"""统计模块测试"""
import math

from backend.stats import mean, std, percentile, percentiles, min_val, max_val


class TestMean:
    def test_normal(self):
        assert mean([1, 2, 3, 4, 5]) == 3.0

    def test_single(self):
        assert mean([42]) == 42.0

    def test_empty(self):
        assert mean([]) == 0.0

    def test_floats(self):
        assert abs(mean([1.5, 2.5, 3.5]) - 2.5) < 1e-9


class TestStd:
    def test_known_std(self):
        data = [2, 4, 4, 4, 5, 5, 7, 9]
        assert abs(std(data) - 2.13809) < 1e-4

    def test_single(self):
        assert std([42]) == 0.0

    def test_two_values(self):
        assert std([0, 2]) == math.sqrt(2)

    def test_empty(self):
        assert std([]) == 0.0


class TestPercentile:
    def test_median(self):
        assert percentile([1, 2, 3, 4, 5], 50) == 3.0

    def test_p0(self):
        assert percentile([1, 2, 3, 4, 5], 0) == 1.0

    def test_p100(self):
        assert percentile([1, 2, 3, 4, 5], 100) == 5.0

    def test_empty(self):
        assert percentile([], 50) == 0.0

    def test_interpolation(self):
        assert percentile([1, 2], 50) == 1.5


class TestPercentiles:
    def test_batch(self):
        result = percentiles([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], [25, 50, 75])
        assert result[50] == 5.5
        assert result[25] > 0
        assert result[75] > result[50]

    def test_empty(self):
        result = percentiles([], [50])
        assert result[50] == 0.0


class TestMinMax:
    def test_min(self):
        assert min_val([3, 1, 2]) == 1

    def test_max(self):
        assert max_val([3, 1, 2]) == 3

    def test_min_empty(self):
        assert min_val([]) == 0.0

    def test_max_empty(self):
        assert max_val([]) == 0.0