"""Crash-safe process registry for native Codex app-server children."""

from __future__ import annotations

import contextlib
import json
import logging
import os
import signal
import subprocess
import uuid
from collections.abc import Generator
from dataclasses import asdict, dataclass
from pathlib import Path

from omnigent.codex_native_state import _codex_native_state_root

try:
    import fcntl
except ImportError:  # pragma: no cover - Windows has no flock.
    fcntl = None  # type: ignore[assignment]

_logger = logging.getLogger(__name__)
_REGISTRY_FILE = "process-registry.json"
_OWNER_LOCK_DIR = "process-owners"
_TAG_ARG_PREFIX = "omnigent_crash_teardown_tag="


@dataclass(frozen=True)
class CodexNativeProcessEntry:
    """
    One crash-reapable native Codex subprocess registry entry.

    :param pid: Child process id.
    :param pgid: Child process group id.
    :param tmux_session_name: Optional tmux session name owned by the child.
    :param session_tag: Unique tag also embedded in the child command line.
    :param owner_lock_path: Lock file held by the parent while it owns
        the child. If the lock is still held during reconciliation, the
        child is a live sibling and must not be reaped.
    """

    pid: int
    pgid: int
    tmux_session_name: str | None
    session_tag: str
    owner_lock_path: str | None = None


@dataclass
class CodexNativeProcessOwnerLock:
    """
    Kernel-backed liveness handle for a native Codex launcher process.

    :param path: Path to the owner lock file.
    :param fd: Open file descriptor holding an exclusive flock.
    """

    path: Path
    fd: int

    def close(self) -> None:
        """
        Release the owner lock.

        :returns: None.
        """
        with contextlib.suppress(OSError):
            fcntl.flock(self.fd, fcntl.LOCK_UN)
        with contextlib.suppress(OSError):
            os.close(self.fd)
        with contextlib.suppress(OSError):
            self.path.unlink()


def codex_native_process_registry_path() -> Path:
    """
    Return the stable on-disk registry file path.

    :returns: Registry path under the existing codex-native state root.
    """
    return _codex_native_state_root() / _REGISTRY_FILE


def acquire_codex_native_process_owner_lock() -> CodexNativeProcessOwnerLock | None:
    """
    Acquire a per-launcher owner lock for crash-safe reconciliation.

    The lock is intentionally held by an open file descriptor for the
    launcher process lifetime. If the launcher crashes, the OS releases
    the flock, making its children eligible for the next reconciliation
    sweep. A healthy concurrent launcher still holds the lock, so its
    child entries are skipped even when their child PID/tag are live.

    :returns: Held owner lock, or ``None`` if it could not be created.
    """
    if fcntl is None:
        return None
    root = _codex_native_state_root() / _OWNER_LOCK_DIR
    try:
        root.mkdir(mode=0o700, parents=True, exist_ok=True)
        path = root / f"{uuid.uuid4().hex}.lock"
        fd = os.open(path, os.O_CREAT | os.O_RDWR | getattr(os, "O_CLOEXEC", 0), 0o600)
        fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
    except OSError:
        _logger.warning("codex-native process owner lock create failed", exc_info=True)
        with contextlib.suppress(NameError, OSError):
            os.close(fd)
        return None
    return CodexNativeProcessOwnerLock(path=path, fd=fd)


def codex_native_session_tag_cmdline_arg(session_tag: str) -> str:
    """
    Return an inert command-line marker carrying the crash-reap tag.

    :param session_tag: Unique per-process tag.
    :returns: Command-line marker value.
    :raises ValueError: If *session_tag* is empty.
    """
    if not session_tag:
        raise ValueError("session_tag must be non-empty")
    return f"{_TAG_ARG_PREFIX}{session_tag}"


def register_codex_native_process(
    *,
    pid: int,
    pgid: int,
    session_tag: str,
    owner_lock_path: Path | str | None,
    tmux_session_name: str | None = None,
    registry_path: Path | None = None,
) -> None:
    """
    Add or replace one native Codex process registry entry.

