"""Persistence for sprite frame label assignments.

Assignments are stored in a JSON sidecar keyed by filename (not frame index),
so resuming a session survives frames being added, removed, or reordered.
"""

import json
from pathlib import Path

SIDECAR_NAME = '.sprite_tags.json'
SCHEMA_VERSION = 1


def sidecar_path(frames_dir: Path) -> Path:
    return frames_dir / SIDECAR_NAME


def save_labels(path: Path, assignments_by_name: dict, labels: list) -> None:
    data = {
        'version': SCHEMA_VERSION,
        'labels': list(labels),
        'assignments': dict(assignments_by_name),
    }
    Path(path).write_text(json.dumps(data, indent=2))


def load_labels(path: Path):
    """Return (assignments_by_name, labels). Missing or invalid file → ({}, [])."""
    path = Path(path)
    if not path.exists():
        return {}, []
    try:
        data = json.loads(path.read_text())
    except (json.JSONDecodeError, OSError, ValueError):
        return {}, []
    assignments = data.get('assignments', {})
    labels = data.get('labels', [])
    if not isinstance(assignments, dict) or not isinstance(labels, list):
        return {}, []
    return assignments, labels


def to_name_keyed(assignments_by_index: dict, frames: list) -> dict:
    """{index: label} → {filename: label}."""
    return {frames[i].name: label for i, label in assignments_by_index.items()}


def to_index_keyed(assignments_by_name: dict, frames: list) -> dict:
    """{filename: label} → {index: label}, dropping files not in `frames`."""
    name_to_index = {p.name: i for i, p in enumerate(frames)}
    return {
        name_to_index[name]: label
        for name, label in assignments_by_name.items()
        if name in name_to_index
    }