from decimal import Decimal

from django.contrib.auth import get_user_model
from django.db import models

User = get_user_model()


class PriceField(models.DecimalField):
    # allowing numbers until 99,999.99
    max_digits = 7
    decimal_places = 2

    def to_python(self, value):
        value = super().to_python(value)
        if isinstance(value, Decimal):
            return value.quantize(Decimal(10) ** -self.decimal_places)
        return value

    def __init__(self, *args, **kwargs):
        kwargs['max_digits'] = self.max_digits
        kwargs['decimal_places'] = self.decimal_places
        super().__init__(*args, **kwargs)


class Subject(models.Model):
    class Meta:
        unique_together = ("user", "name")

    user = models.ForeignKey(
        to=User, on_delete=models.CASCADE, editable=False,
        related_name="subjects", related_query_name="subject",
    )
    name = models.CharField(max_length=64)

    def __str__(self):
        return self.name


class Transaction(models.Model):
    class Meta:
        get_latest_by = "booking_date"

    amount = PriceField()
    booking_date = models.DateField()
    subject = models.ForeignKey(
        to=Subject, on_delete=models.CASCADE,
        related_name="transactions", related_query_name="transaction",
    )