Merge pull request #149 from fschuh/main_test

Support for incremental merges of two export folders

.gitignore

@@ -138,7 +138,9 @@ __main__
 
 # Dev time intermidiates & temp files
 result/
+output/
 WhatsApp/
+AppDomainGroup-group.net.whatsapp.WhatsApp.shared/
 /*.db
 /*.db-*
 /myout

README.md

@@ -231,6 +231,19 @@ Contact Enrichment:
                         Use with --enrich-from-vcards. When numbers in the vcf file does not have a country code, this
                         will be used. 1 is for US, 66 for Thailand etc. Most likely use the number of your own country
 
+Incremental Merging:
+  --incremental-merge   Performs an incremental merge of two exports. Requires setting both --source-
+                        dir and --target-dir. The chats (JSON files only) and media from the source
+                        directory will be merged into the target directory. No chat messages or media
+                        will be deleted from the target directory; only new chat messages and media
+                        will be added to it. This enables chat messages and media to be deleted from
+                        the device to free up space, while ensuring they are preserved in the exported
+                        backups.
+  --source-dir SOURCE_DIR
+                        Sets the source directory. Used for performing incremental merges.
+  --target-dir TARGET_DIR
+                        Sets the target directory. Used for performing incremental merges.
+
 Miscellaneous:
   -s, --showkey         Show the HEX key used to decrypt the database
   --check-update        Check for updates (require Internet access)

Whatsapp_Chat_Exporter/__main__.py

@@ -13,7 +13,7 @@ from Whatsapp_Chat_Exporter import ios_handler, ios_media_handler
 from Whatsapp_Chat_Exporter.data_model import ChatCollection, ChatStore
 from Whatsapp_Chat_Exporter.utility import APPLE_TIME, Crypt, check_update, DbType
 from Whatsapp_Chat_Exporter.utility import readable_to_bytes, sanitize_filename
-from Whatsapp_Chat_Exporter.utility import import_from_json, bytes_to_readable
+from Whatsapp_Chat_Exporter.utility import import_from_json, incremental_merge, bytes_to_readable
 from argparse import ArgumentParser, SUPPRESS
 from datetime import datetime
 from getpass import getpass
@@ -34,12 +34,12 @@ def setup_argument_parser() -> ArgumentParser:
     """Set up and return the argument parser with all options."""
     parser = ArgumentParser(
         description='A customizable Android and iOS/iPadOS WhatsApp database parser that '
-                  'will give you the history of your WhatsApp conversations in HTML '
-                  'and JSON. Android Backup Crypt12, Crypt14 and Crypt15 supported.',
+        'will give you the history of your WhatsApp conversations in HTML '
+        'and JSON. Android Backup Crypt12, Crypt14 and Crypt15 supported.',
         epilog=f'WhatsApp Chat Exporter: {importlib.metadata.version("whatsapp_chat_exporter")} Licensed with MIT. See '
-              'https://wts.knugi.dev/docs?dest=osl for all open source licenses.'
+        'https://wts.knugi.dev/docs?dest=osl for all open source licenses.'
     )
-    
+
     # Device type arguments
     device_group = parser.add_argument_group('Device Type')
     device_group.add_argument(
@@ -54,7 +54,7 @@ def setup_argument_parser() -> ArgumentParser:
         "-e", "--exported", dest="exported", default=None,
         help="Define the target as exported chat file and specify the path to the file"
     )
-    
+
     # Input file paths
     input_group = parser.add_argument_group('Input Files')
     input_group.add_argument(
@@ -86,7 +86,7 @@ def setup_argument_parser() -> ArgumentParser:
         "--wab", "--wa-backup", dest="wab", default=None,
         help="Path to contact database in crypt15 format"
     )
-    
+
     # Output options
     output_group = parser.add_argument_group('Output Options')
     output_group.add_argument(
@@ -109,7 +109,7 @@ def setup_argument_parser() -> ArgumentParser:
         "--size", "--output-size", "--split", dest="size", nargs='?', const=0, default=None,
         help="Maximum (rough) size of a single output file in bytes, 0 for auto"
     )
-    
+
     # JSON formatting options
     json_group = parser.add_argument_group('JSON Options')
     json_group.add_argument(
@@ -128,7 +128,7 @@ def setup_argument_parser() -> ArgumentParser:
         "--import", dest="import_json", default=False, action='store_true',
         help="Import JSON file and convert to HTML output"
     )
-    
+
     # HTML options
     html_group = parser.add_argument_group('HTML Options')
     html_group.add_argument(
@@ -155,7 +155,7 @@ def setup_argument_parser() -> ArgumentParser:
         "--headline", dest="headline", default="Chat history with ??",
         help="The custom headline for the HTML output. Use '??' as a placeholder for the chat name"
     )
-    
+
     # Media handling
     media_group = parser.add_argument_group('Media Handling')
     media_group.add_argument(
@@ -166,7 +166,7 @@ def setup_argument_parser() -> ArgumentParser:
         "--create-separated-media", dest="separate_media", default=False, action='store_true',
         help="Create a copy of the media seperated per chat in <MEDIA>/separated/ directory"
     )
-    
+
     # Filtering options
     filter_group = parser.add_argument_group('Filtering Options')
     filter_group.add_argument(
@@ -195,7 +195,7 @@ def setup_argument_parser() -> ArgumentParser:
               "Setting this flag will cause the exporter to render those. "
               "This is useful if chat(s) are missing from the output")
     )
-    
+
     # Contact enrichment
     contact_group = parser.add_argument_group('Contact Enrichment')
     contact_group.add_argument(
@@ -206,7 +206,34 @@ def setup_argument_parser() -> ArgumentParser:
         "--default-country-code", dest="default_country_code", default=None,
         help="Use with --enrich-from-vcards. When numbers in the vcf file does not have a country code, this will be used. 1 is for US, 66 for Thailand etc. Most likely use the number of your own country"
     )
-    
+
+    # Incremental merging
+    inc_merging_group = parser.add_argument_group('Incremental Merging')
+    inc_merging_group.add_argument(
+        "--incremental-merge",
+        dest="incremental_merge",
+        default=False,
+        action='store_true',
+        help=("Performs an incremental merge of two exports. "
+              "Requires setting both --source-dir and --target-dir. "
+              "The chats (JSON files only) and media from the source directory will be merged into the target directory. "
+              "No chat messages or media will be deleted from the target directory; only new chat messages and media will be added to it. "
+              "This enables chat messages and media to be deleted from the device to free up space, while ensuring they are preserved in the exported backups."
+              )
+    )
+    inc_merging_group.add_argument(
+        "--source-dir",
+        dest="source_dir",
+        default=None,
+        help="Sets the source directory. Used for performing incremental merges."
+    )
+    inc_merging_group.add_argument(
+        "--target-dir",
+        dest="target_dir",
+        default=None,
+        help="Sets the target directory. Used for performing incremental merges."
+    )
+
     # Miscellaneous
     misc_group = parser.add_argument_group('Miscellaneous')
     misc_group.add_argument(
@@ -233,7 +260,7 @@ def setup_argument_parser() -> ArgumentParser:
         "--max-bruteforce-worker", dest="max_bruteforce_worker", default=10, type=int,
         help="Specify the maximum number of worker for bruteforce decryption."
     )
-    
+
     return parser
 
