"""Explicit translation policy for generated motion, in Blender's Z-up coordinates."""
import numpy as np


def root_offsets(positions, scale, mode='world'):
    positions = np.asarray(positions, dtype=np.float64)
    if positions.ndim != 2 or positions.shape[1] != 3 or not len(positions) or not np.isfinite(positions).all():
        raise ValueError('Root positions must be finite frame-by-XYZ coordinates')
    if not np.isfinite(scale) or scale <= 0:
        raise ValueError('Root motion scale must be positive and finite')
    if mode not in {'world', 'in-place'}:
        raise ValueError(f'Unknown root motion policy: {mode}')
    offsets = (positions - positions[0]) * scale
    if mode == 'in-place':
        offsets[:, :2] = 0
    return offsets