"""FC-inbound proxy runtime driver — wraps `BlackoutSpoofProxy` for scenarios.

This is the runtime piece invoked by FT-N-04 (`test_ft_n_04_blackout_spoof`)
to drive a coordinated GPS spoofing window. The schedule itself is owned
by `fixtures/injectors/blackout_spoof.py`; the proxy state machine
(activate / process_inbound_message / in_window) is owned by
`fixtures/injectors/fc_proxy.BlackoutSpoofProxy`. What was missing — and
what this module adds — is the scenario-facing entry point that:

1. Loads the schedule from disk via `BlackoutSpoofProxy.from_schedule_file`.
2. Optionally activates the proxy against a caller-supplied monotonic
   clock (so the scenario can later verify wall-clock alignment).
3. Writes a small `proxy_drive_report.json` audit record into
   `${E2E_SITL_REPLAY_DIR}` so downstream evaluators (the
   `sitl_observer.read_gps_health_samples` /
   `read_consistency_check_events` consumers in FT-N-04) can correlate.

This driver is **FDR-replay mode only** — it does NOT plumb the proxy
into a live MAVLink router/FC inbound transport. The replay-fixture
builder pre-bakes the spoofed-GPS-rejected events into the FDR JSON
files that the offline `sitl_observer` reads. Live-mode driving (real
router + real FC) is a separate live-mode infrastructure ticket.

Public-boundary discipline: imports only stdlib +
`fixtures.injectors.fc_proxy` (an existing test-side module). Zero
`from gps_denied_onboard ...` imports.
"""

from __future__ import annotations

import json
import os
from dataclasses import asdict, dataclass
from pathlib import Path
from typing import Callable

from fixtures.injectors.fc_proxy import BlackoutSpoofProxy

NowMsProvider = Callable[[], int]

_ENV_VAR = "E2E_SITL_REPLAY_DIR"
_REPORT_FILENAME = "proxy_drive_report.json"


@dataclass(frozen=True)
class ProxyDriveReport:
    """Audit record of one `drive_fc_proxy` invocation.

    Persisted as `proxy_drive_report.json` under the replay-dir root so
    downstream evaluators can confirm the schedule was actually applied
    rather than silently skipped.
    """

    schedule_path: str
    window_start_ms: int
    window_end_ms: int
    spoof_frame_count: int
    alignment_err_ms: int
    was_replay_mode: bool


def drive_fc_proxy(
    schedule_path: Path,
    *,
    now_ms_provider: NowMsProvider | None = None,
    replay_dir: Path | None = None,
) -> ProxyDriveReport:
    """Drive the FC-inbound spoof proxy from `schedule_path`.

    `schedule_path` — JSON written by `blackout_spoof.materialize`.
    `now_ms_provider` — when supplied, the proxy is activated and the
        report carries the resulting `alignment_err_ms`. When None,
        the driver runs in replay mode and reports `alignment_err_ms=0`.
    `replay_dir` — when supplied (or resolved from `E2E_SITL_REPLAY_DIR`),
        the report is written as JSON into that directory. When both
        are absent, no file is written.

    Raises `FileNotFoundError` when `schedule_path` is missing
    (propagated from `BlackoutSpoofProxy.from_schedule_file`) and
    `ValueError` (wrapped) when the JSON cannot be parsed.
    """
    try:
        proxy = BlackoutSpoofProxy.from_schedule_file(schedule_path)
    except json.JSONDecodeError as exc:
        raise ValueError(
            f"malformed schedule JSON at {schedule_path}: {exc.msg}"
        ) from exc

    if now_ms_provider is not None:
        activation = proxy.activate(now_ms_provider=now_ms_provider)
        alignment_err_ms = int(activation.alignment_err_ms)
        was_replay_mode = False
    else:
        alignment_err_ms = 0
        was_replay_mode = True

    report = ProxyDriveReport(
        schedule_path=str(schedule_path),
        window_start_ms=proxy.window_start_ms,
        window_end_ms=proxy.window_end_ms,
        spoof_frame_count=proxy.spoof_frame_count,
        alignment_err_ms=alignment_err_ms,
        was_replay_mode=was_replay_mode,
    )

    target_dir = replay_dir if replay_dir is not None else _resolve_replay_dir()
    if target_dir is not None:
        target_dir.mkdir(parents=True, exist_ok=True)
        (target_dir / _REPORT_FILENAME).write_text(json.dumps(asdict(report)))

    return report


def _resolve_replay_dir() -> Path | None:
    """Resolve `E2E_SITL_REPLAY_DIR`. Returns None when unset or empty."""
    raw = os.environ.get(_ENV_VAR, "").strip()
    if not raw:
        return None
    return Path(raw)