"""Gateway lifecycle ledger — durable termination-reason evidence (NS-608).

The gateway already has *graceful* shutdown forensics
(:mod:`gateway.shutdown_forensics` — who sent the SIGTERM) and an exit-path
diagnostic log (``gateway-exit-diag.log`` — every way ``asyncio.run`` can
return).  What it does NOT have is any record of an **unclean death**: a
SIGKILL, a kernel OOM kill, or the whole VM dying takes the process out
before any handler runs, so the next boot has no idea the previous life
ended violently — support tickets like NS-608 then require manually
cross-correlating four log files and two external APIs to answer "what
killed the gateway?".

This module closes that gap with a tiny state machine persisted to
``<HERMES_HOME>/state/gateway.lifecycle.json``:

* On startup, :func:`record_startup` reads the sentinel left by the
  previous life.  ``phase == "running"`` means that life never reached any
  exit path → it died uncleanly.  The finding — including the last
  heartbeat's memory sample, which is the closest thing to a pre-death
  telemetry snapshot — is appended to ``gateway-exit-diag.log`` as a
  ``gateway.previous_unclean_exit`` record and logged at WARNING.  The
  sentinel is then rewritten as ``phase=running`` for the new life.
* On every clean exit path, :func:`mark_exited` rewrites the sentinel as
  ``phase=exited`` with the exit code and a reason string.  Wired into
  ``_exit_after_graceful_shutdown`` (the single funnel for all graceful
  exits, #53107) and the two watchdog ``os._exit`` sites in
  :mod:`gateway.shutdown_watchdog`.

:func:`sample_memory` provides the cheap (<1ms, pure /proc reads) memory
snapshot that :func:`gateway.shutdown_watchdog.write_loop_heartbeat`
embeds in the 30s heartbeat — giving every unclean-death report a
"memory available N seconds before death" data point so OOM crash cycles
are classifiable from the volume alone (no Prometheus retention races).

Everything here is best-effort: a forensics failure must never affect the
gateway lifecycle it is observing.
"""

from __future__ import annotations

import json
import logging
import os
import time
from datetime import datetime, timezone
from pathlib import Path
from typing import Any, Dict, Optional

logger = logging.getLogger(__name__)

_LIFECYCLE_RELATIVE = ("state", "gateway.lifecycle.json")
_EXIT_DIAG_RELATIVE = ("logs", "gateway-exit-diag.log")

# Heuristic OOM-suspicion thresholds applied to the last heartbeat's memory
# sample.  Deliberately conservative: this only annotates the report with a
# hint; classification stays with the human reading the evidence.
_LOW_MEM_AVAILABLE_KIB = 64 * 1024  # < 64 MiB available
_LOW_MEM_AVAILABLE_FRACTION = 0.05  # < 5% of MemTotal available


def _process_hermes_home() -> Path:
    """HERMES_HOME for process-level identity files (ignore task overrides)."""
    val = os.environ.get("HERMES_HOME", "").strip()
    if val:
        return Path(val)
    from hermes_constants import get_hermes_home

    return get_hermes_home()


def get_lifecycle_sentinel_path(home: Optional[Path] = None) -> Path:
    """Return ``<HERMES_HOME>/state/gateway.lifecycle.json``."""
    base = home if home is not None else _process_hermes_home()
    return base.joinpath(*_LIFECYCLE_RELATIVE)


def sample_memory() -> Dict[str, Any]:
    """Cheap memory snapshot: own RSS + system availability + swap.

