"""Round 39: playlist merges stop losing your track order.

Three defects, and it took all three to scramble `a nissa one`:

* `_merge_playlist` was a 2-way union with no common ancestor — it took one
  side's order wholesale and *appended* the other side's extras, so a track
  inserted in the middle on one machine arrived at the bottom on the other.
* Whose order won was decided by the file's mtime, and the last column is
  stretch-sized — so resizing the window rewrote the open playlist's JSON and
  "most recently edited" meant "most recently resized".
* Those cosmetic rewrites were themselves handing Syncthing conflicts.
"""
import json
import random

import pytest

from lintunes.models import Library, Playlist, PlaylistType
from lintunes.storage import json_storage, conflict_resolver
from lintunes.storage.conflict_resolver import merge_track_order


def _save(tmp_path, playlists=()):
    lib = Library()
    for p in playlists:
        lib.playlists[p.persistent_id] = p
    json_storage.save_library(lib, tmp_path)
    return lib


def _conflict_name(original: str) -> str:
    stem, _, ext = original.rpartition(".")
    return f"{stem}.sync-conflict-20240101-120000-ABCDEFG.{ext}"


class TestAnchoredOrder:
    """merge_track_order: a track inserted in the middle stays in the middle."""

    def test_middle_insert_is_not_appended(self):
        # The other copy slipped 99 between 2 and 3. It belongs there, not last.
        assert merge_track_order([1, 2, 3, 4], [1, 2, 99, 3, 4]) == [1, 2, 99, 3, 4]

    def test_both_sides_inserted_at_different_points(self):
        assert merge_track_order([1, 7, 2, 3], [1, 2, 8, 3]) == [1, 7, 2, 8, 3]

    def test_consecutive_inserts_keep_their_relative_order(self):
        assert merge_track_order([1, 2], [1, 8, 9, 2]) == [1, 8, 9, 2]

    def test_a_leading_insert_goes_to_the_head(self):
        assert merge_track_order([1, 2, 3], [7, 1, 2, 3]) == [7, 1, 2, 3]

    def test_primary_decides_the_order_of_shared_tracks(self):
        # Both copies hold 1-2-3; primary reversed them. Primary wins.
        assert merge_track_order([3, 2, 1], [1, 2, 3]) == [3, 2, 1]

    def test_trailing_insert_still_lands_after_its_anchor(self):
        assert merge_track_order([1, 2, 3], [1, 2, 3, 4]) == [1, 2, 3, 4]

    @pytest.mark.parametrize("primary,secondary", [
        ([], []),
        ([1, 2, 3], []),
        ([], [1, 2, 3]),
        ([1, 2, 3], [4, 5, 6]),          # disjoint
        ([1, 2, 2, 3], [1, 2, 3, 3]),    # the same track twice
    ])
    def test_edge_cases_never_drop_a_track(self, primary, secondary):
        merged = merge_track_order(primary, secondary)
        assert set(merged) == set(primary) | set(secondary)

    def test_nothing_is_ever_dropped(self):
        """The invariant that matters most: a merge is a union, always."""
        rng = random.Random(39)
        for _ in range(300):
            base = rng.sample(range(20), rng.randint(0, 10))
            a = [t for t in base if rng.random() > 0.3] + rng.sample(range(20, 30), 2)
            b = [t for t in base if rng.random() > 0.3] + rng.sample(range(30, 40), 2)
            rng.shuffle(a)
            merged = merge_track_order(a, b)
            assert set(merged) == set(a) | set(b)
            # Primary's entries keep primary's exact sequence — only tracks it
            # never had get woven in between them.
            assert [t for t in merged if t in set(a)] == a


class TestHonestDateModified:
    """The merge decides on the playlist's own date_modified, not file mtime."""

    def _setup(self, tmp_path, ours, theirs, our_stamp, their_stamp):
        pl = Playlist(name="a nissa one", persistent_id="AAAA1111",
                      playlist_type=PlaylistType.REGULAR, track_ids=ours,
                      date_modified=our_stamp)
        _save(tmp_path, [pl])
        pfile = tmp_path / "playlists" / "AAAA1111.json"
        other = json.loads(pfile.read_text())
        other["track_ids"] = theirs
        if their_stamp is None:
            other.pop("date_modified", None)
        else:
            other["date_modified"] = their_stamp
        cfile = tmp_path / "playlists" / _conflict_name("AAAA1111.json")
        cfile.write_text(json.dumps(other))
        return pfile, cfile

    def test_a_resize_no_longer_beats_a_reorder(self, tmp_path):
        """The `a nissa one` regression. We reordered; the other machine only
        opened it and resized the window, so its *file* is newer — but its
        date_modified is older, and our order must survive."""
        pfile, cfile = self._setup(
            tmp_path,
            ours=[3, 1, 2],           # we carefully reordered
            theirs=[1, 2, 3],         # they never touched the contents
            our_stamp="2026-08-20T18:00:00",
            their_stamp="2026-08-19T09:00:00")
        import os, time
        os.utime(cfile, (time.time() + 100, time.time() + 100))  # their file is newer

        summaries = conflict_resolver.resolve_conflicts(tmp_path)

        assert json.loads(pfile.read_text())["track_ids"] == [3, 1, 2]
        assert "this machine" in summaries[0].lines[0]

    def test_the_genuinely_newer_edit_still_wins(self, tmp_path):
        pfile, _ = self._setup(
            tmp_path, ours=[1, 2, 3], theirs=[3, 2, 1],
            our_stamp="2026-08-19T09:00:00",
            their_stamp="2026-08-20T18:00:00")

