tests/test_active_section.py

"""Tests for the active-section / intro-skip detector."""

from __future__ import annotations

import numpy as np
import pytest

from backend.features import ANALYSIS_WINDOW_S, detect_active_section


SR = 22050


def test_short_track_returns_full_range():
    y = np.random.randn(int(60 * SR)).astype(np.float32) * 0.5
    start, end = detect_active_section(y, SR, target_s=ANALYSIS_WINDOW_S)
    assert start == 0.0
    assert abs(end - 60.0) < 1.0


def test_quiet_intro_is_skipped():
    """Intro at 5% amplitude, loud section at 80% — detector must land on the loud part."""
    intro = np.random.randn(int(120 * SR)).astype(np.float32) * 0.05
    loud = np.random.randn(int(90 * SR)).astype(np.float32) * 0.8
    outro = np.random.randn(int(60 * SR)).astype(np.float32) * 0.1
    y = np.concatenate([intro, loud, outro])

    start, end = detect_active_section(y, SR, target_s=90.0)
    # Window should overlap heavily with the loud section.
    assert 100 <= start <= 140, f"start {start} should be near 120s"
    assert end - start == pytest.approx(90.0, abs=1.0)


def test_uniform_energy_returns_a_valid_window():
    """No clear energy gradient — any window of the target size is acceptable
    as long as it sits inside the track and has the right length."""
    y = (np.random.randn(int(200 * SR)) * 0.3).astype(np.float32)
    start, end = detect_active_section(y, SR, target_s=90.0)
    assert 0.0 <= start <= 200.0 - 90.0
    assert end - start == pytest.approx(90.0, abs=1.0)


def test_loud_section_at_end():
    quiet = np.random.randn(int(180 * SR)).astype(np.float32) * 0.05
    loud = np.random.randn(int(90 * SR)).astype(np.float32) * 0.9
    y = np.concatenate([quiet, loud])
    start, end = detect_active_section(y, SR, target_s=90.0)
    assert start >= 170, f"expected window near end (~180s), got {start}"


def test_zero_signal_returns_first_window():
    """Pathological all-zero input should not crash."""
    y = np.zeros(int(200 * SR), dtype=np.float32)
    start, end = detect_active_section(y, SR, target_s=90.0)
    assert start == 0.0
    assert end == pytest.approx(90.0, abs=1.0)


def test_target_longer_than_track_returns_full():
    y = np.random.randn(int(45 * SR)).astype(np.float32) * 0.4
    start, end = detect_active_section(y, SR, target_s=90.0)
    assert start == 0.0
    assert end == pytest.approx(45.0, abs=1.0)