    :param pid: Child process id.
    :param pgid: Child process group id.
    :param session_tag: Unique tag embedded in the child command line.
    :param owner_lock_path: Lock file held by the launcher process.
    :param tmux_session_name: Optional tmux session name owned by the child.
    :param registry_path: Test override for the registry file path.
    :returns: None.
    """
    if pid <= 0 or pgid <= 0 or not session_tag:
        return
    entry = CodexNativeProcessEntry(
        pid=pid,
        pgid=pgid,
        tmux_session_name=tmux_session_name,
        session_tag=session_tag,
        owner_lock_path=str(owner_lock_path) if owner_lock_path is not None else None,
    )
    path = registry_path or codex_native_process_registry_path()
    with _registry_lock(path):
        entries = [
            existing for existing in _read_registry(path) if existing.session_tag != session_tag
        ]
        entries.append(entry)
        _write_registry(path, entries)


def unregister_codex_native_process(
    session_tag: str,
    *,
    registry_path: Path | None = None,
) -> None:
    """
    Remove one native Codex process registry entry.

    :param session_tag: Unique per-process registry tag.
    :param registry_path: Test override for the registry file path.
    :returns: None.
    """
    if not session_tag:
        return
    path = registry_path or codex_native_process_registry_path()
    with _registry_lock(path):
        entries = [entry for entry in _read_registry(path) if entry.session_tag != session_tag]
        _write_registry(path, entries)


def reconcile_codex_native_process_registry(*, registry_path: Path | None = None) -> None:
    """
    Reap crash-leftover native Codex children recorded by prior runs.

    PID reuse is guarded by requiring the live process command line to
    still contain the entry's unique session tag before killing anything.

    :param registry_path: Test override for the registry file path.
    :returns: None.
    """
    path = registry_path or codex_native_process_registry_path()
    with _registry_lock(path):
        survivors: list[CodexNativeProcessEntry] = []
        for entry in _read_registry(path):
            if _owner_lock_held(entry.owner_lock_path):
                survivors.append(entry)
                continue
            if not _pid_alive(entry.pid):
                continue
            if not _process_cmdline_has_tag(entry.pid, entry.session_tag):
                continue
            if not _terminate_process_group(entry.pgid):
                survivors.append(entry)
                continue
            _reap_tmux_session(entry.tmux_session_name)
        _write_registry(path, survivors)


@contextlib.contextmanager
def _registry_lock(path: Path) -> Generator[None, None, None]:
    """
    Serialize the read-modify-write on the shared registry file.

    The registry is a single host-global file mutated by every concurrent
    launcher, so an unlocked read-modify-write can drop an entry written by
    another launcher between its read and its write — leaving an orphan that
    crash reconciliation can never reap. An exclusive flock on a sibling lock
    file makes the whole sequence atomic across processes. Degrades to a no-op
    when locking is unavailable (Windows, or a lock-file failure).

    :param path: Registry file path being mutated.
    :returns: Context manager guarding the mutation.
    """
    if fcntl is None:
        yield
        return
    fd = None
    try:
        path.parent.mkdir(mode=0o700, parents=True, exist_ok=True)
        fd = os.open(str(path) + ".lock", os.O_CREAT | os.O_RDWR, 0o600)
        fcntl.flock(fd, fcntl.LOCK_EX)
    except OSError:
        _logger.warning("codex-native process registry lock failed", exc_info=True)
        if fd is not None:
            with contextlib.suppress(OSError):
                os.close(fd)
            fd = None
    try:
        yield
    finally:
        if fd is not None:
            with contextlib.suppress(OSError):
                fcntl.flock(fd, fcntl.LOCK_UN)
            with contextlib.suppress(OSError):
                os.close(fd)


def _read_registry(path: Path) -> list[CodexNativeProcessEntry]:
    try:
        raw = path.read_text(encoding="utf-8")
    except FileNotFoundError:
        return []
    except OSError:
        _logger.warning("codex-native process registry read failed", exc_info=True)
        return []
    try:
        payload = json.loads(raw)
    except json.JSONDecodeError:
        _logger.warning("codex-native process registry JSON is malformed; ignoring")
        return []
    if not isinstance(payload, list):
        return []
    entries: list[CodexNativeProcessEntry] = []
    for item in payload:
        entry = _entry_from_json(item)
        if entry is not None:
            entries.append(entry)
    return entries