 
@@ -245,50 +272,59 @@ def validate_args(parser: ArgumentParser, args) -> None:
     if not args.android and not args.ios and not args.exported and not args.import_json:
         parser.error("You must define the device type.")
     if args.no_html and not args.json and not args.text_format:
-        parser.error("You must either specify a JSON output file, text file output directory or enable HTML output.")
+        parser.error(
+            "You must either specify a JSON output file, text file output directory or enable HTML output.")
     if args.import_json and (args.android or args.ios or args.exported or args.no_html):
-        parser.error("You can only use --import with -j and without --no-html, -a, -i, -e.")
+        parser.error(
+            "You can only use --import with -j and without --no-html, -a, -i, -e.")
     elif args.import_json and not os.path.isfile(args.json):
         parser.error("JSON file not found.")
+    if args.incremental_merge and (args.source_dir is None or args.target_dir is None):
+        parser.error(
+            "You must specify both --source-dir and --target-dir for incremental merge.")
     if args.android and args.business:
         parser.error("WhatsApp Business is only available on iOS for now.")
     if "??" not in args.headline:
         parser.error("--headline must contain '??' for replacement.")
-    
+
     # JSON validation
     if args.json_per_chat and args.json and (
-        (args.json.endswith(".json") and os.path.isfile(args.json)) or 
+        (args.json.endswith(".json") and os.path.isfile(args.json)) or
         (not args.json.endswith(".json") and os.path.isfile(args.json))
     ):
-        parser.error("When --per-chat is enabled, the destination of --json must be a directory.")
-    
+        parser.error(
+            "When --per-chat is enabled, the destination of --json must be a directory.")
+
     # vCards validation
     if args.enrich_from_vcards is not None and args.default_country_code is None:
-        parser.error("When --enrich-from-vcards is provided, you must also set --default-country-code")
-    
+        parser.error(
+            "When --enrich-from-vcards is provided, you must also set --default-country-code")
+
     # Size validation
     if args.size is not None and not isinstance(args.size, int) and not args.size.isnumeric():
         try:
             args.size = readable_to_bytes(args.size)
         except ValueError:
-            parser.error("The value for --split must be ended in pure bytes or with a proper unit (e.g., 1048576 or 1MB)")
-    
+            parser.error(
+                "The value for --split must be ended in pure bytes or with a proper unit (e.g., 1048576 or 1MB)")
+
     # Date filter validation and processing
     if args.filter_date is not None:
         process_date_filter(parser, args)
-    
+
     # Crypt15 key validation
     if args.key is None and args.backup is not None and args.backup.endswith("crypt15"):
         args.key = getpass("Enter your encryption key: ")
-    
+
     # Theme validation
     if args.whatsapp_theme:
         args.template = "whatsapp_new.html"
-    
+
     # Chat filter validation
     if args.filter_chat_include is not None and args.filter_chat_exclude is not None:
-        parser.error("Chat inclusion and exclusion filters cannot be used together.")
-    
+        parser.error(
+            "Chat inclusion and exclusion filters cannot be used together.")
+
     validate_chat_filters(parser, args.filter_chat_include)
     validate_chat_filters(parser, args.filter_chat_exclude)
 
@@ -298,21 +334,24 @@ def validate_chat_filters(parser: ArgumentParser, chat_filter: Optional[List[str
     if chat_filter is not None:
         for chat in chat_filter:
             if not chat.isnumeric():
-                parser.error("Enter a phone number in the chat filter. See https://wts.knugi.dev/docs?dest=chat")
+                parser.error(
+                    "Enter a phone number in the chat filter. See https://wts.knugi.dev/docs?dest=chat")
 
 
 def process_date_filter(parser: ArgumentParser, args) -> None:
     """Process and validate date filter arguments."""
     if " - " in args.filter_date:
         start, end = args.filter_date.split(" - ")
-        start = int(datetime.strptime(start, args.filter_date_format).timestamp())
+        start = int(datetime.strptime(
+            start, args.filter_date_format).timestamp())
         end = int(datetime.strptime(end, args.filter_date_format).timestamp())
-        
+
         if start < 1009843200 or end < 1009843200:
             parser.error("WhatsApp was first released in 2009...")
         if start > end:
-            parser.error("The start date cannot be a moment after the end date.")
-        
+            parser.error(
+                "The start date cannot be a moment after the end date.")
+
         if args.android:
             args.filter_date = f"BETWEEN {start}000 AND {end}000"
         elif args.ios:
@@ -324,13 +363,15 @@ def process_date_filter(parser: ArgumentParser, args) -> None:
 def process_single_date_filter(parser: ArgumentParser, args) -> None:
     """Process single date comparison filters."""
     if len(args.filter_date) < 3:
-        parser.error("Unsupported date format. See https://wts.knugi.dev/docs?dest=date")
-        
-    _timestamp = int(datetime.strptime(args.filter_date[2:], args.filter_date_format).timestamp())
-    
+        parser.error(
+            "Unsupported date format. See https://wts.knugi.dev/docs?dest=date")
+
+    _timestamp = int(datetime.strptime(
+        args.filter_date[2:], args.filter_date_format).timestamp())
+
     if _timestamp < 1009843200:
         parser.error("WhatsApp was first released in 2009...")
-    
+
     if args.filter_date[:2] == "> ":
         if args.android:
             args.filter_date = f">= {_timestamp}000"
@@ -342,7 +383,8 @@ def process_single_date_filter(parser: ArgumentParser, args) -> None:
         elif args.ios:
             args.filter_date = f"<= {_timestamp - APPLE_TIME}"
     else:
-        parser.error("Unsupported date format. See https://wts.knugi.dev/docs?dest=date")
+        parser.error(
+            "Unsupported date format. See https://wts.knugi.dev/docs?dest=date")
 
 
 def setup_contact_store(args) -> Optional['ContactsFromVCards']:
@@ -356,7 +398,8 @@ def setup_contact_store(args) -> Optional['ContactsFromVCards']:
             )
             exit(1)
         contact_store = ContactsFromVCards()
-        contact_store.load_vcf_file(args.enrich_from_vcards, args.default_country_code)
+        contact_store.load_vcf_file(
+            args.enrich_from_vcards, args.default_country_code)
         return contact_store
     return None
 
