From 332215ea2eee1293d0aa61d39ac7ae14e363d06d Mon Sep 17 00:00:00 2001
From: Lonami Exo <totufals@hotmail.com>
Date: Thu, 31 Aug 2023 23:05:49 +0200
Subject: [PATCH] Bring client parsers for commonmark and HTML

---
 client/pyproject.toml                         |   1 +
 client/src/telethon/_impl/client/__init__.py  |   0
 .../telethon/_impl/client/parsers/__init__.py |  11 +
 .../src/telethon/_impl/client/parsers/html.py | 207 ++++++++++++++++++
 .../telethon/_impl/client/parsers/markdown.py | 191 ++++++++++++++++
 .../telethon/_impl/client/parsers/strings.py  |  75 +++++++
 client/tests/test_parsers.py                  | 151 +++++++++++++
 7 files changed, 636 insertions(+)
 create mode 100644 client/src/telethon/_impl/client/__init__.py
 create mode 100644 client/src/telethon/_impl/client/parsers/__init__.py
 create mode 100644 client/src/telethon/_impl/client/parsers/html.py
 create mode 100644 client/src/telethon/_impl/client/parsers/markdown.py
 create mode 100644 client/src/telethon/_impl/client/parsers/strings.py
 create mode 100644 client/tests/test_parsers.py

diff --git a/client/pyproject.toml b/client/pyproject.toml
index 3052714c..bd940936 100644
--- a/client/pyproject.toml
+++ b/client/pyproject.toml
@@ -21,6 +21,7 @@ classifiers = [
 dependencies = [
   "pyaes~=1.6",
   "rsa~=4.9",
+  "markdown-it-py~=3.0",
 ]
 dynamic = ["version"]
 
diff --git a/client/src/telethon/_impl/client/__init__.py b/client/src/telethon/_impl/client/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/client/src/telethon/_impl/client/parsers/__init__.py b/client/src/telethon/_impl/client/parsers/__init__.py
new file mode 100644
index 00000000..4d3985fb
--- /dev/null
+++ b/client/src/telethon/_impl/client/parsers/__init__.py
@@ -0,0 +1,11 @@
+from .html import parse as parse_html_message
+from .html import unparse as generate_html_message
+from .markdown import parse as parse_markdown_message
+from .markdown import unparse as generate_markdown_message
+
+__all__ = [
+    "generate_html_message",
+    "parse_html_message",
+    "generate_markdown_message",
+    "parse_markdown_message",
+]
diff --git a/client/src/telethon/_impl/client/parsers/html.py b/client/src/telethon/_impl/client/parsers/html.py
new file mode 100644
index 00000000..e7b8f739
--- /dev/null
+++ b/client/src/telethon/_impl/client/parsers/html.py
@@ -0,0 +1,207 @@
+from collections import deque
+from html import escape
+from html.parser import HTMLParser
+from typing import Any, Deque, Dict, Iterable, List, Optional, Tuple, Type, cast
+
+from ...tl.abcs import MessageEntity
+from ...tl.types import (
+    MessageEntityBlockquote,
+    MessageEntityBold,
+    MessageEntityCode,
+    MessageEntityEmail,
+    MessageEntityItalic,
+    MessageEntityMentionName,
+    MessageEntityPre,
+    MessageEntitySpoiler,
+    MessageEntityStrike,
+    MessageEntityTextUrl,
+    MessageEntityUnderline,
+    MessageEntityUrl,
+)
+from .strings import add_surrogate, del_surrogate, strip_text, within_surrogate
+
+
+class HTMLToTelegramParser(HTMLParser):
+    def __init__(self) -> None:
+        super().__init__()
+        self.text = ""
+        self.entities: List[MessageEntity] = []
+        self._building_entities: Dict[str, MessageEntity] = {}
+        self._open_tags: Deque[str] = deque()
+        self._open_tags_meta: Deque[Optional[str]] = deque()
+
+    def handle_starttag(
+        self, tag: str, attrs_seq: List[Tuple[str, Optional[str]]]
+    ) -> None:
+        self._open_tags.appendleft(tag)
+        self._open_tags_meta.appendleft(None)
+
+        attrs = dict(attrs_seq)
+        EntityType: Optional[Type[MessageEntity]] = None
+        args = {}
+        if tag == "strong" or tag == "b":
+            EntityType = MessageEntityBold
+        elif tag == "em" or tag == "i":
+            EntityType = MessageEntityItalic
+        elif tag == "u":
+            EntityType = MessageEntityUnderline
+        elif tag == "del" or tag == "s":
+            EntityType = MessageEntityStrike
+        elif tag == "blockquote":
+            EntityType = MessageEntityBlockquote
+        elif tag == "details":
+            EntityType = MessageEntitySpoiler
+        elif tag == "code":
+            try:
+                # If we're in the middle of a <pre> tag, this <code> tag is
+                # probably intended for syntax highlighting.
