feat(telegram): markdown support

nanobot/channels/telegram.py

@@ -1,7 +1,7 @@
 """Telegram channel implementation using python-telegram-bot."""
 
 import asyncio
-from typing import Any
+import re
 
 from loguru import logger
 from telegram import Update
@@ -13,6 +13,69 @@ from nanobot.channels.base import BaseChannel
 from nanobot.config.schema import TelegramConfig
 
 
+def _markdown_to_telegram_html(text: str) -> str:
+    """
+    Convert markdown to Telegram-safe HTML.
+    """
+    if not text:
+        return ""
+    
+    # 1. Extract and protect code blocks (preserve content from other processing)
+    code_blocks: list[str] = []
+    def save_code_block(m: re.Match) -> str:
+        code_blocks.append(m.group(1))
+        return f"\x00CB{len(code_blocks) - 1}\x00"
+    
+    text = re.sub(r'```[\w]*\n?([\s\S]*?)```', save_code_block, text)
+    
+    # 2. Extract and protect inline code
+    inline_codes: list[str] = []
+    def save_inline_code(m: re.Match) -> str:
+        inline_codes.append(m.group(1))
+        return f"\x00IC{len(inline_codes) - 1}\x00"
+    
+    text = re.sub(r'`([^`]+)`', save_inline_code, text)
+    
+    # 3. Headers # Title -> just the title text
+    text = re.sub(r'^#{1,6}\s+(.+)$', r'\1', text, flags=re.MULTILINE)
+    
+    # 4. Blockquotes > text -> just the text (before HTML escaping)
+    text = re.sub(r'^>\s*(.*)$', r'\1', text, flags=re.MULTILINE)
+    
+    # 5. Escape HTML special characters
+    text = text.replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;")
+    
+    # 6. Links [text](url) - must be before bold/italic to handle nested cases
+    text = re.sub(r'\[([^\]]+)\]\(([^)]+)\)', r'<a href="\2">\1</a>', text)
+    
+    # 7. Bold **text** or __text__
+    text = re.sub(r'\*\*(.+?)\*\*', r'<b>\1</b>', text)
+    text = re.sub(r'__(.+?)__', r'<b>\1</b>', text)
+    
+    # 8. Italic _text_ (avoid matching inside words like some_var_name)
+    text = re.sub(r'(?<![a-zA-Z0-9])_([^_]+)_(?![a-zA-Z0-9])', r'<i>\1</i>', text)
+    
+    # 9. Strikethrough ~~text~~
+    text = re.sub(r'~~(.+?)~~', r'<s>\1</s>', text)
+    
+    # 10. Bullet lists - item -> • item
+    text = re.sub(r'^[-*]\s+', '• ', text, flags=re.MULTILINE)
+    
+    # 11. Restore inline code with HTML tags
+    for i, code in enumerate(inline_codes):
+        # Escape HTML in code content
+        escaped = code.replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;")
+        text = text.replace(f"\x00IC{i}\x00", f"<code>{escaped}</code>")
+    
+    # 12. Restore code blocks with HTML tags
+    for i, code in enumerate(code_blocks):
+        # Escape HTML in code content
+        escaped = code.replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;")
+        text = text.replace(f"\x00CB{i}\x00", f"<pre><code>{escaped}</code></pre>")
+    
+    return text
+
+
 class TelegramChannel(BaseChannel):
     """
     Telegram channel using long polling.
@@ -96,14 +159,25 @@ class TelegramChannel(BaseChannel):
         try:
             # chat_id should be the Telegram chat ID (integer)
             chat_id = int(msg.chat_id)
+            # Convert markdown to Telegram HTML
+            html_content = _markdown_to_telegram_html(msg.content)
             await self._app.bot.send_message(
                 chat_id=chat_id,
-                text=msg.content
+                text=html_content,
+                parse_mode="HTML"
             )
         except ValueError:
             logger.error(f"Invalid chat_id: {msg.chat_id}")
         except Exception as e:
-            logger.error(f"Error sending Telegram message: {e}")
+            # Fallback to plain text if HTML parsing fails
+            logger.warning(f"HTML parse failed, falling back to plain text: {e}")
+            try:
+                await self._app.bot.send_message(
+                    chat_id=int(msg.chat_id),
+                    text=msg.content
+                )
+            except Exception as e2:
+                logger.error(f"Error sending Telegram message: {e2}")
     
     async def _on_start(self, update: Update, context: ContextTypes.DEFAULT_TYPE) -> None:
         """Handle /start command."""