@@ -366,9 +409,9 @@ def decrypt_android_backup(args) -> int:
     if args.key is None or args.backup is None:
         print("You must specify the backup file with -b and a key with -k")
         return 1
-    
+
     print("Decryption key specified, decrypting WhatsApp backup...")
-    
+
     # Determine crypt type
     if "crypt12" in args.backup:
         crypt = Crypt.CRYPT12
@@ -379,7 +422,7 @@ def decrypt_android_backup(args) -> int:
     else:
         print("Unknown backup format. The backup file must be crypt12, crypt14 or crypt15.")
         return 1
-    
+
     # Get key
     keyfile_stream = False
     if not os.path.isfile(args.key) and all(char in string.hexdigits for char in args.key.replace(" ", "")):
@@ -387,10 +430,10 @@ def decrypt_android_backup(args) -> int:
     else:
         key = open(args.key, "rb")
         keyfile_stream = True
-    
+
     # Read backup
     db = open(args.backup, "rb").read()
-    
+
     # Process WAB if provided
     error_wa = 0
     if args.wab:
@@ -407,7 +450,7 @@ def decrypt_android_backup(args) -> int:
         )
         if isinstance(key, io.IOBase):
             key.seek(0)
-    
+
     # Decrypt message database
     error_message = android_crypt.decrypt_backup(
         db,
@@ -419,7 +462,7 @@ def decrypt_android_backup(args) -> int:
         keyfile_stream=keyfile_stream,
         max_worker=args.max_bruteforce_worker
     )
-    
+
     # Handle errors
     if error_wa != 0:
         return error_wa
@@ -444,7 +487,7 @@ def handle_decrypt_error(error: int) -> None:
 def process_contacts(args, data: ChatCollection, contact_store=None) -> None:
     """Process contacts from the database."""
     contact_db = args.wa if args.wa else "wa.db" if args.android else "ContactsV2.sqlite"
-    
+
     if os.path.isfile(contact_db):
         with sqlite3.connect(contact_db) as db:
             db.row_factory = sqlite3.Row
@@ -457,42 +500,42 @@ def process_contacts(args, data: ChatCollection, contact_store=None) -> None:
 def process_messages(args, data: ChatCollection) -> None:
     """Process messages, media and vcards from the database."""
     msg_db = args.db if args.db else "msgstore.db" if args.android else args.identifiers.MESSAGE
-    
+
     if not os.path.isfile(msg_db):
         print(
             "The message database does not exist. You may specify the path "
             "to database file with option -d or check your provided path."
         )
         exit(6)
-    
+
     filter_chat = (args.filter_chat_include, args.filter_chat_exclude)
-    
+
     with sqlite3.connect(msg_db) as db:
         db.row_factory = sqlite3.Row
-        
+
         # Process messages
         if args.android:
             message_handler = android_handler
         else:
             message_handler = ios_handler
-            
+
         message_handler.messages(
-            db, data, args.media, args.timezone_offset, 
+            db, data, args.media, args.timezone_offset,
             args.filter_date, filter_chat, args.filter_empty
         )
-        
+
         # Process media
         message_handler.media(
-            db, data, args.media, args.filter_date, 
+            db, data, args.media, args.filter_date,
             filter_chat, args.filter_empty, args.separate_media
         )
-        
+
         # Process vcards
         message_handler.vcard(
-            db, data, args.media, args.filter_date, 
+            db, data, args.media, args.filter_date,
             filter_chat, args.filter_empty
         )
-        
+
         # Process calls
         process_calls(args, db, data, filter_chat)
 
@@ -511,9 +554,10 @@ def handle_media_directory(args) -> None:
     """Handle media directory copying or moving."""
     if os.path.isdir(args.media):
         media_path = os.path.join(args.output, args.media)
-        
+
         if os.path.isdir(media_path):
-            print("\nWhatsApp directory already exists in output directory. Skipping...", end="\n")
+            print(
+                "\nWhatsApp directory already exists in output directory. Skipping...", end="\n")
         else:
             if args.move_media:
                 try:
@@ -534,7 +578,7 @@ def create_output_files(args, data: ChatCollection, contact_store=None) -> None:
         # Enrich from vcards if available
         if contact_store and not contact_store.is_empty():
             contact_store.enrich_from_vcards(data)
-            
+
         android_handler.create_html(
             data,
             args.output,
@@ -546,12 +590,12 @@ def create_output_files(args, data: ChatCollection, contact_store=None) -> None:
             args.whatsapp_theme,
             args.headline
         )
-    
+
     # Create text files if requested
     if args.text_format:
         print("Writing text file...")
         android_handler.create_txt(data, args.text_format)
-    
+
     # Create JSON files if requested
     if args.json and not args.import_json:
         export_json(args, data, contact_store)
@@ -562,11 +606,11 @@ def export_json(args, data: ChatCollection, contact_store=None) -> None:
     # Enrich from vcards if available
     if contact_store and not contact_store.is_empty():
         contact_store.enrich_from_vcards(data)
-    
+
     # Convert ChatStore objects to JSON
     if isinstance(data.get(next(iter(data), None)), ChatStore):
         data = {jik: chat.to_json() for jik, chat in data.items()}
-    
+
     # Export as a single file or per chat
     if not args.json_per_chat:
         export_single_json(args, data)
@@ -590,11 +634,11 @@ def export_multiple_json(args, data: Dict) -> None:
     """Export data to multiple JSON files, one per chat."""
     # Adjust output path if needed
     json_path = args.json[:-5] if args.json.endswith(".json") else args.json
-    
+
     # Create directory if it doesn't exist
     if not os.path.isdir(json_path):
         os.makedirs(json_path, exist_ok=True)
-    
+
     # Export each chat
     total = len(data.keys())
     for index, jik in enumerate(data.keys()):
@@ -602,11 +646,11 @@ def export_multiple_json(args, data: Dict) -> None:
             contact = data[jik]["name"].replace('/', '')
         else:
             contact = jik.replace('+', '')
-            
+
         with open(f"{json_path}/{sanitize_filename(contact)}.json", "w") as f:
             file_content = json.dumps(
-                {jik: data[jik]}, 
-                ensure_ascii=not args.avoid_encoding_json, 
+                {jik: data[jik]},
+                ensure_ascii=not args.avoid_encoding_json,
                 indent=args.pretty_print_json
             )
             f.write(file_content)
@@ -617,7 +661,7 @@ def export_multiple_json(args, data: Dict) -> None:
 def process_exported_chat(args, data: ChatCollection) -> None:
     """Process an exported chat file."""
     exported_handler.messages(args.exported, data, args.assume_first_as_me)
-    
+
     if not args.no_html:
         android_handler.create_html(
             data,
@@ -630,7 +674,7 @@ def process_exported_chat(args, data: ChatCollection) -> None:
             args.whatsapp_theme,
             args.headline
         )
-    
+
     # Copy files to output directory
     for file in glob.glob(r'*.*'):
         shutil.copy(file, args.output)
@@ -641,23 +685,23 @@ def main():
     # Set up and parse arguments
     parser = setup_argument_parser()
     args = parser.parse_args()
-    
+
     # Check for updates
     if args.check_update:
         exit(check_update())
-    
+
     # Validate arguments
     validate_args(parser, args)
-    
+
     # Create output directory if it doesn't exist
     os.makedirs(args.output, exist_ok=True)
-    
+
     # Initialize data collection
     data = ChatCollection()
-    
+
     # Set up contact store for vCard enrichment if needed
     contact_store = setup_contact_store(args)
-    
+
     if args.import_json:
         # Import from JSON
         import_from_json(args.json, data)
@@ -681,13 +725,13 @@ def main():
             # Set default media path if not provided
             if args.media is None:
                 args.media = "WhatsApp"
-                
+
             # Set default DB paths if not provided
             if args.db is None:
                 args.db = "msgstore.db"
             if args.wa is None:
                 args.wa = "wa.db"
-                
+
             # Decrypt backup if needed
             if args.key is not None:
                 error = decrypt_android_backup(args)
@@ -700,34 +744,50 @@ def main():
             else:
                 from Whatsapp_Chat_Exporter.utility import WhatsAppIdentifier as identifiers
             args.identifiers = identifiers
-            
+
             # Set default media path if not provided
             if args.media is None:
                 args.media = identifiers.DOMAIN
-                
+
             # Extract media from backup if needed
             if args.backup is not None:
                 if not os.path.isdir(args.media):
-                    ios_media_handler.extract_media(args.backup, identifiers, args.decrypt_chunk_size)
+                    ios_media_handler.extract_media(
+                        args.backup, identifiers, args.decrypt_chunk_size)
                 else:
-                    print("WhatsApp directory already exists, skipping WhatsApp file extraction.")
-                    
+                    print(
+                        "WhatsApp directory already exists, skipping WhatsApp file extraction.")
+
             # Set default DB paths if not provided
             if args.db is None:
                 args.db = identifiers.MESSAGE
             if args.wa is None:
                 args.wa = "ContactsV2.sqlite"
-        
-        # Process contacts
-        process_contacts(args, data, contact_store)
-        
-        # Process messages, media, and calls
-        process_messages(args, data)
-        
-        # Create output files
-        create_output_files(args, data, contact_store)
-        
-        # Handle media directory
-        handle_media_directory(args)
 