+                #
+                # Syntax highlighting is set with
+                #     <code class='language-...'>codeblock</code>
+                # inside <pre> tags
+                pre = self._building_entities["pre"]
+                assert isinstance(pre, MessageEntityPre)
+                if cls := attrs.get("class"):
+                    pre.language = cls[len("language-") :]
+            except KeyError:
+                EntityType = MessageEntityCode
+        elif tag == "pre":
+            EntityType = MessageEntityPre
+            args["language"] = ""
+        elif tag == "a":
+            url = attrs.get("href")
+            if not url:
+                return
+            if url.startswith("mailto:"):
+                url = url[len("mailto:") :]
+                EntityType = MessageEntityEmail
+            else:
+                if self.get_starttag_text() == url:
+                    EntityType = MessageEntityUrl
+                else:
+                    EntityType = MessageEntityTextUrl
+                    args["url"] = del_surrogate(url)
+                    url = None
+            self._open_tags_meta.popleft()
+            self._open_tags_meta.appendleft(url)
+
+        if EntityType and tag not in self._building_entities:
+            Et = cast(Any, EntityType)
+            self._building_entities[tag] = Et(
+                offset=len(self.text),
+                # The length will be determined when closing the tag.
+                length=0,
+                **args,
+            )
+
+    def handle_data(self, text: str) -> None:
+        previous_tag = self._open_tags[0] if len(self._open_tags) > 0 else ""
+        if previous_tag == "a":
+            url = self._open_tags_meta[0]
+            if url:
+                text = url
+
+        for entity in self._building_entities.values():
+            assert hasattr(entity, "length")
+            entity.length += len(text)
+
+        self.text += text
+
+    def handle_endtag(self, tag: str) -> None:
+        try:
+            self._open_tags.popleft()
+            self._open_tags_meta.popleft()
+        except IndexError:
+            pass
+        entity = self._building_entities.pop(tag, None)
+        if entity and hasattr(entity, "length") and entity.length:
+            self.entities.append(entity)
+
+
+def parse(html: str) -> Tuple[str, List[MessageEntity]]:
+    """
+    Parses the given HTML message and returns its stripped representation
+    plus a list of the MessageEntity's that were found.
+
+    :param html: the message with HTML to be parsed.
+    :return: a tuple consisting of (clean message, [message entities]).
