from __future__ import annotations

from collections.abc import Iterator


def html5_sse_event(event: str, fragment: str) -> str:
    data = "\n".join(f"data: {line}" for line in fragment.splitlines())
    return f"event: {event}\nretry: 5000\n{data}\n\n"


def html5_sse_if_changed(last_fragments: dict[str, str], event: str, fragment: str) -> Iterator[str]:
    if last_fragments.get(event) == fragment:
        return
    last_fragments[event] = fragment
    yield html5_sse_event(event, fragment)


def html5_sse_comment(message: str) -> str:
    return f": {message}\n\n"