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


class LockerBank(models.Model):
    """A set of locker units, placed together"""

    name = models.CharField(max_length=200)
    location = models.CharField(max_length=200)
    slug = models.SlugField(unique=True)

    def __str__(self):
        return f"{self.name} ({self.units.count()} units)"


class LockerUnit(models.Model):
    """A standalone set of lockers"""

    bank = models.ForeignKey(
        LockerBank, on_delete=models.SET_NULL, related_name="units", null=True
    )
    index = models.PositiveIntegerField()
    first_letter = models.CharField(
        max_length=1, validators=[validators.RegexValidator("[A-Z]")], unique=True
    )
    first_number = models.PositiveIntegerField()
    rows = models.PositiveIntegerField(default=5)
    columns = models.PositiveIntegerField(default=2)

    class Meta:
        # TODO: add constraint to check for letter overlaps
        constraints = [
            models.UniqueConstraint(fields=["bank", "index"], name="unique_bank_index")
        ]
        ordering = ["index"]

    def letter_for_column(self, column: int) -> str:
        return chr(column + ord(self.first_letter))

    def number_for_locker(self, column: int, row: int) -> int:
        return row + self.first_number + column * self.rows

    @property
    def iter_doors(self):
        for row in range(self.rows):
            for column in range(self.columns):
                # TODO: filter could be optimized
                yield (
                    self.letter_for_column(column),
                    self.number_for_locker(column, row),
                    self.rentals.filter(row=row, column=column),
                )


# TODO: add check constraint to ensure that column and number are within locker_unit bounds
# TODO: add unique constraint on (unit, row, column)?
class LockerRental(models.Model):
    """A rental of a single locker"""

    locker_unit = models.ForeignKey(
        LockerUnit, on_delete=models.CASCADE, related_name="rentals"
    )
    column = models.PositiveIntegerField()
    row = models.PositiveIntegerField()
    user = models.ForeignKey(get_user_model(), on_delete=models.CASCADE)

    @property
    def address(self) -> str:
        letter = self.locker_unit.letter_for_column(self.column)
        number = self.locker_unit.number_for_locker(self.column, self.row)
        return f"{self.locker_unit}-{letter}{number}"

    def __str__(self):
        return f"{self.user}: {self.address}"