"""Minimal job queue for Agent orchestration: create, atomically claim, complete, fail."""
from datetime import datetime, timezone

from sqlalchemy import select, update

from .models import Job

_VALID_KINDS = {"REPROCESS_ALL", "REPROCESS_PRODUCTS"}
_MAX_ERROR_LENGTH = 2000


def create_job(session, agent, kind, payload=None):
    if kind not in _VALID_KINDS:
        raise ValueError(f"unsupported job kind: {kind}")
    job = Job(agent_id=agent.id, kind=kind, status="PENDING", payload=payload or {})
    session.add(job)
    session.commit()
    return job


def claim_next_job(session, agent):
    """Atomically claim the oldest PENDING job for this agent only.
    A single UPDATE...WHERE status='PENDING' guards against two concurrent
    pollers (this agent or any other) claiming the same job twice."""
    candidate = session.scalar(
        select(Job.id)
        .where(Job.agent_id == agent.id, Job.status == "PENDING")
        .order_by(Job.created_at.asc())
        .limit(1)
    )
    if candidate is None:
        return None
    now = datetime.now(timezone.utc)
    result = session.execute(
        update(Job)
        .where(Job.id == candidate, Job.status == "PENDING")
        .values(status="RUNNING", started_at=now, attempts=Job.attempts + 1)
    )
    session.commit()
    if result.rowcount != 1:
        return None  # another poller won the race; caller can poll again
    return session.get(Job, candidate)


def complete_job(session, job, result_summary):
    result = session.execute(
        update(Job)
        .where(Job.id == job.id, Job.status == "RUNNING")
        .values(status="COMPLETED", finished_at=datetime.now(timezone.utc), result_summary=result_summary)
    )
    session.commit()
    return result.rowcount == 1


def fail_job(session, job, error):
    sanitized = str(error)[:_MAX_ERROR_LENGTH]
    result = session.execute(
        update(Job)
        .where(Job.id == job.id, Job.status == "RUNNING")
        .values(status="FAILED", finished_at=datetime.now(timezone.utc), error=sanitized)
    )
    session.commit()
    return result.rowcount == 1