from sqlalchemy.sql import exists
from models import db, Event, user_event_association
from services.UserService import UserService
from datetime import datetime
from flask import g

class EventService:
    @staticmethod
    def create_event(data):
        new_event = Event(
            title=data['title'],
            description=data.get('description', ''),
            location=data.get('location', ''),
            duedate=datetime.strptime(data['duedate'], '%Y-%m-%dT%H:%M:%S'),
            user_id=data['user_id']
        )
        db.session.add(new_event)
        db.session.commit()
        return new_event

    @staticmethod
    def get_upcoming_events(user_id):
        events=Event.query.filter_by(deleted=False).all()
        if(events):
            return [event.to_dict() for event in events]
        else:
            return []

    @staticmethod
    def get_event_by_id(event_id, user_id):
        event = Event.query.filter_by(id=event_id,user_id=user_id, deleted=False).first()
        if(event):
            return event.to_dict()
        else:
            return []
    
    @staticmethod
    def update_event(event_id, data):
        event = Event.query.get(event_id)
        if not event:
            return None
        event.title = data['title']
        event.description = data.get('description', '')
        event.location = data.get('location', '')
        event.time = datetime.strptime(data['duedate'], '%Y-%m-%dT%H:%M:%S')
        db.session.commit()
        return event
    
    @staticmethod
    def delete_event(event_id):
        event = Event.query.filter_by(id=event_id, deleted=False).first()
        if event:
            event.deleted = True
            db.session.commit()
        else:
            return None
        return event


    @staticmethod
    def attend_event(event_id):
        user_id = g.user_id  # Assuming user_id is stored in Flask's global g object
        # Check if the event is valid and in the future
        event = Event.query.filter(
            Event.id == event_id,
            Event.duedate > datetime.now(),
            Event.deleted == False
        ).first()

        if not event:
            return {'error': 'Event not found or already passed'}

        # Check if the user is already associated with the event
        is_already_attending = db.session.query(exists().where(
            user_event_association.c.user_id == user_id,
            user_event_association.c.event_id == event_id
        )).scalar()

        if is_already_attending:
            return {'error': 'User already attending this event'}

        # Add the user to the event
        user = UserService.get_user_by_id(user_id)
        if not user:
            return {'error': 'User not found'}

        event.users.append(user)
        db.session.commit()

        return {'message': 'User successfully added to the event'}


    @staticmethod
    def unattend_event(event_id):
        user_id = g.user_id  # Assuming user_id is stored in Flask's global g object
        # Check if the event is valid and in the future
        event = Event.query.filter(
            Event.id == event_id,
            Event.duedate > datetime.now(),
            Event.deleted == False
        ).first()

        if not event:
            return {'error': 'Event not found or already passed'}

        # Check if the user is already associated with the event
        is_already_attending = db.session.query(exists().where(
            user_event_association.c.user_id == user_id,
            user_event_association.c.event_id == event_id
        )).scalar()

        if not is_already_attending:
            return {'error': 'User not attending this event'}

        # Remove the user from the event
        user = UserService.get_user_by_id(user_id)
        if not user:
            return {'error': 'User not found'}

        event.users.remove(user)
        db.session.commit()

        return {'message': 'User successfully removed from the event'}