"""AZ-919 — `AltitudeProvider` Protocol + `EskfNominalAltitudeProvider` contract.

Pins the gating rules that the GSD scale-recovery work (AZ-920) and the
degraded-mode signal (AZ-921) build on top of.
"""

from __future__ import annotations

from typing import Any

import numpy as np

from gps_denied_onboard._types.state import IsamState
from gps_denied_onboard.helpers.altitude_provider import (
    AltitudeProvider,
    EskfNominalAltitudeProvider,
)


class _FakeEstimator:
    """Minimal ESKF stand-in exposing only the attrs the provider reads."""

    def __init__(
        self,
        *,
        nominal_pos_z: float,
        takeoff_origin_set: bool,
        isam2_state: IsamState,
    ) -> None:
        self._nominal_pos = np.array([0.0, 0.0, nominal_pos_z], dtype=np.float64)
        self._takeoff_origin_set: tuple[Any, float, float] | None = (
            ("origin-sentinel", 1.0, 1.0) if takeoff_origin_set else None
        )
        self._isam2_state = isam2_state


def test_provider_is_runtime_checkable_protocol() -> None:
    provider = EskfNominalAltitudeProvider(estimator_supplier=lambda: None)

    assert isinstance(provider, AltitudeProvider)


def test_returns_none_when_supplier_yields_none() -> None:
    provider = EskfNominalAltitudeProvider(estimator_supplier=lambda: None)

    assert provider.agl_m(now_ns=1_000_000_000) is None


def test_returns_none_before_takeoff_origin_is_anchored() -> None:
    # Arrange — origin not yet set, even though nominal_pos has a value.
    estimator = _FakeEstimator(
        nominal_pos_z=42.0,
        takeoff_origin_set=False,
        isam2_state=IsamState.INIT,
    )
    provider = EskfNominalAltitudeProvider(estimator_supplier=lambda: estimator)

    assert provider.agl_m(now_ns=1_000_000_000) is None


def test_returns_nominal_pos_z_after_origin_is_anchored() -> None:
    # Arrange
    estimator = _FakeEstimator(
        nominal_pos_z=83.5,
        takeoff_origin_set=True,
        isam2_state=IsamState.TRACKING,
    )
    provider = EskfNominalAltitudeProvider(estimator_supplier=lambda: estimator)

    # Act + Assert
    assert provider.agl_m(now_ns=1_000_000_000) == 83.5


def test_returns_none_when_estimator_is_lost() -> None:
    # Arrange — origin anchored and altitude is non-zero, but the
    # filter has flipped to LOST; the AGL signal is no longer trustworthy.
    estimator = _FakeEstimator(
        nominal_pos_z=120.0,
        takeoff_origin_set=True,
        isam2_state=IsamState.LOST,
    )
    provider = EskfNominalAltitudeProvider(estimator_supplier=lambda: estimator)

    assert provider.agl_m(now_ns=1_000_000_000) is None


def test_supplier_is_re_resolved_per_call() -> None:
    # Arrange — the composition root builds C1 before C5, so the
    # supplier must read from a mutable container at call time.
    holder: dict[str, _FakeEstimator] = {}
    provider = EskfNominalAltitudeProvider(
        estimator_supplier=lambda: holder.get("c5_state"),
    )

    # Act — first call: C5 not yet built.
    first = provider.agl_m(now_ns=1_000_000_000)
    # Then C5 lands in the dict.
    holder["c5_state"] = _FakeEstimator(
        nominal_pos_z=37.0,
        takeoff_origin_set=True,
        isam2_state=IsamState.TRACKING,
    )
    second = provider.agl_m(now_ns=2_000_000_000)

    # Assert
    assert first is None
    assert second == 37.0