"""Tests for replayer.metrics percentile + summary helpers (B5)."""

from __future__ import annotations

import math

from replayer.metrics import _percentile


def test_percentile_single_value():
    assert _percentile([42.0], 0.50) == 42.0
    assert _percentile([42.0], 0.99) == 42.0


def test_percentile_two_values_interpolates():
    # For [0, 10] linear interpolation gives p50=5.0, p90=9.0.
    assert math.isclose(_percentile([0.0, 10.0], 0.50), 5.0)
    assert math.isclose(_percentile([0.0, 10.0], 0.90), 9.0)


def test_percentile_endpoints():
    vals = [1.0, 2.0, 3.0, 4.0, 5.0]
    assert _percentile(vals, 0.0) == 1.0
    assert _percentile(vals, 1.0) == 5.0


def test_percentile_matches_numpy_linear_default():
    # Independently computed using numpy's default linear interpolation;
    # we hardcode the expectations so the test does not depend on numpy.
    vals = [1.0, 2.0, 4.0, 8.0, 16.0, 32.0]
    # rank for p50 = 0.5 * 5 = 2.5 -> 0.5 * 4 + 0.5 * 8 = 6.0
    assert math.isclose(_percentile(vals, 0.50), 6.0)
    # rank for p90 = 0.9 * 5 = 4.5 -> 0.5 * 16 + 0.5 * 32 = 24.0
    assert math.isclose(_percentile(vals, 0.90), 24.0)
    # rank for p99 = 0.99 * 5 = 4.95 -> 0.05 * 16 + 0.95 * 32 = 31.2
    assert math.isclose(_percentile(vals, 0.99), 31.2)


def test_percentile_no_off_by_one_at_boundary():
    # Regression: previous round-based implementation returned the wrong
    # element when rank fell exactly on an integer.
    vals = [10.0, 20.0, 30.0]
    # rank for p50 = 0.5 * 2 = 1.0 -> exactly element 1 -> 20.0
    assert _percentile(vals, 0.50) == 20.0