defmodule MoundHunters.Boundary do
  @moduledoc """
  Ohio state boundary checking using point-in-polygon algorithm.
  """

  # Simplified Ohio bounding box for fast preliminary check
  # More precise polygon would be loaded from GeoJSON
  @ohio_bbox %{
    min_lat: 38.403,
    max_lat: 42.327,
    min_lng: -84.820,
    max_lng: -80.519
  }

  # Ohio state boundary polygon (simplified)
  # Source: Github -> PublicaMundi/MappingAPI us-states.json
  # Coordinates are [lng, lat] pairs per GeoJSON spec
  @ohio_polygon [
    {-80.518598, 41.978802},
    {-80.518598, 40.636951},
    {-80.666475, 40.582182},
    {-80.595275, 40.472643},
    {-80.600752, 40.319289},
    {-80.737675, 40.078303},
    {-80.830783, 39.711348},
    {-81.219646, 39.388209},
    {-81.345616, 39.344393},
    {-81.455155, 39.410117},
    {-81.570170, 39.267716},
    {-81.685186, 39.273193},
    {-81.811156, 39.081500},
    {-81.783771, 38.966484},
    {-81.887833, 38.873376},
    {-82.035710, 39.026731},
    {-82.221926, 38.785745},
    {-82.172634, 38.632391},
    {-82.293127, 38.577622},
    {-82.331465, 38.446175},
    {-82.594358, 38.424267},
    {-82.731282, 38.561191},
    {-82.846298, 38.588575},
    {-82.890113, 38.758361},
    {-83.032514, 38.725499},
    {-83.142052, 38.626914},
    {-83.519961, 38.703591},
    {-83.678792, 38.632391},
    {-83.903347, 38.769315},
    {-84.215533, 38.807653},
    {-84.231963, 38.895284},
    {-84.434610, 39.103408},
    {-84.817996, 39.103408},
    {-84.801565, 40.500028},
    {-84.807042, 41.694001},
    {-83.454238, 41.732339},
    {-83.065375, 41.595416},
    {-82.933929, 41.513262},
    {-82.835344, 41.589939},
    {-82.616266, 41.431108},
    {-82.479343, 41.381815},
    {-82.013803, 41.513262},
    {-81.739956, 41.485877},
    {-81.444201, 41.672093},
    {-81.011523, 41.852832},
    {-80.518598, 41.978802},
    {-80.518598, 41.978802}
  ]

  @doc """
  Check if coordinates are within Ohio boundaries.
  Returns :ok or {:error, reason}
  """
  def check_bounds(lat, lng) when is_number(lat) and is_number(lng) do
    cond do
      not in_bounding_box?(lat, lng) ->
        {:error, "Coordinates outside Ohio bounding box"}

      not in_polygon?(lng, lat, @ohio_polygon) ->
        {:error, "Coordinates outside Ohio boundary"}

      true ->
        :ok
    end
  end

  def check_bounds(_lat, _lng) do
    {:error, "Invalid coordinates"}
  end

  defp in_bounding_box?(lat, lng) do
    lat >= @ohio_bbox.min_lat and lat <= @ohio_bbox.max_lat and
      lng >= @ohio_bbox.min_lng and lng <= @ohio_bbox.max_lng
  end

  # Ray casting algorithm for point-in-polygon test
  # Returns true if point (x, y) is inside the polygon
  defp in_polygon?(x, y, polygon) do
    n = length(polygon)

    polygon
    |> Enum.with_index()
    |> Enum.reduce(false, fn {{xi, yi}, i}, inside ->
      j = rem(i + n - 1, n)
      {xj, yj} = Enum.at(polygon, j)

      intersects =
        yi > y != yj > y and
          x < (xj - xi) * (y - yi) / (yj - yi) + xi

      if intersects, do: not inside, else: inside
    end)
  end

  @doc """
  Format coordinates to 6 decimal places for consistent lookups.
  """
  def format_lookup_id(lat, lng) do
    lat_str = :erlang.float_to_binary(lat / 1.0, decimals: 6)
    lng_str = :erlang.float_to_binary(lng / 1.0, decimals: 6)
    "#{lat_str},#{lng_str}"
  end
end