"""Single place to recognise router sentinels.

``route_message()`` normally returns text to post back to the user. Two
special values are protocol instead of a reply, and every adapter must
catch them before sending anything:

- ``__AUDIO__:<path>`` — a TTS result; the payload is a WAV path to attach.
- ``__STEERED__`` — the message was injected into an in-flight turn; the
  adapter should react (not reply) and post nothing.

Zero dependencies on adapters or router — importable standalone.
"""
from __future__ import annotations

AUDIO_PREFIX = "__AUDIO__:"
STEERED = "__STEERED__"


def audio_path(response: str | None) -> str | None:
    """Return the WAV path if `response` is an audio sentinel, else None."""
    if response and response.startswith(AUDIO_PREFIX):
        return response[len(AUDIO_PREFIX):]
    return None


def is_steered(response: str | None) -> bool:
    """True if `response` is the steering-acknowledgement sentinel."""
    return response == STEERED


if __name__ == "__main__":
    assert audio_path("__AUDIO__:/tmp/x.wav") == "/tmp/x.wav"
    assert audio_path("hello") is None
    assert audio_path("") is None
    assert audio_path(None) is None
    assert is_steered("__STEERED__") is True
    assert is_steered("__STEERED__ ") is False
    assert is_steered("") is False
    assert is_steered(None) is False
    print("ok")