from datetime import datetime
from sqlalchemy import Column, Integer, Float, DateTime, String, ForeignKey
from sqlalchemy.orm import relationship, backref
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class Sensor(Base):
    __tablename__ = 'sensor'
    
    id = Column(Integer, primary_key=True)
    name = Column(String)
    description = Column(String, default="")

    def __init__(self, name, description=""):
        self.name = name
        self.description = description
        
    def __repr__(self):
        return "<Sensor('%s','%s','%s')>" % (self.id, self.name, self.description)




class Value(Base):
    __tablename__ = 'value'

    id = Column(Integer, primary_key=True)
    timestamp = Column(DateTime)
    sensor_id = Column(Integer, ForeignKey("sensor.id"))
    sensor = relationship(Sensor, backref=backref('values', order_by=timestamp))
    value = Column(Float(precision=4))

    def __init__(self, sensor, value, timestamp=datetime.now()):
        self.sensor  = sensor
        self.value = value
        self.timestamp = timestamp

    def __repr__(self):
        return "<Value('%s','%s','%s','%s'>" % (self.id, self.sensor, self.value, self.timestamp)