# See the Zulip URL spec at https://zulip.com/api/zulip-urls
#
# Keep this synchronized with web/src/topic_link_util.ts

import re

from zerver.lib.url_encoding import encode_channel, encode_hash_component
from zerver.models.messages import Message

invalid_stream_topic_regex = re.compile(r"[`>*&\[\]]|(\$\$)")


def will_produce_broken_stream_topic_link(word: str) -> bool:
    return bool(invalid_stream_topic_regex.search(word))


TOPIC_LINK_SYNTAX_FOR_DISPLAY = "#{channel_name} > {topic_name}"

escape_mapping = {
    "`": "`",
    ">": ">",
    "*": "*",
    "&": "&",
    "$$": "$$",
    "[": "[",
    "]": "]",
}


def escape_invalid_stream_topic_characters(text: str) -> str:
    return re.sub(
        invalid_stream_topic_regex,
        lambda match: escape_mapping.get(match.group(0), match.group(0)),
        text,
    )


def get_message_link_label(
    stream_name: str, topic_name: str | None = None, message_id: int | None = None
) -> str:
    """The text label for a channel/topic/message Markdown link, of the form
    "#channel > topic @ 💬" (matching the web app's "Copy link to message").

    Characters that would break the surrounding Markdown link syntax are
    escaped, and an empty topic is shown using its fallback display name.
    """
    escape = escape_invalid_stream_topic_characters
    text = f"#{escape(stream_name)}"
    if topic_name is not None:
        if topic_name == "":
            topic_name = Message.EMPTY_TOPIC_FALLBACK_NAME
        text += f" > {escape(topic_name)}"

    if message_id is not None:
        text += " @ 💬"

    return text


def get_fallback_markdown_link(
    stream_id: int, stream_name: str, topic_name: str | None = None, message_id: int | None = None
) -> str:
    """
    Helper that should only be called by other methods in this file.

    Generates the vanilla markdown link syntax for a stream/topic/message link, as
    a fallback for cases where the nicer Zulip link syntax would not
    render properly due to special characters in the channel or topic name.
    """
    link = f"#narrow/channel/{encode_channel(stream_id, stream_name)}"
    if topic_name is not None:
        link += f"/topic/{encode_hash_component(topic_name)}"

    if message_id is not None:
        link += f"/near/{message_id}"

    text = get_message_link_label(stream_name, topic_name, message_id)
    return f"[{text}]({link})"


def get_message_link_syntax(
    stream_id: int, stream_name: str, topic_name: str, message_id: int
) -> str:
    # If the stream/topic name is such that it will
    # generate an invalid #**stream>topic@message_id** syntax,
    # we revert to generating the normal markdown syntax for a link.
    if will_produce_broken_stream_topic_link(topic_name) or will_produce_broken_stream_topic_link(
        stream_name
    ):
        return get_fallback_markdown_link(stream_id, stream_name, topic_name, message_id)
    return f"#**{stream_name}>{topic_name}@{message_id}**"


def get_stream_topic_link_syntax(stream_id: int, stream_name: str, topic_name: str) -> str:
    # If the stream/topic name is such that it will generate an invalid #**stream>topic** syntax,
    # we revert to generating the normal markdown syntax for a link.
    if will_produce_broken_stream_topic_link(topic_name) or will_produce_broken_stream_topic_link(
        stream_name
    ):
        return get_fallback_markdown_link(stream_id, stream_name, topic_name)
    return f"#**{stream_name}>{topic_name}**"


def get_stream_link_syntax(stream_id: int, stream_name: str) -> str:
    # If the stream name is such that it will generate an invalid #**stream** syntax,
    # we revert to generating the normal markdown syntax for a link.
    if will_produce_broken_stream_topic_link(stream_name):
        return get_fallback_markdown_link(stream_id, stream_name)
    return f"#**{stream_name}**"