"""The auto-completion gate.

Phase 2a already decides, correctly and fail-closed. This does not re-decide;
it supplies real evidence to that decision and, only if three independent gates
agree, asks the transition boundary to commit.

Three gates, all of which must hold:
  * the global switch is on (default off),
  * the backend has observed evidence that it reaches a quiescent state,
  * the job itself opted in.

Everything else is refusal. A failure anywhere -- an unreadable manifest, an
exception in the policy, an unknown decision -- holds. "Could not decide" is
never "done".
"""
from __future__ import annotations

import logging
import os
import re
from pathlib import Path
from typing import Any, Dict, List, Optional

from lib_py.delegation import finalize
from lib_py.loop import policy, store

logger = logging.getLogger("loop.autocomplete")

FLAG = "MAM_AUTO_COMPLETE"
BACKENDS_FLAG = "MAM_AUTO_COMPLETE_BACKENDS"

# Backends with recorded evidence that they reach a quiescent state. Auto
# completion infers "finished" from stillness, so a backend whose stillness has
# never been observed has no basis for the inference. agy has only been seen
# working; hermes and opencode have no observations at all.
EVIDENCE_BACKED_BACKENDS = ("claude", "grok", "codex")

# The `agent` recorded on a job is a delegate key. Matching these exactly rather
# than by prefix keeps a future `claude-something-unverified` from inheriting
# evidence that was never collected for it.
EVIDENCE_BACKED_AGENT_KEYS = (
    "claude", "claude-code", "grok", "grok-build", "codex", "codex-cli",
)

# A reviewer's verdict token, matched the way run_loop.sh matches it.
VERDICT_LINE = re.compile(r"^\[VERDICT: (PASS|NOT PASS)\][ \t]*\r?$")

SOURCE = "auto_complete"


def enabled() -> bool:
    """Default off. Read per call so an operator can flip it without a restart."""
    return os.environ.get(FLAG, "0") == "1"


def allowed_backends() -> tuple:
    """The allowlist may be narrowed by an operator, never widened.

    Widening would need new observations, so an unknown name in the environment
    is dropped rather than trusted.
    """
    raw = os.environ.get(BACKENDS_FLAG)
    if not raw:
        return EVIDENCE_BACKED_BACKENDS
    requested = [name.strip() for name in raw.split(",") if name.strip()]
    return tuple(n for n in requested if n in EVIDENCE_BACKED_BACKENDS)


class GateResult(object):
    __slots__ = ("committed", "decision", "reason")

    def __init__(self, committed, decision, reason):
        self.committed = committed
        self.decision = decision
        self.reason = reason

    def __repr__(self):  # pragma: no cover - debugging aid
        return "GateResult(committed={!r}, {!r}, {!r})".format(
            self.committed, self.decision, self.reason)


def _allowed_agent_keys() -> tuple:
    allowed = allowed_backends()
    return tuple(k for k in EVIDENCE_BACKED_AGENT_KEYS
                 if any(k == b or k.startswith(b + "-") for b in allowed))


def _gates_open(record: Dict[str, Any]) -> Optional[str]:
    """None when every gate passes, else why one did not."""
    from lib_py.delegation import engine

    if not enabled():
        return "auto-completion is disabled ({}=0)".format(FLAG)
    if not engine.cas_enabled():
        # The operations note promises this switch disables auto-completion too,
        # and it must: inferred completion is built on the CAS boundary, so
        # committing while that boundary is rolled back would bypass it.
        return "the CAS engine is rolled back (MAM_ENGINE_CAS=0)"
    backend = record.get("agent") or ""
    if backend not in _allowed_agent_keys():
        return "backend {!r} has no observed quiescent-state evidence".format(backend)
    if not record.get("auto_complete"):
        return "job did not opt in to auto-completion"
    return None


def _verdict_present(report_path) -> bool:
    """A reviewer's report must end with its verdict token.

    Phase 0 made this a safety contract: without a verdict, a reviewer job may
    never be promoted to completed. run_loop.sh reads a missing token as NOT
    PASS, so auto-completing before the token exists would start a correction
    round against a review that was never finished.
    """
    try:
        lines = Path(report_path).read_text(encoding="utf-8").splitlines()
    except OSError:
        return False
    for line in reversed(lines):
        if line.strip():
            return bool(VERDICT_LINE.match(line))
    return False


def _scenario_matches(job_id, scenario, dispatch) -> Optional[str]:
    """The evidence must be about this job and this dispatch.

