##
# This file is part of TALER
#  (C) 2014, 2015, 2016 INRIA
#
#  TALER is free software; you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation; either version 3, or
# (at your option) any later version. TALER is distributed in the
# hope that it will be useful, but WITHOUT ANY WARRANTY; without
# even the implied warranty of MERCHANTABILITY or FITNESS FOR A
# PARTICULAR PURPOSE.  See the GNU General Public License for more
# details.
#
# You should have received a copy of the GNU General Public License
# along with TALER; see the file COPYING.  If not, see
# <http://www.gnu.org/licenses/>
#
#  @author Marcello Stanisci
#  @author Florian Dold

from __future__ import unicode_literals
from typing import Any, Tuple
from django.contrib.auth.models import User
from django.db import models
from django.conf import settings
from django.core.exceptions import \
    ValidationError, \
    ObjectDoesNotExist
from .amount import Amount, BadFormatAmount, NumberTooBig

class InvalidAmount(Amount):
    def __init__(self, currency):
        super(InvalidAmount, self).__init__(currency, value=float('nan'), fraction=float('nan'))

    def stringify(self, ndigits, pretty):
        return "Invalid Amount, please report"
    def dump(self):
        return "Invalid Amount, please report"

##
# Helper function that instantiates a zero-valued @a Amount
# object.
def get_zero_amount() -> Amount:
    return Amount(settings.TALER_CURRENCY)


##
# Custom implementation of the @a Amount class as a database type.
class AmountField(models.Field):
    description = 'Amount object in Taler style'

    ##
    # Return the database type of the serialized amount.
    #
    # @param self the object itself.
    # @param connection the database connection.
    # @return type of the serialized amount: varchar.
    def db_type(self, connection: Any) -> str:
        return "varchar"

    ##
    # Stringifies the Amount object to feed the DB connector.
    #
    # @param self the object itself.
    # @para value the @a Amount object to be serialized.
    def get_prep_value(self, value: Amount) -> str:
        if not value:
            return "%s:0.0" % settings.TALER_CURRENCY
        if settings.TALER_CURRENCY != value.currency:
            raise CurrencyMismatch(settings.TALER_CURRENCY,
                                   value.currency)
        return value.stringify(settings.TALER_DIGITS)

    ##
    # Parse the stringified Amount back to Python.
    #
    # @param value serialized amount coming from the database.
    #        (It is just a string in the usual CURRENCY:X.Y form)
    # @param args currently unused.
    # @return the @a Amount object.
    @staticmethod
    def from_db_value(value: str, *args) -> Amount:
        del args # pacify PEP checkers
        if value is None:
            return Amount.parse(settings.TALER_CURRENCY)
        try:
            return Amount.parse(value)
        except NumberTooBig:
            # Keep the currency right to avoid causing
            # exceptions if some operation is attempted
            # against this invalid amount.  NOTE that the
            # value is defined as NaN, so no actual/useful
            # amount will ever be generated using this one.
            # And more, the NaN value will make it easier
            # to scan the database to find these faulty
            # amounts.
            # We also decide to not raise exception here
            # because they would propagate in too many places
            # in the code, and it would be too verbose to
            # just try-cactch any possible exception situation.
            return InvalidAmount(settings.TALER_CURRENCY)


    ##
    # Parse the stringified Amount back to Python. FIXME:
    # why this serializer consider _more_ cases respect to the
    # one above ('from_db_value')?
    #
    # @param value serialized amount coming from the database.
    #        (It is just a string in the usual CURRENCY:X.Y form)
    # @param args currently unused.
    # @return the @a Amount object.
    def to_python(self, value: Any) -> Amount:
        if isinstance(value, Amount):
            return value
        try:
            if value is None:
                return Amount.parse(settings.TALER_CURRENCY)
            return Amount.parse(value)
        except BadFormatAmount:
            raise ValidationError(
                "Invalid input for an amount string: %s" % value)

##
# The class representing a bank account.
class BankAccount(models.Model):
    is_public = models.BooleanField(default=False)
    debit = models.BooleanField(default=False)
    account_no = models.AutoField(primary_key=True)
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    amount = AmountField(default=get_zero_amount)

##
# The class representing a bank transaction.
class BankTransaction(models.Model):
    amount = AmountField(default=False)
    debit_account = models.ForeignKey(
        BankAccount,
        on_delete=models.CASCADE,
        db_index=True,
        related_name="debit_account")
    credit_account = models.ForeignKey(
        BankAccount,
        on_delete=models.CASCADE,
        db_index=True,
        related_name="credit_account")
    subject = models.CharField(
        default="(no subject given)", max_length=200)
    date = models.DateTimeField(
        auto_now=True, db_index=True)
    cancelled = models.BooleanField(default=False)