Add first and last interaction timeline events for WhatsApp chats

Extract one record per ZWACHATSESSION with the first and last stored
message dates, the session's own last-message date, the group creation
date and message counts. Each chat produces chat_first_message and
chat_last_message timeline events, and groups a group_created event.
The session last-message date is preferred over the newest stored
message because it survives message deletion.

tests/ios_backup/test_whatsapp.py

@@ -6,8 +6,62 @@
 import logging
 
 from mvt.common.indicators import Indicators
+from mvt.common.module import run_module
 from mvt.ios.modules.mixed.whatsapp import Whatsapp
 
+from ..utils import get_ios_backup_folder
+
+
+def test_extraction():
+    m = Whatsapp(target_path=get_ios_backup_folder())
+    run_module(m)
+
+    messages = [r for r in m.results if "ZTEXT" in r]
+    sessions = [r for r in m.results if r.get("record_type") == "chat_session"]
+    assert len(messages) == 3
+    assert len(sessions) == 2
+
+    linked = next(r for r in messages if r.get("links"))
+    assert linked["links"] == ["https://example.org/news"]
+
+    alice = next(s for s in sessions if s["partner_name"] == "Alice Example")
+    assert alice["contact_jid"] == "14155550100@s.whatsapp.net"
+    assert alice["first_stored_message_date"] == "2025-08-27 15:06:40.000000"
+    assert alice["last_message_date"] == "2025-08-28 18:53:20.000000"
+    assert alice["group_creation_date"] is None
+    assert alice["stored_message_count"] == 2
+
+    group = next(s for s in sessions if s["partner_name"] == "Example Group")
+    assert group["group_creation_date"] == "2025-08-21 20:13:20.000000"
+    assert group["first_stored_message_date"] == "2025-08-29 22:40:00.000000"
+    # The last stored message predates the session's own last-message date:
+    # the newest message in this chat was deleted.
+    assert group["last_stored_message_date"] == "2025-08-29 22:40:00.000000"
+    assert group["last_message_date"] == "2025-08-31 02:26:40.000000"
+
+    # 3 message events plus first/last per chat and the group creation.
+    assert len(m.timeline) == 8
+    events = {
+        (entry["event"], entry["timestamp"]): entry["data"]
+        for entry in m.timeline
+    }
+    assert events[("chat_first_message", "2025-08-27 15:06:40.000000")] == (
+        "First stored message in WhatsApp chat with "
+        "'Alice Example' (14155550100@s.whatsapp.net)"
+    )
+    assert events[("chat_last_message", "2025-08-28 18:53:20.000000")] == (
+        "Last message in WhatsApp chat with "
+        "'Alice Example' (14155550100@s.whatsapp.net)"
+    )
+    assert events[("group_created", "2025-08-21 20:13:20.000000")] == (
+        "WhatsApp group chat 'Example Group' "
+        "(120000000000000001@g.us) was created"
+    )
+    assert ("chat_first_message", "2025-08-29 22:40:00.000000") in events
+    assert ("chat_last_message", "2025-08-31 02:26:40.000000") in events
+
+    assert len(m.alertstore.alerts) == 0
+
 
 def test_collect_url_results_includes_expansion():
     module = Whatsapp(

tests/ios_fs/test_filesystem.py

@@ -15,8 +15,8 @@ class TestFilesystem:
     def test_filesystem(self):
         m = Filesystem(target_path=get_ios_backup_folder())
         run_module(m)
-        assert len(m.results) == 19
-        assert len(m.timeline) == 19
+        assert len(m.results) == 21
+        assert len(m.timeline) == 21
         assert len(m.alertstore.alerts) == 0
 
     def test_detection(self, indicator_file):
@@ -29,6 +29,6 @@ class TestFilesystem:
         )
         m.indicators = ind
         run_module(m)
-        assert len(m.results) == 19
-        assert len(m.timeline) == 19
+        assert len(m.results) == 21
+        assert len(m.timeline) == 21
         assert len(m.alertstore.alerts) == 1