from django.db import models
from django.utils import timezone

from apps.core.models import TimeStampedModel, UUIDModel


def generate_order_number() -> str:
    year = timezone.now().year
    prefix = f"STN-{year}-"
    last = (
        ProcessingOrder.objects.filter(order_number__startswith=prefix)
        .order_by("-order_number")
        .first()
    )
    if last:
        try:
            seq = int(last.order_number.rsplit("-", 1)[1]) + 1
        except (IndexError, ValueError):
            seq = 1
    else:
        seq = 1
    return f"{prefix}{seq:06d}"


class ProcessingOrder(UUIDModel, TimeStampedModel):
    class Status(models.TextChoices):
        DRAFT = "draft", "Draft"
        AWAITING_CONFIRMATION = "awaiting_confirmation", "Awaiting confirmation"
        CONFIRMED = "confirmed", "Confirmed"
        PROCESSING = "processing", "Processing"
        COMPLETED = "completed", "Completed"
        CANCELLED = "cancelled", "Cancelled"

    order_number = models.CharField(max_length=32, unique=True, blank=True)
    customer = models.ForeignKey("accounts.Customer", on_delete=models.PROTECT, related_name="orders")
    reservation = models.OneToOneField(
        "reservations.Reservation", null=True, blank=True, on_delete=models.SET_NULL, related_name="order"
    )
    # Workflow version is immutable per order — historical orders never change.
    workflow_version = models.ForeignKey(
        "workflows.WorkflowVersion", on_delete=models.PROTECT, related_name="orders"
    )
    gross_weight_kg = models.DecimalField(max_digits=12, decimal_places=2, null=True, blank=True)
    tare_weight_kg = models.DecimalField(max_digits=12, decimal_places=2, null=True, blank=True)
    net_weight_kg = models.DecimalField(max_digits=12, decimal_places=2, null=True, blank=True)
    selected_step_keys = models.JSONField(default=list, blank=True)
    price_snapshot = models.JSONField(default=dict, blank=True)
    currency = models.CharField(max_length=8, default="IRR")
    status = models.CharField(max_length=24, choices=Status.choices, default=Status.DRAFT)
    confirmed_at = models.DateTimeField(null=True, blank=True)
    terms_accepted = models.BooleanField(default=False)

    class Meta:
        ordering = ["-created_at"]

    def save(self, *args, **kwargs):
        if not self.order_number:
            self.order_number = generate_order_number()
        super().save(*args, **kwargs)

    def __str__(self) -> str:
        return self.order_number or str(self.id)