    Without this the gate will happily complete one job using another job's
    evidence: the policy only checks a scenario against the dispatch context
    carried inside that same scenario, which is self-consistent by construction.
    """
    context = scenario.get("dispatch_context") or {}
    if context.get("job_id") != job_id:
        return "evidence is for job {!r}, not {!r}".format(context.get("job_id"), job_id)
    for field in ("attempt_id", "agent_session_uuid", "pane_process_generation"):
        expected = dispatch.get(field)
        if expected is None:
            return "no recorded dispatch {} to compare the evidence against".format(field)
        if context.get(field) != expected:
            return "evidence {} {!r} does not match the recorded dispatch {!r}".format(
                field, context.get(field), expected)
    return None


def evaluate(job_id, scenario, registry_dir=None, workspace=None,
             report_dir=None) -> GateResult:
    # `report_dir` keeps a default only so the signature stays callable from a
    # supervisor that has not resolved it yet; omitting it is a refusal, not a
    # shortcut. See the check at the top of the body.
    """Decide, and commit only if every gate agrees.

    `scenario` is the composite evidence the watcher assembled, in the same shape
    the phase 0 fixtures use, so the decision is made by exactly the code the
    scenario contracts already pin.
    """
    from lib_py.delegation import engine, mqtt_common

    registry_dir = registry_dir or mqtt_common.DEFAULT_REGISTRY_DIR
    try:
        record = mqtt_common.load_job(job_id, registry_dir)
    except FileNotFoundError:
        return GateResult(False, "hold", "no such job")

    closed = _gates_open(record)
    if closed:
        return GateResult(False, "hold", closed)

    # Independent verification is mandatory, never conditional on the caller
    # remembering an argument. Skipping it would put the collector's own flags
    # back in charge of the decision, which is the self-certification this whole
    # design exists to avoid.
    if report_dir is None:
        return GateResult(False, "hold",
                          "no report directory to independently verify the manifest against")

    dispatch = store.load_dispatch(job_id, workspace)
    if not dispatch:
        return GateResult(False, "hold", "no recorded dispatch to attribute this completion to")

    mismatch = _scenario_matches(job_id, scenario, dispatch)
    if mismatch:
        return GateResult(False, "hold", mismatch)

    # The evidence must belong to the attempt that is currently running, and the
    # commit must be refused if that stops being true while this runs. Comparing
    # here alone is not enough: the job can complete, be re-dispatched and
    # claimed again before the terminal write, after which a status check alone
    # would let stale evidence finish a new attempt.
    from lib_py.delegation import engine as _engine

    token = record.get(_engine.DISPATCH_TOKEN_FIELD)
    if not token:
        return GateResult(False, "hold",
                          "job has no dispatch token to bind this decision to")
    if dispatch.get("dispatch_token") != token:
        return GateResult(False, "hold",
                          "evidence belongs to a superseded dispatch of this job")

    verdict = finalize.verify_manifest(
        report_dir, job_id, expected_attempt=dispatch.get("attempt_id"),
        expected_artifacts=record.get("expected_artifacts") or [])
    if not verdict.ok:
        return GateResult(False, "hold", verdict.reason)

    # A reviewer that has not written its verdict has not finished reviewing.
    if str(record.get("role") or "").lower() == "reviewer":
        if not _verdict_present(verdict.manifest["report_path"]):
            return GateResult(False, "hold",
                              "reviewer report carries no verdict token on its last line")

    try:
        decision = policy.decide(scenario)
    except Exception as exc:  # a policy that cannot decide has not approved
        logger.warning("policy raised for %s: %s", job_id, exc)
        return GateResult(False, "hold", "policy error: {}".format(exc))

    if not decision.would_complete:
        return GateResult(False, decision.decision, decision.reason)

    # The attempt guard lives here, in the evidence, not in the record: a record
    # carries a loop-iteration counter, which is a different thing.
    result = engine.transition(
        job_id, "completed", registry_dir=registry_dir,
        expected_status="running", expected_dispatch_token=token, source=SOURCE,
        fields={"completed_by": SOURCE, "auto_complete_reason": decision.reason},
        notify="completed",
    )
    if not result.committed:
        # A late explicit terminal, or a job that moved on. The boundary refused;
        # that is the boundary doing its job, not an error here.
        logger.info("auto-completion declined for %s: %s", job_id, result.reason)
        return GateResult(False, "hold", result.reason)

    logger.info("auto-completed %s (%s)", job_id, decision.reason)
    return GateResult(True, decision.decision, decision.reason)