def _write_registry(path: Path, entries: list[CodexNativeProcessEntry]) -> None:
    try:
        path.parent.mkdir(mode=0o700, parents=True, exist_ok=True)
        payload = [asdict(entry) for entry in entries]
        tmp = path.with_suffix(".json.tmp")
        tmp.write_text(json.dumps(payload, separators=(",", ":")) + "\n", encoding="utf-8")
        os.replace(tmp, path)
    except OSError:
        _logger.warning("codex-native process registry write failed", exc_info=True)


def _entry_from_json(item: object) -> CodexNativeProcessEntry | None:
    if not isinstance(item, dict):
        return None
    pid = item.get("pid")
    pgid = item.get("pgid")
    session_tag = item.get("session_tag")
    tmux_session_name = item.get("tmux_session_name")
    owner_lock_path = item.get("owner_lock_path")
    if not isinstance(pid, int) or pid <= 0:
        return None
    if not isinstance(pgid, int) or pgid <= 0:
        return None
    if not isinstance(session_tag, str) or not session_tag:
        return None
    if tmux_session_name is not None and not isinstance(tmux_session_name, str):
        tmux_session_name = None
    if owner_lock_path is not None and not isinstance(owner_lock_path, str):
        owner_lock_path = None
    return CodexNativeProcessEntry(
        pid=pid,
        pgid=pgid,
        tmux_session_name=tmux_session_name,
        session_tag=session_tag,
        owner_lock_path=owner_lock_path,
    )


def _owner_lock_held(owner_lock_path: str | None) -> bool:
    if not owner_lock_path:
        return False
    if fcntl is None:
        return False
    try:
        fd = os.open(owner_lock_path, os.O_RDWR)
    except FileNotFoundError:
        return False
    except OSError:
        return True
    try:
        try:
            fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
        except BlockingIOError:
            return True
        except OSError:
            return True
        return False
    finally:
        with contextlib.suppress(OSError):
            fcntl.flock(fd, fcntl.LOCK_UN)
        with contextlib.suppress(OSError):
            os.close(fd)


def _pid_alive(pid: int) -> bool:
    try:
        os.kill(pid, 0)
    except ProcessLookupError:
        return False
    except PermissionError:
        return True
    except OSError:
        return False
    return True


def _process_cmdline_has_tag(pid: int, session_tag: str) -> bool:
    needle = codex_native_session_tag_cmdline_arg(session_tag)
    cmdline = _process_cmdline(pid)
    return needle in cmdline


def _process_cmdline(pid: int) -> str:
    proc_cmdline = Path("/proc") / str(pid) / "cmdline"
    with contextlib.suppress(OSError):
        raw = proc_cmdline.read_bytes()
        if raw:
            return raw.replace(b"\x00", b" ").decode("utf-8", errors="replace")
    try:
        proc = subprocess.run(
            ["ps", "-p", str(pid), "-ww", "-o", "command="],
            check=False,
            stdout=subprocess.PIPE,
            stderr=subprocess.DEVNULL,
            text=True,
            timeout=2.0,
        )
    except (OSError, subprocess.TimeoutExpired):
        return ""
    return proc.stdout.strip() if proc.returncode == 0 else ""


def _terminate_process_group(pgid: int) -> bool:
    if os.name == "posix":
        try:
            os.killpg(pgid, signal.SIGTERM)
        except ProcessLookupError:
            return True
        except (PermissionError, OSError):
            return False
        return True
    return False


def _reap_tmux_session(tmux_session_name: str | None) -> None:
    if not tmux_session_name:
        return
    if _tmux_session_exists(tmux_session_name):
        _kill_tmux_session(tmux_session_name)


def _tmux_session_exists(tmux_session_name: str) -> bool:
    try:
        proc = subprocess.run(
            ["tmux", "has-session", "-t", tmux_session_name],
            check=False,
            stdout=subprocess.DEVNULL,
            stderr=subprocess.DEVNULL,
            timeout=2.0,
        )
    except (OSError, subprocess.TimeoutExpired):
        return False
    return proc.returncode == 0


def _kill_tmux_session(tmux_session_name: str) -> None:
    with contextlib.suppress(OSError, subprocess.TimeoutExpired):
        subprocess.run(
            ["tmux", "kill-session", "-t", tmux_session_name],
            check=False,
            stdout=subprocess.DEVNULL,
            stderr=subprocess.DEVNULL,
            timeout=2.0,
        )