fix: Check for visible changes to diagrams

capella2polarion/elements/api_helper.py

@@ -1,12 +1,16 @@
 # Copyright DB Netz AG and contributors
 # SPDX-License-Identifier: Apache-2.0
 """Capella2Polarion specific helper functions to use the API."""
+import base64
 import collections.abc as cabc
+import io
 import logging
+import re
 import typing as t
 
 import polarion_rest_api_client as polarion_api
 from capellambse.model import common
+from PIL import Image, ImageChops
 
 from capella2polarion.elements import serialize
 
@@ -41,6 +45,10 @@ def patch_work_item(
     if new := receiver(obj, ctx):
         wid = ctx["POLARION_ID_MAP"][obj.uuid]
         old: serialize.CapellaWorkItem = ctx["POLARION_WI_MAP"][obj.uuid]
+
+        if _type == "diagram" and svg_diff(old.description, new.description):
+            return
+
         if new == old:
             return
 
@@ -72,6 +80,39 @@ def patch_work_item(
             logger.error("Updating work item %r failed. %s", wi, error.args[0])
 
 
+def pixel_diff(old: str, new: str) -> bool:
+    """Return True if the pixels of the diagrams differ."""
+    encoded_old = old.replace("data:image/", "").split(";base64,", 1)[1]
+    encoded_new = new.replace("data:image/", "").split(";base64,", 1)[1]
+
+    decoded_old = base64.b64decode(encoded_old)
+    decoded_new = base64.b64decode(encoded_new)
+
+    image_old = Image.open(io.BytesIO(decoded_old))
+    image_new = Image.open(io.BytesIO(decoded_new))
+
+    diff = ImageChops.difference(image_old, image_new)
+
+    return bool(diff.getbbox())
+
+
+def svg_diff(old: str, new: str) -> bool:
+    """Return True if the visible elements of the diagram SVGs differ."""
+    encoded_old = old.replace("data:image/svg+xml;base64,", "")
+    encoded_new = new.replace("data:image/svg+xml;base64,", "")
+
+    decoded_old = base64.b64decode(encoded_old).decode("utf-8").splitlines()
+    decoded_new = base64.b64decode(encoded_new).decode("utf-8").splitlines()
+
+    for i, d_old in enumerate(decoded_old):
+        if re.sub(r'id=["\'][^"\']*["\']', "", d_old) != re.sub(
+            r'id=["\'][^"\']*["\']', "", decoded_new[i]
+        ):
+            return True
+
+    return False
+
+
 def handle_links(
     left: cabc.Iterable[polarion_api.WorkItemLink],
     right: cabc.Iterable[polarion_api.WorkItemLink],