"""This module asserts correct runtime behaviour of the :mod:`pyrate.plan.geometry.helpers` functions
for calculating differences.
"""

# Python standard
from abc import ABC
from abc import abstractmethod
from math import isfinite
from math import isnan
import warnings

# Typing
from typing import Callable
from typing import Sequence
from typing import Tuple

# Generic testing
from unittest import TestCase

# Numeric testing
from numpy import allclose
from numpy import array

# Hypothesis testing
from hypothesis import given
import hypothesis.strategies as st

# Test helpers
from pyrate.plan.geometry.helpers import difference_direction
from pyrate.plan.geometry.helpers import difference_latitude
from pyrate.plan.geometry.helpers import difference_longitude
from pyrate.plan.geometry.helpers import ScalarOrArray


class TestDifference(TestCase, ABC):
    """Makes sure the distance measure is well-behaved.

    Keep in mind that it is formally not a metric since the triangle inequality does not hold.
    """

    @abstractmethod
    def _get_difference_function(self) -> Callable[[ScalarOrArray, ScalarOrArray], ScalarOrArray]:
        """Get the function to be tested."""

    @abstractmethod
    def _get_max(self) -> float:
        """Get the desired maximum value (inclusive)."""

    @abstractmethod
    def _get_concrete_examples(self) -> Sequence[Tuple[float, float, float]]:
        """Get some concrete values to be tested as a sequence of ``(value a, value b, distance between)``."""

    @given(st.floats(), st.floats())
    def test_distance_measuring_commutes_and_is_in_bounds(self, first: float, second: float) -> None:
        """Assures flipping the sides when calculating distances does not make a significant difference."""

        with warnings.catch_warnings():
            warnings.simplefilter("ignore")
            distance_1 = self._get_difference_function()(first, second)
            distance_2 = self._get_difference_function()(second, first)

        if isfinite(distance_1) and isfinite(distance_1):
            # make sure it commutes
            self.assertAlmostEqual(distance_1, distance_2)

            # make sure the distance is always positive
            self.assertGreaterEqual(distance_1, 0.0)
            self.assertGreaterEqual(distance_2, 0.0)

            # make sure the distance is within bounds
            self.assertLessEqual(distance_1, self._get_max())
            self.assertLessEqual(distance_2, self._get_max())

        else:
            self.assertTrue(isnan(distance_1))
            self.assertTrue(isnan(distance_2))

    @given(st.floats())
    def test_distance_measuring_to_itself_is_zero(self, thing: float) -> None:
        """Assures flipping the sides when calculating distances does not make a significant difference."""

        with warnings.catch_warnings():
            warnings.simplefilter("ignore")
            distance = self._get_difference_function()(thing, thing)

        # make sure the distance is always positive and very close to zero
        if isfinite(distance):
            self.assertGreaterEqual(distance, 0.0)
            self.assertAlmostEqual(distance, 0.0)
        else:
            self.assertTrue(isnan(distance))

    def test_concrete_examples(self) -> None:
        """Checks the result for the concrete examples given in :meth:`~_get_concrete_examples`."""
        function = self._get_difference_function()

        for index, (value_a, value_b, expected_result) in enumerate(self._get_concrete_examples()):
            with self.subTest(f"example triple #{index}"):
                self.assertAlmostEqual(function(value_a, value_b), expected_result, delta=1e-12)

    def test_concrete_examples_as_array(self) -> None:
        """Checks the result for the concrete examples given in :meth:`~_get_concrete_examples`."""
        function = self._get_difference_function()
        data = array(self._get_concrete_examples()).T
        self.assertTrue(allclose(function(data[0, :], data[1, :]), data[2, :]))


class TestDifferenceLatitude(TestDifference):
    """Tests :func:`pyrate.plan.geometry.helpers.difference_latitude`."""

    def _get_difference_function(self) -> Callable[[ScalarOrArray, ScalarOrArray], ScalarOrArray]:
        return difference_latitude

    def _get_max(self) -> float:
        return 180.0

    def _get_concrete_examples(self) -> Sequence[Tuple[float, float, float]]:
        return [
            (0, 0, 0),
            (-90, 90, 180),
            (-89.5, 0, 89.5),
            (-89.5, 0.5, 90),
            (-89.5, -0.5, 89),
            (-45, 45, 90),
        ]


class TestDifferenceLongitude(TestDifference):
    """Tests :func:`pyrate.plan.geometry.helpers.difference_longitude`."""

    def _get_difference_function(self) -> Callable[[ScalarOrArray, ScalarOrArray], ScalarOrArray]:
        return difference_longitude

    def _get_max(self) -> float:
        return 180.0

    def _get_concrete_examples(self) -> Sequence[Tuple[float, float, float]]:
        return [
            (0, 0, 0),
            (-90, 90, 180),
            (-89.5, 0, 89.5),
            (-89.5, 0.5, 90),
            (-89.5, -0.5, 89),
            (180, -180, 0),
            (100, -100, 160),
            (-45, 45, 90),
        ]


class TestDifferenceDirection(TestDifference):
    """Tests :func:`pyrate.plan.geometry.helpers.difference_direction`."""

    def _get_difference_function(self) -> Callable[[ScalarOrArray, ScalarOrArray], ScalarOrArray]:
        return difference_direction

    def _get_max(self) -> float:
        return 180.0

    def _get_concrete_examples(self) -> Sequence[Tuple[float, float, float]]:
        return [
            (0, 0, 0),
            (-90, 90, 180),
            (0, 360, 0),
            (10, -10, 20),
            (10, 350, 20),
            (370, 20, 10),
        ]


# Do not execute the base class as a test, see https://stackoverflow.com/a/43353680/3753684
del TestDifference