"""Unit tests for engine.py's pure continuation planning — the source-length ->
mask-bounds + total-length-cap math. No model, no GPU: `plan_continuation` is a
pure function, so these run anywhere torch+numpy import."""
import pytest

import engine


def test_normal_request_maps_to_tail_mask():
    total, new, mstart, mend = engine.plan_continuation(30, 60)
    assert total == 60
    assert new == 30
    # the mask runs from where the source ends to the total length
    assert mstart == 30
    assert mend == 60


def test_total_capped_at_120():
    total, new, mstart, mend = engine.plan_continuation(30, 200)
    assert total == engine.MAX_TOTAL_SECONDS == 120
    assert new == 90
    assert mstart == 30 and mend == 120


def test_min_new_floor_enforced():
    # asking for barely-longer-than-source still generates at least MIN_NEW
    total, new, mstart, mend = engine.plan_continuation(30, 31)
    assert new == engine.MIN_NEW_SECONDS == 5
    assert total == 35
    assert mstart == 30 and mend == 35


def test_mask_always_brackets_the_new_region():
    for src, req in [(15, 40), (29.5, 60), (50, 90), (10, 120)]:
        total, new, mstart, mend = engine.plan_continuation(src, req)
        assert mstart == src                       # mask starts at the seam
        assert mend == total                       # …and runs to the end
        assert abs((mend - mstart) - new) < 1e-6   # masked span == new audio
        assert total <= engine.MAX_TOTAL_SECONDS


def test_source_at_max_keeps_min_new():
    # the longest allowed clip still gets exactly MIN_NEW of continuation
    total, new, mstart, mend = engine.plan_continuation(engine.MAX_SOURCE_SECONDS, 130)
    assert total == engine.MAX_TOTAL_SECONDS == 120
    assert new == engine.MIN_NEW_SECONDS == 5
    assert mend > mstart                              # mask never inverts


def test_overlong_source_raises_not_inverts():
    # the old bug: source >= cap produced an inverted mask and a silent
    # no-op continuation. now it must raise instead.
    for src in (116, 120, 125, 200):
        with pytest.raises(ValueError):
            engine.plan_continuation(src, 60)


def test_no_plan_ever_inverts_the_mask():
    for src in [1, 15, 29.5, 60, 90, 110, 115]:
        total, new, mstart, mend = engine.plan_continuation(src, 60)
        assert mend > mstart        # mask_end strictly after mask_start
        assert new >= engine.MIN_NEW_SECONDS - 1e-6


def test_constants_match_sa3_contract():
    assert engine.SR == 44100
    assert engine.STEPS == 8
    assert engine.SAMPLER == "pingpong"
    assert engine.MAX_TOTAL_SECONDS == 120