    Pure ``/proc`` reads, Linux-only (returns ``{}`` elsewhere), never
    raises.  Values in KiB to match the kernel's units.
    """
    sample: Dict[str, Any] = {}
    try:
        with open("/proc/self/status", encoding="utf-8") as fh:
            for line in fh:
                if line.startswith("VmRSS:"):
                    sample["rss_kib"] = int(line.split()[1])
                    break
    except (OSError, ValueError, IndexError):
        pass
    try:
        meminfo: Dict[str, int] = {}
        wanted = {"MemTotal", "MemAvailable", "SwapTotal", "SwapFree"}
        with open("/proc/meminfo", encoding="utf-8") as fh:
            for line in fh:
                key = line.split(":", 1)[0]
                if key in wanted:
                    meminfo[key] = int(line.split()[1])
                    if len(meminfo) == len(wanted):
                        break
        if "MemTotal" in meminfo:
            sample["mem_total_kib"] = meminfo["MemTotal"]
        if "MemAvailable" in meminfo:
            sample["mem_available_kib"] = meminfo["MemAvailable"]
        if "SwapTotal" in meminfo and "SwapFree" in meminfo:
            sample["swap_used_kib"] = meminfo["SwapTotal"] - meminfo["SwapFree"]
    except (OSError, ValueError, IndexError):
        pass
    return sample


def _read_json(path: Path) -> Optional[Dict[str, Any]]:
    try:
        data = json.loads(path.read_text(encoding="utf-8"))
    except (OSError, ValueError):
        return None
    return data if isinstance(data, dict) else None


def _write_sentinel(payload: Dict[str, Any], home: Optional[Path]) -> None:
    path = get_lifecycle_sentinel_path(home)
    try:
        from utils import atomic_json_write

        path.parent.mkdir(parents=True, exist_ok=True)
        atomic_json_write(path, payload, indent=None)
    except Exception:
        logger.debug("Failed to write lifecycle sentinel", exc_info=True)


def _append_exit_diag(record: Dict[str, Any], home: Optional[Path]) -> None:
    """Append a JSON line to gateway-exit-diag.log (same format as the CLI's
    ``_exit_diag`` records so existing tooling greps both)."""
    base = home if home is not None else _process_hermes_home()
    path = base.joinpath(*_EXIT_DIAG_RELATIVE)
    try:
        path.parent.mkdir(parents=True, exist_ok=True)
        with path.open("a", encoding="utf-8") as fh:
            fh.write(json.dumps(record, default=str) + "\n")
    except OSError:
        logger.debug("Failed to append unclean-exit record", exc_info=True)


def _pid_alive_with_start_time(pid: Any, start_time: Any) -> bool:
    """True when ``pid`` is a live process matching ``start_time`` (±2s).

    Guards the takeover race: during ``--replace`` the old gateway can still
    be mid-teardown when the new one boots — a live matching owner is a
    planned handover, not an unclean death.
    """
    try:
        pid_int = int(pid)
    except (TypeError, ValueError):
        return False
    if pid_int <= 0:
        return False
    try:
        # NOT os.kill(pid, 0): on Windows that sends CTRL_C_EVENT to the
        # target's console group (bpo-14484). _pid_exists is the repo's
        # canonical no-kill cross-platform probe (psutil-backed).
        from gateway.status import _pid_exists

        if not _pid_exists(pid_int):
            return False
    except Exception:
        return False
    if start_time is None:
        return True  # alive; can't disambiguate PID reuse — err on "alive"
    try:
        from gateway.status import get_process_start_time

        actual = get_process_start_time(pid_int)
        if actual is None:
            return True
        return abs(float(actual) - float(start_time)) <= 2.0
    except Exception:
        return True


def detect_unclean_exit(home: Optional[Path] = None) -> Optional[Dict[str, Any]]:
    """Inspect the previous life's sentinel; return an evidence dict when it
    died uncleanly, else ``None``.  Read-only — does not rewrite the sentinel.
    """
    sentinel = _read_json(get_lifecycle_sentinel_path(home))
    if not sentinel or sentinel.get("phase") != "running":
        return None
    if _pid_alive_with_start_time(sentinel.get("pid"), sentinel.get("start_time")):
        return None  # live owner — planned takeover in flight, not a death

    evidence: Dict[str, Any] = {
        "prior_pid": sentinel.get("pid"),
        "prior_started_at": sentinel.get("started_at"),
        "prior_start_time": sentinel.get("start_time"),
    }