+    """
+    if not html:
+        return html, []
+
+    parser = HTMLToTelegramParser()
+    parser.feed(add_surrogate(html))
+    text = strip_text(parser.text, parser.entities)
+    return del_surrogate(text), parser.entities
+
+
+ENTITY_TO_FORMATTER = {
+    MessageEntityBold: ("<strong>", "</strong>"),
+    MessageEntityItalic: ("<em>", "</em>"),
+    MessageEntityCode: ("<code>", "</code>"),
+    MessageEntityUnderline: ("<u>", "</u>"),
+    MessageEntityStrike: ("<del>", "</del>"),
+    MessageEntityBlockquote: ("<blockquote>", "</blockquote>"),
+    MessageEntitySpoiler: ("<details>", "</details>"),
+    MessageEntityPre: lambda e, _: (
+        '<pre><code class="language-{}">'.format(e.language) if e.language else "<pre>",
+        "</code></pre>" if e.language else "</pre>",
+    ),
+    MessageEntityEmail: lambda _, t: ('<a href="mailto:{}">'.format(t), "</a>"),
+    MessageEntityUrl: lambda _, t: ('<a href="{}">'.format(t), "</a>"),
+    MessageEntityTextUrl: lambda e, _: ('<a href="{}">'.format(escape(e.url)), "</a>"),
+    MessageEntityMentionName: lambda e, _: (
+        '<a href="tg://user?id={}">'.format(e.user_id),
+        "</a>",
+    ),
+}
+
+
+def unparse(text: str, entities: Iterable[MessageEntity]) -> str:
+    """
+    Performs the reverse operation to .parse(), effectively returning HTML
+    given a normal text and its MessageEntity's.
+
+    :param text: the text to be reconverted into HTML.
+    :param entities: the MessageEntity's applied to the text.
+    :return: a HTML representation of the combination of both inputs.
+    """
+    if not text:
+        return text
+    elif not entities:
+        return escape(text)
+
+    text = add_surrogate(text)
+    insert_at: List[Tuple[int, str]] = []
+    for entity in entities:
+        assert hasattr(entity, "offset") and hasattr(entity, "length")
+        s = entity.offset
+        e = entity.offset + entity.length
+        delimiter = ENTITY_TO_FORMATTER.get(type(entity), None)
+        if delimiter:
+            if callable(delimiter):
+                delim = delimiter(entity, text[s:e])
+            else:
+                delim = delimiter
+            insert_at.append((s, delim[0]))
+            insert_at.append((e, delim[1]))
+
+    insert_at.sort(key=lambda t: t[0])
+    next_escape_bound = len(text)
+    while insert_at:
+        # Same logic as markdown.py
+        at, what = insert_at.pop()
+        while within_surrogate(text, at):
+            at += 1
+
+        text = (
+            text[:at]
+            + what
+            + escape(text[at:next_escape_bound])
+            + text[next_escape_bound:]
+        )
+        next_escape_bound = at
+
+    text = escape(text[:next_escape_bound]) + text[next_escape_bound:]
+
+    return del_surrogate(text)
diff --git a/client/src/telethon/_impl/client/parsers/markdown.py b/client/src/telethon/_impl/client/parsers/markdown.py
new file mode 100644
index 00000000..4701d531
--- /dev/null
+++ b/client/src/telethon/_impl/client/parsers/markdown.py
@@ -0,0 +1,191 @@
+import re
+from typing import Any, Iterator, List, Tuple
+
+import markdown_it
+import markdown_it.token
+
+from ...tl.abcs import MessageEntity
+from ...tl.types import (
+    MessageEntityBlockquote,
+    MessageEntityBold,
+    MessageEntityCode,
+    MessageEntityItalic,
+    MessageEntityMentionName,
+    MessageEntityPre,
+    MessageEntityStrike,
+    MessageEntityTextUrl,
+    MessageEntityUnderline,
+)
+from .strings import add_surrogate, del_surrogate, within_surrogate
+
+MARKDOWN = markdown_it.MarkdownIt().enable("strikethrough")
+DELIMITERS = {
+    MessageEntityBlockquote: ("> ", ""),
+    MessageEntityBold: ("**", "**"),
+    MessageEntityCode: ("`", "`"),
+    MessageEntityItalic: ("_", "_"),
+    MessageEntityStrike: ("~~", "~~"),
+    MessageEntityUnderline: ("# ", ""),
+}
+
+# Not trying to be complete; just enough to have an alternative (mostly for inline underline).
+# The fact headings are treated as underline is an implementation detail.
