unshackle/tests/tracks/test_webvtt_merge.py

"""Regression tests for segmented-WebVTT merging (``core/utils/webvtt.py``).

The merge used to round-trip cues through pycaption's reader/writer (and a pysubs2
pre-normalization step), both of which silently dropped inline formatting despite
``preserve_formatting=True``. It is now a pure string-level splice: cue
timing lines, settings, and payload are kept verbatim, so span tags
(``<i>``/``<u>``/``<b>``), ASS-style overrides (``{\\an8}``), and entities all
survive, while duplicate headers collapse and boundary-duplicate cues dedupe.
"""

from __future__ import annotations

from unshackle.core.utils.webvtt import merge_segmented_webvtt, rebase_webvtt, timestamp_ms

# Two segments, each a full WebVTT document with its own X-TIMESTAMP-MAP header,
# as they arrive concatenated from a DASH/HLS subtitle stream. The first cue carries
# span tags, an {\an8} override, a cue setting, and a literal &lt; entity.
SEGMENTED_VTT = (
    "WEBVTT\n"
    "X-TIMESTAMP-MAP=MPEGTS:900000,LOCAL:00:00:00.000\n\n"
    "00:00:01.000 --> 00:00:03.000 line:10% align:center\n"
    "<i>Hello</i> {\\an8}world <u>und</u> <b>bold</b> 5 &lt; 6\n\n"
    "WEBVTT\n"
    "X-TIMESTAMP-MAP=MPEGTS:1800000,LOCAL:00:00:00.000\n\n"
    "00:00:04.000 --> 00:00:06.000\n"
    "<i>Second</i> cue\n"
)


def test_merge_preserves_inline_formatting():
    out = merge_segmented_webvtt(SEGMENTED_VTT, segment_durations=[900000, 900000], timescale=1)
    for tag in ("<i>", "</i>", "<u>", "</u>", "<b>", "</b>", "{\\an8}"):
        assert tag in out, f"{tag!r} was stripped from merged output:\n{out}"


def test_merge_preserves_cue_settings_and_entities():
    out = merge_segmented_webvtt(SEGMENTED_VTT, segment_durations=[900000, 900000], timescale=1)
    assert "line:10% align:center" in out  # cue positioning survives
    assert "&lt;" in out  # a literal entity is not turned into a stray tag


def test_merge_collapses_headers_into_single_document():
    out = merge_segmented_webvtt(SEGMENTED_VTT, segment_durations=[900000, 900000], timescale=1)
    assert out.count("WEBVTT") == 1
    assert "X-TIMESTAMP-MAP" not in out


def test_merge_dedupes_boundary_duplicate_cues():
    # A cue that spans a segment boundary is emitted in both segments; the merge
    # should collapse the adjacent identical pair into one.
    dup = SEGMENTED_VTT + (
        "\nWEBVTT\n"
        "X-TIMESTAMP-MAP=MPEGTS:2700000,LOCAL:00:00:00.000\n\n"
        "00:00:04.000 --> 00:00:06.000\n"
        "<i>Second</i> cue\n"
    )
    out = merge_segmented_webvtt(dup, segment_durations=[900000, 900000, 900000], timescale=1)
    assert out.count("<i>Second</i> cue") == 1, f"boundary duplicate not deduped:\n{out}"


def test_merge_keeps_timing_lines_verbatim():
    # String-level merge must not re-render timestamps (pycaption shortened
    # 00:00:01.000 -> 00:01.000) and must keep the settings tail untouched.
    out = merge_segmented_webvtt(SEGMENTED_VTT, segment_durations=[900000, 900000], timescale=1)
    assert "00:00:01.000 --> 00:00:03.000 line:10% align:center" in out
    assert "00:00:04.000 --> 00:00:06.000" in out


