v0.29.0: Cassette friend mode — browse a friend's library, cassette songs

- A ▾ cut from the right end of the Library button (shown once there's a
  friend) opens a popup of friends. Choosing one enters friend mode: the
  button becomes "<Name>'s Library" in light purple, the sidebar lists
  their shared playlists with a UFO follow toggle on each, and the content
  area is their library — browse only, nothing plays or edits.
- A cassette column on the far left and cassette buttons on every artist
  and album: pressed grey = send me this, medium grey on hover to let go.
  An artist cassettes all its albums and tracks (a snapshot).
- Bottom bar: Hide tracks I have (exact matches: artist, album, title,
  length within 2 s); close matches show light grey. Size of what's
  cassetted against free space: orange when Syncthing would stall at its
  free-space floor, red when it won't fit.
- Save and Close writes requests.json; Cancel discards; the ▾ or quitting
  with changes asks Save / Don't Save / Cancel.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -481,6 +481,18 @@ persistence) → GUI (Qt widgets that read the manager and connect to its signal
   `syncthing` run a real handshake with `pytest --syncthing`. The service
   starts from `run_gui`, never from constructing `MainWindow` — tests build
   windows by the dozen and must not reach a real Syncthing.
+  **Friend mode** (`gui/friend_mode.py`, entered from the ▾ beside Library)
+  shows a friend's `library.json` through a second `LibraryView` over
+  `cassette/friend_library.FriendSource` — the slice of `LibraryManager` that
+  view reads, read-only. Their track ids are *theirs*: the table is
+  `set_read_only(True)` (no play, no drag, no copy into my playlists, only
+  "lookup on youtube"), and the cassette column is `track_table.CASSETTE_FIELD`
+  (registered in `COLUMN_MAP`, deliberately not `ALL_COLUMNS`), live only
+  where `cassette_hooks` is set. Nothing is written until Save and Close
+  (`service.save_requests` → `requests.json`); any other exit with changes
+  asks "Save changes?". `cassette/matching.py` is best effort (exact vs
+  fuzzy); `cassette/space.py` judges the music disk (red) and Syncthing's
+  `minDiskFree` floor on the cassette disk (orange) separately.
 
 - **`lintunes/cast/`** — Chromecast playback (Connections menu), using the
   **media-receiver model**: `server.py` runs a `ThreadingHTTPServer` on an

lintunes/__init__.py

@@ -1,3 +1,3 @@
 """LinTunes — iTunes-style music library manager and player for Linux."""
 
-__version__ = "0.28.0"
+__version__ = "0.29.0"

lintunes/cassette/friend_library.py

@@ -0,0 +1,97 @@
+"""A friend's shared library, read from their folder, for browsing.
+
+``load_friend_library`` turns their ``library.json`` / ``playlists.json``
+(written by their ``share.py``) into ``Track`` objects and a simple playlist
+list — **their** track ids, never mixed into mine. The files may be missing
+(nothing synced yet), half-synced or garbled: every failure is an empty
+library, never a crash.
+
+``FriendSource`` is the small slice of ``LibraryManager`` that ``LibraryView``
+reads, over that library and read-only: edits are dropped, settings aren't
+saved anywhere, and there are no playlists of mine to "show in".
+"""
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from pathlib import Path
+
+from PyQt6.QtCore import QObject, pyqtSignal
+
+from lintunes.cassette import publish, share
+from lintunes.models import Track
+from lintunes.models.library import Library
+from lintunes.models.playlist import PlaylistSettings
+
+CASSETTE_FIELD = "cassette"
+FRIEND_COLUMNS = [CASSETTE_FIELD, "name", "total_time", "artist", "album",
+                  "genre", "year"]
+
+
+@dataclass
+class FriendPlaylist:
+    pid: str
+    name: str
+    track_ids: list = field(default_factory=list)
+    smart: bool = False
+
+
+@dataclass
+class FriendLibrary:
+    name: str = ""
+    tracks: dict = field(default_factory=dict)       # their id -> Track
+    playlists: list = field(default_factory=list)    # FriendPlaylist, by name
+
+    def playlist(self, pid: str) -> FriendPlaylist | None:
+        return next((p for p in self.playlists if p.pid == pid), None)
+
+
+def load_friend_library(in_dir: Path, fallback_name: str = "") -> FriendLibrary:
+    intro = publish.read_intro(in_dir)
+    result = FriendLibrary(name=str(intro.get("name") or fallback_name))
+    data = publish.read_json(in_dir / share.LIBRARY_FILE, {})
+    for entry in (data.get("tracks", []) if isinstance(data, dict) else []):
+        if not isinstance(entry, dict) or not isinstance(entry.get("id"), int):
+            continue
+        fields = {k: v for k, v in entry.items() if k in share.SHARED_FIELDS}
+        try:
+            track = Track.from_dict(fields)
+        except TypeError:
+            continue
+        track.track_id = entry["id"]
+        result.tracks[track.track_id] = track
+    data = publish.read_json(in_dir / share.PLAYLISTS_FILE, {})
+    for entry in (data.get("playlists", []) if isinstance(data, dict) else []):
+        if not isinstance(entry, dict) or not entry.get("id"):
+            continue
+        ids = [t for t in entry.get("track_ids", [])
+               if isinstance(t, int) and t in result.tracks]
+        result.playlists.append(FriendPlaylist(
+            pid=str(entry["id"]), name=str(entry.get("name") or "Untitled"),
+            track_ids=ids, smart=bool(entry.get("smart"))))
+    result.playlists.sort(key=lambda p: p.name.casefold())
+    return result
+
+
+class FriendSource(QObject):
+    """What LibraryView needs from a manager, over a friend's library."""
+
+    track_updated = pyqtSignal(int)
+    track_fields_edited = pyqtSignal(int, list)
+
+    def __init__(self, tracks: dict, parent=None):
+        super().__init__(parent)
+        self.library = Library(tracks=dict(tracks))
+        self.library.library_settings = PlaylistSettings(
+            visible_columns=list(FRIEND_COLUMNS), sort_column="artist")
+
+    def set_tracks(self, tracks: dict):
+        self.library.tracks = dict(tracks)
+
+    def playlists_containing(self, track_id):
+        return []
+
+    def edit_track_fields(self, *args, **kwargs):
+        pass  # read-only
+
+    def mark_library_settings_dirty(self):
+        pass  # column choices in friend mode live for the visit only

