"""Windowed channel sync: only fetch what is newer than what we already have.

The whole point is request economy against YouTube, so these tests assert on the
`limit` values handed to yt-dlp (which become `playlistend`, i.e. how many
continuation pages get requested), not just on the refs that come back.
"""
from __future__ import annotations

import pytest

from yt_scraper.discover import discover_incremental
from yt_scraper.store import VideoRef


def _ref(vid: str, upload_date: str | None = None, url: str | None = None) -> VideoRef:
    return VideoRef(
        video_id=vid,
        channel_id="UC1",
        title=vid,
        url=url or f"https://www.youtube.com/watch?v={vid}",
        upload_date=upload_date,
    )


def _fake_channel(monkeypatch, catalog: list[VideoRef], calls: list | None = None):
    """Patch discover_channel with a channel whose /videos tab is `catalog`
    (newest first) and that honours `limit` the way playlistend does."""

    def fake(url, sleep_subrequests=2.0, limit=None):
        if calls is not None:
            calls.append(limit)
        return ("UC1", "Alpha", "http://avatar", catalog[:limit] if limit else list(catalog))

    monkeypatch.setattr("yt_scraper.discover.discover_channel", fake)


def test_stops_at_first_run_of_known_videos(monkeypatch):
    catalog = [_ref(f"v{i:03d}") for i in range(500)]
    known = {r.video_id for r in catalog[5:]}  # everything except the 5 newest
    calls: list = []
    _fake_channel(monkeypatch, catalog, calls)

    result = discover_incremental("https://y/@alpha/videos", known, window=30, overlap=3)

    assert calls == [30], "one pass only — must not paginate the whole channel"
    assert result.fetched == 30
    assert [r.video_id for r in result.new_refs] == [f"v{i:03d}" for i in range(5)]
    assert result.caught_up is True
    assert result.full_scan is False


def test_widens_window_when_the_whole_window_is_new(monkeypatch):
    catalog = [_ref(f"v{i:03d}") for i in range(500)]
    known = {r.video_id for r in catalog[100:]}  # 100 new uploads since last sync
    calls: list = []
    _fake_channel(monkeypatch, catalog, calls)

    result = discover_incremental("https://y/@alpha/videos", known, window=30, overlap=3)

    # 30 -> 60 -> 120: doubles only as far as needed, never the full 500.
    assert calls == [30, 60, 120]
    assert result.new_count == 100
    assert result.caught_up is True


def test_gives_up_at_max_window_and_says_so(monkeypatch):
    catalog = [_ref(f"v{i:03d}") for i in range(500)]
    calls: list = []
    _fake_channel(monkeypatch, catalog, calls)

    result = discover_incremental(
        "https://y/@alpha/videos", {"not-in-this-channel"}, window=10, max_window=40, overlap=3
    )

    assert calls == [10, 20, 40]
    assert result.caught_up is False, "caller must be able to tell the scan was truncated"
    assert result.fetched == 40


def test_no_local_history_walks_the_whole_channel(monkeypatch):
    catalog = [_ref(f"v{i:03d}") for i in range(120)]
    calls: list = []
    _fake_channel(monkeypatch, catalog, calls)

    result = discover_incremental("https://y/@alpha/videos", set(), window=30)

    assert calls == [None], "a first sync has no boundary to stop at"
    assert result.full_scan is True
    assert result.new_count == 120


def test_short_channel_is_exhausted_in_one_pass(monkeypatch):
    catalog = [_ref("a"), _ref("b")]
    calls: list = []
    _fake_channel(monkeypatch, catalog, calls)

    result = discover_incremental("https://y/@alpha/videos", {"b"}, window=30)

    assert calls == [30]
    assert result.exhausted is True
    assert result.caught_up is True
    assert [r.video_id for r in result.new_refs] == ["a"]


def test_keep_filter_applies_before_the_overlap_check(monkeypatch):
    """Shorts the store never recorded must not keep the window widening."""
    catalog = [
        _ref("s1", url="https://www.youtube.com/shorts/s1"),
        _ref("s2", url="https://www.youtube.com/shorts/s2"),
        _ref("s3", url="https://www.youtube.com/shorts/s3"),
        _ref("known1"),
        _ref("known2"),
        _ref("known3"),
    ] + [_ref(f"v{i}") for i in range(50)]
    calls: list = []
    _fake_channel(monkeypatch, catalog, calls)

    result = discover_incremental(
        "https://y/@alpha/videos",
        {"known1", "known2", "known3"},
        window=6,
        overlap=3,
        keep=lambda r: "/shorts/" not in (r.url or ""),
    )

    assert calls == [6], "the three known long-form videos end the scan"
    assert result.new_refs == []


def test_upload_date_cutoff_stops_the_scan_when_dates_are_available(monkeypatch):
    catalog = [
        _ref("n1", "20260701"),
        _ref("n2", "20260630"),
        _ref("o1", "20250101"),
        _ref("o2", "20241231"),
    ] + [_ref(f"old{i}", "20200101") for i in range(50)]
    calls: list = []
    _fake_channel(monkeypatch, catalog, calls)

    result = discover_incremental(
        "https://y/@alpha/videos", {"unrelated"}, window=4, overlap=2, since="20260601"
    )

    assert calls == [4], "entries older than the watermark end the scan"
    assert result.caught_up is True


@pytest.mark.parametrize("window,overlap", [(0, 0), (-5, -1)])
def test_degenerate_settings_are_clamped(monkeypatch, window, overlap):
    catalog = [_ref("a"), _ref("b")]
    calls: list = []
    _fake_channel(monkeypatch, catalog, calls)

    result = discover_incremental("https://y/@alpha/videos", {"b"}, window=window, overlap=overlap)

    assert calls and calls[0] >= 1
    assert result.fetched >= 1