    # Enrich with the last heartbeat: when did the loop last prove liveness,
    # and what did memory look like at that moment?
    try:
        from gateway.shutdown_watchdog import get_loop_heartbeat_path

        hb = _read_json(get_loop_heartbeat_path(home))
    except Exception:
        hb = None
    if hb:
        evidence["last_heartbeat_at"] = hb.get("updated_at")
        mem = hb.get("mem")
        if isinstance(mem, dict):
            evidence["last_heartbeat_mem"] = mem
            total = mem.get("mem_total_kib")
            avail = mem.get("mem_available_kib")
            if isinstance(avail, int) and (
                avail < _LOW_MEM_AVAILABLE_KIB
                or (
                    isinstance(total, int)
                    and total > 0
                    and avail / total < _LOW_MEM_AVAILABLE_FRACTION
                )
            ):
                evidence["suspected_oom"] = True
    return evidence


def record_startup(home: Optional[Path] = None) -> Optional[Dict[str, Any]]:
    """Boot-time entry point: report any unclean previous exit, then claim
    the sentinel for the current life.

    Returns the unclean-exit evidence dict (also persisted to
    ``gateway-exit-diag.log`` and logged at WARNING) or ``None``.  Never
    raises.
    """
    evidence: Optional[Dict[str, Any]] = None
    try:
        evidence = detect_unclean_exit(home)
        if evidence is not None:
            record = {
                "ts": datetime.now(timezone.utc).isoformat(),
                "tag": "gateway.previous_unclean_exit",
                "pid": os.getpid(),
                **evidence,
            }
            _append_exit_diag(record, home)
            logger.warning(
                "Previous gateway life (pid=%s, started_at=%s) exited UNCLEANLY "
                "(no exit path ran — SIGKILL / OOM / VM death). "
                "last_heartbeat_at=%s last_mem=%s suspected_oom=%s",
                evidence.get("prior_pid"),
                evidence.get("prior_started_at"),
                evidence.get("last_heartbeat_at"),
                evidence.get("last_heartbeat_mem"),
                evidence.get("suspected_oom", False),
            )
    except Exception:
        logger.debug("Unclean-exit detection failed", exc_info=True)

    try:
        _write_sentinel(
            {
                "phase": "running",
                "pid": os.getpid(),
                "start_time": time.time(),
                "started_at": datetime.now(timezone.utc).isoformat(),
            },
            home,
        )
    except Exception:
        logger.debug("Failed to claim lifecycle sentinel", exc_info=True)
    return evidence


def mark_exited(
    exit_code: Optional[int] = None,
    reason: str = "graceful_shutdown",
    home: Optional[Path] = None,
) -> None:
    """Mark the current life as cleanly exited.  Idempotent, never raises.

    Only rewrites the sentinel when it is provably owned by this process —
    during a ``--replace`` takeover the replacement claims the sentinel
    before the old process finishes teardown, and the old life must not
    clobber the new owner's ``running`` phase on its way out.  A sentinel
    with ``pid=None`` (or a malformed pid) has *unknown* ownership and is
    likewise left alone: we must not overwrite evidence we cannot prove is
    ours with a ``clean exit`` claim.
    """
    try:
        sentinel = _read_json(get_lifecycle_sentinel_path(home))
        if sentinel is not None and sentinel.get("pid") != os.getpid():
            return
        _write_sentinel(
            {
                "phase": "exited",
                "pid": os.getpid(),
                "exit_code": exit_code,
                "exit_reason": reason,
                "exited_at": datetime.now(timezone.utc).isoformat(),
            },
            home,
        )
    except Exception:
        logger.debug("Failed to mark lifecycle sentinel exited", exc_info=True)


def read_prior_exit_label(profile_home: Path) -> str:
    """Container-boot helper: one-word summary of how the profile's last
    gateway life ended.  ``clean`` / ``unclean`` / ``unknown`` (no sentinel
    or never ran).  Read-only and exception-free — used by
    ``hermes_cli.container_boot`` to annotate ``container-boot.log``.
    """
    try:
        sentinel = _read_json(get_lifecycle_sentinel_path(profile_home))
        if not sentinel:
            return "unknown"
        phase = sentinel.get("phase")
        if phase == "exited":
            return "clean"
        if phase == "running":
            # At container boot the old PID namespace is gone — any
            # "running" sentinel is from a life that never exited cleanly.
            return "unclean"
    except Exception:
        pass
    return "unknown"