Update markdown parser to support nested entities

telethon/extensions/markdown.py

@@ -4,6 +4,7 @@ for use within the library, which attempts to handle emojies correctly,
 since they seem to count as two characters and it's a bit strange.
 """
 import re
+import warnings
 
 from ..helpers import add_surrogate, del_surrogate, strip_text
 from ..tl import TLObject
@@ -25,6 +26,10 @@ DEFAULT_URL_RE = re.compile(r'\[([\S\s]+?)\]\((.+?)\)')
 DEFAULT_URL_FORMAT = '[{0}]({1})'
 
 
+def overlap(a, b, x, y):
+    return max(a, x) < min(b, y)
+
+
 def parse(message, delimiters=None, url_re=None):
     """
     Parses the given markdown message and returns its stripped representation
@@ -48,85 +53,80 @@ def parse(message, delimiters=None, url_re=None):
             return message, []
         delimiters = DEFAULT_DELIMITERS
 
+    # Build a regex to efficiently test all delimiters at once
+    delim_re = re.compile('|'.join('({})'.format(re.escape(k)) for k in delimiters))
+
     # Cannot use a for loop because we need to skip some indices
     i = 0
     result = []
-    current = None
-    end_delimiter = None
 
     # Work on byte level with the utf-16le encoding to get the offsets right.
     # The offset will just be half the index we're at.
     message = add_surrogate(message)
     while i < len(message):
-        if url_re and current is None:
+        m = delim_re.match(message, pos=i)
-            # If we're not inside a previous match since Telegram doesn't allow
+
-            # nested message entities, try matching the URL from the i'th pos.
+        # Did we find some delimiter here at `i`?
-            url_match = url_re.match(message, pos=i)
+        if m:
-            if url_match:
+            delim = next(filter(None, m.groups()))
+
+            # +1 to avoid matching right after (e.g. "****")
+            end = message.find(delim, i + len(delim) + 1)
+
+            # Did we find the earliest closing tag?
+            if end != -1:
+
+                # Remove the delimiter from the string
+                message = ''.join((
+                        message[:i],
+                        message[i + len(delim):end],
+                        message[end + len(delim):]
+                ))
+
+                # Check other affected entities
+                for ent in result:
+                    # If the end is after our start, it is affected
+                    if ent.offset + ent.length > i:
+                        ent.length -= len(delim)
+
+                # Append the found entity
+                ent = delimiters[delim]
+                if ent == MessageEntityPre:
+                    result.append(ent(i, end - i - len(delim), ''))  # has 'lang'
+                else:
+                    result.append(ent(i, end - i - len(delim)))
+
+                # No nested entities inside code blocks
+                if ent in (MessageEntityCode, MessageEntityPre):
+                    i = end
+
+                continue
+
+        elif url_re:
+            m = url_re.match(message, pos=i)
+            if m:
                 # Replace the whole match with only the inline URL text.
                 message = ''.join((
-                    message[:url_match.start()],
+                    message[:m.start()],
-                    url_match.group(1),
+                    m.group(1),
-                    message[url_match.end():]
+                    message[m.end():]
                 ))
 
+                delim_size = m.end() - m.start() - len(m.group())
+                for ent in result:
+                    # If the end is after our start, it is affected
+                    if ent.offset + ent.length > m.start():
+                        ent.length -= delim_size
+
                 result.append(MessageEntityTextUrl(
-                    offset=url_match.start(), length=len(url_match.group(1)),
+                    offset=m.start(), length=len(m.group(1)),
-                    url=del_surrogate(url_match.group(2))
+                    url=del_surrogate(m.group(2))
                 ))
-                i += len(url_match.group(1))
+                i += len(m.group(1))
-                # Next loop iteration, don't check delimiters, since
-                # a new inline URL might be right after this one.
                 continue
 
