class ValidationError(Exception):
    pass

class Field(object):
    creation_counter = 0

    def __init__(self, name=None, max_length=0, required=True):
        self.name = name
        self._value = None
        self.max_length = max_length
        self.required = required
        self.creation_counter = Field.creation_counter
        Field.creation_counter += 1

    def validate(self):
        raise NotImplemented()

    def get_data(self):
        raise NotImplemented()
    
    def __setvalue(self, value):
        self._value = value

    def __getvalue(self):   
        return self._value
    
    value = property(__getvalue, __setvalue)

    def __repr__(self):
        return self.name


class TextField(Field):    
    def validate(self):
        if self.value == None and self.required:
            raise ValidationError("value required")
        if len(self.value) > self.max_length:
            raise ValidationError("value is too long")

    def get_data(self):
        return (self.value or "").encode('ascii').ljust(self.max_length)

class StateField(TextField):
    def __init__(self, name=None, required=True):
        return super(StateField, self).__init__(name=name, max_length=2, required=required)

class MoneyField(Field):
    def validate(self):
        if self.value == None and self.required:
            raise ValidationError("value required")
        if len(str(int((self.value or 0)*100))) > self.max_length:
            raise ValidationError("value is too long")

    def get_data(self):
        return str(int((self.value or 0)*100)).encode('ascii').zfill(self.max_length)