from app import db
from datetime import datetime
import json

class MoodleSyncTask(db.Model):
    """
    Cola persistente de eventos y tareas de sincronización asíncrona hacia Moodle 4.1.
    Garantiza tolerancia a fallos ante caídas o saturación del servidor Moodle,
    incorporando reintentos exponenciales y Dead Letter Queue (DLQ).
    """
    __tablename__ = 'moodle_sync_tasks'

    id = db.Column(db.Integer, primary_key=True)
    action = db.Column(db.String(50), nullable=False, index=True) # CREATE_USER, UPDATE_USER, ENROL_USER, UNENROL_USER, ASSIGN_ROLE
    entity_type = db.Column(db.String(50), nullable=False) # user, commission, enrollment
    entity_id = db.Column(db.String(100), nullable=True)
    _payload = db.Column('payload', db.Text, nullable=False) # JSON serializado en Text
    status = db.Column(db.String(20), default='PENDING', index=True) # PENDING, PROCESSING, RETRYING, COMPLETED, FAILED
    attempts = db.Column(db.Integer, default=0)
    max_attempts = db.Column(db.Integer, default=5)
    error_message = db.Column(db.Text, nullable=True)
    next_retry_at = db.Column(db.DateTime, default=datetime.utcnow, index=True)
    created_at = db.Column(db.DateTime, default=datetime.utcnow)
    updated_at = db.Column(db.DateTime, default=datetime.utcnow, onupdate=datetime.utcnow)

    def __init__(self, **kwargs):
        if 'payload' in kwargs:
            raw_payload = kwargs.pop('payload')
            if isinstance(raw_payload, (dict, list)):
                kwargs['_payload'] = json.dumps(raw_payload)
            else:
                kwargs['_payload'] = str(raw_payload or '{}')
        super().__init__(**kwargs)

    @property
    def payload(self):
        try:
            return json.loads(self._payload) if self._payload else {}
        except Exception:
            return {}

    @payload.setter
    def payload(self, val):
        if isinstance(val, (dict, list)):
            self._payload = json.dumps(val)
        else:
            self._payload = str(val or '{}')

    def get_payload_dict(self):
        return self.payload

    def to_dict(self):
        return {
            'id': self.id,
            'action': self.action,
            'entity_type': self.entity_type,
            'entity_id': self.entity_id,
            'payload': self.payload,
            'status': self.status,
            'attempts': self.attempts,
            'max_attempts': self.max_attempts,
            'error_message': self.error_message,
            'next_retry_at': self.next_retry_at.isoformat() if self.next_retry_at else None,
            'created_at': self.created_at.isoformat() if self.created_at else None,
            'updated_at': self.updated_at.isoformat() if self.updated_at else None
        }

    def __repr__(self):
        return f'<MoodleSyncTask #{self.id} {self.action} [{self.status}]>'