Add 'available' filter for BuildLine API endpoint (#5186)

* Add 'available' filter for BuildLine API endpoint

- Fixes missing filter
- Closes https://github.com/inventree/InvenTree/issues/1839

* Bump API version

InvenTree/build/api.py

@@ -1,6 +1,6 @@
 """JSON API for the Build app."""
 
-from django.db.models import F
+from django.db.models import F, Q
 from django.urls import include, path, re_path
 from django.utils.translation import gettext_lazy as _
 from django.contrib.auth.models import User
@@ -297,6 +297,25 @@ class BuildLineFilter(rest_filters.FilterSet):
         else:
             return queryset.filter(allocated__lt=F('quantity'))
 
+    available = rest_filters.BooleanFilter(label=_('Available'), method='filter_available')
+
+    def filter_available(self, queryset, name, value):
+        """Filter by whether there is sufficient stock available for each BuildLine:
+
+        To determine this, we need to know:
+
+        - The quantity required for each BuildLine
+        - The quantity available for each BuildLine
+        - The quantity allocated for each BuildLine
+        """
+
+        flt = Q(quantity__lte=F('total_available_stock') + F('allocated'))
+
+        if str2bool(value):
+            return queryset.filter(flt)
+        else:
+            return queryset.exclude(flt)
+
 
 class BuildLineEndpoint:
     """Mixin class for BuildLine API endpoints."""