import numpy as np
from merlin.features.gaze import GazeEstimator, GazeDirection

_LEFT_IRIS = 468
_RIGHT_IRIS = 473
_LEFT_INNER = 133
_RIGHT_OUTER = 263


def _face(n: int = 478) -> np.ndarray:
    return np.zeros((n, 3), dtype=np.float32)


def _set_gaze_center(face: np.ndarray) -> None:
    """Iris centers at midpoint of eye span → center gaze."""
    face[_LEFT_INNER] = [0.3, 0.5, 0.0]
    face[_RIGHT_OUTER] = [0.7, 0.5, 0.0]
    mid = (face[_LEFT_INNER] + face[_RIGHT_OUTER]) / 2.0
    face[_LEFT_IRIS] = mid.copy()
    face[_RIGHT_IRIS] = mid.copy()


def _set_gaze_left(face: np.ndarray) -> None:
    """Iris centers shifted left relative to eye span."""
    face[_LEFT_INNER] = [0.3, 0.5, 0.0]
    face[_RIGHT_OUTER] = [0.7, 0.5, 0.0]
    face[_LEFT_IRIS] = [0.35, 0.5, 0.0]
    face[_RIGHT_IRIS] = [0.35, 0.5, 0.0]


def test_center_gaze_label():
    face = _face()
    _set_gaze_center(face)
    g = GazeEstimator().estimate(face)
    assert g.label == "center"


def test_left_gaze_label():
    face = _face()
    _set_gaze_left(face)
    g = GazeEstimator().estimate(face)
    assert g.label == "left"


def test_zero_eye_width_returns_center():
    """Degenerate case: all landmarks at same point → center."""
    face = _face()
    g = GazeEstimator().estimate(face)
    assert g.dx == 0.0 and g.dy == 0.0


def test_gazeresult_is_frozen():
    g = GazeDirection(dx=0.1, dy=0.2)
    import pytest

    with pytest.raises((AttributeError, TypeError)):
        g.dx = 0.5