from django.db import models
from django.core.validators import MinValueValidator


class Category(models.Model):
    name = models.CharField(max_length=100)
    description = models.TextField(blank=True)
    created_at = models.DateTimeField(auto_now_add=True)
    
    def __str__(self):
        return self.name


class UnitOfMeasure(models.Model):
    name = models.CharField(max_length=50)
    abbreviation = models.CharField(max_length=10)
    
    def __str__(self):
        return self.name


class Product(models.Model):
    PRODUCT_TYPES = [
        ('raw_material', 'Raw Material'),
        ('finished_good', 'Finished Good'),
        ('component', 'Component'),
    ]
    
    code = models.CharField(max_length=50, unique=True)
    name = models.CharField(max_length=200)
    description = models.TextField(blank=True)
    category = models.ForeignKey(Category, on_delete=models.SET_NULL, null=True, blank=True)
    unit_of_measure = models.ForeignKey(UnitOfMeasure, on_delete=models.SET_NULL, null=True)
    product_type = models.CharField(max_length=20, choices=PRODUCT_TYPES)
    reorder_level = models.DecimalField(max_digits=10, decimal_places=2, default=0)
    selling_price = models.DecimalField(max_digits=10, decimal_places=2, null=True, blank=True)
    cost_price = models.DecimalField(max_digits=10, decimal_places=2, null=True, blank=True)
    is_active = models.BooleanField(default=True)
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at = models.DateTimeField(auto_now=True)
    
    def __str__(self):
        return f"{self.code} - {self.name}"


class Warehouse(models.Model):
    name = models.CharField(max_length=100)
    location = models.CharField(max_length=200)
    is_active = models.BooleanField(default=True)
    created_at = models.DateTimeField(auto_now_add=True)
    
    def __str__(self):
        return self.name


class Inventory(models.Model):
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    warehouse = models.ForeignKey(Warehouse, on_delete=models.CASCADE)
    quantity = models.DecimalField(max_digits=10, decimal_places=2, default=0)
    reserved_quantity = models.DecimalField(max_digits=10, decimal_places=2, default=0)
    updated_at = models.DateTimeField(auto_now=True)
    
    class Meta:
        unique_together = ('product', 'warehouse')
    
    @property
    def available_quantity(self):
        return self.quantity - self.reserved_quantity


class StockMovement(models.Model):
    MOVEMENT_TYPES = [
        ('in', 'Stock In'),
        ('out', 'Stock Out'),
        ('adjustment', 'Adjustment'),
        ('transfer', 'Transfer'),
    ]
    
    product = models.ForeignKey(Product, on_delete=models.CASCADE)
    warehouse = models.ForeignKey(Warehouse, on_delete=models.CASCADE)
    movement_type = models.CharField(max_length=20, choices=MOVEMENT_TYPES)
    quantity = models.DecimalField(max_digits=10, decimal_places=2)
    reference_number = models.CharField(max_length=100, blank=True)
    notes = models.TextField(blank=True)
    created_by = models.ForeignKey('accounts.User', on_delete=models.SET_NULL, null=True)
    created_at = models.DateTimeField(auto_now_add=True)