-        print("Everything is done!")
+        if args.incremental_merge:
+            incremental_merge(
+                args.source_dir,
+                args.target_dir,
+                args.media,
+                args.pretty_print_json,
+                args.avoid_encoding_json
+            )
+            print("Incremental merge completed successfully.")
+        else:
+            # Process contacts
+            process_contacts(args, data, contact_store)
+
+            # Process messages, media, and calls
+            process_messages(args, data)
+
+            # Create output files
+            create_output_files(args, data, contact_store)
+
+            # Handle media directory
+            handle_media_directory(args)
+
+        print("Everything is done!")
+
+
+if __name__ == "__main__":
+    main()

Whatsapp_Chat_Exporter/data_model.py

@@ -7,6 +7,7 @@ class Timing:
     """
     Handles timestamp formatting with timezone support.
     """
+
     def __init__(self, timezone_offset: Optional[int]) -> None:
         """
         Initialize Timing object.
@@ -27,7 +28,7 @@ class Timing:
         Returns:
             Optional[str]: Formatted timestamp string, or None if timestamp is None
         """
-        if timestamp:
+        if timestamp is not None:
             timestamp = timestamp / 1000 if timestamp > 9999999999 else timestamp
             return datetime.fromtimestamp(timestamp, TimeZone(self.timezone_offset)).strftime(format)
         return None
@@ -37,6 +38,7 @@ class TimeZone(tzinfo):
     """
     Custom timezone class with fixed offset.
     """
+
     def __init__(self, offset: int) -> None:
         """
         Initialize TimeZone object.
@@ -151,6 +153,7 @@ class ChatStore:
     """
     Stores chat information and messages.
     """
+
     def __init__(self, type: str, name: Optional[str] = None, media: Optional[str] = None) -> None:
         """
         Initialize ChatStore object.
@@ -159,7 +162,7 @@ class ChatStore:
             type (str): Device type (IOS or ANDROID)
             name (Optional[str]): Chat name
             media (Optional[str]): Path to media folder
-        
+
         Raises:
             TypeError: If name is not a string or None
         """
@@ -182,7 +185,7 @@ class ChatStore:
         self.their_avatar_thumb = None
         self.status = None
         self.media_base = ""
-    
+
     def __len__(self) -> int:
         """Get number of chats. Required for dict-like access."""
         return len(self._messages)
@@ -192,7 +195,7 @@ class ChatStore:
         if not isinstance(message, Message):
             raise TypeError("message must be a Message object")
         self._messages[id] = message
-    
+
     def get_message(self, id: str) -> 'Message':
         """Get a message from the chat store."""
         return self._messages.get(id)
@@ -211,13 +214,28 @@ class ChatStore:
             'their_avatar': self.their_avatar,
             'their_avatar_thumb': self.their_avatar_thumb,
             'status': self.status,
+            'media_base': self.media_base,
             'messages': {id: msg.to_json() for id, msg in self._messages.items()}
         }
 
+    @classmethod
+    def from_json(cls, data: Dict) -> 'ChatStore':
+        """Create a chat store from JSON data."""
+        chat = cls(data.get("type"), data.get("name"))
+        chat.my_avatar = data.get("my_avatar")
+        chat.their_avatar = data.get("their_avatar")
+        chat.their_avatar_thumb = data.get("their_avatar_thumb")
+        chat.status = data.get("status")
+        chat.media_base = data.get("media_base")
+        for id, msg_data in data.get("messages", {}).items():
+            message = Message.from_json(msg_data)
+            chat.add_message(id, message)
+        return chat
+
     def get_last_message(self) -> 'Message':
         """Get the most recent message in the chat."""
         return tuple(self._messages.values())[-1]
-    
+
     def items(self):
         """Get message items pairs."""
         return self._messages.items()
@@ -230,18 +248,40 @@ class ChatStore:
         """Get all message keys in the chat."""
         return self._messages.keys()
 
+    def merge_with(self, other: 'ChatStore'):
+        """Merge another ChatStore into this one.
+
+        Args:
+            other (ChatStore): The ChatStore to merge with
+
+        """
+        if not isinstance(other, ChatStore):
+            raise TypeError("Can only merge with another ChatStore object")
+
+        # Update fields if they are not None in the other ChatStore
+        self.name = other.name or self.name
+        self.type = other.type or self.type
+        self.my_avatar = other.my_avatar or self.my_avatar
+        self.their_avatar = other.their_avatar or self.their_avatar
+        self.their_avatar_thumb = other.their_avatar_thumb or self.their_avatar_thumb
+        self.status = other.status or self.status
+
+        # Merge messages
+        self._messages.update(other._messages)
+
 
