"""
Transcription Provider Registry
================================

Central map of registered STT providers. Populated by plugins at
import-time via :meth:`PluginContext.register_transcription_provider`;
consumed by :mod:`tools.transcription_tools` to dispatch
:func:`transcribe_audio` calls to the active plugin backend **when**
the configured ``stt.provider`` name is not a built-in.

Built-ins-always-win
--------------------
Plugin names that collide with a built-in STT provider (``local``,
``local_command``, ``groq``, ``openai``, ``mistral``, ``xai``) are
rejected at registration with a warning. This invariant is also
re-checked at dispatch time in
:func:`tools.transcription_tools._dispatch_to_plugin_provider`.
"""

from __future__ import annotations

import logging
import threading
from typing import Dict, List, Optional

from agent.transcription_provider import TranscriptionProvider

logger = logging.getLogger(__name__)


# Names reserved for native built-in STT handlers. Plugins cannot
# register a name in this set — the registration call is rejected with
# a warning. **Kept in sync with ``BUILTIN_STT_PROVIDERS`` in
# :mod:`tools.transcription_tools`** — a regression test in
# ``tests/agent/test_transcription_registry.py::TestBuiltinSync``
# fails if the two lists drift. Importing from
# ``tools.transcription_tools`` directly would create a circular
# dependency (``tools.transcription_tools`` imports
# ``agent.transcription_registry`` for dispatch).
_BUILTIN_NAMES = frozenset({
    "local",
    "local_command",
    "groq",
    "openai",
    "mistral",
    "xai",
})


_providers: Dict[str, TranscriptionProvider] = {}
_lock = threading.Lock()


def register_provider(provider: TranscriptionProvider) -> None:
    """Register a transcription provider.

    Rejects:

    - Non-:class:`TranscriptionProvider` instances (raises :class:`TypeError`).
    - Empty/whitespace ``.name`` (raises :class:`ValueError`).
    - Names colliding with a built-in (logs a warning, silently
      ignores — built-ins-always-win invariant).

    Re-registration (same ``name``) overwrites the previous entry and
    logs a debug message — makes hot-reload scenarios (tests, dev
    loops) behave predictably.
    """
    if not isinstance(provider, TranscriptionProvider):
        raise TypeError(
            f"register_provider() expects a TranscriptionProvider instance, "
            f"got {type(provider).__name__}"
        )
    name = provider.name
    if not isinstance(name, str) or not name.strip():
        raise ValueError("Transcription provider .name must be a non-empty string")
    key = name.strip().lower()
    if key in _BUILTIN_NAMES:
        logger.warning(
            "Transcription provider '%s' shadows a built-in name; registration "
            "ignored. Built-in STT providers (%s) always win — pick a different "
            "name.",
            key, ", ".join(sorted(_BUILTIN_NAMES)),
        )
        return
    with _lock:
        existing = _providers.get(key)
        _providers[key] = provider
    if existing is not None:
        logger.debug(
            "Transcription provider '%s' re-registered (was %r)",
            key, type(existing).__name__,
        )
    else:
        logger.debug(
            "Registered transcription provider '%s' (%s)",
            key, type(provider).__name__,
        )


def list_providers() -> List[TranscriptionProvider]:
    """Return all registered providers, sorted by name."""
    with _lock:
        items = list(_providers.values())
    return sorted(items, key=lambda p: p.name)


def get_provider(name: str) -> Optional[TranscriptionProvider]:
    """Return the provider registered under *name*, or None.

    Name matching is case-insensitive and whitespace-tolerant — mirrors
    how ``tools.transcription_tools._get_provider`` normalizes the
    configured ``stt.provider`` value.
    """
    if not isinstance(name, str):
        return None
    return _providers.get(name.strip().lower())


def _reset_for_tests() -> None:
    """Clear the registry. **Test-only.**"""
    with _lock:
        _providers.clear()
