"""Keep user UI data separate from replaceable release defaults."""
from __future__ import annotations

import json
import os
import shutil
import tempfile
from contextlib import contextmanager
from pathlib import Path
from threading import RLock

_migration_lock = RLock()


def atomic_write(path: Path, content: str) -> None:
    """A failed save leaves the previous complete file available."""
    temporary = None
    try:
        with tempfile.NamedTemporaryFile(mode="w", encoding="utf-8", dir=path.parent,
                                         prefix=path.name + ".", suffix=".tmp", delete=False) as stream:
            temporary = Path(stream.name)
            stream.write(content)
            stream.flush()
            os.fsync(stream.fileno())
        os.replace(temporary, path)
    finally:
        if temporary is not None:
            temporary.unlink(missing_ok=True)


@contextmanager
def _exclusive_migration(directory: Path):
    # Startup can run in several server processes, including on Windows.
    with _migration_lock, (directory / ".migration.lock").open("a+b") as stream:
        stream.seek(0, os.SEEK_END)
        if not stream.tell():
            stream.write(b"0")
            stream.flush()
        stream.seek(0)
        if os.name == "nt":
            import msvcrt
            msvcrt.locking(stream.fileno(), msvcrt.LK_LOCK, 1)
        else:
            import fcntl
            fcntl.flock(stream.fileno(), fcntl.LOCK_EX)
        try:
            yield
        finally:
            stream.seek(0)
            if os.name == "nt":
                msvcrt.locking(stream.fileno(), msvcrt.LK_UNLCK, 1)
            else:
                fcntl.flock(stream.fileno(), fcntl.LOCK_UN)


def prepare_ui_storage(settings_dir: Path, *, filenames: tuple[str, ...], legacy_filename: str) -> Path:
    configured = os.getenv("HOCKEY_UI_DATA_DIR", "").strip()
    directory = Path(configured).expanduser() if configured else settings_dir / "local"
    if configured and not directory.is_absolute():
        raise ValueError("HOCKEY_UI_DATA_DIR должен содержать абсолютный путь")
    directory.mkdir(parents=True, exist_ok=True)
    with _exclusive_migration(directory):
        for filename in filenames:
            name = Path(filename).name
            destination = directory / name
            if destination.exists():
                continue
            source = settings_dir / name
            if not source.exists():
                source = settings_dir / Path(legacy_filename).name
            if source.exists():
                content = source.read_text(encoding="utf-8-sig")
                try:
                    valid = isinstance(json.loads(content), dict)
                except (ValueError, TypeError):
                    valid = False
                if not valid:
                    raise ValueError(f"Не удалось перенести настройки интерфейса: {source.name} повреждён")
                atomic_write(destination, content)
        # Import recovery history exactly once. Otherwise every restart resurrects
        # old backups that rolling retention already removed.
        old_backups = settings_dir / "backups"
        new_backups = directory / "backups"
        new_backups.mkdir(exist_ok=True)
        marker = directory / ".ui_backups_migrated_v1.json"
        if not marker.exists():
            for filename in (*filenames, legacy_filename):
                for source in old_backups.glob(Path(filename).stem + "_*.json"):
                    destination = new_backups / source.name
                    if not destination.exists():
                        shutil.copy2(source, destination)
            atomic_write(marker, json.dumps({"completed": True, "version": 1}))
    return directory