lintunes/cassette/matching.py

@@ -0,0 +1,95 @@
+"""Do I already have this song? Best effort — the user is the final judge.
+
+* **exact**: normalized artist, album and title all match and the durations
+  are within ~2 s. Friend mode can hide these ("Hide tracks I have").
+* **fuzzy**: normalized artist and title match (a different album, a
+  different length). Shown light grey, never hidden: a live take or a
+  remaster is worth a second look, not a silent skip.
+
+Normalizing folds case and accents, turns punctuation into spaces, drops a
+featured-artist credit ("feat.", "ft.", "featuring", "with" in brackets) and a
+leading "The", so "The Beatles — Hey Jude (Remastered)" and "beatles - hey
+jude" land together for the fuzzy check. The artist key prefers album artist,
+the same spelling the browser files a song under.
+"""
+from __future__ import annotations
+
+import re
+import unicodedata
+
+EXACT = "exact"
+FUZZY = "fuzzy"
+DURATION_SLACK_MS = 2000
+
+_FEAT_BRACKET = re.compile(
+    r"[\(\[]\s*(feat\.?|ft\.?|featuring|with)\s[^\)\]]*[\)\]]", re.IGNORECASE)
+_FEAT_TAIL = re.compile(r"\s+(feat\.?|ft\.?|featuring)\s+.*$", re.IGNORECASE)
+_EDITION = re.compile(
+    r"[\(\[][^\)\]]*\b(remaster(ed)?|deluxe|edition|version|mono|stereo|"
+    r"bonus track)\b[^\)\]]*[\)\]]", re.IGNORECASE)
+_LEADING_THE = re.compile(r"^the\s+")
+_PUNCT = re.compile(r"[^\w\s]", re.UNICODE)
+_SPACE = re.compile(r"\s+")
+
+
+def normalize(text: str) -> str:
+    text = text or ""
+    text = _FEAT_BRACKET.sub(" ", text)
+    text = _FEAT_TAIL.sub("", text)
+    text = _EDITION.sub(" ", text)
+    text = unicodedata.normalize("NFKD", text)
+    text = "".join(c for c in text if not unicodedata.combining(c))
+    text = text.casefold().replace("&", " and ")
+    text = _PUNCT.sub(" ", text)
+    text = _SPACE.sub(" ", text).strip()
+    return _LEADING_THE.sub("", text)
+
+
+def _artist(track) -> str:
+    return getattr(track, "album_artist", "") or getattr(track, "artist", "")
+
+
+def _keys(track) -> tuple[str, str, str]:
+    """(artist, album, title), normalized. A track's own artist is tried too
+    (see LibraryIndex), since one side may have an album artist and the
+    other not."""
+    return (normalize(_artist(track)), normalize(getattr(track, "album", "")),
+            normalize(getattr(track, "name", "")))
+
+
+class LibraryIndex:
+    """My library, indexed once per friend-mode visit."""
+
+    def __init__(self, tracks):
+        self._exact: dict[tuple, list[int]] = {}
+        self._fuzzy: set[tuple] = set()
+        for track in tracks:
+            title = normalize(track.name)
+            album = normalize(track.album)
+            for artist in self._artists(track):
+                self._exact.setdefault((artist, album, title), []).append(
+                    track.total_time or 0)
+                self._fuzzy.add((artist, title))
+
+    @staticmethod
+    def _artists(track) -> set[str]:
+        names = {normalize(track.artist), normalize(track.album_artist)}
+        names.discard("")
+        return names or {""}
+
+    def classify(self, track) -> str | None:
+        """EXACT, FUZZY or None for a friend's track."""
+        title = normalize(track.name)
+        if not title:
+            return None
+        album = normalize(track.album)
+        duration = track.total_time or 0
+        fuzzy = False
+        for artist in self._artists(track):
+            for mine in self._exact.get((artist, album, title), ()):
+                if not duration or not mine or \
+                        abs(mine - duration) <= DURATION_SLACK_MS:
+                    return EXACT
+            if (artist, title) in self._fuzzy:
+                fuzzy = True
+        return FUZZY if fuzzy else None

lintunes/cassette/requests.py

@@ -0,0 +1,28 @@
+"""``requests.json``: the friend's track ids I want sent, in my folder to them.
+
+Rewritten only on Save and Close in friend mode and when pruning (a delivery
+arrived, or they stopped offering something) — never as you click.
+"""
+from __future__ import annotations
+
+from pathlib import Path
+
+from lintunes.cassette import publish
+
+REQUESTS_FILE = "requests.json"
+
+
+def write_requests(out: Path, track_ids) -> bool:
+    publish.prepare_out_dir(out)
+    return publish.write_json_if_changed(out / REQUESTS_FILE, {
+        "format": publish.FORMAT_VERSION,
+        "tracks": sorted({int(t) for t in track_ids}),
+    })
+
+
+def read_requests(folder: Path) -> set[int]:
+    """The ids a requests.json asks for; empty when missing or garbled."""
+    data = publish.read_json(folder / REQUESTS_FILE, {})
+    if not isinstance(data, dict):
+        return set()
+    return {t for t in data.get("tracks", []) if isinstance(t, int)}

lintunes/cassette/service.py

@@ -237,6 +237,23 @@ class CassetteService(QObject):
                     changed.append(token)
         return changed
 
+    # ---- requests ----
+
+    def save_requests(self, token: str, cassetted, followed, requested):
+        """Friend mode's Save and Close: remember what I cassetted and which
+        playlists I follow, and tell the friend (``requests.json`` in my
+        folder to them) which of their track ids to send."""
+        from lintunes.cassette import requests as req
+        with self._lock:
+            friend = self._state.friends.get(token)
+            if friend is None:
+                return
+            friend.cassetted = sorted(int(t) for t in cassetted)
+            friend.followed = sorted(followed)
+            self._save()
+            req.write_requests(out_dir(self.root, token), requested)
+        self.changed.emit()
+
     # ---- user actions ----
 
     def create_invite(self) -> str:

lintunes/cassette/space.py

@@ -0,0 +1,49 @@
+"""Will the songs I cassetted fit?
+
+Two disks matter, and they may be the same one:
+
+* the **music** disk, where imported songs end up — if they don't fit there,
+  they don't fit (**full**, red);
+* the disk holding the cassette folders, where Syncthing lands each delivery
+  first — Syncthing stops syncing a folder once its disk drops below the
+  folder's ``minDiskFree`` (1 % by default), so getting close to that is
+  **tight** (orange): the songs would fit, but syncing would stall.
+"""
+from __future__ import annotations
+
+import shutil
+from pathlib import Path
+
+OK = "ok"
+TIGHT = "tight"
+FULL = "full"
+
+
+def verdict(need: int, music_free: int, cassette_free: int,
+            floor_bytes: int) -> str:
+    if need > music_free:
+        return FULL
+    if cassette_free - need < floor_bytes:
+        return TIGHT
+    return OK
+
+
+def disk_usage(path: Path):
+    """shutil.disk_usage of the nearest existing ancestor, or None."""
+    path = Path(path)
+    for candidate in (path, *path.parents):
+        if candidate.exists():
+            try:
+                return shutil.disk_usage(candidate)
+            except OSError:
+                return None
+    return None
+
+
+def human(size: int) -> str:
+    size = float(max(0, size))
+    for unit in ("B", "KB", "MB", "GB", "TB"):
+        if size < 1000 or unit == "TB":
+            return f"{size:.0f} {unit}" if unit in ("B", "KB") else f"{size:.1f} {unit}"
+        size /= 1000
+    return f"{size:.1f} TB"

