Source code for inventory.models

from django.db import models
from django.db.models.signals import post_save
from django.dispatch import receiver
from django.core.validators import MaxValueValidator, MinValueValidator
from accounts.models import User




class Inventory(models.Model):
    item_name = models.CharField(max_length=255)
    description = models.TextField()
    unit_price = models.DecimalField(
        max_digits=10, decimal_places=2, validators=[MinValueValidator(0.0)]
    )
    stock_quantity = models.PositiveIntegerField()
    location = models.CharField(max_length=255)
    date_added = models.DateTimeField(auto_now_add=True)
    last_updated = models.DateTimeField(auto_now=True)
    image = models.ImageField(upload_to="inventory", null=True, blank=True)
    procurement_officer = models.ForeignKey(User, on_delete=models.CASCADE)

    def __str__(self):
        return str(self.item_name)





class HistoricalInventory(models.Model):
    stock_quantity = models.PositiveIntegerField()
    demand = models.PositiveIntegerField(default=0)
    datetime = models.DateTimeField()
    inventory = models.ForeignKey(Inventory, on_delete=models.CASCADE)

    def __str__(self):
        return f"{self.inventory.item_name} - {self.datetime}"





class OptimizedInventory(models.Model):
    demand = models.FloatField(validators=[MinValueValidator(0.0)])
    ordering_cost = models.FloatField(validators=[MinValueValidator(0.0)])
    holding_cost = models.FloatField(validators=[MinValueValidator(0.01)])
    lead_time = models.PositiveIntegerField(null=True, blank=True)
    service_level = models.FloatField(
        validators=[MinValueValidator(0.0), MaxValueValidator(1.0)],
        null=True,
        blank=True,
    )
    safety_stock = models.FloatField(
        null=True, blank=True, validators=[MinValueValidator(0.0)]
    )
    reorder_point = models.FloatField(
        null=True, blank=True, validators=[MinValueValidator(0.0)]
    )
    shelf_life = models.PositiveIntegerField(null=True, blank=True)
    storage_limit = models.PositiveIntegerField(null=True, blank=True)
    eoq = models.FloatField(null=True, blank=True, validators=[MinValueValidator(0.0)])
    inventory = models.OneToOneField(Inventory, on_delete=models.CASCADE)

    def __str__(self):
        return str(self.inventory.item_name)





@receiver(post_save, sender=Inventory)
def create_historical_inventory(sender, instance, created, **kwargs):
    timestamp = instance.last_updated if not created else instance.date_added
    latest_historical_inventory = (
        HistoricalInventory.objects.filter(inventory=instance)
        .order_by("-datetime")
        .first()
    )

    demand = 0
    if latest_historical_inventory:
        demand = max(
            0, latest_historical_inventory.stock_quantity - instance.stock_quantity
        )

    HistoricalInventory.objects.create(
        stock_quantity=instance.stock_quantity,
        datetime=timestamp,
        inventory=instance,
        demand=demand,
    )