import uuid
from decimal import Decimal

from django.core.validators import MinValueValidator
from django.db import models


class SaleEventType(models.TextChoices):
    SALE = "sale", "Продажа"
    RETURN = "return", "Возврат"


class Sale(models.Model):
    """Normalized sale/order event supplied by an external or internal system."""

    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    project = models.ForeignKey(
        "commerce.ExternalProject", null=True, blank=True, on_delete=models.PROTECT
    )
    source = models.ForeignKey(
        "commerce.SourceSystem",
        on_delete=models.PROTECT,
        related_name="sales",
        verbose_name="Источник",
    )
    source_record = models.ForeignKey(
        "commerce.SourceRecord",
        on_delete=models.SET_NULL,
        null=True,
        blank=True,
        related_name="sales",
        verbose_name="Исходная запись",
    )
    external_id = models.CharField("Внешний ID", max_length=255)
    event_type = models.CharField(
        "Тип операции",
        max_length=16,
        choices=SaleEventType.choices,
        default=SaleEventType.SALE,
    )
    number = models.CharField("Номер", max_length=128, blank=True)
    channel = models.CharField("Канал продаж", max_length=64, blank=True, db_index=True)
    customer_external_id = models.CharField(
        "ID клиента в источнике", max_length=255, blank=True
    )
    customer_name = models.CharField("Клиент", max_length=255, blank=True)
    status = models.CharField("Статус источника", max_length=128, blank=True)
    counts_as_sale = models.BooleanField(
        "Учитывать в продажах",
        default=True,
        help_text="Отключается для отменённых или тестовых заказов.",
    )
    currency = models.CharField("Валюта", max_length=3, default="RUB")
    occurred_at = models.DateTimeField("Дата операции", db_index=True)
    source_updated_at = models.DateTimeField(
        "Изменено в источнике", null=True, blank=True
    )
    created_at = models.DateTimeField("Создано", auto_now_add=True)
    updated_at = models.DateTimeField("Обновлено", auto_now=True)

    class Meta:
        verbose_name = "Продажа"
        verbose_name_plural = "Продажи"
        ordering = ["-occurred_at", "-created_at"]
        constraints = [
            models.UniqueConstraint(
                fields=["source", "external_id"],
                name="commerce_sale_source_external",
            )
        ]
        indexes = [
            models.Index(
                fields=["counts_as_sale", "occurred_at"],
                name="commerce_sale_counted_date",
            )
        ]

    def __str__(self):
        return self.number or f"{self.source.code}:{self.external_id}"


class SaleLine(models.Model):
    """Product-level monetary fact within a sale."""

    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    sale = models.ForeignKey(
        Sale,
        on_delete=models.CASCADE,
        related_name="lines",
        verbose_name="Продажа",
    )
    product = models.ForeignKey(
        "commerce.Product",
        on_delete=models.PROTECT,
        null=True,
        blank=True,
        related_name="sale_lines",
        verbose_name="Товар",
    )
    external_id = models.CharField("Внешний ID позиции", max_length=255)
    external_product_id = models.CharField(
        "Внешний ID товара", max_length=255, blank=True
    )
    external_sku = models.CharField("Внешний артикул", max_length=128, blank=True)
    name = models.CharField("Название в источнике", max_length=255, blank=True)
    quantity = models.DecimalField(
        "Количество",
        max_digits=18,
        decimal_places=4,
        default=Decimal("1"),
        validators=[MinValueValidator(Decimal("0"))],
    )
    gross_amount = models.DecimalField(
        "Сумма до скидки",
        max_digits=18,
        decimal_places=2,
        default=Decimal("0"),
        validators=[MinValueValidator(Decimal("0"))],
    )
    discount_amount = models.DecimalField(
        "Скидка",
        max_digits=18,
        decimal_places=2,
        default=Decimal("0"),
        validators=[MinValueValidator(Decimal("0"))],
    )
    cost_amount = models.DecimalField(
        "Себестоимость",
        max_digits=18,
        decimal_places=2,
        default=Decimal("0"),
        validators=[MinValueValidator(Decimal("0"))],
    )
    metadata = models.JSONField("Дополнительные данные", default=dict, blank=True)

    class Meta:
        verbose_name = "Позиция продажи"
        verbose_name_plural = "Позиции продаж"
        constraints = [
            models.UniqueConstraint(
                fields=["sale", "external_id"],
                name="commerce_sale_line_identity",
            ),
            models.CheckConstraint(
                condition=models.Q(discount_amount__lte=models.F("gross_amount")),
                name="commerce_sale_line_discount_lte_gross",
            ),
        ]
        indexes = [
            models.Index(fields=["product", "sale"], name="commerce_line_product_sale")
        ]

    @property
    def net_amount(self):
        return self.gross_amount - self.discount_amount

    def __str__(self):
        return self.name or self.external_sku or self.external_id