lintunes/gui/cassette_art.py

@@ -0,0 +1,144 @@
+"""Cassette's two little pictures, painted (no image files to ship or theme).
+
+* The **cassette button**: a small embossed square with a tape glyph. Raised
+  when off; pressed in and grey when on ("I want this"); a medium grey on
+  hover over a pressed one, to say a click would let it go. Functionally
+  it's a checkbox — the tape is reserved for asking friends for songs.
+* The **UFO**: a friend's playlist. Light purple when followed, a grey
+  outline when not.
+
+Plus friend mode's light purple, shared by everything that says "you're in
+someone else's library".
+"""
+from __future__ import annotations
+
+from PyQt6.QtCore import QPointF, QRectF, Qt
+from PyQt6.QtGui import (
+    QBrush, QColor, QIcon, QLinearGradient, QPainter, QPainterPath, QPen,
+    QPixmap,
+)
+
+FRIEND_PURPLE = QColor("#cdb4f2")        # button tint in friend mode
+FRIEND_PURPLE_DARK = QColor("#9b76d6")   # its border / pressed shade
+UFO_PURPLE = QColor("#b38ee8")
+
+OFF, ON, PARTIAL = "off", "on", "partial"
+
+ON_GREY = QColor("#9c9c9c")
+ON_HOVER_GREY = QColor("#bdbdbd")
+
+
+def friend_button_qss(selector: str = "QPushButton", padding: str = "3px 12px") -> str:
+    """Light purple, embossed like every other button."""
+    light = FRIEND_PURPLE.lighter(106).name()
+    dark = FRIEND_PURPLE.darker(104).name()
+    return (f"{selector} {{ background: qlineargradient(x1:0, y1:0, x2:0, y2:1,"
+            f" stop:0 {light}, stop:0.5 {FRIEND_PURPLE.name()}, stop:1 {dark});"
+            f" color: black; border: 1px solid {FRIEND_PURPLE_DARK.name()};"
+            f" border-radius: 4px; padding: {padding}; min-height: 0; }}"
+            f"{selector}:pressed {{ background: {FRIEND_PURPLE_DARK.name()}; }}")
+
+
+def button_rect(cell: QRectF, margin: float = 2.0) -> QRectF:
+    """The square the button occupies inside a cell (left-aligned)."""
+    side = max(8.0, min(cell.height(), cell.width()) - 2 * margin)
+    return QRectF(cell.left() + margin, cell.top() + (cell.height() - side) / 2,
+                  side, side)
+
+
+def paint_cassette_button(painter: QPainter, rect: QRectF, state: str,
+                          hovered: bool, palette) -> None:
+    painter.save()
+    painter.setRenderHint(QPainter.RenderHint.Antialiasing)
+    base = palette.button().color()
+    mid = palette.mid().color()
+    box = QRectF(rect).adjusted(0.5, 0.5, -0.5, -0.5)
+    radius = max(2.0, box.width() * 0.18)
+
+    gradient = QLinearGradient(box.topLeft(), box.bottomLeft())
+    if state == OFF:
+        top = base.lighter(112 if hovered else 106)
+        gradient.setColorAt(0, top)
+        gradient.setColorAt(1, base.darker(106))
+    else:
+        fill = ON_HOVER_GREY if hovered else ON_GREY
+        if state == PARTIAL:
+            fill = QColor(fill).lighter(118)
+        gradient.setColorAt(0, fill.darker(108))   # pressed in: lit from below
+        gradient.setColorAt(1, fill.lighter(106))
+    painter.setBrush(QBrush(gradient))
+    painter.setPen(QPen(mid, 1))
+    painter.drawRoundedRect(box, radius, radius)
+
+    ink = QColor(palette.text().color())
+    if state != OFF:
+        ink = QColor("#303030")
+    ink.setAlpha(200 if state != OFF else 150)
+    _paint_tape(painter, box, ink, half=(state == PARTIAL))
+    painter.restore()
+
+
+def _paint_tape(painter: QPainter, box: QRectF, ink: QColor, half=False):
+    """A cassette: body, label window, two reels."""
+    w, h = box.width(), box.height()
+    body = QRectF(box.left() + w * 0.16, box.top() + h * 0.28,
+                  w * 0.68, h * 0.46)
+    pen = QPen(ink, max(1.0, w / 16))
+    painter.setPen(pen)
+    painter.setBrush(Qt.BrushStyle.NoBrush)
+    painter.drawRoundedRect(body, body.height() * 0.15, body.height() * 0.15)
+    reel_r = body.height() * 0.17
+    cy = body.top() + body.height() * 0.45
+    for fx in (0.3, 0.7):
+        painter.drawEllipse(QPointF(body.left() + body.width() * fx, cy),
+                            reel_r, reel_r)
+    # the bottom trapezoid where the tape shows
+    path = QPainterPath()
+    path.moveTo(body.left() + body.width() * 0.22, body.bottom())
+    path.lineTo(body.left() + body.width() * 0.3, body.bottom() - body.height() * 0.22)
+    path.lineTo(body.left() + body.width() * 0.7, body.bottom() - body.height() * 0.22)
+    path.lineTo(body.left() + body.width() * 0.78, body.bottom())
+    painter.drawPath(path)
+    if half:
+        painter.drawLine(QPointF(body.left() + body.width() * 0.4, cy),
+                         QPointF(body.left() + body.width() * 0.6, cy))
+
+
+def paint_ufo(painter: QPainter, rect: QRectF, color: QColor,
+              filled: bool = True) -> None:
+    painter.save()
+    painter.setRenderHint(QPainter.RenderHint.Antialiasing)
+    w, h = rect.width(), rect.height()
+    pen = QPen(color.darker(135) if filled else color, max(1.0, w / 14))
+    painter.setPen(pen)
+    dome = QRectF(rect.left() + w * 0.32, rect.top() + h * 0.2,
+                  w * 0.36, h * 0.4)
+    saucer = QRectF(rect.left() + w * 0.06, rect.top() + h * 0.38,
+                    w * 0.88, h * 0.3)
+    if filled:
+        painter.setBrush(color.lighter(125))
+    else:
+        painter.setBrush(Qt.BrushStyle.NoBrush)
+    painter.drawChord(dome, 0, 180 * 16)
+    painter.setBrush(color if filled else Qt.BrushStyle.NoBrush)
+    painter.drawEllipse(saucer)
+    # three little lights
+    painter.setBrush(color.lighter(160) if filled else Qt.BrushStyle.NoBrush)
+    r = w * 0.045
+    for fx in (0.3, 0.5, 0.7):
+        painter.drawEllipse(QPointF(rect.left() + w * fx,
+                                    saucer.center().y() + saucer.height() * 0.1),
+                            r, r)
+    painter.restore()
+
+
+def ufo_icon(size: int = 32, followed: bool = True,
+             color: QColor | None = None) -> QIcon:
+    pixmap = QPixmap(size, size)
+    pixmap.fill(Qt.GlobalColor.transparent)
+    painter = QPainter(pixmap)
+    paint_ufo(painter, QRectF(1, 1, size - 2, size - 2),
+              color or (UFO_PURPLE if followed else QColor("#8a8a8a")),
+              filled=followed)
+    painter.end()
+    return QIcon(pixmap)

lintunes/gui/cassette_ui.py

@@ -9,7 +9,7 @@ from __future__ import annotations
 
 from PyQt6.QtCore import QObject, QTimer
 from PyQt6.QtGui import QAction
-from PyQt6.QtWidgets import QDialog, QMessageBox
+from PyQt6.QtWidgets import QDialog, QMenu, QMessageBox
 
 from lintunes.cassette import host
 from lintunes.cassette import syncthing_api as st
@@ -36,6 +36,7 @@ class CassetteUi(QObject):
         self._actions: list[QAction] = []
         self._service_factory = service_factory
         self.service = None
+        self.friend_mode = None   # FriendMode while browsing a friend
 
