"""Cross-process mutation lock for one user's knowledge-base library."""
from __future__ import annotations

import hashlib
from contextlib import contextmanager, nullcontext
from pathlib import Path
from typing import Iterator, Optional
from uuid import UUID

from .file_store import FileLockBusy, interprocess_file_lock


class KbBusyError(RuntimeError):
    """The target knowledge base is being mutated by another process."""


def _user_root(workspace_dir: Path, user_id: UUID) -> Path:
    return Path(workspace_dir) / "users" / str(user_id)


def kb_lock_path(user_root: Path, kb_name: str) -> Path:
    digest = hashlib.sha256(kb_name.encode("utf-8")).hexdigest()[:32]
    return Path(user_root) / ".kb" / ".locks" / f"{digest}.lock"


@contextmanager
def kb_mutation_lock(
    workspace_dir: Path,
    user_id: UUID,
    kb_name: str,
    *,
    timeout_seconds: Optional[float] = 0,
) -> Iterator[None]:
    try:
        with interprocess_file_lock(
            kb_lock_path(_user_root(workspace_dir, user_id), kb_name),
            timeout_seconds=timeout_seconds,
        ):
            yield
    except FileLockBusy as e:
        raise KbBusyError(kb_name) from e


@contextmanager
def kb_mutation_lock_for_path(
    target: Path,
    user_root: Optional[Path],
    *,
    timeout_seconds: Optional[float] = 0,
) -> Iterator[None]:
    """Lock the containing ``.kb/<name>`` library; no-op outside ``.kb``."""
    if user_root is None:
        with nullcontext():
            yield
        return
    try:
        rel = Path(target).resolve().relative_to(Path(user_root).resolve())
    except (OSError, ValueError):
        with nullcontext():
            yield
        return
    if len(rel.parts) < 3 or rel.parts[0] != ".kb" or rel.parts[1].startswith("."):
        with nullcontext():
            yield
        return
    try:
        with interprocess_file_lock(
            kb_lock_path(Path(user_root), rel.parts[1]),
            timeout_seconds=timeout_seconds,
        ):
            yield
    except FileLockBusy as e:
        raise KbBusyError(rel.parts[1]) from e


def kb_is_locked(workspace_dir: Path, user_id: UUID, kb_name: str) -> bool:
    try:
        with kb_mutation_lock(workspace_dir, user_id, kb_name):
            return False
    except KbBusyError:
        return True