"""Composition-root factories for C8 (AZ-390 / E-C8).

Lazy-imports the per-variant adapter classes so the ADR-002 build-flag
gate stays honest: the binary's bootstrap (one module per
``BUILD_FC_*`` / ``BUILD_GCS_*`` combination) registers the concrete
strategy via :func:`register_fc_adapter` / :func:`register_gcs_adapter`
ahead of `build_fc_adapter` / `build_gcs_adapter`.

A second binding to the outbound emit thread is rejected (AC-6); the
single-writer invariant for outbound is enforced statically by the
composition root, not by the adapter itself.
"""

from __future__ import annotations

import os
import threading
from collections.abc import Callable
from typing import Any, Final

from gps_denied_onboard.components.c8_fc_adapter.errors import (
    FcAdapterConfigError,
    GcsAdapterConfigError,
)
from gps_denied_onboard.components.c8_fc_adapter.interface import (
    FcAdapter,
    GcsAdapter,
)
from gps_denied_onboard.config import Config
from gps_denied_onboard.logging import get_logger

__all__ = [
    "OutboundThreadAlreadyBoundError",
    "bind_outbound_emit_thread",
    "build_fc_adapter",
    "build_gcs_adapter",
    "clear_outbound_thread_binding",
    "clear_strategy_registries",
    "list_registered_fc_strategies",
    "list_registered_gcs_strategies",
    "register_fc_adapter",
    "register_gcs_adapter",
]


# ----------------------------------------------------------------------
# Strategy registries (single source of truth; populated by binary
# bootstrap modules per ADR-002).

FcAdapterFactory = Callable[..., FcAdapter]
GcsAdapterFactory = Callable[..., GcsAdapter]

_FC_REGISTRY: dict[str, FcAdapterFactory] = {}
_GCS_REGISTRY: dict[str, GcsAdapterFactory] = {}

# Mapping from strategy slug -> documented BUILD_*_ flag name. The
# build-flag gate (AC-4) checks ``os.environ`` for the canonical name
# because flag state is a build-time artifact, not a config-time
# artifact.
_FC_BUILD_FLAGS: Final[dict[str, str]] = {
    "ardupilot_plane": "BUILD_FC_ARDUPILOT_PLANE",
    "inav": "BUILD_FC_INAV",
}
_GCS_BUILD_FLAGS: Final[dict[str, str]] = {
    "qgc_mavlink": "BUILD_GCS_QGC_MAVLINK",
}


def register_fc_adapter(strategy: str, factory: FcAdapterFactory) -> None:
    """Register a concrete `FcAdapter` strategy.

    Called from the per-binary bootstrap module (e.g.
    ``runtime_root._bootstrap_ap.py``) under the matching
    ``BUILD_FC_<VARIANT>`` flag. Duplicate registration with a
    different factory is a build error.
    """
    existing = _FC_REGISTRY.get(strategy)
    if existing is not None and existing is not factory:
        raise FcAdapterConfigError(f"duplicate FcAdapter registration for strategy {strategy!r}")
    _FC_REGISTRY[strategy] = factory


def register_gcs_adapter(strategy: str, factory: GcsAdapterFactory) -> None:
    existing = _GCS_REGISTRY.get(strategy)
    if existing is not None and existing is not factory:
        raise GcsAdapterConfigError(f"duplicate GcsAdapter registration for strategy {strategy!r}")
    _GCS_REGISTRY[strategy] = factory


def clear_strategy_registries() -> None:
    """Reset both registries; intended for unit-test isolation only."""
    _FC_REGISTRY.clear()
    _GCS_REGISTRY.clear()


def list_registered_fc_strategies() -> list[str]:
    return sorted(_FC_REGISTRY)


def list_registered_gcs_strategies() -> list[str]:
    return sorted(_GCS_REGISTRY)


# ----------------------------------------------------------------------
# Single-writer outbound thread enforcement (Invariant 8 / AC-6).


class OutboundThreadAlreadyBoundError(RuntimeError):
    """Raised on a second :func:`bind_outbound_emit_thread` call."""