-        if end_delimiter is None:
-            # We're not expecting any delimiter, so check them all
-            for d, m in delimiters.items():
-                # Slice the string at the current i'th position to see if
-                # it matches the current delimiter d, otherwise skip it.
-                if message[i:i + len(d)] != d:
-                    continue
-
-                if message[i + len(d):i + 2 * len(d)] == d:
-                    # The same delimiter can't be right afterwards, if
-                    # this were the case we would match empty strings
-                    # like `` which we don't want to.
-                    continue
-
-                # Get rid of the delimiter by slicing it away
-                message = message[:i] + message[i + len(d):]
-                if m == MessageEntityPre:
-                    # Special case, also has 'lang'
-                    current = m(i, None, '')
-                else:
-                    current = m(i, None)
-
-                end_delimiter = d  # We expect the same delimiter.
-                break
-
-        elif message[i:i + len(end_delimiter)] == end_delimiter:
-            message = message[:i] + message[i + len(end_delimiter):]
-            current.length = i - current.offset
-            result.append(current)
-            current, end_delimiter = None, None
-            # Don't increment i here as we matched a delimiter,
-            # and there may be a new one right after. This is
-            # different than when encountering the first delimiter,
-            # as we already know there won't be the same right after.
-            continue
-
-        # Next iteration
         i += 1
 
-    # We may have found some a delimiter but not its ending pair.
-    # If this is the case, we want to insert the delimiter character back.
-    if current is not None:
-        message = (
-            message[:current.offset]
-            + end_delimiter
-            + message[current.offset:]
-        )
-
     message = strip_text(message, result)
     return del_surrogate(message), result
 
@@ -148,55 +148,35 @@ def unparse(text, entities, delimiters=None, url_fmt=None):
             return text
         delimiters = DEFAULT_DELIMITERS
 
-    if url_fmt is None:
+    if url_fmt is not None:
-        url_fmt = DEFAULT_URL_FORMAT
+        warnings.warn('url_fmt is deprecated')  # since it complicates everything *a lot*
 
     if isinstance(entities, TLObject):
         entities = (entities,)
-    else:
-        entities = tuple(sorted(entities, key=lambda e: e.offset, reverse=True))
 
     text = add_surrogate(text)
     delimiters = {v: k for k, v in delimiters.items()}
+    insert_at = []
     for entity in entities:
         s = entity.offset
         e = entity.offset + entity.length
         delimiter = delimiters.get(type(entity), None)
         if delimiter:
-            text = text[:s] + delimiter + text[s:e] + delimiter + text[e:]
+            insert_at.append((s, delimiter))
-        elif url_fmt:
+            insert_at.append((e, delimiter))
+        else:
             url = None
             if isinstance(entity, MessageEntityTextUrl):
                 url = entity.url
             elif isinstance(entity, MessageEntityMentionName):
                 url = 'tg://user?id={}'.format(entity.user_id)
             if url:
-                # It's possible that entities are malformed and end up in the
+                insert_at.append((s, '['))
-                # middle of some character, like emoji, by using malformed
+                insert_at.append((e, ']({})'.format(url)))
-                # clients or bots. Try decoding the current one to check if
-                # this is the case, and if it is, advance the entity.
-                while e <= len(text):
-                    try:
-                        del_surrogate(text[s:e])
-                        break
-                    except UnicodeDecodeError:
-                        e += 1
-                else:
-                    # Out of bounds, no luck going forward
-                    while e > s:
-                        try:
-                            del_surrogate(text[s:e])
-                            break
-                        except UnicodeDecodeError:
-                            e -= 1
-                    else:
-                        # No luck going backwards either, ignore entity
-                        continue
 
-                text = (
+    insert_at.sort(key=lambda t: t[0])
-                    text[:s] +
+    while insert_at:
-                    add_surrogate(url_fmt.format(text[s:e], url)) +
+        at, what = insert_at.pop()
-                    text[e:]
+        text = text[:at] + what + text[at:]
-                )
 
     return del_surrogate(text)