0},
        %{obstructed: false, dist_km: 20.0},
        %{obstructed: true, dist_km: 30.0},
        %{obstructed: false, dist_km: 40.0},
        %{obstructed: false, dist_km: 50.0}
      ]

      assert Viewshed.find_reach_km(points, 50.0) == 20.0
    end

    test "returns first interior point distance when obstruction is at second point" do
      points = [
        %{obstructed: false, dist_km: 0.0},
        %{obstructed: true, dist_km: 5.0},
        %{obstructed: false, dist_km: 10.0}
      ]

      # First point is endpoint (excluded), second is first interior and is obstructed
      # No clear interior point before it, return minimum
      assert Viewshed.find_reach_km(points, 10.0) == 0.0
    end

    test "ignores endpoint obstruction flags" do
      # Endpoints (first/last) are never counted as obstructed by TerrainAnalysis
      # but just to be safe, find_reach_km skips them
      points = [
        %{obstructed: true, dist_km: 0.0},
        %{obstructed: false, dist_km: 25.0},
        %{obstructed: true, dist_km: 50.0}
      ]

      assert Viewshed.find_reach_km(points, 50.0) == 50.0
    end
  end

  describe "analyse_ray/5" do
    test "returns full range for flat terrain with antenna heights" do
      profile =
        for i <- 0..10 do
          f = i / 10
          %{lat: 32.9 + f * 0.09, lon: -97.0, d: f, elev: 200.0, dist_km: f * 10.0}
        end

      result = Viewshed.analyse_ray(profile, 10.0, 10.0, 2.4, 2.4)
      assert result.reach_km == 10.0
    end

    test "detects obstruction and returns reduced reach" do
      # Use 10km total so earth bulge is negligible (~0.7m) and
      # the 500m peak at index 5 is the only obstruction.
      profile =
        for i <- 0..10 do
          f = i / 10
          elev = if i == 5, do: 500.0, else: 200.0
          %{lat: 32.9 + f * 0.009, lon: -97.0, d: f, elev: elev, dist_km: f * 10.0}
        end

      result = Viewshed.analyse_ray(profile, 10.0, 10.0, 2.4, 2.4)
      assert result.reach_km < 10.0
      assert result.reach_km > 0.0
    end
  end
end