     # ---- the service (host machine only) ----
 
@@ -51,6 +52,7 @@ class CassetteUi(QObject):
             else:
                 from lintunes.cassette.service import CassetteService
                 self.service = CassetteService(parent=self)
+            self.service.changed.connect(self._refresh_selector)
             self.service.notice.connect(self._on_notice)
             self.service.step_failed.connect(self._on_step_failed)
             self.service.friends_added.connect(self._republish_timer.start)
@@ -84,6 +86,65 @@ class CassetteUi(QObject):
                 self._on_step_failed("Updating what your friends can see",
                                      str(exc))
 
+    # ---- the ▾ library selector / friend mode ----
+
+    def _refresh_selector(self):
+        """The ▾ shows once there's a friend to choose."""
+        has_friends = self.service is not None and bool(self.service.state().friends)
+        sidebar = getattr(self._window, "sidebar", None)
+        if sidebar is not None and sidebar.friend_button.isHidden() == has_friends:
+            sidebar.set_friend_selector_visible(has_friends)
+
+    def show_friend_menu(self):
+        """The ▾ was clicked. With unsaved friend-mode changes, settle those
+        first; then offer my library and each friend by display name."""
+        if self.service is None:
+            return
+        if self.friend_mode is not None and self.friend_mode.is_dirty():
+            if not self.friend_mode.confirm_leave():
+                return
+        sidebar = self._window.sidebar
+        menu = QMenu(self._window)
+        mine = menu.addAction("My Library")
+        mine.setEnabled(self.friend_mode is not None and self.friend_mode.active)
+        menu.addSeparator()
+        friends = sorted(self.service.state().friends.values(),
+                         key=lambda f: f.name.casefold())
+        by_action = {}
+        for friend in friends:
+            action = menu.addAction(friend.name)
+            by_action[action] = friend.token
+        button = sidebar.friend_button
+        chosen = menu.exec(button.mapToGlobal(button.rect().bottomLeft()))
+        if chosen is None:
+            return
+        if chosen is mine:
+            self.leave_friend_mode()
+        elif chosen in by_action:
+            self.enter_friend_mode(by_action[chosen])
+
+    def enter_friend_mode(self, token: str):
+        from lintunes.gui.friend_mode import FriendMode
+        if self.friend_mode is not None and self.friend_mode.active:
+            if not self.friend_mode.confirm_leave():
+                return
+        music_dir = None
+        if self._manager is not None:
+            music_dir = self._manager.organize_root()
+        self.friend_mode = FriendMode(
+            self._window, self.service, self._manager.library,
+            music_dir or self.service.root)
+        self.friend_mode.enter(token)
+
+    def leave_friend_mode(self):
+        if self.friend_mode is not None and self.friend_mode.active:
+            self.friend_mode.confirm_leave()
+
+    def confirm_quit(self) -> bool:
+        if self.friend_mode is None or not self.friend_mode.active:
+            return True
+        return self.friend_mode.confirm_leave()
+
     def shutdown(self):
         if self.service is not None:
             self.service.stop()

