membersystem/src/accounting/models.py

"""Models for the accounting app."""

from hashlib import md5
from typing import Self

from django.conf import settings
from django.db import models
from django.db.models.aggregates import Sum
from django.utils.translation import gettext as _
from django.utils.translation import pgettext_lazy
from djmoney.models.fields import MoneyField
from djmoney.money import Money


class CreatedModifiedAbstract(models.Model):
    """Abstract model to track creation and modification of objects."""

    modified = models.DateTimeField(auto_now=True, verbose_name=_("modified"))
    created = models.DateTimeField(auto_now_add=True, verbose_name=_("created"))

    class Meta:
        abstract = True


class Account(CreatedModifiedAbstract):
    """An account for a user.

    This is the model where we can give access to several users, such that they
    can decide which account to use to pay for something.
    """

    owner = models.ForeignKey("auth.User", on_delete=models.PROTECT)

    def __str__(self) -> str:
        return f"Account of {self.owner.get_full_name()}"

    @property
    def balance(self) -> Money:
        """Return the balance of the account."""
        return self.transactions.all().aggregate(Sum("amount")).get("amount", 0)


class Transaction(CreatedModifiedAbstract):
    """A transaction.

    Tracks in and outgoing events of an account. When an order is received, an
    amount is subtracted, when a payment is received, an amount is added.
    """

    account = models.ForeignKey(
        Account,
        on_delete=models.PROTECT,
        related_name="transactions",
    )
    amount = MoneyField(
        verbose_name=_("amount"),
        max_digits=16,
        decimal_places=2,
        help_text=_("This will include VAT"),
    )
    description = models.CharField(max_length=1024, verbose_name=_("description"))

    def __str__(self) -> str:
        return f"Transaction of {self.amount} for {self.account}"


class Order(CreatedModifiedAbstract):
    """An order.

    Scoped out: Contents of invoices will have to be tracked either here or in
    a separate Invoice model. This is undecided because we are not generating
    invoices at the moment.
    """

    user = models.ForeignKey("auth.User", on_delete=models.PROTECT)
    account = models.ForeignKey(Account, on_delete=models.PROTECT)

    description = models.CharField(max_length=1024, verbose_name=_("description"))

    price = MoneyField(
        verbose_name=_("price (excl. VAT)"),
        max_digits=16,
        decimal_places=2,
    )
    vat = MoneyField(verbose_name=_("VAT"), max_digits=16, decimal_places=2)

    is_paid = models.BooleanField(default=False, verbose_name=_("is paid"))

    class Meta:
        verbose_name = pgettext_lazy("accounting term", "Order")
        verbose_name_plural = pgettext_lazy("accounting term", "Orders")

    def __str__(self) -> str:
        return f"Order ID {self.display_id}"

    @property
    def total(self) -> Money:
        """Return the total price of the order."""
        return self.price + self.vat

    @property
    def display_id(self) -> str:
        """Return an id for the order."""
        return str(self.id).zfill(6)

    @property
    def payment_token(self) -> str:
        """Return a token for the payment."""
        pk = str(self.pk).encode("utf-8")
        x = md5()  # noqa: S324
        x.update(pk)
        extra_hash = (settings.SECRET_KEY + "blah").encode("utf-8")
        x.update(extra_hash)
        return x.hexdigest()


class Payment(CreatedModifiedAbstract):
    """A payment is a transaction that is made to pay for an order."""

    amount = MoneyField(max_digits=16, decimal_places=2)
    order = models.ForeignKey(Order, on_delete=models.PROTECT)

    description = models.CharField(max_length=1024, verbose_name=_("description"))

    stripe_charge_id = models.CharField(max_length=255, blank=True)

    class Meta:
        verbose_name = _("payment")
        verbose_name_plural = _("payments")

    def __str__(self) -> str:
        return f"Payment ID {self.display_id}"

    @property
    def display_id(self) -> str:
        """Return an id for the payment."""
        return str(self.id).zfill(6)

    @classmethod
    def from_order(cls, order: Order) -> Self:
        """Create a payment from an order."""
        return cls.objects.create(
            order=order,
            user=order.user,
            amount=order.total,
            description=order.description,
        )