+TAG_PATTERN = re.compile(r"<\s*(/?)\s*(\w+)")
+HTML_TO_TYPE = {
+    "i": ("em_close", "em_open"),
+    "em": ("em_close", "em_open"),
+    "b": ("strong_close", "strong_open"),
+    "strong": ("strong_close", "strong_open"),
+    "s": ("s_close", "s_open"),
+    "del": ("s_close", "s_open"),
+    "u": ("heading_open", "heading_close"),
+    "mark": ("heading_open", "heading_close"),
+}
+
+
+def expand_inline_and_html(
+    tokens: List[markdown_it.token.Token],
+) -> Iterator[markdown_it.token.Token]:
+    for token in tokens:
+        if token.type == "inline":
+            if token.children:
+                yield from expand_inline_and_html(token.children)
+        elif token.type == "html_inline":
+            match = TAG_PATTERN.match(token.content)
+            if match:
+                close, tag = match.groups()
+                tys = HTML_TO_TYPE.get(tag.lower())
+                if tys:
+                    token.type = tys[bool(close)]
+                    token.nesting = -1 if close else 1
+                    yield token
+        else:
+            yield token
+
+
+def parse(message: str) -> Tuple[str, List[MessageEntity]]:
+    """
+    Parses the given markdown message and returns its stripped representation
+    plus a list of the MessageEntity's that were found.
+    """
+    if not message:
+        return message, []
+
+    entities: List[MessageEntity]
+    token: markdown_it.token.Token
+
+    def push(ty: Any, **extra: object) -> None:
+        nonlocal message, entities, token
+        if token.nesting > 0:
+            entities.append(ty(offset=len(message), length=0, **extra))
+        else:
+            for entity in reversed(entities):
+                if isinstance(entity, ty):
+                    entity.length = len(message) - entity.offset
+                    break
+
+    parsed = MARKDOWN.parse(add_surrogate(message.strip()))
+    message = ""
+    entities = []
+    last_map = [0, 0]
+    for token in expand_inline_and_html(parsed):
+        if token.map is not None and token.map != last_map:
+            # paragraphs, quotes fences have a line mapping. Use it to determine how many newlines to insert.
+            # But don't inssert any (leading) new lines if we're yet to reach the first textual content, or
+            # if the mappings are the same (e.g. a quote then opens a paragraph but the mapping is equal).
+            if message:
+                message += "\n" + "\n" * (token.map[0] - last_map[-1])
+            last_map = token.map
+
+        if token.type in ("blockquote_close", "blockquote_open"):
+            push(MessageEntityBlockquote)
+        elif token.type == "code_block":
+            entities.append(
+                MessageEntityPre(
+                    offset=len(message), length=len(token.content), language=""
+                )
+            )
+            message += token.content
+        elif token.type == "code_inline":
+            entities.append(
+                MessageEntityCode(offset=len(message), length=len(token.content))
+            )
+            message += token.content
+        elif token.type in ("em_close", "em_open"):
+            push(MessageEntityItalic)
+        elif token.type == "fence":
+            entities.append(
+                MessageEntityPre(
+                    offset=len(message), length=len(token.content), language=token.info
+                )
+            )
+            message += token.content[:-1]  # remove a single trailing newline
+        elif token.type == "hardbreak":
+            message += "\n"
+        elif token.type in ("heading_close", "heading_open"):
+            push(MessageEntityUnderline)
+        elif token.type == "hr":
+            message += "\u2015\n\n"
+        elif token.type in ("link_close", "link_open"):
+            if (
+                token.markup != "autolink"
+            ):  # telegram already picks up on these automatically
+                push(MessageEntityTextUrl, url=token.attrs.get("href"))
+        elif token.type in ("s_close", "s_open"):
+            push(MessageEntityStrike)
+        elif token.type == "softbreak":
+            message += " "
+        elif token.type in ("strong_close", "strong_open"):
+            push(MessageEntityBold)
+        elif token.type == "text":
+            message += token.content
+
+    return del_surrogate(message), entities
+
+
+def unparse(text: str, entities: List[MessageEntity]) -> str:
+    """
+    Performs the reverse operation to .parse(), effectively returning
+    markdown-like syntax given a normal text and its MessageEntity's.
