accounts/apps/wallet/models.py

import datetime
import uuid

from django.db import models
from django.db import transaction
from django.db.models import F
from django.utils.translation import gettext_lazy as _
from model_utils.choices import Choices
from rest_framework.exceptions import APIException, ValidationError

from .constans import STATE_CHOICES
from apps.users.models import User


class TransactionManager(models.Manager):
    def create_transaction(
            self,
            amount,
            payee: User,
            payer: User = None,
            delay=0,
            # detail_id=None,
            application_client_id=None,
            # state=None,
            uuid=None
    ):
        if not (isinstance(payer, User) or payer is None):
            raise ValidationError('payer type not valid')
        if not isinstance(payee, User):
            raise ValidationError('payee type not valid')
        if not amount > 0:
            raise ValidationError('amount should be greater than zero')
        if not delay >= 0:
            raise ValidationError('delay should be greater than equal zero')

        transaction = self.model(
            uuid=uuid,
            payer=payer,
            payee=payee,
            amount=amount,
            delay=delay,
            # detail_id=detail_id,
            application_client_id=application_client_id
        )
        # if state:
        #     transaction.state = state

        transaction.save()
        return transaction


class Transaction(models.Model):
    state_choices = STATE_CHOICES
    uuid = models.UUIDField(primary_key=True, editable=False, default=uuid.uuid4, unique=True,
                            db_index=True)  # reserve_code
    amount = models.IntegerField(_('amount'), blank=False)
    delay = models.IntegerField(default=0, blank=True)  # number of days for delayed payments
    payer = models.ForeignKey(User, on_delete=models.PROTECT, related_name='payments', blank=True, null=True)
    payee = models.ForeignKey(User, on_delete=models.PROTECT, related_name='receipts')
    state = models.IntegerField(choices=STATE_CHOICES, default=STATE_CHOICES.created)
    create = models.DateTimeField(_('create'), blank=True, null=True, auto_now=True)
    last_update = models.DateTimeField(_('last update'), blank=True, null=True, auto_now=True)
    application_client_id = models.CharField(max_length=100, db_index=True, null=True)
    detail_id = models.IntegerField(null=True, blank=True)  # TODO: or better detail url

    objects = TransactionManager()

    # class Meta:
    #     unique_together = ('application_client_id', 'detail_id',)

    def pay(self, payer=None):
        if not self.payer and not payer:
            raise APIException('payer identification error')

        if self.payer and payer and not self.payer == payer:
            raise APIException('payer identification error')

        # TODO: check bundry conditions
        if not self.state == STATE_CHOICES.created:
            raise APIException('this transaction is not ready to pay')

        if not self.payer:
            self.payer = payer

        with transaction.atomic():
            self.last_update = datetime.datetime.now()

            if self.payer.balance < self.amount:
                raise APIException('not enough balance')

            self.payer.balance = F('balance') - self.amount
            self.payer.save(update_fields=['balance'])

            self.payer.refresh_from_db()
            if self.payer.balance < 0:
                raise APIException('not enough balance')

            if self.delay:
                self.state = STATE_CHOICES.delayed
                self.save()

            else:
                self.payee.balance = F('balance') + self.amount
                self.payee.save(update_fields=['balance'])

                self.state = STATE_CHOICES.success
                self.save()

            self.save()
        return self

    def receipt(self):
        # TODO: check bundry conditions
        if not self.state == STATE_CHOICES.delayed:
            raise APIException('this transaction is not delayed')

        with transaction.atomic():
            self.last_update = datetime.datetime.now()
            self.payee.balance = F('balance') + self.amount
            self.state = STATE_CHOICES.success
            self.payee.save()
            self.save()

    def submit(self):
        if not self.payer:
            raise APIException('payer identification error')

        if not self.payee:
            raise APIException('payee identification error')

        # TODO: check bundry conditions
        if not self.state == STATE_CHOICES.created:
            raise APIException('this transaction is not ready to pay')

        with transaction.atomic():
            self.last_update = datetime.datetime.now()

            if self.payer.balance < self.amount:
                raise APIException('not enough balance')

            self.payer.balance = F('balance') - self.amount
            self.payer.save(update_fields=['balance'])

            self.payer.refresh_from_db()
            self.state = STATE_CHOICES.pending
            if self.payer.balance < 0:
                raise APIException('not enough balance')

            self.save()
        return self

    def verify(self):
        # TODO: check bundry conditions
        if not self.state == STATE_CHOICES.pending:
            raise APIException('this transaction is not pending')

        with transaction.atomic():
            self.last_update = datetime.datetime.now()
            self.payee.balance = F('balance') + self.amount
            self.state = STATE_CHOICES.success
            self.payee.save()
            self.save()

    def __str__(self):
        return f"{self.payer} -> {self.payee} ({self.uuid}): {self.amount}"