from decimal import Decimal

from django.conf import settings
from django.core.validators import MinValueValidator, RegexValidator
from django.db import models


class ReportingEntry(models.Model):
    """Supplementary, documented facts absent from the operational sources.

    Purchases and cash movements are not automatically expensed again in profit:
    sales already carry their cost of goods. Corrections retain the audit trail.
    """

    class Kind(models.TextChoices):
        PRODUCTION = "production", "Выпуск продукции"
        PURCHASE = "purchase", "Закупка для производства"
        TAX = "tax", "Уплаченные налоги сотрудника"
        OVERHEAD = "overhead", "Общие расходы"
        CASH_IN = "cash_in", "Поступление денег"
        CASH_OUT = "cash_out", "Выплата денег"

    kind = models.CharField(max_length=16, choices=Kind.choices)
    date = models.DateField("Дата факта", db_index=True)
    reference = models.CharField("Документ / уникальный номер", max_length=200)
    description = models.CharField("Описание", max_length=500, blank=True)
    external_project = models.ForeignKey(
        "commerce.ExternalProject", null=True, blank=True, on_delete=models.PROTECT
    )
    project = models.ForeignKey(
        "projects.Project", null=True, blank=True, on_delete=models.PROTECT
    )
    product = models.ForeignKey(
        "commerce.Product", null=True, blank=True, on_delete=models.PROTECT
    )
    employee = models.ForeignKey(
        settings.AUTH_USER_MODEL, null=True, blank=True, on_delete=models.PROTECT
    )
    quantity = models.DecimalField(
        max_digits=18,
        decimal_places=4,
        default=0,
        validators=[MinValueValidator(Decimal("0"))],
    )
    amount = models.DecimalField(
        max_digits=18,
        decimal_places=2,
        default=0,
        validators=[MinValueValidator(Decimal("0"))],
    )
    currency = models.CharField(
        max_length=3, default="RUB", validators=[RegexValidator(r"^[A-Z]{3}$")]
    )
    created_by = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        on_delete=models.PROTECT,
        related_name="reporting_entries_created",
    )
    created_at = models.DateTimeField(auto_now_add=True)
    voided_at = models.DateTimeField(null=True, blank=True)
    voided_by = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        null=True,
        blank=True,
        on_delete=models.PROTECT,
        related_name="reporting_entries_voided",
    )

    class Meta:
        ordering = ["-date", "-pk"]
        constraints = [
            models.UniqueConstraint(
                fields=["kind", "reference"], name="reporting_entry_reference_unique"
            ),
            models.CheckConstraint(
                condition=models.Q(amount__gte=0, quantity__gte=0),
                name="reporting_entry_nonnegative",
            ),
            models.CheckConstraint(
                condition=(
                    models.Q(
                        kind="production",
                        product__isnull=False,
                        employee__isnull=True,
                        quantity__gt=0,
                        amount=0,
                    )
                    | models.Q(kind="purchase", employee__isnull=True, amount__gt=0)
                    | models.Q(
                        kind="tax",
                        employee__isnull=False,
                        product__isnull=True,
                        amount__gt=0,
                        quantity=0,
                    )
                    | models.Q(
                        kind__in=["overhead", "cash_in", "cash_out"],
                        product__isnull=True,
                        employee__isnull=True,
                        amount__gt=0,
                        quantity=0,
                    )
                ),
                name="reporting_entry_kind_fields",
            ),
        ]