From e05b0ebe46b2197ef3bfa7caa4a672d06fb946c2 Mon Sep 17 00:00:00 2001
From: Davte <davte@libero.it>
Date: Mon, 1 Jul 2019 23:36:45 +0200
Subject: [PATCH] Split text in several messages if it hits Telegram limits

---
 davtelepot/bot.py | 80 +++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 71 insertions(+), 9 deletions(-)

diff --git a/davtelepot/bot.py b/davtelepot/bot.py
index 26fdcf8..03ace8e 100644
--- a/davtelepot/bot.py
+++ b/davtelepot/bot.py
@@ -15,7 +15,7 @@ from aiohttp import web
 
 # Project modules
 from api import TelegramBot, TelegramError
-from utilities import get_secure_key, make_lines_of_buttons
+from utilities import escape_html_chars, get_secure_key, make_lines_of_buttons
 
 # Do not log aiohttp `INFO` and `DEBUG` levels
 logging.getLogger('aiohttp').setLevel(logging.WARNING)
@@ -36,6 +36,7 @@ class Bot(TelegramBot):
                             "Please retry later...")
     _authorization_denied_message = None
     _unknown_command_message = None
+    TELEGRAM_MESSAGES_MAX_LEN = 4096
 
     def __init__(
         self, token, hostname='', certificate=None, max_connections=40,
@@ -604,8 +605,58 @@ class Bot(TelegramBot):
             "but this handler does nothing yet."
         )
 
+    @staticmethod
+    def split_message_text(text, limit=None, parse_mode='HTML'):
+        r"""Split text if it hits telegram limits for text messages.
+
+        Split at `\n` if possible.
+        Add a `[...]` at the end and beginning of split messages,
+        with proper code markdown.
+        """
+        if parse_mode == 'HTML':
+            text = escape_html_chars(text)
+        tags = (
+            ('`', '`')
+            if parse_mode == 'Markdown'
+            else ('<code>', '</code>')
+            if parse_mode.lower() == 'html'
+            else ('', '')
+        )
+        if limit is None:
+            limit = Bot.TELEGRAM_MESSAGES_MAX_LEN - 100
+        # Example text: "lines\nin\nreversed\order"
+        text = text.split("\n")[::-1]  # ['order', 'reversed', 'in', 'lines']
+        text_part_number = 0
+        while len(text) > 0:
+            temp = []
+            text_part_number += 1
+            while (
+                len(text) > 0
+                and len(
+                    "\n".join(temp + [text[-1]])
+                ) < limit
+            ):
+                # Append lines of `text` in order (`.pop` returns the last
+                # line in text) until the addition of the next line would hit
+                # the `limit`.
+                temp.append(text.pop())
+            # If graceful split failed (last line was longer than limit)
+            if len(temp) == 0:
+                # Force split last line
+                temp.append(text[-1][:limit])
+                text[-1] = text[-1][limit:]
+            text_chunk = "\n".join(temp)  # Re-join this group of lines
+            prefix, suffix = '', ''
+            is_last = len(text) > 0
+            if text_part_number > 1:
+                prefix = f"{tags[0]}[...]{tags[1]}\n"
+            if is_last:
+                suffix = f"\n{tags[0]}[...]{tags[1]}"
+            yield (prefix + text_chunk + suffix), is_last
+        return
+
     async def send_message(self, chat_id=None, text=None,
-                           parse_mode=None,
+                           parse_mode='HTML',
                            disable_web_page_preview=None,
                            disable_notification=None,
                            reply_to_message_id=None,
@@ -636,15 +687,26 @@ class Bot(TelegramBot):
             and text != self.authorization_denied_message
         ):
             reply_markup = self.default_keyboard
-        return await self.sendMessage(
-            chat_id=chat_id,
+        if not text:
+            return
+        parse_mode = str(parse_mode)
+        text_chunks = self.split_message_text(
             text=text,
-            parse_mode=parse_mode,
-            disable_web_page_preview=disable_web_page_preview,
-            disable_notification=disable_notification,
-            reply_to_message_id=reply_to_message_id,
-            reply_markup=reply_markup
+            limit=self.__class__.TELEGRAM_MESSAGES_MAX_LEN - 100,
+            parse_mode=parse_mode
         )
+        for text_chunk, is_last in text_chunks:
+            _reply_markup = (reply_markup if is_last else None)
+            sent_message_update = await self.sendMessage(
+                chat_id=chat_id,
+                text=text_chunk,
+                parse_mode=parse_mode,
+                disable_web_page_preview=disable_web_page_preview,
+                disable_notification=disable_notification,
+                reply_to_message_id=reply_to_message_id,
+                reply_markup=_reply_markup
+            )
+        return sent_message_update
 
     async def answer_inline_query(self,
                                   inline_query_id=None,