"""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
from typing import Any, Dict, List, Optional

from lib_py.loop import finalize, 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")

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 _gates_open(record: Dict[str, Any]) -> Optional[str]:
    """None when all three gates pass, else why they did not."""
    if not enabled():
        return "auto-completion is disabled ({}=0)".format(FLAG)
    backend = record.get("agent") or ""
    # `agent` may be a delegate key such as `claude-code`; match on the prefix.
    if not any(backend == b or backend.startswith(b) for b in allowed_backends()):
        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 evaluate(job_id, scenario, registry_dir=None, workspace=None,
             report_dir=None) -> GateResult:
    """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)

    # The manifest is verified against the file on disk, not against itself, and
    # against any side effects this job declared it would perform.
    dispatch = store.load_dispatch(job_id, workspace) or {}
    attempt = dispatch.get("attempt_id")
    if report_dir is not None:
        verdict = finalize.verify_manifest(
            report_dir, job_id, expected_attempt=attempt,
            expected_artifacts=record.get("expected_artifacts") or [])
        if not verdict.ok:
            return GateResult(False, "hold", verdict.reason)

    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", 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)