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

ModelBase = declarative_base()

class Sensor(ModelBase):
    __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)

# http://www.sqlalchemy.org/docs/05/reference/ext/declarative.html#inheritance-configuration
class Value(ModelBase):
    __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))

    discriminator = Column('type', String(50))
    __mapper_args__ = {'polymorphic_on': discriminator}

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

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

    def value(self):
        raise NotImplementedException()

class ValueFloat(Value):
    __mapper_args__ = {'polymorphic_identity': 'float'}
    value_float = Column(Float(precision=4))
    
    def __init__(self, sensor, value, timestamp=datetime.now()):
        Value.__init__(self, sensor, timestamp)
        self.value_float = value

    def value(self):
        return self.value_float

class ValueInt(Value):
    __mapper_args__ = {'polymorphic_identity': 'int'}
    value_int = Column(Integer)

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

    def value(self):
        return self.value_int

class ValueString(Value):
    __mapper_args__ = {'polymorphic_identity': 'string'}
    value_string = Column(String)

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

    def value(self):
        return self.value_string