From ba542dcbdb6a4fdc4c5599d515003090ed47fc91 Mon Sep 17 00:00:00 2001
From: Oliver Walters <oliver.henry.walters@gmail.com>
Date: Wed, 17 Feb 2021 13:06:18 +1100
Subject: [PATCH] Auto-fill build quantity

---
 InvenTree/build/forms.py |  5 +++++
 InvenTree/build/views.py | 22 +++++++++++++++-------
 InvenTree/part/models.py | 39 +++++++++++++++++++++++++++++++--------
 3 files changed, 51 insertions(+), 15 deletions(-)

diff --git a/InvenTree/build/forms.py b/InvenTree/build/forms.py
index f5764b9d93..061ae0d16d 100644
--- a/InvenTree/build/forms.py
+++ b/InvenTree/build/forms.py
@@ -39,6 +39,11 @@ class EditBuildForm(HelperForm):
         help_text=_('Target date for build completion. Build will be overdue after this date.')
     )
 
+    quantity = RoundingDecimalFormField(
+        max_digits=10, decimal_places=5,
+        help_text=_('Number of items to build')
+    )
+
     class Meta:
         model = Build
         fields = [
diff --git a/InvenTree/build/views.py b/InvenTree/build/views.py
index 76cc9bcfde..18971d74a6 100644
--- a/InvenTree/build/views.py
+++ b/InvenTree/build/views.py
@@ -675,6 +675,14 @@ class BuildCreate(AjaxCreateView):
 
         initials = super(BuildCreate, self).get_initial().copy()
 
+
+        initials['parent'] = self.request.GET.get('parent', None)
+
+        # User has provided a SalesOrder ID
+        initials['sales_order'] = self.request.GET.get('sales_order', None)
+
+        initials['quantity'] = self.request.GET.get('quantity', 1)
+
         part = self.request.GET.get('part', None)
 
         if part:
@@ -684,18 +692,18 @@ class BuildCreate(AjaxCreateView):
                 # User has provided a Part ID
                 initials['part'] = part
                 initials['destination'] = part.get_default_location()
+
+                to_order = part.quantity_to_order
+
+                if to_order < 1:
+                    to_order = 1
+
+                initials['quantity'] = to_order
             except (ValueError, Part.DoesNotExist):
                 pass
 
         initials['reference'] = Build.getNextBuildNumber()
 
-        initials['parent'] = self.request.GET.get('parent', None)
-
-        # User has provided a SalesOrder ID
-        initials['sales_order'] = self.request.GET.get('sales_order', None)
-
-        initials['quantity'] = self.request.GET.get('quantity', 1)
-
         # Pre-fill the issued_by user
         initials['issued_by'] = self.request.user
 
diff --git a/InvenTree/part/models.py b/InvenTree/part/models.py
index c5e562ec80..82a7073612 100644
--- a/InvenTree/part/models.py
+++ b/InvenTree/part/models.py
@@ -976,20 +976,43 @@ class Part(MPTTModel):
 
         return quantity
 
+    def required_order_quantity(self):
+        """
+        Return total required to fulfil orders
+        """
+
+        return self.required_build_order_quantity() + self.required_sales_order_quantity()
+
     @property
     def quantity_to_order(self):
-        """ Return the quantity needing to be ordered for this part. """
+        """
+        Return the quantity needing to be ordered for this part.
+        
+        Here, an "order" could be one of:
+        - Build Order
+        - Sales Order
 
-        # How many do we need to have "on hand" at any point?
-        required = self.net_stock - self.minimum_stock
+        To work out how many we need to order:
 
-        if required < 0:
-            return abs(required)
+        Stock on hand = self.total_stock
+        Required for orders = self.required_order_quantity()
+        Currently on order = self.on_order
+        Currently building = self.quantity_being_built
+        
+        """
 
-        # Do not need to order any
-        return 0
+        # Total requirement
+        required = self.required_order_quantity()
+
+        # Subtract stock levels
+        required -= max(self.total_stock, self.minimum_stock)
+
+        # Subtract quantity on order
+        required -= self.on_order
+
+        # Subtract quantity being built
+        required -= self.quantity_being_built
 
-        required = self.net_stock
         return max(required, 0)
 
     @property