import uuid
from decimal import Decimal

from django.db import models


class StockSnapshot(models.Model):
    """Point-in-time stock observation supplied by a source system."""

    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    product = models.ForeignKey(
        "commerce.Product",
        on_delete=models.CASCADE,
        related_name="stock_snapshots",
        verbose_name="Товар",
    )
    source = models.ForeignKey(
        "commerce.SourceSystem",
        on_delete=models.PROTECT,
        related_name="stock_snapshots",
        verbose_name="Источник",
    )
    warehouse_external_id = models.CharField("ID склада", max_length=255)
    warehouse_name = models.CharField("Склад", max_length=255, blank=True)
    quantity = models.DecimalField(
        "Остаток", max_digits=18, decimal_places=4, default=Decimal("0")
    )
    reserved = models.DecimalField(
        "Резерв", max_digits=18, decimal_places=4, default=Decimal("0")
    )
    in_transit = models.DecimalField(
        "В пути", max_digits=18, decimal_places=4, default=Decimal("0")
    )
    captured_at = models.DateTimeField("Дата снимка", db_index=True)
    metadata = models.JSONField("Дополнительные данные", default=dict, blank=True)
    created_at = models.DateTimeField("Создано", auto_now_add=True)

    class Meta:
        verbose_name = "Снимок остатка"
        verbose_name_plural = "Снимки остатков"
        ordering = ["-captured_at"]
        constraints = [
            models.UniqueConstraint(
                fields=["product", "source", "warehouse_external_id", "captured_at"],
                name="commerce_stock_snapshot_identity",
            )
        ]
        indexes = [
            models.Index(
                fields=["product", "source", "warehouse_external_id", "-captured_at"],
                name="commerce_stock_latest",
            )
        ]

    @property
    def available(self):
        return self.quantity - self.reserved

    def __str__(self):
        warehouse = self.warehouse_name or self.warehouse_external_id
        return f"{self.product.sku} · {warehouse} · {self.quantity}"