from django.db import models
from django.core.validators import MinValueValidator
from django.utils.translation import gettext_lazy as _
from decimal import Decimal

class ManufacturingOrder(models.Model):
    """Simple manufacturing order without BOM - just input end product result"""
    
    ORDER_STATUS = [
        ('completed', 'Completed'),
        ('in_progress', 'In Progress'),
        ('cancelled', 'Cancelled'),
    ]
    
    order_number = models.CharField(max_length=50, unique=True, help_text='Unique manufacturing order number')
    date = models.DateField()
    product = models.ForeignKey('inventory.Product', on_delete=models.CASCADE, related_name='manufacturing_orders')
    quantity = models.DecimalField(
        max_digits=10, 
        decimal_places=2,
        validators=[MinValueValidator(Decimal('0.01'))]
    )
    
    # Manufacturing details
    notes = models.TextField(blank=True, help_text='Manufacturing notes and instructions')
    status = models.CharField(max_length=20, choices=ORDER_STATUS, default='completed')
    
    # Cost tracking (optional)
    labor_cost = models.DecimalField(
        max_digits=10, 
        decimal_places=2, 
        default=0,
        validators=[MinValueValidator(Decimal('0'))]
    )
    overhead_cost = models.DecimalField(
        max_digits=10, 
        decimal_places=2, 
        default=0,
        validators=[MinValueValidator(Decimal('0'))]
    )
    total_cost = models.DecimalField(
        max_digits=10, 
        decimal_places=2, 
        default=0,
        validators=[MinValueValidator(Decimal('0'))]
    )
    
    # User tracking
    created_by = models.ForeignKey('users.CustomUser', on_delete=models.SET_NULL, null=True)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    
    class Meta:
        ordering = ['-date', '-created_at']
        verbose_name = _('Manufacturing Order')
        verbose_name_plural = _('Manufacturing Orders')
    
    def __str__(self):
        return f"MO-{self.order_number} - {self.product.name} ({self.quantity})"
    
    def save(self, *args, **kwargs):
        """Override save to calculate total cost and update product stock"""
        # Calculate total cost
        self.total_cost = self.labor_cost + self.overhead_cost
        
        # If this is a new order and status is completed, add to inventory
        if not self.pk and self.status == 'completed':
            # Update product stock
            self.product.current_stock += self.quantity
            
            # Update product cost price if this is the first manufacturing order
            if self.product.manufacturing_orders.count() == 0:
                self.product.cost_price = self.total_cost / self.quantity
            else:
                # Calculate weighted average cost
                total_quantity = self.product.manufacturing_orders.aggregate(
                    total=models.Sum('quantity')
                )['total'] or 0
                total_cost = self.product.manufacturing_orders.aggregate(
                    total=models.Sum('total_cost')
                )['total'] or 0
                
                if total_quantity > 0:
                    self.product.cost_price = total_cost / total_quantity
            
            self.product.save()
        
        super().save(*args, **kwargs)
    
    def get_unit_cost(self):
        """Calculate unit cost for this manufacturing order"""
        if self.quantity > 0:
            return self.total_cost / self.quantity
        return Decimal('0')
    
    def get_profit_margin(self):
        """Calculate potential profit margin if product has selling price"""
        if self.product.selling_price > 0:
            unit_cost = self.get_unit_cost()
            if unit_cost > 0:
                return ((self.product.selling_price - unit_cost) / unit_cost) * 100
        return Decimal('0')

class ManufacturingLine(models.Model):
    """Manufacturing line/workstation information"""
    
    name = models.CharField(max_length=100)
    description = models.TextField(blank=True)
    capacity_per_hour = models.DecimalField(
        max_digits=8, 
        decimal_places=2, 
        blank=True, 
        null=True,
        help_text='Production capacity per hour'
    )
    is_active = models.BooleanField(default=True)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    
    class Meta:
        ordering = ['name']
        verbose_name = _('Manufacturing Line')
        verbose_name_plural = _('Manufacturing Lines')
    
    def __str__(self):
        return self.name

class ManufacturingOrderLine(models.Model):
    """Individual line items for manufacturing orders (optional for future expansion)"""
    
    manufacturing_order = models.ForeignKey(ManufacturingOrder, on_delete=models.CASCADE, related_name='lines')
    manufacturing_line = models.ForeignKey(ManufacturingLine, on_delete=models.SET_NULL, null=True, blank=True)
    start_time = models.DateTimeField(blank=True, null=True)
    end_time = models.DateTimeField(blank=True, null=True)
    actual_quantity = models.DecimalField(
        max_digits=10, 
        decimal_places=2,
        validators=[MinValueValidator(Decimal('0'))]
    )
    notes = models.TextField(blank=True)
    
    class Meta:
        verbose_name = _('Manufacturing Order Line')
        verbose_name_plural = _('Manufacturing Order Lines')
    
    def __str__(self):
        return f"{self.manufacturing_order.order_number} - Line {self.id}"
    
    def get_duration(self):
        """Calculate duration of manufacturing line operation"""
        if self.start_time and self.end_time:
            return self.end_time - self.start_time
        return None