def test_merge_splices_triple_duplicate_into_one():
    # A cue spanning two boundaries appears in three consecutive segments; the
    # kept cue must be extended each time (latent bug: extending the dropped one).
    vtt = (
        "WEBVTT\n\n00:00:01.000 --> 00:00:02.000\nSame cue\n\n"
        "WEBVTT\n\n00:00:02.000 --> 00:00:03.000\nSame cue\n\n"
        "WEBVTT\n\n00:00:03.000 --> 00:00:04.000\nSame cue\n"
    )
    out = merge_segmented_webvtt(vtt)
    assert out.count("Same cue") == 1
    assert "00:00:01.000 --> 00:00:04.000" in out


def test_merge_duplicate_ending_earlier_keeps_later_end():
    # A boundary duplicate that ends BEFORE the kept cue must not shorten it: the
    # splice extends only. Here the kept cue runs to 00:00:05.000 and the duplicate
    # is a brief 00:00:04.900 -> 00:00:04.950 re-emission of the same payload.
    vtt = "WEBVTT\n\n00:00:01.000 --> 00:00:05.000\n[music]\n\nWEBVTT\n\n00:00:04.900 --> 00:00:04.950\n[music]\n"
    out = merge_segmented_webvtt(vtt)
    assert out.count("[music]") == 1
    assert "00:00:01.000 --> 00:00:05.000" in out, f"kept cue was truncated:\n{out}"
    assert "00:00:04.950" not in out


def test_merge_drops_cue_ids_and_notes_keeps_style():
    vtt = (
        "WEBVTT\n\n"
        "STYLE\n::cue { color: red }\n\n"
        "NOTE a comment\n\n"
        "some-cue-id-42\n00:00:01.000 --> 00:00:02.000\nHello\n"
    )
    out = merge_segmented_webvtt(vtt)
    assert "Hello" in out
    assert "some-cue-id-42" not in out
    assert "NOTE" not in out
    assert "STYLE\n::cue { color: red }" in out  # kept; players without STYLE support ignore it


def test_merge_dedupes_repeated_style_blocks_before_cues():
    # Every segment repeats the same STYLE block; keep exactly one, before the first cue.
    style = "WEBVTT\n\nSTYLE\n::cue { color: red }\n\n"
    vtt = style + "00:00:01.000 --> 00:00:02.000\nOne\n\n" + style + "00:00:03.000 --> 00:00:04.000\nTwo\n"
    out = merge_segmented_webvtt(vtt)
    assert out.count("STYLE") == 1
    assert out.index("STYLE") < out.index("-->")


def test_merge_skips_malformed_timing_line():
    vtt = "WEBVTT\n\ngarbage --> not-a-time\nBroken\n\n00:00:01.000 --> 00:00:02.000\nGood\n"
    out = merge_segmented_webvtt(vtt)
    assert "Good" in out
    assert "Broken" not in out


def test_rebase_moves_live_clock_cues_to_zero():
    vtt = "WEBVTT\n\n498024:05:44.300 --> 498024:05:44.829 line:0.01%\nText\n"
    out = rebase_webvtt(vtt, timestamp_ms("498024:00:14.700"))
    assert "00:05:29.600 --> 00:05:30.129 line:0.01%\nText" in out


def test_rebase_moves_cues_when_the_first_is_carried_over_from_before_the_offset():
    vtt = "WEBVTT\n\n03:59:43.500 --> 03:59:45.000\nCarried\n\n04:03:32.598 --> 04:03:32.698\nNext\n"
    out = rebase_webvtt(vtt, timestamp_ms("03:59:44.000"), 2002)
    assert "00:00:00.000 --> 00:00:01.000\nCarried" in out
    assert "00:03:48.598 --> 00:03:48.698\nNext" in out


def test_rebase_leaves_a_later_period_with_a_small_offset_alone():
    vtt = "WEBVTT\n\n00:00:05.000 --> 00:00:12.000\nText\n"
    assert rebase_webvtt(vtt, 10_000, 2000) == vtt


def test_rebase_leaves_presentation_time_cues_alone():
    # a second pass, or a VOD period with a non-zero offset, must not shift again
    vtt = "WEBVTT\n\n00:05:29.600 --> 00:05:30.129\nText\n"
    assert rebase_webvtt(vtt, 1_792_886_414_700) == vtt
    assert rebase_webvtt(vtt, 0) == vtt