+
+    Because there are many possible ways for markdown to produce a certain
+    output, this function cannot invert .parse() perfectly.
+    """
+    if not text or not entities:
+        return text
+
+    text = add_surrogate(text)
+    insert_at: List[Tuple[int, str]] = []
+    for entity in entities:
+        assert hasattr(entity, "offset")
+        assert hasattr(entity, "length")
+        s = entity.offset
+        e = entity.offset + entity.length
+        delimiter = DELIMITERS.get(type(entity), None)
+        if delimiter:
+            insert_at.append((s, delimiter[0]))
+            insert_at.append((e, delimiter[1]))
+        elif isinstance(entity, MessageEntityPre):
+            insert_at.append((s, f"```{entity.language}\n"))
+            insert_at.append((e, "```\n"))
+        elif isinstance(entity, MessageEntityTextUrl):
+            insert_at.append((s, "["))
+            insert_at.append((e, f"]({entity.url})"))
+        elif isinstance(entity, MessageEntityMentionName):
+            insert_at.append((s, "["))
+            insert_at.append((e, f"](tg://user?id={entity.user_id})"))
+
+    insert_at.sort(key=lambda t: t[0])
+    while insert_at:
+        at, what = insert_at.pop()
+
+        # If we are in the middle of a surrogate nudge the position by -1.
+        # Otherwise we would end up with malformed text and fail to encode.
+        # For example of bad input: "Hi \ud83d\ude1c"
+        # https://en.wikipedia.org/wiki/UTF-16#U+010000_to_U+10FFFF
+        while within_surrogate(text, at):
+            at += 1
+
+        text = text[:at] + what + text[at:]
+
+    return del_surrogate(text)
diff --git a/client/src/telethon/_impl/client/parsers/strings.py b/client/src/telethon/_impl/client/parsers/strings.py
new file mode 100644
index 00000000..1d7f8fb3
--- /dev/null
+++ b/client/src/telethon/_impl/client/parsers/strings.py
@@ -0,0 +1,75 @@
+import struct
+from typing import List, Optional
+
+from ...tl.abcs import MessageEntity
+
+
+def add_surrogate(text: str) -> str:
+    return "".join(
+        # SMP -> Surrogate Pairs (Telegram offsets are calculated with these).
+        # See https://en.wikipedia.org/wiki/Plane_(Unicode)#Overview for more.
+        "".join(chr(y) for y in struct.unpack("<HH", x.encode("utf-16le")))
+        if (0x10000 <= ord(x) <= 0x10FFFF)
+        else x
+        for x in text
+    )
+
+
+def del_surrogate(text: str) -> str:
+    return text.encode("utf-16", "surrogatepass").decode("utf-16")
+
+
+def within_surrogate(text: str, index: int, *, length: Optional[int] = None) -> bool:
+    """
+    `True` if ``index`` is within a surrogate (before and after it, not at!).
+    """
+    if length is None:
+        length = len(text)
+
+    return (
+        1 < index < len(text)  # in bounds
+        and "\ud800" <= text[index - 1] <= "\udfff"  # previous is
+        and "\ud800" <= text[index] <= "\udfff"  # current is
+    )
+
+
+def strip_text(text: str, entities: List[MessageEntity]) -> str:
+    """
+    Strips whitespace from the given text modifying the provided entities.
+
+    This assumes that there are no overlapping entities, that their length
+    is greater or equal to one, and that their length is not out of bounds.