 class Message:
     """
     Represents a single message in a chat.
     """
+
     def __init__(
             self,
             *,
             from_me: Union[bool, int],
             timestamp: int,
             time: Union[int, float, str],
-            key_id: int,
+            key_id: Union[int, str],
             received_timestamp: int,
             read_timestamp: int,
             timezone_offset: int = 0,
@@ -266,7 +306,7 @@ class Message:
         self.from_me = bool(from_me)
         self.timestamp = timestamp / 1000 if timestamp > 9999999999 else timestamp
         timing = Timing(timezone_offset)
-        
+
         if isinstance(time, (int, float)):
             self.time = timing.format_timestamp(self.timestamp, "%H:%M")
         elif isinstance(time, str):
@@ -281,10 +321,22 @@ class Message:
         self.sender = None
         self.safe = False
         self.mime = None
-        self.message_type = message_type,
-        self.received_timestamp = timing.format_timestamp(received_timestamp, "%Y/%m/%d %H:%M")
-        self.read_timestamp = timing.format_timestamp(read_timestamp, "%Y/%m/%d %H:%M")
-        
+        self.message_type = message_type
+        if isinstance(received_timestamp, (int, float)):
+            self.received_timestamp = timing.format_timestamp(
+                received_timestamp, "%Y/%m/%d %H:%M")
+        elif isinstance(received_timestamp, str):
+            self.received_timestamp = received_timestamp
+        else:
+            self.received_timestamp = None
+        if isinstance(read_timestamp, (int, float)):
+            self.read_timestamp = timing.format_timestamp(
+                read_timestamp, "%Y/%m/%d %H:%M")
+        elif isinstance(read_timestamp, str):
+            self.read_timestamp = read_timestamp
+        else:
+            self.read_timestamp = None
+
         # Extra attributes
         self.reply = None
         self.quoted_data = None
@@ -309,5 +361,32 @@ class Message:
             'quoted_data': self.quoted_data,
             'caption': self.caption,
             'thumb': self.thumb,
-            'sticker': self.sticker
-        }
+            'sticker': self.sticker,
+            'message_type': self.message_type,
+            'received_timestamp': self.received_timestamp,
+            'read_timestamp': self.read_timestamp
+        }
+
+    @classmethod
+    def from_json(cls, data: Dict) -> 'Message':
+        message = cls(
+            from_me=data["from_me"],
+            timestamp=data["timestamp"],
+            time=data["time"],
+            key_id=data["key_id"],
+            message_type=data.get("message_type"),
+            received_timestamp=data.get("received_timestamp"),
+            read_timestamp=data.get("read_timestamp")
+        )
+        message.media = data.get("media")
+        message.meta = data.get("meta")
+        message.data = data.get("data")
+        message.sender = data.get("sender")
+        message.safe = data.get("safe")
+        message.mime = data.get("mime")
+        message.reply = data.get("reply")
+        message.quoted_data = data.get("quoted_data")
+        message.caption = data.get("caption")
+        message.thumb = data.get("thumb")
+        message.sticker = data.get("sticker")
+        return message

Whatsapp_Chat_Exporter/utility.py

@@ -5,6 +5,7 @@ import os
 import unicodedata
 import re
 import math
+import shutil
 from bleach import clean as sanitize
 from markupsafe import Markup
 from datetime import datetime, timedelta
@@ -15,8 +16,9 @@ try:
     from enum import StrEnum, IntEnum
 except ImportError:
     # < Python 3.11
-    # This should be removed when the support for Python 3.10 ends.
+    # This should be removed when the support for Python 3.10 ends. (31 Oct 2026)
     from enum import Enum
+
     class StrEnum(str, Enum):
         pass
 
@@ -71,7 +73,7 @@ def bytes_to_readable(size_bytes: int) -> str:
         A human-readable string representing the file size.
     """
     if size_bytes == 0:
-       return "0B"
+        return "0B"
     size_name = ("B", "KB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB")
     i = int(math.floor(math.log(size_bytes, 1024)))
     p = math.pow(1024, i)
@@ -99,7 +101,7 @@ def readable_to_bytes(size_str: str) -> int:
         'TB': 1024**4,
         'PB': 1024**5,
         'EB': 1024**6,
-        'ZB': 1024**7, 
+        'ZB': 1024**7,
         'YB': 1024**8
     }
     size_str = size_str.upper().strip()
@@ -154,7 +156,8 @@ def check_update():
     else:
         with raw:
             package_info = json.load(raw)
-            latest_version = tuple(map(int, package_info["info"]["version"].split(".")))
+            latest_version = tuple(
+                map(int, package_info["info"]["version"].split(".")))
             __version__ = importlib.metadata.version("whatsapp_chat_exporter")
             current_version = tuple(map(int, __version__.split(".")))
             if current_version < latest_version:
@@ -173,17 +176,17 @@ def check_update():
 
 
 def rendering(
-        output_file_name,
-        template,
-        name,
-        msgs,
-        contact,
-        w3css,
-        chat,
-        headline,
-        next=False,
-        previous=False
-    ):
+    output_file_name,
+    template,
+    name,
+    msgs,
+    contact,
+    w3css,
+    chat,
+    headline,
+    next=False,
+    previous=False
+):
     if chat.their_avatar_thumb is None and chat.their_avatar is not None:
         their_avatar_thumb = chat.their_avatar
     else:
@@ -255,7 +258,89 @@ def import_from_json(json_file: str, data: Dict[str, ChatStore]):
             message.sticker = msg.get("sticker")
             chat.add_message(id, message)
         data[jid] = chat
-        print(f"Importing chats from JSON...({index + 1}/{total_row_number})", end="\r")
+        print(
+            f"Importing chats from JSON...({index + 1}/{total_row_number})", end="\r")
+
+
+def incremental_merge(source_dir: str, target_dir: str, media_dir: str, pretty_print_json: int, avoid_encoding_json: bool):
+    """Merges JSON files from the source directory into the target directory.
+
+    Args:
+        source_dir (str): The path to the source directory containing JSON files.
+        target_dir (str): The path to the target directory to merge into.
+        media_dir (str): The path to the media directory.
+    """
+    json_files = [f for f in os.listdir(source_dir) if f.endswith('.json')]
+    if not json_files:
+        print("No JSON files found in the source directory.")
+        return
+
+    print("JSON files found:", json_files)
+
+    for json_file in json_files:
+        source_path = os.path.join(source_dir, json_file)
+        target_path = os.path.join(target_dir, json_file)
+
+        if not os.path.exists(target_path):
+            print(f"Copying '{json_file}' to target directory...")
+            os.makedirs(target_dir, exist_ok=True)
+            shutil.copy2(source_path, target_path)
+        else:
+            print(
+                f"Merging '{json_file}' with existing file in target directory...")
+            with open(source_path, 'r') as src_file, open(target_path, 'r') as tgt_file:
+                source_data = json.load(src_file)
+                target_data = json.load(tgt_file)
+
+                # Parse JSON into ChatStore objects using from_json()
+                source_chats = {jid: ChatStore.from_json(
+                    chat) for jid, chat in source_data.items()}
+                target_chats = {jid: ChatStore.from_json(
+                    chat) for jid, chat in target_data.items()}
+
+                # Merge chats using merge_with()
+                for jid, chat in source_chats.items():
+                    if jid in target_chats:
+                        target_chats[jid].merge_with(chat)
+                    else:
+                        target_chats[jid] = chat
+
+                # Serialize merged data
+                merged_data = {jid: chat.to_json()
+                               for jid, chat in target_chats.items()}
+
+                # Check if the merged data differs from the original target data
+                if json.dumps(merged_data, sort_keys=True) != json.dumps(target_data, sort_keys=True):
+                    print(
+                        f"Changes detected in '{json_file}', updating target file...")
+                    with open(target_path, 'w') as merged_file:
+                        json.dump(
+                            merged_data,
+                            merged_file,
+                            indent=pretty_print_json,
+                            ensure_ascii=not avoid_encoding_json,
+                        )
+                else:
+                    print(
+                        f"No changes detected in '{json_file}', skipping update.")
+
+    # Merge media directories
+    source_media_path = os.path.join(source_dir, media_dir)
+    target_media_path = os.path.join(target_dir, media_dir)
+    print(
+        f"Merging media directories. Source: {source_media_path}, target: {target_media_path}")
+    if os.path.exists(source_media_path):
+        for root, _, files in os.walk(source_media_path):
+            relative_path = os.path.relpath(root, source_media_path)
+            target_root = os.path.join(target_media_path, relative_path)
+            os.makedirs(target_root, exist_ok=True)
+            for file in files:
+                source_file = os.path.join(root, file)
+                target_file = os.path.join(target_root, file)
+                # we only copy if the file doesn't exist in the target or if the source is newer
+                if not os.path.exists(target_file) or os.path.getmtime(source_file) > os.path.getmtime(target_file):
+                    print(f"Copying '{source_file}' to '{target_file}'...")
+                    shutil.copy2(source_file, target_file)
 
