src/case_zero/tts/supertonic_provider.py

"""Supertonic TTS - lightning-fast, on-device, ~99M-param ONNX voices.

Each suspect gets a distinct preset voice (M1-M5 / F1-F5). Lazily loaded and excluded
from unit coverage (needs the supertonic package + ONNX assets). Falls back to
unavailable so the game degrades to text-only.
"""

from __future__ import annotations

from pathlib import Path

from ..schemas.suspect import VoiceAssignment

# Males 0-4, females 5-9, matching tts.assignment.assign_voice's gendered speaker_id.
_VOICES = ("M1", "M2", "M3", "M4", "M5", "F1", "F2", "F3", "F4", "F5")


class SupertonicProvider:  # pragma: no cover - requires the supertonic package + models
    is_local = True

    def __init__(self) -> None:
        self.available = False
        self._tts = None
        self._styles: dict[str, object] = {}
        try:
            from supertonic import TTS

            self._tts = TTS(auto_download=True)
            self.available = True
        except Exception:
            self.available = False

    def _style(self, name: str):
        if name not in self._styles:
            self._styles[name] = self._tts.get_voice_style(voice_name=name)  # type: ignore[union-attr]
        return self._styles[name]

    def synth_to_file(self, text: str, voice: VoiceAssignment | None, out_path: Path) -> Path | None:
        if not self.available or self._tts is None or not text.strip():
            return None
        name = _VOICES[(voice.speaker_id if voice else 0) % len(_VOICES)]
        # length_scale (0.95-1.15) -> a gentle per-suspect speed variation around 1.0.
        speed = round(2.05 - (voice.length_scale if voice else 1.05), 2)
        speed = min(1.2, max(0.85, speed))
        try:
            wav, _ = self._tts.synthesize(  # type: ignore[union-attr]
                text=text, lang="en", voice_style=self._style(name), total_steps=6, speed=speed
            )
            out_path.parent.mkdir(parents=True, exist_ok=True)
            self._tts.save_audio(wav, str(out_path))  # type: ignore[union-attr]
            return out_path
        except Exception:
            return None