Adds option for duplicating an existing purchase order (#3567)

* Adds option for duplicating an existing purchase order

- Copy line items across

* Update API version

* JS linting

* Adds option for duplication of extra lines

* Decimal point rounding fix

* Unit tests for PO duplication via the API

InvenTree/order/test_api.py

@@ -225,6 +225,64 @@ class PurchaseOrderTest(OrderTest):
             expected_code=201
         )
 
+    def test_po_duplicate(self):
+        """Test that we can duplicate a PurchaseOrder via the API"""
+
+        self.assignRole('purchase_order.add')
+
+        po = models.PurchaseOrder.objects.get(pk=1)
+
+        self.assertTrue(po.lines.count() > 0)
+
+        # Add some extra line items to this order
+        for idx in range(5):
+            models.PurchaseOrderExtraLine.objects.create(
+                order=po,
+                quantity=idx + 10,
+                reference='some reference',
+            )
+
+        data = self.get(reverse('api-po-detail', kwargs={'pk': 1})).data
+
+        del data['pk']
+        del data['reference']
+
+        data['duplicate_order'] = 1
+        data['duplicate_line_items'] = True
+        data['duplicate_extra_lines'] = False
+
+        data['reference'] = 'PO-9999'
+
+        # Duplicate via the API
+        response = self.post(
+            reverse('api-po-list'),
+            data,
+            expected_code=201
+        )
+
+        # Order is for the same supplier
+        self.assertEqual(response.data['supplier'], po.supplier.pk)
+
+        po_dup = models.PurchaseOrder.objects.get(pk=response.data['pk'])
+
+        self.assertEqual(po_dup.extra_lines.count(), 0)
+        self.assertEqual(po_dup.lines.count(), po.lines.count())
+
+        data['reference'] = 'PO-9998'
+        data['duplicate_line_items'] = False
+        data['duplicate_extra_lines'] = True
+
+        response = self.post(
+            reverse('api-po-list'),
+            data,
+            expected_code=201,
+        )
+
+        po_dup = models.PurchaseOrder.objects.get(pk=response.data['pk'])
+
+        self.assertEqual(po_dup.extra_lines.count(), po.extra_lines.count())
+        self.assertEqual(po_dup.lines.count(), 0)
+
     def test_po_cancel(self):
         """Test the PurchaseOrderCancel API endpoint."""
         po = models.PurchaseOrder.objects.get(pk=1)