 
 def sanitize_filename(file_name: str) -> str:
@@ -335,23 +420,29 @@ def get_chat_condition(filter: Optional[List[str]], include: bool, columns: List
     if filter is not None:
         conditions = []
         if len(columns) < 2 and jid is not None:
-            raise ValueError("There must be at least two elements in argument columns if jid is not None")
+            raise ValueError(
+                "There must be at least two elements in argument columns if jid is not None")
         if jid is not None:
             if platform == "android":
                 is_group = f"{jid}.type == 1"
             elif platform == "ios":
                 is_group = f"{jid} IS NOT NULL"
             else:
-                raise ValueError("Only android and ios are supported for argument platform if jid is not None")
+                raise ValueError(
+                    "Only android and ios are supported for argument platform if jid is not None")
         for index, chat in enumerate(filter):
             if include:
-                conditions.append(f"{' OR' if index > 0 else ''} {columns[0]} LIKE '%{chat}%'")
+                conditions.append(
+                    f"{' OR' if index > 0 else ''} {columns[0]} LIKE '%{chat}%'")
                 if len(columns) > 1:
-                    conditions.append(f" OR ({columns[1]} LIKE '%{chat}%' AND {is_group})")
+                    conditions.append(
+                        f" OR ({columns[1]} LIKE '%{chat}%' AND {is_group})")
             else:
-                conditions.append(f"{' AND' if index > 0 else ''} {columns[0]} NOT LIKE '%{chat}%'")
+                conditions.append(
+                    f"{' AND' if index > 0 else ''} {columns[0]} NOT LIKE '%{chat}%'")
                 if len(columns) > 1:
-                    conditions.append(f" AND ({columns[1]} NOT LIKE '%{chat}%' AND {is_group})")
+                    conditions.append(
+                        f" AND ({columns[1]} NOT LIKE '%{chat}%' AND {is_group})")
         return f"AND ({' '.join(conditions)})"
     else:
         return ""
@@ -446,7 +537,7 @@ def determine_metadata(content: sqlite3.Row, init_msg: Optional[str]) -> Optiona
         else:
             msg = f"{old} changed their number to {new}"
     elif content["action_type"] == 46:
-        return # Voice message in PM??? Seems no need to handle.
+        return  # Voice message in PM??? Seems no need to handle.
     elif content["action_type"] == 47:
         msg = "The contact is an official business account"
     elif content["action_type"] == 50:
@@ -463,7 +554,8 @@ def determine_metadata(content: sqlite3.Row, init_msg: Optional[str]) -> Optiona
     elif content["action_type"] == 67:
         return  # (PM) this contact use secure service from Facebook???
     elif content["action_type"] == 69:
-        return  # (PM) this contact use secure service from Facebook??? What's the difference with 67????
+        # (PM) this contact use secure service from Facebook??? What's the difference with 67????
+        return
     else:
         return  # Unsupported
     return msg
@@ -490,7 +582,8 @@ def get_status_location(output_folder: str, offline_static: str) -> str:
     w3css_path = os.path.join(static_folder, "w3.css")
     if not os.path.isfile(w3css_path):
         with urllib.request.urlopen(w3css) as resp:
-            with open(w3css_path, "wb") as f: f.write(resp.read())
+            with open(w3css_path, "wb") as f:
+                f.write(resp.read())
     w3css = os.path.join(offline_static, "w3.css")
 
 
@@ -521,6 +614,7 @@ def setup_template(template: Optional[str], no_avatar: bool, experimental: bool
     template_env.filters['sanitize_except'] = sanitize_except
     return template_env.get_template(template_file)
 
+
 # iOS Specific
 APPLE_TIME = 978307200
 
@@ -541,23 +635,31 @@ def slugify(value: str, allow_unicode: bool = False) -> str:
     if allow_unicode:
         value = unicodedata.normalize('NFKC', value)
     else:
-        value = unicodedata.normalize('NFKD', value).encode('ascii', 'ignore').decode('ascii')
+        value = unicodedata.normalize('NFKD', value).encode(
+            'ascii', 'ignore').decode('ascii')
     value = re.sub(r'[^\w\s-]', '', value.lower())
     return re.sub(r'[-\s]+', '-', value).strip('-_')
 
 
 class WhatsAppIdentifier(StrEnum):
-    MESSAGE = "7c7fba66680ef796b916b067077cc246adacf01d" # AppDomainGroup-group.net.whatsapp.WhatsApp.shared-ChatStorage.sqlite
-    CONTACT = "b8548dc30aa1030df0ce18ef08b882cf7ab5212f" # AppDomainGroup-group.net.whatsapp.WhatsApp.shared-ContactsV2.sqlite
-    CALL = "1b432994e958845fffe8e2f190f26d1511534088" # AppDomainGroup-group.net.whatsapp.WhatsApp.shared-CallHistory.sqlite
+    # AppDomainGroup-group.net.whatsapp.WhatsApp.shared-ChatStorage.sqlite
+    MESSAGE = "7c7fba66680ef796b916b067077cc246adacf01d"
+    # AppDomainGroup-group.net.whatsapp.WhatsApp.shared-ContactsV2.sqlite
+    CONTACT = "b8548dc30aa1030df0ce18ef08b882cf7ab5212f"
+    # AppDomainGroup-group.net.whatsapp.WhatsApp.shared-CallHistory.sqlite
+    CALL = "1b432994e958845fffe8e2f190f26d1511534088"
     DOMAIN = "AppDomainGroup-group.net.whatsapp.WhatsApp.shared"
 