_outbound_lock = threading.Lock()
_outbound_bound_thread: int | None = None


def bind_outbound_emit_thread(thread_ident: int | None = None) -> int:
    """Bind ``thread_ident`` (defaults to the caller) as the sole emit thread.

    A second call from any thread raises
    :class:`OutboundThreadAlreadyBoundError`. The runtime root calls
    this once per process before wiring outbound emit; the result is
    the canonical thread id the adapter checks on every outbound call.
    """
    global _outbound_bound_thread
    ident = thread_ident if thread_ident is not None else threading.get_ident()
    with _outbound_lock:
        if _outbound_bound_thread is not None and _outbound_bound_thread != ident:
            raise OutboundThreadAlreadyBoundError(
                f"outbound emit thread already bound to {_outbound_bound_thread}; "
                f"refused to re-bind to {ident}"
            )
        _outbound_bound_thread = ident
        return ident


def clear_outbound_thread_binding() -> None:
    """Reset the outbound-thread binding; intended for unit-test isolation."""
    global _outbound_bound_thread
    with _outbound_lock:
        _outbound_bound_thread = None


# ----------------------------------------------------------------------
# Build helpers — invoked by `compose_root` after C5 (FC) and after
# the FC adapter (GCS).


def build_fc_adapter(config: Config, **deps: Any) -> FcAdapter:
    """Resolve and build the configured `FcAdapter` strategy.

    Validates the build-flag gate (AC-4); raises
    :class:`FcAdapterConfigError` with the disabled-flag name when the
    requested strategy is not linked into the running binary.
    """
    strategy = config.fc.adapter
    flag_name = _FC_BUILD_FLAGS.get(strategy)
    if flag_name is None:
        # config.fc.adapter went through FcConfig validation, so an
        # unknown strategy here means we forgot to add it to the
        # build-flag table — fail loudly.
        raise FcAdapterConfigError(f"FC strategy {strategy!r} has no BUILD_FC_* flag mapping")
    if os.environ.get(flag_name, "ON").upper() == "OFF":
        raise FcAdapterConfigError(
            f"{flag_name} is OFF — strategy {strategy!r} is not linked into this binary"
        )
    factory = _FC_REGISTRY.get(strategy)
    if factory is None:
        raise FcAdapterConfigError(
            f"FC strategy {strategy!r} is selected by config.fc.adapter but "
            f"not registered; registered strategies: "
            f"{list_registered_fc_strategies()}"
        )
    adapter = factory(config=config, **deps)
    _log_strategy_loaded(
        kind="c8.adapter.strategy_loaded",
        strategy=strategy,
        port_device=config.fc.port_device,
    )
    return adapter


def build_gcs_adapter(config: Config, **deps: Any) -> GcsAdapter:
    """Resolve and build the configured `GcsAdapter` strategy (AC-7)."""
    strategy = config.gcs.adapter
    flag_name = _GCS_BUILD_FLAGS.get(strategy)
    if flag_name is None:
        raise GcsAdapterConfigError(f"GCS strategy {strategy!r} has no BUILD_GCS_* flag mapping")
    if os.environ.get(flag_name, "ON").upper() == "OFF":
        raise GcsAdapterConfigError(
            f"{flag_name} is OFF — strategy {strategy!r} is not linked into this binary"
        )
    factory = _GCS_REGISTRY.get(strategy)
    if factory is None:
        raise GcsAdapterConfigError(
            f"GCS strategy {strategy!r} is selected by config.gcs.adapter but "
            f"not registered; registered strategies: "
            f"{list_registered_gcs_strategies()}"
        )
    adapter = factory(config=config, **deps)
    _log_strategy_loaded(
        kind="c8.gcs.strategy_loaded",
        strategy=strategy,
        port_device=config.gcs.port_device,
    )
    return adapter


def _log_strategy_loaded(*, kind: str, strategy: str, port_device: str) -> None:
    log = get_logger("runtime_root.fc_factory")
    log.info(
        f"{kind}: strategy={strategy} port_device={port_device}",
        extra={
            "kind": kind,
            "kv": {"strategy": strategy, "port_device": port_device},
        },
    )