"""Fallback-Ketten: versuchen mehrere Provider der Reihe nach.

Faellt der primaere Provider aus (Timeout/Fehler), wird transparent der naechste
versucht. Erfolgreicher Fallback und Provider-Fehler werden als Metrik erfasst.
"""

from collections.abc import AsyncIterator

from app.metrics import metrics


class _Chain:
    def __init__(self, module: str, entries: list[tuple[str, object]]):
        self.module = module
        self.entries = entries  # [(provider_name, provider), ...]

    def _on_error(self, name: str) -> None:
        metrics.inc("provider_error_total", {"module": self.module, "provider": name})

    def _on_fallback(self) -> None:
        metrics.inc("provider_fallback_total", {"module": self.module})


class FallbackSTTProvider(_Chain):
    async def transcribe(self, audio_bytes, fmt, language=None) -> str:
        last_exc = None
        for index, (name, provider) in enumerate(self.entries):
            try:
                result = await provider.transcribe(audio_bytes, fmt, language=language)
                if index > 0:
                    self._on_fallback()
                return result
            except Exception as exc:  # noqa: BLE001 - bewusst breit fuer Resilienz
                last_exc = exc
                self._on_error(name)
        raise last_exc


class FallbackLLMProvider(_Chain):
    async def complete(self, text, history=None, session_id=None, language=None) -> str:
        last_exc = None
        for index, (name, provider) in enumerate(self.entries):
            try:
                result = await provider.complete(
                    text, history=history, session_id=session_id, language=language
                )
                if index > 0:
                    self._on_fallback()
                return result
            except Exception as exc:  # noqa: BLE001
                last_exc = exc
                self._on_error(name)
        raise last_exc

    async def stream(self, text, history=None, session_id=None, language=None) -> AsyncIterator[str]:
        last_exc = None
        for index, (name, provider) in enumerate(self.entries):
            produced = False
            try:
                async for delta in provider.stream(
                    text, history=history, session_id=session_id, language=language
                ):
                    produced = True
                    yield delta
                if index > 0:
                    self._on_fallback()
                return
            except Exception as exc:  # noqa: BLE001
                last_exc = exc
                self._on_error(name)
                if produced:
                    # Schon Token gesendet -> kein Fallback mehr moeglich.
                    raise
        raise last_exc


class FallbackTTSProvider(_Chain):
    async def synthesize(self, text, voice=None, audio_format="pcm") -> bytes:
        last_exc = None
        for index, (name, provider) in enumerate(self.entries):
            try:
                result = await provider.synthesize(text, voice=voice, audio_format=audio_format)
                if index > 0:
                    self._on_fallback()
                return result
            except Exception as exc:  # noqa: BLE001
                last_exc = exc
                self._on_error(name)
        raise last_exc