lintunes/gui/friend_mode.py

@@ -0,0 +1,358 @@
+"""Friend mode: browsing a friend's shared library and cassetting songs.
+
+Entered from the ▾ beside Library. The Library button becomes "<Name>'s
+Library" in light purple, the sidebar lists their shared playlists (a UFO on
+each is the follow toggle), and the content area shows their library as if
+it were LinTunes on their machine — except **nothing plays** (the audio isn't
+here) and nothing edits. A cassette column on the far left, and cassette
+buttons on every artist and album, say "send me this".
+
+Nothing is saved as you go. **Save and Close** writes my requests file and
+returns to my library; **Cancel** drops the changes. Leaving any other way
+with unsaved changes (the ▾ again, quitting) asks "Save changes?".
+
+The bottom bar carries the controls for the visit: **Hide tracks I have**
+(exact matches disappear; fuzzy ones are always shown, in light grey), how
+much the cassetted songs weigh against free space, and the two purple
+buttons.
+"""
+from __future__ import annotations
+
+from PyQt6.QtCore import QObject, Qt, pyqtSignal
+from PyQt6.QtGui import QColor
+from PyQt6.QtWidgets import (
+    QCheckBox, QHBoxLayout, QLabel, QMessageBox, QPushButton, QVBoxLayout,
+    QWidget,
+)
+
+from lintunes.cassette import matching, space
+from lintunes.cassette import syncthing_api as st
+from lintunes.cassette.friend_library import (
+    FRIEND_COLUMNS, FriendSource, load_friend_library,
+)
+from lintunes.cassette.state import in_dir
+from lintunes.gui import cassette_art
+from lintunes.gui.cassette_art import OFF, ON, PARTIAL
+from lintunes.models.playlist import PlaylistSettings
+
+FUZZY_GREY = QColor("#9a9a9a")
+TIGHT_ORANGE = "#d9822b"
+FULL_RED = "#d0342c"
+
+SAVE = "save"
+DISCARD = "discard"
+STAY = "stay"
+
+
+def ask_save_changes(parent) -> str:
+    """Plain words, three answers."""
+    box = QMessageBox(parent)
+    box.setWindowTitle("Save changes?")
+    box.setText("Save changes?")
+    box.setInformativeText("You changed which songs and playlists you want "
+                           "from your friend.")
+    save = box.addButton("Save", QMessageBox.ButtonRole.AcceptRole)
+    discard = box.addButton("Don't Save", QMessageBox.ButtonRole.DestructiveRole)
+    box.addButton(QMessageBox.StandardButton.Cancel)
+    box.setDefaultButton(save)
+    box.exec()
+    clicked = box.clickedButton()
+    if clicked is save:
+        return SAVE
+    if clicked is discard:
+        return DISCARD
+    return STAY
+
+
+class FriendPlaylistPane(QWidget):
+    """One of the friend's playlists, in its own order, read-only."""
+
+    def __init__(self, parent=None):
+        super().__init__(parent)
+        from lintunes.gui.track_table import TrackTableView
+        layout = QVBoxLayout(self)
+        layout.setContentsMargins(0, 0, 0, 0)
+        layout.setSpacing(0)
+        self.title = QLabel()
+        font = self.title.font()
+        font.setBold(True)
+        self.title.setFont(font)
+        self.title.setContentsMargins(8, 2, 8, 2)
+        layout.addWidget(self.title)
+        self.table = TrackTableView(playlist_mode=True)
+        self.table.set_read_only(True)
+        self.table.set_content_editable(False)
+        self.table.apply_settings(PlaylistSettings(
+            visible_columns=list(FRIEND_COLUMNS), sort_column="#"))
+        layout.addWidget(self.table)
+
+    def show_playlist(self, name: str, tracks: list):
+        self.title.setText(name)
+        self.table.set_tracks(tracks)
+
+
+class FriendMode(QObject):
+    """One visit to one friend's library."""
+
+    left = pyqtSignal()   # back in my own library
+
+    def __init__(self, window, service, my_library, music_dir, parent=None):
+        super().__init__(parent or window)
+        self._window = window
+        self._service = service
+        self._my_library = my_library
+        self._music_dir = music_dir
+        self.token: str | None = None
+        self._widgets: list[QWidget] = []
+        self._view = None
+        self._pane = None
+        self._floor: tuple[float, str] | None = None
+
+    @property
+    def active(self) -> bool:
+        return self.token is not None
+
+    # ---- entering / leaving ----
+
+    def enter(self, token: str):
+        from lintunes.gui.library_view import LibraryView
+        state = self._service.state()
+        friend = state.friends[token]
+        self.token = token
+        self._friend_name = friend.name
+        self.library = load_friend_library(in_dir(self._service.root, token),
+                                           friend.name)
+        self.cassetted = {t for t in friend.cassetted if t in self.library.tracks}
+        self.followed = {p for p in friend.followed
+                         if self.library.playlist(p) is not None}
+        self._saved = (set(self.cassetted), set(self.followed))
+        index = matching.LibraryIndex(self._my_library.tracks.values())
+        self.matches = {tid: index.classify(track)
+                        for tid, track in self.library.tracks.items()}
+        self._min_disk_free(friend.in_folder)
+
+        self._source = FriendSource(self.library.tracks, self)
+        self._view = LibraryView(self._source)
+        self._view.table.set_read_only(True)
+        self._view.enable_cassette(self.state_of, self.toggle)
+        self._view.table.model_.foreground_for = self._foreground
+        self._pane = FriendPlaylistPane()
+        self._pane.table.cassette_hooks = (lambda tid: self.state_of([tid]),
+                                           lambda tid: self._toggle_in_pane(tid))
+        self._pane.table.model_.foreground_for = self._foreground
+        content = self._window.content_stack
+        content.addWidget(self._view)
+        content.addWidget(self._pane)
+        content.setCurrentWidget(self._view)
+
+        sidebar = self._window.sidebar
+        sidebar.show_friend(f"{self.library.name}'s Library",
+                            self.library.playlists, self.followed)
+        sidebar.friend_library_selected.connect(self._show_library)
+        sidebar.friend_playlist_selected.connect(self._show_playlist)
+        sidebar.follow_toggled.connect(self._toggle_follow)
+        self._build_bar()
+        self._refresh_bar()
+
+    def _leave(self):
+        sidebar = self._window.sidebar
+        for signal, slot in ((sidebar.friend_library_selected, self._show_library),
+                             (sidebar.friend_playlist_selected, self._show_playlist),
+                             (sidebar.follow_toggled, self._toggle_follow)):
+            try:
+                signal.disconnect(slot)
+            except TypeError:
+                pass
+        sidebar.show_mine()
+        bar = self._window.statusBar()
+        for widget in self._widgets:
+            bar.removeWidget(widget)
+            widget.deleteLater()
+        self._widgets = []
+        content = self._window.content_stack
+        for widget in (self._view, self._pane):
+            if widget is not None:
+                content.removeWidget(widget)
+                widget.deleteLater()
+        self._view = self._pane = None
+        self.token = None
+        self._window.show_my_library()
+        self.left.emit()
+
+    # ---- the bottom bar ----
+
+    def _build_bar(self):
+        bar = self._window.statusBar()
+        self.hide_have = QCheckBox("Hide tracks I have")
+        self.hide_have.setToolTip(
+            "Hide songs that match one of yours exactly (artist, album, title "
+            "and length). Close matches stay, in grey.")
+        self.hide_have.toggled.connect(self._apply_hide)
+        self.size_label = QLabel()
+        self.save_button = QPushButton("Save and Close")
+        self.cancel_button = QPushButton("Cancel")
+        for button in (self.save_button, self.cancel_button):
+            # Compact: they live in the status bar.
+            button.setStyleSheet(cassette_art.friend_button_qss(padding="1px 10px"))
+        self.save_button.clicked.connect(self.save_and_close)
+        self.cancel_button.clicked.connect(self.cancel)
+        holder = QWidget()
+        row = QHBoxLayout(holder)
+        row.setContentsMargins(0, 0, 4, 0)
+        row.setSpacing(8)
+        for widget in (self.hide_have, self.size_label, self.save_button,
+                       self.cancel_button):
+            row.addWidget(widget)
+        bar.addPermanentWidget(holder)
+        self._widgets = [holder]
+
+    def _min_disk_free(self, folder_id: str):
+        try:
+            client = self._service.client()
+            self._floor = client.min_disk_free(folder_id)
+        except st.SyncthingError:
+            self._floor = (1.0, "%")   # Syncthing's default
+
+    def space_state(self) -> tuple[str, int, int]:
+        """(verdict, bytes needed, bytes free on the music disk)."""
+        need = sum(self.library.tracks[t].size for t in self.wanted_ids()
+                   if t in self.library.tracks)
+        music = space.disk_usage(self._music_dir)
+        cassette = space.disk_usage(self._service.root)
+        music_free = music.free if music else 0
+        if cassette is None:
+            return space.OK, need, music_free
+        value, unit = self._floor or (1.0, "%")
+        floor = st.disk_floor_bytes(value, unit, cassette.total)
+        return (space.verdict(need, music_free, cassette.free, floor),
+                need, music_free)
+
+    def _refresh_bar(self):
+        verdict, need, free = self.space_state()
+        text = f"Cassetted {space.human(need)} · {space.human(free)} free"
+        color = {space.TIGHT: TIGHT_ORANGE, space.FULL: FULL_RED}.get(verdict)
+        self.size_label.setText(text)
+        self.size_label.setStyleSheet(f"color: {color}; font-weight: bold;"
+                                      if color else "")
+        self.size_label.setToolTip({
+            space.TIGHT: "These would fit, but they'd leave so little room "
+                         "that Syncthing stops syncing.",
+            space.FULL: "There isn't room for these songs.",
+        }.get(verdict, ""))
+
+    # ---- views ----
+
+    def _show_library(self):
+        self._window.content_stack.setCurrentWidget(self._view)
+
+    def _show_playlist(self, pid: str):
+        playlist = self.library.playlist(pid)
+        if playlist is None:
+            return
+        tracks = [self.library.tracks[t] for t in playlist.track_ids
+                  if t in self.library.tracks
+                  and not self._hidden(t)]
+        self._pane.show_playlist(playlist.name, tracks)
+        self._window.content_stack.setCurrentWidget(self._pane)
+
+    def _hidden(self, tid: int) -> bool:
+        return self.hide_have.isChecked() and self.matches.get(tid) == matching.EXACT
+
+    def _apply_hide(self, on: bool):
+        tracks = {tid: t for tid, t in self.library.tracks.items()
+                  if not self._hidden(tid)}
+        self._source.set_tracks(tracks)
+        self._view.reload()
+        current = self._window.sidebar.friend_list.currentItem()
+        if current is not None and self._window.content_stack.currentWidget() is self._pane:
+            self._show_playlist(current.data(Qt.ItemDataRole.UserRole))
+
+    def _foreground(self, track):
+        if self.matches.get(track.track_id) == matching.FUZZY:
+            return FUZZY_GREY
+        return None
+
+    # ---- cassetting ----
+
+    def state_of(self, ids) -> str:
+        if not ids:
+            return OFF
+        hits = sum(1 for t in ids if t in self.cassetted)
+        if hits == 0:
+            return OFF
+        return ON if hits == len(ids) else PARTIAL
+
+    def toggle(self, ids):
+        """All on → all off; otherwise all on (so a partly-cassetted artist
+        becomes fully cassetted — the snapshot of what's there now)."""
+        ids = [t for t in ids if t in self.library.tracks]
+        if ids and all(t in self.cassetted for t in ids):
+            self.cassetted.difference_update(ids)
+        else:
+            self.cassetted.update(ids)
+        self._refresh_bar()
+
+    def _toggle_in_pane(self, tid: int):
+        self.toggle([tid])
+        if self._view is not None:
+            self._view.refresh_cassette()
+
+    def _toggle_follow(self, pid: str):
+        on = pid not in self.followed
+        (self.followed.add if on else self.followed.discard)(pid)
+        self._window.sidebar.friend_list.set_followed(pid, on)
+        self._refresh_bar()
+
+    def wanted_ids(self) -> set[int]:
+        """What to ask for: cassetted songs plus every song of a followed
+        playlist."""
+        wanted = set(self.cassetted)
+        for pid in self.followed:
+            playlist = self.library.playlist(pid)
+            if playlist is not None:
+                wanted.update(playlist.track_ids)
+        return wanted
+
+    # ---- saving ----
+
+    def is_dirty(self) -> bool:
+        return self.active and (self.cassetted, self.followed) != self._saved
+
+    def save_and_close(self) -> bool:
+        verdict, need, free = self.space_state()
+        if verdict != space.OK:
+            if verdict == space.FULL:
+                text = (f"These songs need {space.human(need)}, but only "
+                        f"{space.human(free)} is free where your music is.")
+            else:
+                text = ("These songs would leave so little free space that "
+                        "Syncthing stops syncing until you make room.")
+            answer = QMessageBox.warning(
+                self._window, "Not Enough Space", text + "\n\nSave anyway?",
+                QMessageBox.StandardButton.Save | QMessageBox.StandardButton.Cancel,
+                QMessageBox.StandardButton.Cancel)
+            if answer != QMessageBox.StandardButton.Save:
+                return False
+        self._service.save_requests(self.token, self.cassetted, self.followed,
+                                    self.wanted_ids())
+        self._leave()
+        return True
+
+    def cancel(self):
+        self._leave()
+
+    def confirm_leave(self) -> bool:
+        """Before leaving by any other door: True when it's fine to go (saved,
+        discarded, or nothing to save); False to stay."""
+        if not self.active:
+            return True
+        if not self.is_dirty():
+            self._leave()
+            return True
+        answer = ask_save_changes(self._window)
+        if answer == SAVE:
+            return self.save_and_close()
+        if answer == DISCARD:
+            self._leave()
+            return True
+        return False

