"""MSP2 frame observer for FT-P-09-iNav (AZ-417 / AC-4.3).

iNav consumes MSP2 over a TCP socket on port 5760. The SUT's
``c8_fc_adapter`` (iNav-side) emits ``MSP2_SENSOR_GPS`` (function ID
0x1F03) frames at a configured cadence (target 5 Hz per AC-2).

This helper owns the pure-logic side of FT-P-09-iNav:

* ``compute_rate_hz`` — given a sequence of frame-arrival timestamps,
  return the observed Hz over a window.
* ``count_frames_by_id`` — filter + tally per MSP function ID.
* ``evaluate_inav_gps_state`` — given a snapshot of iNav's ``gpsSol``
  + ``provider`` after replay, assert AC-3 (fix_type ≥ 3, provider =
  MSP, numSat matches the emitted value).

The TCP-probe + actual MSP frame capture path is owned by AZ-407
(``runner.helpers.sitl_observer``) and the iNav SITL docker compose
service. This module only consumes already-captured data.

Public-boundary discipline: does NOT import any ``src/gps_denied_onboard``
symbol.
"""

from __future__ import annotations

from dataclasses import dataclass
from typing import Sequence

MSP2_SENSOR_GPS_FUNCTION_ID = 0x1F03
DEFAULT_TARGET_RATE_HZ = 5.0
MIN_OBSERVED_RATE_HZ = 4.5  # AC-2: ≥4.5 Hz observed for 5 Hz target
MIN_FIX_TYPE = 3  # AC-3: gpsSol.fixType ≥ 3
REQUIRED_PROVIDER = "MSP"  # AC-3: provider=MSP (no fallback to internal GPS)


@dataclass(frozen=True)
class MspFrameSample:
    """One MSP frame as captured by the SITL-side observer."""

    monotonic_ms: int
    function_id: int


@dataclass(frozen=True)
class InavGpsSnapshot:
    """Snapshot of iNav's ``gpsSol`` + provider state after replay."""

    fix_type: int
    num_sat: int
    provider: str


@dataclass(frozen=True)
class RateReport:
    """Observed rate over a window with pass/fail vs spec target."""

    frame_count: int
    window_ms: int
    observed_rate_hz: float
    target_rate_hz: float
    min_required_hz: float

    @property
    def passes(self) -> bool:
        return (
            self.window_ms > 0
            and self.observed_rate_hz >= self.min_required_hz
        )


@dataclass(frozen=True)
class InavGpsReport:
    """Evaluation of iNav GPS state against AC-3."""

    snapshot: InavGpsSnapshot
    expected_num_sat: int
    fix_type_ok: bool
    provider_ok: bool
    num_sat_ok: bool

    @property
    def passes(self) -> bool:
        return self.fix_type_ok and self.provider_ok and self.num_sat_ok


def count_frames_by_id(samples: Sequence[MspFrameSample]) -> dict[int, int]:
    """Tally per MSP function ID."""
    counts: dict[int, int] = {}
    for s in samples:
        counts[s.function_id] = counts.get(s.function_id, 0) + 1
    return counts


def compute_rate_hz(
    samples: Sequence[MspFrameSample],
    *,
    function_id: int = MSP2_SENSOR_GPS_FUNCTION_ID,
    target_rate_hz: float = DEFAULT_TARGET_RATE_HZ,
    min_required_hz: float = MIN_OBSERVED_RATE_HZ,
) -> RateReport:
    """Compute observed Hz for the given function_id over the sample window.

    The window is ``[first_sample.monotonic_ms, last_sample.monotonic_ms]``
    inclusive. A window of zero ms (≤1 matching sample) is reported but
    will not pass.
    """
    if min_required_hz < 0:
        raise ValueError(f"min_required_hz must be ≥0, got {min_required_hz}")
    filtered = [s for s in samples if s.function_id == function_id]
    if len(filtered) < 2:
        return RateReport(
            frame_count=len(filtered),
            window_ms=0,
            observed_rate_hz=0.0,
            target_rate_hz=target_rate_hz,
            min_required_hz=min_required_hz,
        )
    window_ms = filtered[-1].monotonic_ms - filtered[0].monotonic_ms
    if window_ms <= 0:
        return RateReport(
            frame_count=len(filtered),
            window_ms=window_ms,
            observed_rate_hz=0.0,
            target_rate_hz=target_rate_hz,
            min_required_hz=min_required_hz,
        )
    # Rate = (count - 1) / (window in seconds); the first frame is the
    # epoch boundary, subsequent frames define the cadence.
    observed = (len(filtered) - 1) / (window_ms / 1000.0)
    return RateReport(
        frame_count=len(filtered),
        window_ms=window_ms,
        observed_rate_hz=observed,
        target_rate_hz=target_rate_hz,
        min_required_hz=min_required_hz,
    )


def evaluate_inav_gps_state(
    snapshot: InavGpsSnapshot,
    *,
    expected_num_sat: int,
    min_fix_type: int = MIN_FIX_TYPE,
    required_provider: str = REQUIRED_PROVIDER,
) -> InavGpsReport:
    """Validate AC-3: fix_type ≥3, provider=MSP, numSat matches emitted value."""
    if expected_num_sat < 0:
        raise ValueError(f"expected_num_sat must be ≥0, got {expected_num_sat}")
    return InavGpsReport(
        snapshot=snapshot,
        expected_num_sat=expected_num_sat,
        fix_type_ok=snapshot.fix_type >= min_fix_type,
        provider_ok=snapshot.provider == required_provider,
        num_sat_ok=snapshot.num_sat == expected_num_sat,
    )