# backend/modules/invoicing/models.py

import datetime
from django.utils import timezone
from core.base_models import BaseModel
from django.db import models, transaction
from django.utils.translation import gettext_lazy as _
from django.conf import settings
from .utils import generate_invoice_number

class Invoice(BaseModel):
    # Identifikacija (UUID i created_at dolaze iz BaseModel)
    invoice_number = models.CharField(max_length=50, unique=True, verbose_name=_("Broj fakture"))
    
    # Relacije
    creator = models.ForeignKey(
        settings.AUTH_USER_MODEL, 
        on_delete=models.PROTECT, 
        related_name="invoices"
    )
    client = models.ForeignKey(
        'crm.Client', 
        on_delete=models.PROTECT, 
        verbose_name=_("Klijent")
    )
    
    # Financijski detalji
    amount = models.DecimalField(max_digits=12, decimal_places=2, verbose_name=_("Iznos"))
    currency = models.CharField(max_length=3, default="EUR")
    tax_rate = models.DecimalField(max_digits=4, decimal_places=2, default=25.00)
    
    # Statusi
    status = models.CharField(
        max_length=20, 
        choices=[
            ('draft', 'Nacrt'),
            ('sent', 'Poslano'),
            ('paid', 'Plaćeno'),
            ('cancelled', 'Stornirano')
        ], 
        default='draft'
    )
    
    due_date = models.DateField(verbose_name=_("Rok plaćanja"))
    
    class Meta:
        # Nasljeđujemo ordering iz BaseModel, ali ga možemo override-ati
        verbose_name = _("Faktura")
        verbose_name_plural = _("Fakture")

    def __str__(self):
        return f"{self.invoice_number} - {self.client}"
    
    def get_total_amount(self):
        return self.items.aggregate(total=models.Sum(models.F('quantity') * models.F('unit_price')))['total'] or 0
    
    def save(self, *args, **kwargs):
        if not self.invoice_number:
            self.invoice_number = generate_invoice_number()
        super().save(*args, **kwargs)

class InvoiceItem(BaseModel):
    # Relacija prema fakturi
    invoice = models.ForeignKey(
        Invoice, 
        on_delete=models.CASCADE, 
        related_name='items',
        verbose_name=_("Faktura")
    )
    
    # Detalji stavke
    description = models.CharField(
        max_length=255, 
        verbose_name=_("Opis stavke")
    )
    quantity = models.DecimalField(
        max_digits=10, 
        decimal_places=2, 
        default=1,
        verbose_name=_("Količina")
    )
    unit_price = models.DecimalField(
        max_digits=12, 
        decimal_places=2, 
        verbose_name=_("Cijena po jedinici")
    )
    
    # Automatski izračun (property ne zauzima prostor u bazi)
    @property
    def total(self):
        return self.quantity * self.unit_price

    class Meta:
        verbose_name = _("Stavka fakture")
        verbose_name_plural = _("Stavke fakture")

    def __str__(self):
        # Koristimo prednost BaseModel __str__ metode
        return f"{self.description} ({self.quantity} x {self.unit_price})"

class InvoiceTransaction(BaseModel):
    # Polja specifična za fakturiranje
    invoice = models.ForeignKey(
        Invoice, 
        on_delete=models.PROTECT, 
        related_name='transactions',
        verbose_name=_("Faktura")
    )
    work_order = models.ForeignKey(
        'fleet.WorkOrder',
        on_delete=models.SET_NULL,
        related_name='invoice_transactions',
        null=True,
        blank=True,
        verbose_name=_("Putni nalog"),
    )
    invoice_number = models.CharField(max_length=50)
    amount = models.DecimalField(max_digits=10, decimal_places=2)
    payment_date = models.DateField(default=timezone.now)
    
    class Meta:
        verbose_name = "Financijski zapis"
        verbose_name_plural = "Financijski zapisi"