Part stocktake (#4069)

* Remove stat context variables

* Revert "Remove stat context variables"

This reverts commit 0989c308d0.

* Allow longer timeout for image download tests

* Create PartStocktake model

Model for representing stocktake entries against any given part

* Admin interface support for new model

* Adds API endpoint for listing stocktake information

* Bump API version

* Enable filtering and ordering for API endpoint

* Add model to permission group

* Add UI hooks for displaying stocktake data for a particular part

* Fix encoded type for 'quantity' field

* Load stocktake table for part

* Add "stocktake" button

* Add "note" field for stocktake

* Add user information when performing stocktake

* First pass at UI elements for performing stocktake

* Add user information to stocktake table

* Auto-calculate quantity based on available stock items

* add stocktake data as tabular inline (admin)

* js linting

* Add indication that a stock item has not been updated recently

* Display last stocktake information on part page

* js style fix

* Test fix for ongoing CI issues

* Add configurable option for controlling default "delete_on_deplete" behaviour

* Add id values to cells

* Hide action buttons (at least for now)

* Adds refresh button to table

* Add API endpoint to delete or edit stocktake entries

* Adds unit test for API list endpoint

* javascript linting

* More unit testing

* Add Part API filter for stocktake

* Add 'last_stocktake' field to Part model

- Gets filled out automatically when a new PartStocktake instance is created

* Update part table to include last_stocktake date

* Add simple unit test

* Fix test

InvenTree/part/models.py

@@ -372,6 +372,7 @@ class Part(InvenTreeBarcodeMixin, MetadataMixin, MPTTModel):
         creation_date: Date that this part was added to the database
         creation_user: User who added this part to the database
         responsible: User who is responsible for this part (optional)
+        last_stocktake: Date at which last stocktake was performed for this Part
     """
 
     objects = PartManager()
@@ -1004,6 +1005,11 @@ class Part(InvenTreeBarcodeMixin, MetadataMixin, MPTTModel):
 
     responsible = models.ForeignKey(User, on_delete=models.SET_NULL, blank=True, null=True, verbose_name=_('Responsible'), related_name='parts_responible')
 
+    last_stocktake = models.DateField(
+        blank=True, null=True,
+        verbose_name=_('Last Stocktake'),
+    )
+
     @property
     def category_path(self):
         """Return the category path of this Part instance"""
@@ -2161,6 +2167,12 @@ class Part(InvenTreeBarcodeMixin, MetadataMixin, MPTTModel):
 
         return params
 
+    @property
+    def latest_stocktake(self):
+        """Return the latest PartStocktake object associated with this part (if one exists)"""
+
+        return self.stocktakes.order_by('-pk').first()
+
     @property
     def has_variants(self):
         """Check if this Part object has variants underneath it."""
@@ -2878,6 +2890,66 @@ class PartPricing(models.Model):
     )
 
 
+class PartStocktake(models.Model):
+    """Model representing a 'stocktake' entry for a particular Part.
+
+    A 'stocktake' is a representative count of available stock:
+    - Performed on a given date
+    - Records quantity of part in stock (across multiple stock items)
+    - Records user information
+    """
+
+    part = models.ForeignKey(
+        Part,
+        on_delete=models.CASCADE,
+        related_name='stocktakes',
+        verbose_name=_('Part'),
+        help_text=_('Part for stocktake'),
+    )
+
+    quantity = models.DecimalField(
+        max_digits=19, decimal_places=5,
+        validators=[MinValueValidator(0)],
+        verbose_name=_('Quantity'),
+        help_text=_('Total available stock at time of stocktake'),
+    )
+
+    date = models.DateField(
+        verbose_name=_('Date'),
+        help_text=_('Date stocktake was performed'),
+        auto_now_add=True
+    )
+
+    note = models.CharField(
+        max_length=250,
+        blank=True,
+        verbose_name=_('Notes'),
+        help_text=_('Additional notes'),
+    )
+
+    user = models.ForeignKey(
+        User, blank=True, null=True,
+        on_delete=models.SET_NULL,
+        related_name='part_stocktakes',
+        verbose_name=_('User'),
+        help_text=_('User who performed this stocktake'),
+    )
+
+
+@receiver(post_save, sender=PartStocktake, dispatch_uid='post_save_stocktake')
+def update_last_stocktake(sender, instance, created, **kwargs):
+    """Callback function when a PartStocktake instance is created / edited"""
+
+    # When a new PartStocktake instance is create, update the last_stocktake date for the Part
+    if created:
+        try:
+            part = instance.part
+            part.last_stocktake = instance.date
+            part.save()
+        except Exception:
+            pass
+
+
 class PartAttachment(InvenTreeAttachment):
     """Model for storing file attachments against a Part object."""