"""
Invoice models for tracking customer billing.
"""
import uuid
from django.db import models
from django.utils import timezone


class Invoice(models.Model):
    """Invoice records"""
    STATUS_CHOICES = (
        ('draft', 'Draft'),
        ('sent', 'Sent'),
        ('paid', 'Paid'),
        ('overdue', 'Overdue'),
        ('cancelled', 'Cancelled'),
    )
    PAYMENT_CHOICES = (
        ('check', 'Check'),
        ('credit_card', 'Credit Card'),
        ('bank_transfer', 'Bank Transfer'),
        ('cash', 'Cash'),
    )
    id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    customer = models.ForeignKey('Customer', on_delete=models.CASCADE, related_name='invoices')
    date = models.DateField()

    # Related items
    accounts = models.ManyToManyField('Account', related_name='invoices', blank=True)
    projects = models.ManyToManyField('Project', related_name='invoices', blank=True)

    # Status and payment
    status = models.CharField(max_length=20, choices=STATUS_CHOICES, default='draft')
    date_paid = models.DateField(blank=True, null=True)
    payment_type = models.CharField(max_length=20, choices=PAYMENT_CHOICES, blank=True, null=True)

    # Financial
    total_amount = models.DecimalField(max_digits=10, decimal_places=2, default=0)

    # Timestamps
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    sent_at = models.DateTimeField(blank=True, null=True)

    class Meta:
        app_label = 'core'
        verbose_name = 'Invoice'
        verbose_name_plural = 'Invoices'
        ordering = ['-date']
        indexes = [
            models.Index(fields=['customer']),
            models.Index(fields=['date']),
            models.Index(fields=['status']),
        ]

    def __str__(self):
        return f"Invoice for {self.customer.name} on {self.date}"

    def save(self, *args, **kwargs):
        """Override save to update timestamps based on status"""
        if self.status == 'sent' and not self.sent_at:
            self.sent_at = timezone.now()
        super().save(*args, **kwargs)

    @property
    def is_paid(self):
        """Check if invoice is paid"""
        return self.status == 'paid'

    @property
    def is_overdue(self):
        """Check if invoice is overdue"""
        # Normally you'd check against a due date field, but we'll use a simple 30 day rule
        if self.status not in ['paid', 'cancelled'] and self.sent_at:
            return (timezone.now().date() - self.date).days > 30
        return False

    @property
    def days_outstanding(self):
        """Calculate days since invoice was sent"""
        if not self.sent_at:
            return 0
        return (timezone.now().date() - self.sent_at.date()).days