 
 class WhatsAppBusinessIdentifier(StrEnum):
-    MESSAGE = "724bd3b98b18518b455a87c1f3ac3a0d189c4466" # AppDomainGroup-group.net.whatsapp.WhatsAppSMB.shared-ChatStorage.sqlite
-    CONTACT = "d7246a707f51ddf8b17ee2dddabd9e0a4da5c552" # AppDomainGroup-group.net.whatsapp.WhatsAppSMB.shared-ContactsV2.sqlite
-    CALL = "b463f7c4365eefc5a8723930d97928d4e907c603" # AppDomainGroup-group.net.whatsapp.WhatsAppSMB.shared-CallHistory.sqlite
-    DOMAIN = "AppDomainGroup-group.net.whatsapp.WhatsAppSMB.shared" 
+    # AppDomainGroup-group.net.whatsapp.WhatsAppSMB.shared-ChatStorage.sqlite
+    MESSAGE = "724bd3b98b18518b455a87c1f3ac3a0d189c4466"
+    # AppDomainGroup-group.net.whatsapp.WhatsAppSMB.shared-ContactsV2.sqlite
+    CONTACT = "d7246a707f51ddf8b17ee2dddabd9e0a4da5c552"
+    # AppDomainGroup-group.net.whatsapp.WhatsAppSMB.shared-CallHistory.sqlite
+    CALL = "b463f7c4365eefc5a8723930d97928d4e907c603"
+    DOMAIN = "AppDomainGroup-group.net.whatsapp.WhatsAppSMB.shared"
+
 
 class JidType(IntEnum):
     PM = 0

pyproject.toml

@@ -60,3 +60,8 @@ include = ["Whatsapp_Chat_Exporter"]
 
 [tool.setuptools.package-data]
 Whatsapp_Chat_Exporter = ["*.html"]
+
+[dependency-groups]
+dev = [
+    "pytest>=8.3.5",
+]

