Unit test for content diff

content.py

@@ -7,6 +7,7 @@ __email__ = "bob@libreserver.org"
 __status__ = "Production"
 __module_group__ = "Core"
 
+import difflib
 import math
 import html
 import os
@@ -1415,3 +1416,52 @@ def import_emoji(base_dir: str, import_filename: str, session) -> None:
                 added += 1
     save_json(emoji_dict, base_dir + '/emoji/default_emoji.json')
     print(str(added) + ' custom emoji added')
+
+
+def content_diff(content: str, prev_content: str) -> str:
+    """Returns a diff for the given content
+    """
+    d = difflib.Differ()
+    text1_lines = content.splitlines()
+    text2_lines = prev_content.splitlines()
+    diff = d.compare(text1_lines, text2_lines)
+
+    diff_content = content
+    diff_text = ''
+    reference_text = ''
+    change_positions = ''
+    for line in diff:
+        if line.startswith('- '):
+            reference_text = line[2:]
+        elif line.startswith('? '):
+            change_positions = line[2:]
+            state = 0
+            ctr = 0
+            for changed_char in change_positions:
+                if state == 0:
+                    if changed_char == '-':
+                        diff_text += \
+                            '<label class="diff_add">' + reference_text[ctr]
+                        ctr += 1
+                        state = 1
+                        continue
+                    elif changed_char == '+':
+                        diff_text += \
+                            '<label class="diff_remove">' + reference_text[ctr]
+                        ctr += 1
+                        state = 1
+                        continue
+                elif state == 1:
+                    if changed_char != '-' and changed_char != '+':
+                        diff_text += '</label>' + reference_text[ctr]
+                        ctr += 1
+                        state = 0
+                        continue
+                diff_text += reference_text[ctr]
+                ctr += 1
+
+            while ctr < len(reference_text):
+                diff_text += reference_text[ctr]
+                ctr += 1
+            diff_content = diff_content.replace(reference_text, diff_text)
+    return diff_content

tests.py

@@ -129,6 +129,7 @@ from inbox import json_post_allows_comments
 from inbox import valid_inbox
 from inbox import valid_inbox_filenames
 from categories import guess_hashtag_category
+from content import content_diff
 from content import bold_reading_string
 from content import safe_web_text
 from content import words_similarity
@@ -6917,6 +6918,19 @@ def _test_bold_reading() -> None:
     assert text_bold == expected
 
 
+def _test_diff_content() -> None:
+    print('diff_content')
+    prev_content = \
+        'Some text before.\nThis is some content.\nThis is another line.'
+    content = \
+        'Some text before.\nThis is some more content.\nThis is another line.'
+    result = content_diff(content, prev_content)
+    expected = 'Some text before.\n' + \
+        'This is some <label class="diff_add">' + \
+        'more </label>content.\nThis is another line.'
+    assert result == expected
+
+
 def run_all_tests():
     base_dir = os.getcwd()
     print('Running tests...')
@@ -6934,6 +6948,7 @@ def run_all_tests():
     _test_checkbox_names()
     _test_thread_functions()
     _test_functions()
+    _test_diff_content()
     _test_bold_reading()
     _test_published_to_local_timezone()
     _test_safe_webtext()