lintunes/gui/library_view.py

@@ -3,8 +3,9 @@ from collections import Counter
 
 from PyQt6.QtWidgets import (
     QWidget, QVBoxLayout, QHBoxLayout, QListWidget, QSplitter, QLineEdit,
+    QStyledItemDelegate, QStyleOptionViewItem, QStyle, QApplication,
 )
-from PyQt6.QtCore import Qt, QTimer, pyqtSignal
+from PyQt6.QtCore import Qt, QTimer, QRectF, QPersistentModelIndex, pyqtSignal
 
 from lintunes.gui.table_settings import TableSettingsMixin
 from lintunes.gui.track_table import TrackTableView
@@ -58,13 +59,93 @@ def _canonical_values(values) -> list[str]:
     return result
 
 
+class _CassetteListDelegate(QStyledItemDelegate):
+    """Paints a cassette button at the left of every value row (friend mode's
+    artist and album columns); the "All" row gets none."""
+
+    def __init__(self, view):
+        super().__init__(view)
+        self._view = view
+
+    def paint(self, painter, option, index):
+        if index.row() == 0 or self._view.cassette_state is None:
+            super().paint(painter, option, index)
+            return
+        from lintunes.gui import cassette_art
+        side = option.rect.height()
+        opt = QStyleOptionViewItem(option)
+        self.initStyleOption(opt, index)
+        opt.rect = option.rect.adjusted(side + 2, 0, 0, 0)
+        style = opt.widget.style() if opt.widget else QApplication.style()
+        # Selection background across the whole row, text after the button.
+        full = QStyleOptionViewItem(option)
+        self.initStyleOption(full, index)
+        full.text = ""
+        style.drawControl(QStyle.ControlElement.CE_ItemViewItem, full,
+                          painter, full.widget)
+        style.drawControl(QStyle.ControlElement.CE_ItemViewItem, opt,
+                          painter, opt.widget)
+        state = self._view.cassette_state(index.data())
+        rect = cassette_art.button_rect(QRectF(option.rect.left(), option.rect.top(),
+                                               side, side))
+        cassette_art.paint_cassette_button(
+            painter, rect, state, self._view.is_cassette_hovered(index),
+            option.palette)
+
+
 class _BrowserList(QListWidget):
     """One column of the genre/artist/album browser."""
 
+    # Friend mode: the value whose cassette button was clicked.
+    cassette_clicked = pyqtSignal(str)
+
     def __init__(self, parent=None):
         super().__init__(parent)
         self.setMinimumWidth(120)
         self.setUniformItemSizes(True)
+        # Callable[[str], "off"|"on"|"partial"] while in friend mode.
+        self.cassette_state = None
+        self._hover: QPersistentModelIndex | None = None
+
+    def enable_cassette(self, state_for):
+        self.cassette_state = state_for
+        if state_for is not None:
+            self.setItemDelegate(_CassetteListDelegate(self))
+            self.setMouseTracking(True)
+        self.viewport().update()
+
+    def _button_hit(self, pos) -> bool:
+        index = self.indexAt(pos)
+        return (self.cassette_state is not None and index.isValid()
+                and index.row() > 0
+                and pos.x() - self.visualRect(index).left()
+                < self.visualRect(index).height() + 2)
+
+    def is_cassette_hovered(self, index) -> bool:
+        return (self._hover is not None and self._hover.isValid()
+                and self._hover.row() == index.row())
+
+    def mouseMoveEvent(self, event):
+        pos = event.position().toPoint()
+        new = QPersistentModelIndex(self.indexAt(pos)) if self._button_hit(pos) else None
+        if new != self._hover:
+            self._hover = new
+            self.viewport().update()
+        super().mouseMoveEvent(event)
+
+    def leaveEvent(self, event):
+        if self._hover is not None:
+            self._hover = None
+            self.viewport().update()
+        super().leaveEvent(event)
+
+    def mousePressEvent(self, event):
+        pos = event.position().toPoint()
+        if event.button() == Qt.MouseButton.LeftButton and self._button_hit(pos):
+            self.cassette_clicked.emit(self.indexAt(pos).data())
+            self.viewport().update()
+            return  # the button, not a navigation
+        super().mousePressEvent(event)
 
     def set_values(self, label: str, values: list[str]):
         current = self.selected_value()
@@ -98,6 +179,7 @@ class LibraryView(TableSettingsMixin, QWidget):
     def __init__(self, manager, parent=None):
         super().__init__(parent)
         self._manager = manager
+        self._cassette = None  # (state_of, toggle) in friend mode
 
         layout = QVBoxLayout(self)
         layout.setContentsMargins(0, 0, 0, 0)
@@ -173,6 +255,51 @@ class LibraryView(TableSettingsMixin, QWidget):
 
         self.reload()
 