        summaries = conflict_resolver.resolve_conflicts(tmp_path)

        assert json.loads(pfile.read_text())["track_ids"] == [3, 2, 1]
        assert "the other machine" in summaries[0].lines[0]

    def test_their_insert_lands_in_position_not_at_the_tail(self, tmp_path):
        pfile, _ = self._setup(
            tmp_path, ours=[1, 2, 3], theirs=[1, 2, 99, 3],
            our_stamp="2026-08-20T18:00:00",
            their_stamp="2026-08-19T09:00:00")

        summaries = conflict_resolver.resolve_conflicts(tmp_path)

        assert json.loads(pfile.read_text())["track_ids"] == [1, 2, 99, 3]
        assert "back in position" in summaries[0].lines[1]

    def test_falls_back_to_mtime_before_the_field_existed(self, tmp_path):
        """Playlists written by an older version carry no stamp."""
        pfile, cfile = self._setup(
            tmp_path, ours=[1, 2, 3], theirs=[3, 2, 1],
            our_stamp=None, their_stamp=None)
        import os, time
        os.utime(cfile, (time.time() + 100, time.time() + 100))

        conflict_resolver.resolve_conflicts(tmp_path)
        assert json.loads(pfile.read_text())["track_ids"] == [3, 2, 1]

    def test_smart_playlist_rules_also_use_date_modified(self, tmp_path):
        from lintunes.smart import SmartCriteria
        pl = Playlist(name="Recent", persistent_id="BBBB2222",
                      playlist_type=PlaylistType.SMART, track_ids=[1],
                      smart_criteria=SmartCriteria(), date_modified="2026-08-20T18:00:00")
        _save(tmp_path, [pl])
        pfile = tmp_path / "playlists" / "BBBB2222.json"
        ours = json.loads(pfile.read_text())
        other = dict(ours)
        other["name"] = "Stale"
        other["date_modified"] = "2026-08-19T09:00:00"
        cfile = tmp_path / "playlists" / _conflict_name("BBBB2222.json")
        cfile.write_text(json.dumps(other))
        import os, time
        os.utime(cfile, (time.time() + 100, time.time() + 100))

        conflict_resolver.resolve_conflicts(tmp_path)
        assert json.loads(pfile.read_text())["name"] == "Recent"


class TestDateModifiedMovesOnlyForContent:
    @pytest.fixture
    def manager(self, tmp_path, qapp, monkeypatch):
        monkeypatch.setenv("XDG_CONFIG_HOME", str(tmp_path / "config"))
        from lintunes.library_manager import LibraryManager
        from lintunes.models import Track
        lib = Library()
        for tid in (1, 2, 3):
            lib.tracks[tid] = Track(track_id=tid, name=f"T{tid}")
        lib.playlists["AAAA1111"] = Playlist(
            name="a nissa one", persistent_id="AAAA1111",
            playlist_type=PlaylistType.REGULAR, track_ids=[1, 2, 3])
        return LibraryManager(lib, tmp_path)

    def _stamp(self, manager):
        return manager.library.playlists["AAAA1111"].date_modified

    def test_reorder_bumps_it(self, manager):
        assert self._stamp(manager) is None
        manager.move_tracks_in_playlist("AAAA1111", [2], 0)
        assert self._stamp(manager) is not None

    def test_add_and_remove_bump_it(self, manager):
        manager.remove_tracks_from_playlist("AAAA1111", [0])
        first = self._stamp(manager)
        assert first is not None
        manager.add_tracks_to_playlist("AAAA1111", [1])
        assert self._stamp(manager) >= first

    def test_undo_bumps_it_too(self, manager):
        manager.move_tracks_in_playlist("AAAA1111", [2], 0)
        before = self._stamp(manager)
        manager.undo_stack.undo()
        assert manager.library.playlists["AAAA1111"].track_ids == [1, 2, 3]
        assert self._stamp(manager) >= before

    def test_a_column_resize_does_not(self, manager):
        """The whole point: cosmetic settings must not look like an edit."""
        manager.mark_playlist_settings_dirty("AAAA1111")
        assert self._stamp(manager) is None


class TestStretchedColumnIsNotPersisted:
    @pytest.fixture
    def table(self, qapp):
        from lintunes.gui.track_table import TrackTableView
        from lintunes.models import Track
        view = TrackTableView()
        view.set_tracks([Track(track_id=1, name="A", artist="B")])
        return view

    def test_a_middle_column_still_persists(self, table):
        seen = []
        table.column_width_changed.connect(lambda f, w: seen.append((f, w)))
        table.horizontalHeader().resizeSection(1, 123)
        assert seen and seen[0][1] == 123

    def test_the_stretched_last_column_does_not(self, table):
        """Qt re-fires sectionResized for the stretched column on every viewport
        width change — a window resize used to rewrite the playlist JSON."""
        header = table.horizontalHeader()
        last = header.logicalIndex(header.count() - 1)
        seen = []
        table.column_width_changed.connect(lambda f, w: seen.append((f, w)))
        header.resizeSection(last, 321)
        assert seen == []

    def test_resizing_the_widget_is_silent(self, table):
        seen = []
        table.column_width_changed.connect(lambda f, w: seen.append((f, w)))
        table.resize(400, 300)
        table.resize(900, 300)
        assert seen == []