from flask_sqlalchemy import SQLAlchemy
from datetime import datetime

db = SQLAlchemy()

class Session(db.Model):
    __tablename__ = 'sessions'

    id = db.Column(db.Integer, primary_key=True)
    user = db.Column(db.String)

    start = db.Column(db.DateTime, default=datetime.utcnow)
    end = db.Column(db.DateTime)

    @classmethod
    def get_current(cls):
        return Session.query.filter(Session.end.is_(None)).first()

    @property
    def interval(self):
        if self.end:
            return self.end - self.start
        return datetime.utcnow() - self.start

    def finish(self):
        if not self.end:
            self.end = datetime.utcnow()