From 4c3032e2f09499b0c34a61c622f40b1420246a4f Mon Sep 17 00:00:00 2001
From: Oliver Walters <oliver.henry.walters@gmail.com>
Date: Sun, 12 May 2019 12:42:06 +1000
Subject: [PATCH] Add function to calculate BOM hash

- Uses hashlib.md5
---
 InvenTree/part/models.py                  | 24 +++++++++++++++++++++++
 InvenTree/part/templates/part/detail.html |  4 ++++
 2 files changed, 28 insertions(+)

diff --git a/InvenTree/part/models.py b/InvenTree/part/models.py
index 06ec2f1955..3c7cc22a32 100644
--- a/InvenTree/part/models.py
+++ b/InvenTree/part/models.py
@@ -25,6 +25,7 @@ from django.db.models.signals import pre_delete
 from django.dispatch import receiver
 
 from fuzzywuzzy import fuzz
+import hashlib
 
 from InvenTree import helpers
 from InvenTree import validators
@@ -473,6 +474,29 @@ class Part(models.Model):
     def used_in_count(self):
         return self.used_in.count()
 
+    @property
+    def get_bom_hash(self):
+        """ Return a checksum hash for the BOM for this part. 
+        Used to determine if the BOM has changed (and needs to be signed off!)
+
+        For hash is calculated from the following fields of each BOM item:
+
+        - Part.full_name (if the part name changes, the BOM checksum is invalidated)
+        - quantity
+        - Note field
+        
+        returns a string representation of a hash object which can be compared with a stored value
+        """
+
+        hash = hashlib.md5('bom seed'.encode())
+
+        for item in self.bom_items.all():
+            hash.update(str(item.sub_part.full_name).encode())
+            hash.update(str(item.quantity).encode())
+            hash.update(str(item.notes).encode())
+
+        return str(hash.digest())
+
     def required_parts(self):
         parts = []
         for bom in self.bom_items.all():
diff --git a/InvenTree/part/templates/part/detail.html b/InvenTree/part/templates/part/detail.html
index ddb0523a83..42c7af0bfe 100644
--- a/InvenTree/part/templates/part/detail.html
+++ b/InvenTree/part/templates/part/detail.html
@@ -51,6 +51,10 @@
             <td><a href="{{ part.URL }}">{{ part.URL }}</a></td>
         </tr>
         {% endif %}
+        <tr>
+            <td>Hash</td>
+            <td>{{ part.get_bom_hash }}</td>
+        </tr>
         <tr>
             <td>Category</td>
             <td>