+    # ---- friend mode (cassette) ----
+
+    def enable_cassette(self, state_of, toggle):
+        """Friend mode: cassette buttons on artists, albums and tracks.
+        ``state_of(track ids)`` -> "off"|"on"|"partial"; ``toggle(track ids)``
+        turns them all on, or all off when they already are. Passing None
+        turns it off."""
+        self._cassette = (state_of, toggle) if state_of else None
+        if state_of is None:
+            self.table.cassette_hooks = None
+            for lst in (self._artist_list, self._album_list):
+                lst.enable_cassette(None)
+            return
+        self.table.cassette_hooks = (lambda tid: state_of([tid]),
+                                     lambda tid: self._toggle([tid]))
+        self._artist_list.enable_cassette(
+            lambda v: state_of(self.group_track_ids("artist", v)))
+        self._album_list.enable_cassette(
+            lambda v: state_of(self.group_track_ids("album", v)))
+        if not getattr(self, "_cassette_wired", False):
+            self._cassette_wired = True
+            self._artist_list.cassette_clicked.connect(
+                lambda v: self._toggle(self.group_track_ids("artist", v)))
+            self._album_list.cassette_clicked.connect(
+                lambda v: self._toggle(self.group_track_ids("album", v)))
+
+    def _toggle(self, ids):
+        if self._cassette is not None and ids:
+            self._cassette[1](ids)
+            self.refresh_cassette()
+
+    def refresh_cassette(self):
+        for widget in (self._artist_list, self._album_list, self.table):
+            widget.viewport().update()
+
+    def group_track_ids(self, kind: str, value: str) -> list[int]:
+        """The tracks a browser row stands for, under the current filters —
+        what cassetting that artist or album asks for."""
+        value = value.casefold()
+        if kind == "artist":
+            return [t.track_id for t in self._filtered_tracks(up_to="genre")
+                    if (t.album_artist or t.artist).casefold() == value]
+        return [t.track_id for t in self._filtered_tracks(up_to="artist")
+                if t.album.casefold() == value]
+
     def set_header_height(self, height: int):
         # Kept in sync with the sidebar Library button and the playlist view's
         # name strip so the tracklist tops line up across views.

lintunes/gui/main_window.py

@@ -209,6 +209,8 @@ class MainWindow(QMainWindow):
         # Wiring
         self._transport.play_clicked.connect(self.play_pause)
         self._sidebar.library_selected.connect(self._show_library)
+        self._sidebar.friend_selector_clicked.connect(
+            self._cassette.show_friend_menu)
         self._sidebar.playlist_selected.connect(self._show_playlist)
         self._sidebar.tree.export_requested.connect(self._export_playlist)
         self._sidebar.art.download_art_requested.connect(
@@ -392,6 +394,19 @@ class MainWindow(QMainWindow):
     def cassette(self) -> CassetteUi:
         return self._cassette
 
+    # What friend mode swaps in and out.
+    @property
+    def content_stack(self):
+        return self._content
+
+    @property
+    def sidebar(self):
+        return self._sidebar
+
+    def show_my_library(self):
+        self._sidebar.reflect_library()
+        self._show_library()
+
     def _add_action(self, menu, text, shortcut, slot):
         action = QAction(text, self)
         if shortcut:
@@ -1684,6 +1699,10 @@ class MainWindow(QMainWindow):
             self._inhibitor.release()
 
     def closeEvent(self, event):
+        # Unsaved cassette choices in friend mode: Save / Don't Save / Cancel.
+        if not self._cassette.confirm_quit():
+            event.ignore()
+            return
         # Quitting mid-transfer abandons a partial file on the device (it
         # self-heals next sync, but silently) — make it a deliberate choice.
         # A link import has nothing half-written on a device to warn about:

lintunes/gui/sidebar.py

@@ -1,6 +1,7 @@
 from PyQt6.QtWidgets import (
     QWidget, QVBoxLayout, QPushButton, QTreeWidget, QTreeWidgetItem, QMenu,
     QInputDialog, QMessageBox, QAbstractItemView, QLineEdit, QApplication,
+    QHBoxLayout, QListWidget, QListWidgetItem, QStackedWidget,
 )
 from PyQt6.QtCore import Qt, QTimer, QPoint, pyqtSignal
 from PyQt6.QtGui import QBrush, QPainter, QPalette, QPixmap
@@ -29,6 +30,13 @@ class SidebarPanel(QWidget):
 
     library_selected = pyqtSignal()
     playlist_selected = pyqtSignal(str)
+    # Friend sharing: the ▾ beside Library was clicked (show the friends
+    # popup), and in friend mode their library / one of their playlists was
+    # chosen, or a playlist's UFO (follow) toggled.
+    friend_selector_clicked = pyqtSignal()
+    friend_library_selected = pyqtSignal()
+    friend_playlist_selected = pyqtSignal(str)
+    follow_toggled = pyqtSignal(str)
 
     def __init__(self, manager, player, parent=None):
         super().__init__(parent)
@@ -36,27 +44,77 @@ class SidebarPanel(QWidget):
         layout.setContentsMargins(0, 0, 0, 0)
         layout.setSpacing(0)
 
+        self.friend_mode = False
+        top = QWidget()
+        top_row = QHBoxLayout(top)
+        top_row.setContentsMargins(0, 0, 0, 0)
+        top_row.setSpacing(0)
         self.library_button = QPushButton("Library")
         self.library_button.setCheckable(True)
         self.library_button.setChecked(True)
+        # The library selector: a small square cut from the button's right
+        # end, flush against it. Shown once there is a friend to choose.
+        self.friend_button = QPushButton("▾")
+        self.friend_button.setToolTip("Browse a friend's library")
+        self.friend_button.setVisible(False)
+        top_row.addWidget(self.library_button, stretch=1)
+        top_row.addWidget(self.friend_button)
         self.refresh_style()
-        layout.addWidget(self.library_button)
+        layout.addWidget(top)
 
+        self._lists = QStackedWidget()
         self.tree = PlaylistTree(manager)
-        layout.addWidget(self.tree, stretch=1)
+        self._lists.addWidget(self.tree)
+        self.friend_list = FriendPlaylistList()
+        self._lists.addWidget(self.friend_list)
+        layout.addWidget(self._lists, stretch=1)
 
         self.art = SidebarArt(player)
         layout.addWidget(self.art)
 
         self.library_button.clicked.connect(self._on_library_clicked)
         self.tree.playlist_selected.connect(self._on_playlist_selected)
+        self.friend_button.clicked.connect(self.friend_selector_clicked)
+        self.friend_list.playlist_selected.connect(self._on_friend_playlist)
+        self.friend_list.follow_toggled.connect(self.follow_toggled)
 
     def _on_library_clicked(self):
         self.library_button.setChecked(True)
+        if self.friend_mode:
+            self.friend_list.clearSelection()
+            self.friend_list.setCurrentItem(None)
+            self.friend_library_selected.emit()
+            return
         self.tree.clearSelection()
         self.tree.setCurrentItem(None)
         self.library_selected.emit()
 
