my.telegram.telegram_backup: support optional extra_where and optional media info extraction for Promnesia

my/telegram/telegram_backup.py

@@ -4,6 +4,7 @@ Telegram data via [fabianonline/telegram_backup](https://github.com/fabianonline
 
 from dataclasses import dataclass
 from datetime import datetime, timezone
+from struct import unpack_from, calcsize
 import sqlite3
 from typing import Dict, Iterator, Optional
 
@@ -43,6 +44,7 @@ class Message:
     chat: Chat
     sender: User
     text: str
+    extra_media_info: Optional[str] = None
 
     @property
     def permalink(self) -> str:
@@ -60,25 +62,41 @@ class Message:
 
 
 Chats = Dict[str, Chat]
-def _message_from_row(r: sqlite3.Row, *, chats: Chats) -> Message:
+def _message_from_row(r: sqlite3.Row, *, chats: Chats, with_extra_media_info: bool) -> Message:
     ts = r['time']
     # desktop export uses UTC (checked by exporting in winter time vs summer time)
     # and telegram_backup timestamps seem same as in desktop export
     time = datetime.fromtimestamp(ts, tz=timezone.utc)
     chat = chats[r['source_id']]
     sender = chats[r['sender_id']]
+
+    extra_media_info: Optional[str] = None
+    if with_extra_media_info and r['has_media'] == 1:
+        # also it's quite hacky, so at least for now it's just an optional attribute behind the flag
+        # defensive because it's a bit tricky to correctly parse without a proper api parser..
+        # maybe later we'll improve it
+        try:
+            extra_media_info = _extract_extra_media_info(data=r['data'])
+        except Exception as e:
+            pass
+
     return Message(
         id=r['message_id'],
         time=time,
         chat=chat,
         sender=User(id=sender.id, name=sender.name),
         text=r['text'],
+        extra_media_info=extra_media_info,
     )
 
 
-def messages() -> Iterator[Message]:
+def messages(*, extra_where: Optional[str]=None, with_extra_media_info: bool=False) -> Iterator[Message]:
-    with sqlite_connection(config.export_path, immutable=True, row_factory='row') as db:
+    messages_query = 'SELECT * FROM messages WHERE message_type NOT IN ("service_message", "empty_message")'
+    if extra_where is not None:
+        messages_query += ' AND ' + extra_where
+    messages_query += ' ORDER BY time'
 
+    with sqlite_connection(config.export_path, immutable=True, row_factory='row') as db:
         chats: Chats = {}
         for r in db.execute('SELECT * FROM chats ORDER BY id'):
             chat = Chat(id=r['id'], name=r['name'], handle=None)
@@ -98,7 +116,69 @@ def messages() -> Iterator[Message]:
             assert chat.id not in chats
             chats[chat.id] = chat
 
-        for r in db.execute('SELECT * FROM messages WHERE message_type NOT IN ("service_message", "empty_message") ORDER BY time'):
+        for r in db.execute(messages_query):
             # seems like the only remaining have message_type = 'message'
-            yield _message_from_row(r, chats=chats)
+            yield _message_from_row(r, chats=chats, with_extra_media_info=with_extra_media_info)
 
+
+def _extract_extra_media_info(data: bytes) -> Optional[str]:
+    # ugh... very hacky, but it does manage to extract from 90% of messages that have media
+    pos = 0
+
+    def skip(count: int) -> None:
+        nonlocal pos
+        pos += count
+
+    def getstring() -> str:
+        # jesus
+        # https://core.telegram.org/type/string
+        if data[pos] == 254:
+            skip(1)
+            (sz1, sz2, sz3) = unpack_from('BBB', data, offset=pos)
+            skip(3)
+            sz = 256 ** 2 * sz3 + 256 * sz2 + sz1
+            short = 0
+        else:
+            (sz, ) = unpack_from('B', data, offset=pos)
+            skip(1)
+            short = 1
+        assert sz > 0, sz
+
+        padding = 0 if (sz + short) % 4 == 0 else 4 - (sz + short) % 4
+
+        (ss,) = unpack_from(f'{sz}s{padding}x', data, offset=pos)
+        skip(sz + padding)
+        try:
+            return ss.decode('utf8')
+        except UnicodeDecodeError as e:
+            raise RuntimeError(f'Failed to decode {ss}') from e
+
+    def debug(count: int=10) -> None:
+        print([hex(x) for x in data[pos: pos + count]])
+        print([chr(x) for x in data[pos: pos + count]])
+
+    header = 'H2xII8xI'
+    (flags, mid, src, ts) = unpack_from(header, data, offset=pos)
+    pos += calcsize(header)
+
+    # see https://core.telegram.org/constructor/message
+    has_media = (flags >> 9) & 1
+    if has_media == 0:
+        return None
+
+    msg_body = getstring()
+    skip(20)
+    url1 = getstring()
+    url2 = getstring()
+    ss_type = getstring()
+    # not sure if assert is really necessary her
+    # assert ss_type in {
+    #     'article',
+    #     'photo',
+    #     'app',
+    #     'video',
+    # }, ss_type
+    link_title = getstring()
+    link_title_2 = getstring()
+    link_description = getstring()
+    return link_description