class ValidationError(Exception):
    pass

class Field(object):
    creation_counter = 0

    def __init__(self, name=None, max_length=0, required=True, uppercase=True):
        self.name = name
        self._value = None
        self.max_length = max_length
        self.required = required
        self.uppercase = uppercase
        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):
        value = self.value or ""
        if self.uppercase:
            value = value.upper()
        return value.ljust(self.max_length).encode('ascii')

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

class EmailField(TextField):
    def __init__(self, name=None, required=True, max_length=None):
        return super(EmailField, self).__init__(name=name, max_length=max_length, 
                                                required=required, uppercase=False)
class NumericField(TextField):
    def validate(self):
        super(NumericField, self).validate()
        try:
            int(self.value)
        except ValueError:
            raise ValidationError("field contains non-numeric characters")
        
class StaticField(TextField):
    def __init__(self, name=None, required=True, value=None):
        super(StaticField, self).__init__(name=name, required=required,
                                            max_length=len(value))
        self._value = value

class BlankField(TextField):
    def get_data(self):
        return " " * self.max_length

class BooleanField(Field):
    def validate(self):
        pass

    def get_data(self):
        return '1' if self._value else '0'

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)