tests/test_incremental_merge.py

@@ -0,0 +1,341 @@
+import os
+import json
+import pytest
+from unittest.mock import patch, mock_open, call, MagicMock
+from Whatsapp_Chat_Exporter.utility import incremental_merge
+from Whatsapp_Chat_Exporter.data_model import ChatStore
+
+# Test data setup
+BASE_PATH = "AppDomainGroup-group.net.whatsapp.WhatsApp.shared"
+chat_data_1 = {
+    "12345678@s.whatsapp.net": {
+        "name": "Friend",
+        "type": "ios",
+        "my_avatar": os.path.join(BASE_PATH, "Media", "Profile", "Photo.jpg"),
+        "their_avatar": os.path.join(BASE_PATH, "Media", "Profile", "12345678-1709851420.thumb"),
+        "their_avatar_thumb": None,
+        "status": None,
+        "messages": {
+            "24690": {
+                "from_me": True,
+                "timestamp": 1463926635.571629,
+                "time": "10:17",
+                "media": False,
+                "key_id": "34B5EF10FBCA37B7E",
+                "meta": False,
+                "data": "I'm here",
+                "safe": False,
+                "sticker": False
+            },
+            "24691": {  # This message only exists in target
+                "from_me": False,
+                "timestamp": 1463926641.571629,
+                "time": "10:17",
+                "media": False,
+                "key_id": "34B5EF10FBCA37B8E",
+                "meta": False,
+                "data": "Great to see you",
+                "safe": False,
+                "sticker": False
+            }
+        }
+    }
+}
+
+chat_data_2 = {
+    "12345678@s.whatsapp.net": {
+        "name": "Friend",
+        "type": "ios",
+        "my_avatar": os.path.join(BASE_PATH, "Media", "Profile", "Photo.jpg"),
+        "their_avatar": os.path.join(BASE_PATH, "Media", "Profile", "12345678-1709851420.thumb"),
+        "their_avatar_thumb": None,
+        "status": None,
+        "messages": {
+            "24690": {
+                "from_me": True,
+                "timestamp": 1463926635.571629,
+                "time": "10:17",
+                "media": False,
+                "key_id": "34B5EF10FBCA37B7E",
+                "meta": False,
+                "data": "I'm here",
+                "safe": False,
+                "sticker": False
+            },
+            "24692": {  # This message only exists in source
+                "from_me": False,
+                "timestamp": 1463926642.571629,
+                "time": "10:17",
+                "media": False,
+                "key_id": "34B5EF10FBCA37B9E",
+                "meta": False,
+                "data": "Hi there!",
+                "safe": False,
+                "sticker": False
+            },
+        }
+    }
+}
+
+# Expected merged data - should contain all messages with all fields initialized as they would be by Message class
+chat_data_merged = {
+    "12345678@s.whatsapp.net": {
+        "name": "Friend",
+        "type": "ios",
+        "my_avatar": os.path.join(BASE_PATH, "Media", "Profile", "Photo.jpg"),
+        "their_avatar": os.path.join(BASE_PATH, "Media", "Profile", "12345678-1709851420.thumb"),
+        "their_avatar_thumb": None,
+        "status": None,
+        "media_base": None,
+        "messages": {
+            "24690": {
+                "from_me": True,
+                "timestamp": 1463926635.571629,
+                "time": "10:17",
+                "media": False,
+                "key_id": "34B5EF10FBCA37B7E",
+                "meta": False,
+                "data": "I'm here",
+                "sender": None,
+                "safe": False,
+                "mime": None,
+                "reply": None,
+                "quoted_data": None,
+                "caption": None,
+                "thumb": None,
+                "sticker": False,
+                "message_type": None,
+                "received_timestamp": None,
+                "read_timestamp": None
+            },
+            "24691": {
+                "from_me": False,
+                "timestamp": 1463926641.571629,
+                "time": "10:17",
+                "media": False,
+                "key_id": "34B5EF10FBCA37B8E",
+                "meta": False,
+                "data": "Great to see you",
+                "sender": None,
+                "safe": False,
+                "mime": None,
+                "reply": None,
+                "quoted_data": None,
+                "caption": None,
+                "thumb": None,
+                "sticker": False,
+                "message_type": None,
+                "received_timestamp": None,
+                "read_timestamp": None
+            },
+            "24692": {
+                "from_me": False,
+                "timestamp": 1463926642.571629,
+                "time": "10:17",
+                "media": False,
+                "key_id": "34B5EF10FBCA37B9E",
+                "meta": False,
+                "data": "Hi there!",
+                "sender": None,
+                "safe": False,
+                "mime": None,
+                "reply": None,
+                "quoted_data": None,
+                "caption": None,
+                "thumb": None,
+                "sticker": False,
+                "message_type": None,
+                "received_timestamp": None,
+                "read_timestamp": None
+            },
+        }
+    }
+}
+
+
+@pytest.fixture
+def mock_filesystem():
+    with (
+        patch("os.path.exists") as mock_exists,
+        patch("os.makedirs") as mock_makedirs,
+        patch("os.path.getmtime") as mock_getmtime,
+        patch("os.listdir") as mock_listdir,
+        patch("os.walk") as mock_walk,
+        patch("shutil.copy2") as mock_copy2,
+    ):
+        yield {
+            "exists": mock_exists,
+            "makedirs": mock_makedirs,
+            "getmtime": mock_getmtime,
+            "listdir": mock_listdir,
+            "walk": mock_walk,
+            "copy2": mock_copy2,
+        }
+
+
+def test_incremental_merge_new_file(mock_filesystem):
+    """Test merging when target file doesn't exist"""
+    source_dir = "/source"
+    target_dir = "/target"
+    media_dir = "media"
+    
+    # Setup mock filesystem
+    mock_filesystem["exists"].side_effect = lambda x: x == "/source"
+    mock_filesystem["listdir"].return_value = ["chat.json"]
+    
+    # Run the function
+    incremental_merge(source_dir, target_dir, media_dir, 2, True)
+    
+    # Verify the operations
+    mock_filesystem["makedirs"].assert_called_once_with(target_dir, exist_ok=True)
+    mock_filesystem["copy2"].assert_called_once_with(
+        os.path.join(source_dir, "chat.json"),
+        os.path.join(target_dir, "chat.json")
+    )
+
+
+def test_incremental_merge_existing_file_with_changes(mock_filesystem):
+    """Test merging when target file exists and has changes"""
+    source_dir = "source"
+    target_dir = "target"
+    media_dir = "media"
+
+    # Setup mock filesystem
+    mock_filesystem["exists"].side_effect = lambda x: True
+    mock_filesystem["listdir"].return_value = ["chat.json"]
+
+    # Mock file operations with consistent path separators
+    source_file = os.path.join(source_dir, "chat.json")
+    target_file = os.path.join(target_dir, "chat.json")
+    mock_file_content = {
+        source_file: json.dumps(chat_data_2),
+        target_file: json.dumps(chat_data_1),
+    }
+
+    written_chunks = []
+
+    def mock_file_write(data):
+        written_chunks.append(data)
+
+    mock_write = MagicMock(side_effect=mock_file_write)
+
+    with patch("builtins.open", mock_open()) as mock_file:
+        def mock_file_read(filename, mode="r"):
+            if mode == 'w':
+                file_mock = mock_open().return_value
+                file_mock.write.side_effect = mock_write
+                return file_mock
+            else:
+                # Use normalized path for lookup
+                norm_filename = os.path.normpath(filename)
+                content = mock_file_content.get(norm_filename, '')
+                file_mock = mock_open(read_data=content).return_value
+                return file_mock
+
+        mock_file.side_effect = mock_file_read
+
+        # Run the function
+        incremental_merge(source_dir, target_dir, media_dir, 2, True)
+
+        # Verify file operations using os.path.join
+        mock_file.assert_any_call(source_file, "r")
+        mock_file.assert_any_call(target_file, "r")
+        mock_file.assert_any_call(target_file, "w")
+
+        # Rest of verification code...
+        assert mock_write.called, "Write method was never called"
+        written_data = json.loads(''.join(written_chunks))
+        assert written_data is not None, "No data was written"
+        assert written_data == chat_data_merged, "Merged data does not match expected result"
+
+        messages = written_data["12345678@s.whatsapp.net"]["messages"]
+        assert "24690" in messages, "Common message should be present"
+        assert "24691" in messages, "Target-only message should be preserved"
+        assert "24692" in messages, "Source-only message should be added"
+        assert len(messages) == 3, "Should have exactly 3 messages"
+
+
+def test_incremental_merge_existing_file_no_changes(mock_filesystem):
+    """Test merging when target file exists but has no changes"""
+    source_dir = "source"
+    target_dir = "target"
+    media_dir = "media"
+
+    # Setup mock filesystem
+    mock_filesystem["exists"].side_effect = lambda x: True
+    mock_filesystem["listdir"].return_value = ["chat.json"]
+
+    # Mock file operations with consistent path separators
+    source_file = os.path.join(source_dir, "chat.json")
+    target_file = os.path.join(target_dir, "chat.json")
+    mock_file_content = {
+        source_file: json.dumps(chat_data_1),
+        target_file: json.dumps(chat_data_1),
+    }
+
+    with patch("builtins.open", mock_open()) as mock_file:
+        def mock_file_read(filename, mode="r"):
+            if mode == 'w':
+                file_mock = mock_open().return_value
+                return file_mock
+            else:
+                # Use normalized path for lookup
+                norm_filename = os.path.normpath(filename)
+                content = mock_file_content.get(norm_filename, '')
+                file_mock = mock_open(read_data=content).return_value
+                return file_mock
+
+        mock_file.side_effect = mock_file_read
+
+        # Run the function
+        incremental_merge(source_dir, target_dir, media_dir, 2, True)
+
+        # Verify no write operations occurred on target file
+        write_calls = [
+            call for call in mock_file.mock_calls if call[0] == "().write"]
+        assert len(write_calls) == 0
+
+
+def test_incremental_merge_media_copy(mock_filesystem):
+    """Test media file copying during merge"""
+    source_dir = "source"
+    target_dir = "target"
+    media_dir = "media"
+
+    # Setup mock filesystem
+    mock_filesystem["exists"].side_effect = lambda x: True
+    mock_filesystem["listdir"].return_value = ["chat.json"]
+    mock_filesystem["walk"].return_value = [
+        (os.path.join(source_dir, "media"), ["subfolder"], ["file1.jpg"]),
+        (os.path.join(source_dir, "media", "subfolder"), [], ["file2.jpg"]),
+    ]
+    mock_filesystem["getmtime"].side_effect = lambda x: 1000 if "source" in x else 500
+
+    # Mock file operations with consistent path separators
+    source_file = os.path.join(source_dir, "chat.json")
+    target_file = os.path.join(target_dir, "chat.json")
+    mock_file_content = {
+        source_file: json.dumps(chat_data_1),
+        target_file: json.dumps(chat_data_1),
+    }
+
+    with patch("builtins.open", mock_open()) as mock_file:
+        def mock_file_read(filename, mode="r"):
+            if mode == 'w':
+                file_mock = mock_open().return_value
+                return file_mock
+            else:
+                # Use normalized path for lookup
+                norm_filename = os.path.normpath(filename)
+                content = mock_file_content.get(norm_filename, '')
+                file_mock = mock_open(read_data=content).return_value
+                return file_mock
+
+        mock_file.side_effect = mock_file_read
+
+        # Run the function
+        incremental_merge(source_dir, target_dir, media_dir, 2, True)
+
+        # Verify media file operations
+        assert mock_filesystem["makedirs"].call_count >= 2  # At least target dir and media dir
+        assert mock_filesystem["copy2"].call_count == 2  # Two media files copied