src/data/bvh_parser.py

"""
BVH file parser for extracting skeleton structure and motion data.

Handles arbitrary BVH files from different sources (Mixamo, LAFAN1, Truebones, etc.)
and converts them into our unified SkeletonGraph + motion tensor format.
"""

import numpy as np
import re
from dataclasses import dataclass
from pathlib import Path
from typing import Optional

from .skeleton_graph import SkeletonGraph, normalize_joint_name


@dataclass
class BVHData:
    """Parsed BVH data."""
    skeleton: SkeletonGraph
    rotations: np.ndarray  # [T, J, 3] Euler angles (degrees)
    root_positions: np.ndarray  # [T, 3]
    fps: float
    num_frames: int
    rotation_order: str  # e.g., 'ZYX'
    local_translations: np.ndarray | None = None  # [T, J, 3] per-frame local translations (if available)


def parse_bvh(filepath: str | Path) -> BVHData:
    """
    Parse a BVH file into skeleton structure + motion data.

    Returns:
        BVHData with skeleton graph, rotations, root positions, and metadata.
    """
    filepath = Path(filepath)
    with open(filepath, 'r') as f:
        content = f.read()

    # Split into HIERARCHY and MOTION sections
    parts = content.split('MOTION')
    if len(parts) != 2:
        raise ValueError(f"Invalid BVH format in {filepath}")

    hierarchy_str = parts[0]
    motion_str = parts[1]

    # Parse hierarchy
    joint_names, parent_indices, rest_offsets, channels_per_joint, rotation_order = (
        _parse_hierarchy(hierarchy_str)
    )

    # Parse motion data
    num_frames, frame_time, motion_data = _parse_motion(motion_str)
    fps = 1.0 / frame_time if frame_time > 0 else 30.0

    # Extract rotations and root positions from channel data
    rest_offsets_arr = np.array(rest_offsets, dtype=np.float32)
    rotations, root_positions, local_translations = _extract_motion_channels(
        motion_data, channels_per_joint, len(joint_names), rest_offsets_arr
    )

    # Build skeleton graph
    skeleton = SkeletonGraph(
        joint_names=joint_names,
        parent_indices=parent_indices,
        rest_offsets=rest_offsets_arr,
    )

    return BVHData(
        skeleton=skeleton,
        rotations=rotations,
        root_positions=root_positions,
        fps=fps,
        num_frames=num_frames,
        rotation_order=rotation_order,
        local_translations=local_translations,
    )


def _parse_hierarchy(hierarchy_str: str):
    """Parse BVH HIERARCHY section."""
    joint_names = []
    parent_indices = []
    rest_offsets = []
    channels_per_joint = []  # list of (num_channels, has_position)
    rotation_order = 'ZYX'  # default

    lines = hierarchy_str.strip().split('\n')
    parent_stack = [-1]  # stack of parent indices
    current_joint_idx = -1

    for line in lines:
        line = line.strip()

        if line.startswith('ROOT') or line.startswith('JOINT'):
            name = line.split()[-1]
            current_joint_idx = len(joint_names)
            joint_names.append(name)
            parent_indices.append(parent_stack[-1])

        elif line.startswith('End Site'):
            # End effector — we'll add it as a leaf joint
            parent_idx = current_joint_idx
            name = f"{joint_names[parent_idx]}_end"
            current_joint_idx = len(joint_names)
            joint_names.append(name)
            parent_indices.append(parent_idx)
            channels_per_joint.append((0, False))

        elif line.startswith('OFFSET'):
            vals = [float(x) for x in line.split()[1:4]]
            rest_offsets.append(vals)

        elif line.startswith('CHANNELS'):
            parts = line.split()
            num_ch = int(parts[1])
            ch_names = parts[2:]
            has_position = any('position' in c.lower() for c in ch_names)
            channels_per_joint.append((num_ch, has_position))

            # Detect rotation order from channel names
            rot_channels = [c for c in ch_names if 'rotation' in c.lower()]
            if rot_channels:
                rotation_order = ''.join(
                    c[0].upper() for c in rot_channels
                )

        elif line == '{':
            parent_stack.append(current_joint_idx)

        elif line == '}':
            parent_stack.pop()
            if parent_stack:
                current_joint_idx = parent_stack[-1]

    return joint_names, parent_indices, rest_offsets, channels_per_joint, rotation_order


def _parse_motion(motion_str: str):
    """Parse BVH MOTION section."""
    lines = motion_str.strip().split('\n')

    num_frames = 0
    frame_time = 1.0 / 30.0
    data_start = 0

    for i, line in enumerate(lines):
        line = line.strip()
        if line.startswith('Frames:'):
            num_frames = int(line.split(':')[1].strip())
        elif line.startswith('Frame Time:'):
            frame_time = float(line.split(':')[1].strip())
        elif line and not line.startswith('Frames') and not line.startswith('Frame'):
            data_start = i
            break

    # Parse frame data
    motion_data = []
    for line in lines[data_start:]:
        line = line.strip()
        if line:
            values = [float(x) for x in line.split()]
            motion_data.append(values)

    motion_data = np.array(motion_data, dtype=np.float32)

    if len(motion_data) != num_frames and len(motion_data) > 0:
        num_frames = len(motion_data)

    return num_frames, frame_time, motion_data


def _extract_motion_channels(
    motion_data: np.ndarray,
    channels_per_joint: list[tuple[int, bool]],
    num_joints: int,
    rest_offsets: np.ndarray = None,
) -> tuple[np.ndarray, np.ndarray, np.ndarray | None]:
    """Extract per-joint rotations, root positions, and local translations.

