"""
Head pose estimation — detect nod, shake, and tilt from Face Mesh landmarks.

Velocity-based: compares nose tip position across consecutive frames.
"""

from __future__ import annotations

from enum import Enum
from typing import Optional

import numpy as np

_NOSE_TIP = 1
_L_CHEEK = 234
_R_CHEEK = 454

NOD_THRESHOLD = 0.015
SHAKE_THRESHOLD = 0.015
TILT_THRESHOLD = 0.012


class HeadGesture(str, Enum):
    NOD = "head_nod"
    SHAKE = "head_shake"
    TILT_LEFT = "head_tilt_left"
    TILT_RIGHT = "head_tilt_right"


class HeadPoseEstimator:
    """Detect head gestures by comparing nose tip position across frames."""

    def __init__(self) -> None:
        self._prev: Optional[np.ndarray] = None

    def update(self, face_landmarks: np.ndarray) -> Optional[HeadGesture]:
        """
        Args:
            face_landmarks: (478, 3) float32 — current frame.

        Returns:
            HeadGesture if detected, else None.
        """
        nose = face_landmarks[_NOSE_TIP]
        if self._prev is None:
            self._prev = nose.copy()
            return None

        delta = nose - self._prev
        self._prev = nose.copy()

        dy = float(delta[1])
        dx = float(delta[0])

        l_cheek = face_landmarks[_L_CHEEK]
        r_cheek = face_landmarks[_R_CHEEK]
        roll = float(l_cheek[1] - r_cheek[1])

        if abs(dy) > NOD_THRESHOLD and abs(dy) > abs(dx):
            return HeadGesture.NOD
        if abs(dx) > SHAKE_THRESHOLD and abs(dx) > abs(dy):
            return HeadGesture.SHAKE
        if abs(roll) > TILT_THRESHOLD:
            return HeadGesture.TILT_LEFT if roll > 0 else HeadGesture.TILT_RIGHT
        return None