+    """
+    if not entities:
+        return text.strip()
+
+    while text and text[-1].isspace():
+        e = entities[-1]
+        assert hasattr(e, "offset") and hasattr(e, "length")
+        if e.offset + e.length == len(text):
+            if e.length == 1:
+                del entities[-1]
+                if not entities:
+                    return text.strip()
+            else:
+                e.length -= 1
+        text = text[:-1]
+
+    while text and text[0].isspace():
+        for i in reversed(range(len(entities))):
+            e = entities[i]
+            assert hasattr(e, "offset") and hasattr(e, "length")
+            if e.offset != 0:
+                e.offset -= 1
+                continue
+
+            if e.length == 1:
+                del entities[0]
+                if not entities:
+                    return text.lstrip()
+            else:
+                e.length -= 1
+
+        text = text[1:]
+
+    return text
diff --git a/client/tests/test_parsers.py b/client/tests/test_parsers.py
new file mode 100644
index 00000000..4541306a
--- /dev/null
+++ b/client/tests/test_parsers.py
@@ -0,0 +1,151 @@
+from telethon._impl.client.parsers import (
+    generate_html_message,
+    generate_markdown_message,
+    parse_html_message,
+    parse_markdown_message,
+)
+from telethon._impl.tl import types
+
+
+def test_parse_leading_markdown() -> None:
+    markdown = "**Hello** world!"
+    text, entities = parse_markdown_message(markdown)
+    assert text == "Hello world!"
+    assert entities == [types.MessageEntityBold(offset=0, length=5)]
+
+
+def test_parse_trailing_markdown() -> None:
+    markdown = "Hello **world!**"
+    text, entities = parse_markdown_message(markdown)
+    assert text == "Hello world!"
+    assert entities == [types.MessageEntityBold(offset=6, length=6)]
+
+
+def test_parse_emoji_markdown() -> None:
+    markdown = "A **little 🦀** here"
+    text, entities = parse_markdown_message(markdown)
+    assert text == "A little 🦀 here"
+    assert entities == [types.MessageEntityBold(offset=2, length=9)]
+
+
+def test_parse_all_entities_markdown() -> None:
+    markdown = "Some **bold** (__strong__), *italics* (_cursive_), inline `code`, a\n```rust\npre\n```\nblock, a [link](https://example.com), and [mentions](tg://user?id=12345678)"
+    text, entities = parse_markdown_message(markdown)
+
+    assert (
+        text
+        == "Some bold (strong), italics (cursive), inline code, a\npre\nblock, a link, and mentions"
+    )
+    assert entities == [
+        types.MessageEntityBold(offset=5, length=4),
+        types.MessageEntityBold(offset=11, length=6),
+        types.MessageEntityItalic(offset=20, length=7),
+        types.MessageEntityItalic(offset=29, length=7),
+        types.MessageEntityCode(offset=46, length=4),
+        types.MessageEntityPre(offset=54, length=4, language="rust"),
+        types.MessageEntityTextUrl(offset=67, length=4, url="https://example.com"),
+        types.MessageEntityTextUrl(offset=77, length=8, url="tg://user?id=12345678"),
+    ]
+
+
+def test_parse_nested_entities_markdown() -> None:
+    # CommonMark won't allow the following="Some **bold _both** italics_"
+    markdown = "Some **bold _both_** _italics_"
+    text, entities = parse_markdown_message(markdown)
+    assert text == "Some bold both italics"
+    assert entities == [
+        types.MessageEntityBold(offset=5, length=9),
+        types.MessageEntityItalic(offset=10, length=4),
+        types.MessageEntityItalic(offset=15, length=7),
+    ]
+
+
+def test_parse_then_unparse_markdown() -> None:
+    markdown = "Some **bold 🤷🏽‍♀️**, _italics_, inline `🤷🏽‍♀️ code`, a\n\n```rust\npre\n```\nblock, a [link](https://example.com), and [mentions](tg://user?id=12345678)"
+    text, entities = parse_markdown_message(markdown)
+    generated = generate_markdown_message(text, entities)
+    assert generated == markdown
+
+
+def test_parse_leading_html() -> None:
+    # Intentionally use different casing to make sure that is handled well
+    html = "<B>Hello</b> world!"