    Returns:
        rotations: [T, J, 3] Euler angles
        root_positions: [T, 3]
        local_translations: [T, J, 3] or None — per-frame local translations
            for joints that have position channels. None if only root has positions.
    """
    T = len(motion_data)
    rotations = np.zeros((T, num_joints, 3), dtype=np.float32)
    root_positions = np.zeros((T, 3), dtype=np.float32)

    # Track which non-root joints have position channels
    has_per_joint_positions = False
    joint_has_pos = [False] * num_joints

    col = 0
    joint_idx = 0

    for num_ch, has_position in channels_per_joint:
        if num_ch == 0:
            joint_idx += 1
            continue

        if has_position and joint_idx == 0:
            # Root joint: extract position (3) + rotation (3)
            root_positions = motion_data[:, col:col + 3].copy()
            rotations[:, 0, :] = motion_data[:, col + 3:col + 6]
            joint_has_pos[0] = True
            col += num_ch
        elif has_position:
            # Non-root with position channels
            rotations[:, joint_idx, :] = motion_data[:, col + 3:col + 6]
            joint_has_pos[joint_idx] = True
            has_per_joint_positions = True
            col += num_ch
        else:
            # Rotation only
            rotations[:, joint_idx, :] = motion_data[:, col:col + 3]
            col += num_ch

        joint_idx += 1

    # Build per-joint local translations if any non-root joint has position channels
    local_translations = None
    if has_per_joint_positions:
        local_translations = np.zeros((T, num_joints, 3), dtype=np.float32)
        # Fill with rest_offsets as default
        if rest_offsets is not None:
            for j in range(num_joints):
                local_translations[:, j, :] = rest_offsets[j]
        # Overwrite with per-frame position data where available
        col = 0
        joint_idx = 0
        for num_ch, has_position in channels_per_joint:
            if num_ch == 0:
                joint_idx += 1
                continue
            if has_position and joint_idx > 0:
                local_translations[:, joint_idx, :] = motion_data[:, col:col + 3]
            col += num_ch
            joint_idx += 1

    return rotations, root_positions, local_translations


def resample_motion(
    rotations: np.ndarray,
    root_positions: np.ndarray,
    source_fps: float,
    target_fps: float = 20.0,
    local_translations: np.ndarray = None,
) -> tuple[np.ndarray, np.ndarray] | tuple[np.ndarray, np.ndarray, np.ndarray]:
    """Resample motion to target FPS via linear interpolation."""
    if abs(source_fps - target_fps) < 0.5:
        if local_translations is not None:
            return rotations, root_positions, local_translations
        return rotations, root_positions

    T_src = len(rotations)
    duration = T_src / source_fps
    T_tgt = int(duration * target_fps)

    src_times = np.linspace(0, duration, T_src)
    tgt_times = np.linspace(0, duration, T_tgt)

    # Interpolate rotations [T, J, 3]
    J = rotations.shape[1]
    new_rots = np.zeros((T_tgt, J, 3), dtype=np.float32)
    for j in range(J):
        for d in range(3):
            new_rots[:, j, d] = np.interp(tgt_times, src_times, rotations[:, j, d])

    # Interpolate root positions [T, 3]
    new_pos = np.zeros((T_tgt, 3), dtype=np.float32)
    for d in range(3):
        new_pos[:, d] = np.interp(tgt_times, src_times, root_positions[:, d])

    # Interpolate local translations if present [T, J, 3]
    if local_translations is not None:
        new_trans = np.zeros((T_tgt, J, 3), dtype=np.float32)
        for j in range(J):
            for d in range(3):
                new_trans[:, j, d] = np.interp(tgt_times, src_times, local_translations[:, j, d])
        return new_rots, new_pos, new_trans

    return new_rots, new_pos


def remove_end_sites(
    joint_names: list[str],
    parent_indices: list[int],
    rest_offsets: np.ndarray,
    rotations: np.ndarray,
) -> tuple[list[str], list[int], np.ndarray, np.ndarray]:
    """Remove End Site joints (they have no channels / zero rotations)."""
    keep_mask = [not name.endswith('_end') for name in joint_names]
    keep_indices = [i for i, k in enumerate(keep_mask) if k]

    # Remap indices
    old_to_new = {old: new for new, old in enumerate(keep_indices)}
    old_to_new[-1] = -1

    new_names = [joint_names[i] for i in keep_indices]
    new_parents = [old_to_new.get(parent_indices[i], -1) for i in keep_indices]
    new_offsets = rest_offsets[keep_indices]
    new_rotations = rotations[:, keep_indices, :]

    return new_names, new_parents, new_offsets, new_rotations