+    text, entities = parse_html_message(html)
+    assert text == "Hello world!"
+    assert entities == [types.MessageEntityBold(offset=0, length=5)]
+
+
+def test_parse_trailing_html() -> None:
+    html = "Hello <strong>world!</strong>"
+    text, entities = parse_html_message(html)
+    assert text == "Hello world!"
+    assert entities == [types.MessageEntityBold(offset=6, length=6)]
+
+
+def test_parse_emoji_html() -> None:
+    html = "A <b>little 🦀</b> here"
+    text, entities = parse_html_message(html)
+    assert text == "A little 🦀 here"
+    assert entities == [types.MessageEntityBold(offset=2, length=9)]
+
+
+def test_parse_all_entities_html() -> None:
+    html = 'Some <b>bold</b> (<strong>strong</strong>), <i>italics</i> (<em>cursive</em>), inline <code>code</code>, a <pre>pre</pre> block, a <a href="https://example.com">link</a>, <details>spoilers</details> and <a href="tg://user?id=12345678">mentions</a>'
+    text, entities = parse_html_message(html)
+    assert (
+        text
+        == "Some bold (strong), italics (cursive), inline code, a pre block, a link, spoilers and mentions"
+    )
+    assert entities == [
+        types.MessageEntityBold(offset=5, length=4),
+        types.MessageEntityBold(offset=11, length=6),
+        types.MessageEntityItalic(offset=20, length=7),
+        types.MessageEntityItalic(offset=29, length=7),
+        types.MessageEntityCode(offset=46, length=4),
+        types.MessageEntityPre(offset=54, length=3, language=""),
+        types.MessageEntityTextUrl(offset=67, length=4, url="https://example.com"),
+        types.MessageEntitySpoiler(offset=73, length=8),
+        types.MessageEntityTextUrl(offset=86, length=8, url="tg://user?id=12345678"),
+    ]
+
+
+def test_parse_pre_with_lang_html() -> None:
+    html = 'Some <pre>pre</pre>, <code>normal</code> and <pre><code class="language-rust">rusty</code></pre> code'
+    text, entities = parse_html_message(html)
+    assert text == "Some pre, normal and rusty code"
+    assert entities == [
+        types.MessageEntityPre(offset=5, length=3, language=""),
+        types.MessageEntityCode(offset=10, length=6),
+        types.MessageEntityPre(offset=21, length=5, language="rust"),
+    ]
+
+
+def test_parse_empty_pre_and_lang_html() -> None:
+    html = 'Some empty <pre></pre> and <code class="language-rust">code</code>'
+    text, entities = parse_html_message(html)
+    assert text == "Some empty  and code"
+    assert entities == [types.MessageEntityCode(offset=16, length=4)]
+
+
+def test_parse_link_no_href_html() -> None:
+    html = "Some <a>empty link</a>, it does nothing"
+    text, entities = parse_html_message(html)
+    assert text == "Some empty link, it does nothing"
+    assert entities == []
+
+
+def test_parse_nested_entities_html() -> None:
+    html = "Some <b>bold <i>both</b> italics</i>"
+    text, entities = parse_html_message(html)
+    assert text == "Some bold both italics"
+    assert entities == [
+        types.MessageEntityBold(offset=5, length=9),
+        types.MessageEntityItalic(offset=10, length=12),
+    ]
+
+
+def test_parse_then_unparse_html() -> None:
+    html = 'Some <strong>bold</strong>, <em>italics</em> inline <code>code</code>, a <pre>pre</pre> block <pre><code class="language-rs">use rust;</code></pre>, a <a href="https://example.com">link</a>, <details>spoilers</details> and <a href="tg://user?id=12345678">mentions</a>'
+    text, entities = parse_html_message(html)
+    generated = generate_html_message(text, entities)
+    assert generated == html