+    def _on_friend_playlist(self, pid: str):
+        self.library_button.setChecked(False)
+        self.friend_playlist_selected.emit(pid)
+
+    # ---- friend mode ----
+
+    def set_friend_selector_visible(self, visible: bool):
+        self.friend_button.setVisible(visible)
+        self.refresh_style()
+
+    def show_friend(self, library_name: str, playlists, followed: set):
+        """Friend mode: the Library button becomes their library (purple) and
+        the tree their shared playlists, each with a UFO follow toggle."""
+        self.friend_mode = True
+        self.library_button.setText(library_name)
+        self.friend_list.set_playlists(playlists, followed)
+        self._lists.setCurrentWidget(self.friend_list)
+        self.library_button.setChecked(True)
+        self.refresh_style()
+
+    def show_mine(self):
+        self.friend_mode = False
+        self.library_button.setText("Library")
+        self._lists.setCurrentWidget(self.tree)
+        self.refresh_style()
+
     def _on_playlist_selected(self, pid: str):
         self.library_button.setChecked(False)
         self.playlist_selected.emit(pid)
@@ -79,21 +137,102 @@ class SidebarPanel(QWidget):
 
     def apply_metrics(self, header_strip: int):
         self.library_button.setFixedHeight(header_strip)
+        self.friend_button.setFixedHeight(header_strip)
+        # Square: the button's own height, minus its vertical margins.
+        self.friend_button.setFixedWidth(max(16, header_strip - 4))
 
     def refresh_style(self):
         """(Re)build the Library button's look from the live palette, so its
-        emboss follows theme changes like every other button's."""
+        emboss follows theme changes like every other button's. With the
+        friend selector showing, the two share a border and have square
+        corners where they meet; in friend mode both turn light purple."""
+        from lintunes.gui.cassette_art import FRIEND_PURPLE, FRIEND_PURPLE_DARK
         palette = QApplication.palette()
         base = palette.color(QPalette.ColorRole.AlternateBase)
         lit = palette.color(QPalette.ColorRole.Highlight)
+        split = not self.friend_button.isHidden()
+        border = "palette(mid)"
+        if self.friend_mode:
+            base = lit = FRIEND_PURPLE
+            border = FRIEND_PURPLE_DARK.name()
+        checked_text = "black" if self.friend_mode else "palette(highlighted-text)"
+        joint = ("border-top-right-radius: 0; border-bottom-right-radius: 0;"
+                 " margin: 2px 0 2px 8px;" if split else
+                 "margin: 2px 4px 2px 8px;")
         self.library_button.setStyleSheet(
             "QPushButton { text-align: left; padding-left: 10px;"
-            "  border: 1px solid palette(mid); border-radius: 4px;"
+            f"  border: 1px solid {border}; border-radius: 4px; {joint}"
-            "  margin: 2px 4px 2px 8px;"
             f"  background: {theme.emboss_gradient(base)}; }}"
             "QPushButton:checked {"
             f"  background: {theme.emboss_gradient(lit, pressed=True)};"
-            "  color: palette(highlighted-text); }")
+            f"  color: {checked_text}; }}")
+        self.friend_button.setStyleSheet(
+            "QPushButton { padding: 0;"
+            f"  border: 1px solid {border}; border-left: none;"
+            "  border-radius: 4px; border-top-left-radius: 0;"
+            "  border-bottom-left-radius: 0; margin: 2px 4px 2px 0;"
+            f"  background: {theme.emboss_gradient(base)}; }}"
+            "QPushButton:pressed {"
+            f"  background: {theme.emboss_gradient(base, pressed=True)}; }}")
+
+
+class FriendPlaylistList(QListWidget):
+    """A friend's shared playlists in friend mode. The UFO at each row's left
+    is the follow toggle: purple when followed, a grey outline when not."""
+
+    playlist_selected = pyqtSignal(str)
+    follow_toggled = pyqtSignal(str)
+
+    def __init__(self, parent=None):
+        super().__init__(parent)
+        self.setUniformItemSizes(True)
+        self._followed: set[str] = set()
+        self.currentItemChanged.connect(self._on_current)
+
+    def set_playlists(self, playlists, followed: set):
+        self._followed = set(followed)
+        self.blockSignals(True)
+        self.clear()
+        for playlist in playlists:
+            item = QListWidgetItem(playlist.name)
+            item.setData(Qt.ItemDataRole.UserRole, playlist.pid)
+            self.addItem(item)
+        self.blockSignals(False)
+        self._refresh_icons()
+
+    def set_followed(self, pid: str, on: bool):
+        (self._followed.add if on else self._followed.discard)(pid)
+        self._refresh_icons()
+
+    def _refresh_icons(self):
+        from lintunes.gui.cassette_art import ufo_icon
+        on, off = ufo_icon(followed=True), ufo_icon(followed=False)
+        for row in range(self.count()):
+            item = self.item(row)
+            followed = item.data(Qt.ItemDataRole.UserRole) in self._followed
+            item.setIcon(on if followed else off)
+            item.setToolTip("Following — plays from your sidebar. Click the "
+                            "UFO to stop." if followed else
+                            "Click the UFO to follow this playlist.")
+
+    def _icon_hit(self, pos) -> bool:
+        index = self.indexAt(pos)
+        if not index.isValid():
+            return False
+        rect = self.visualRect(index)
+        return pos.x() - rect.left() < self.iconSize().width() + 8
+
+    def mousePressEvent(self, event):
+        pos = event.position().toPoint()
+        if event.button() == Qt.MouseButton.LeftButton and self._icon_hit(pos):
+            pid = self.indexAt(pos).data(Qt.ItemDataRole.UserRole)
+            self.follow_toggled.emit(pid)
+            return
+        super().mousePressEvent(event)
+
+    def _on_current(self, current, _previous):
+        if current is not None:
+            self.playlist_selected.emit(current.data(Qt.ItemDataRole.UserRole))
 
 
 class SidebarArt(QWidget):

lintunes/gui/track_table.py

@@ -85,6 +85,13 @@ ALL_COLUMNS = [
 
 COLUMN_MAP = {col[0]: col for col in ALL_COLUMNS}
 
+# Friend sharing's "ask for this song" column. Registered so a view can show
+# it, but not in ALL_COLUMNS: only views that turn on ``cassette_hooks`` offer
+# it in the header menu, and it always sits first.
+CASSETTE_FIELD = "cassette"
+CASSETTE_COLUMN = (CASSETTE_FIELD, "", 30)
+COLUMN_MAP[CASSETTE_FIELD] = CASSETTE_COLUMN
+
 
 def format_time(ms: int) -> str:
     if ms <= 0:
@@ -156,7 +163,11 @@ class RatingDelegate(QStyledItemDelegate):
 
     def paint(self, painter, option, index):
         model = self._view.model_
-        if model.fields[index.column()] != "rating":
+        field = model.fields[index.column()]
+        if field == CASSETTE_FIELD:
+            self._paint_cassette(painter, option, index)
+            return
+        if field != "rating":
             super().paint(painter, option, index)
             return
         opt = QStyleOptionViewItem(option)
@@ -194,6 +205,23 @@ class RatingDelegate(QStyledItemDelegate):
         painter.restore()
 
 
+    def _paint_cassette(self, painter, option, index):
+        from lintunes.gui import cassette_art
+        opt = QStyleOptionViewItem(option)
+        self.initStyleOption(opt, index)
+        opt.text = ""
+        style = opt.widget.style() if opt.widget else QApplication.style()
+        style.drawControl(QStyle.ControlElement.CE_ItemViewItem, opt,
+                          painter, opt.widget)
+        state = self._view.cassette_state_at(index)
+        if state is None:
+            return
+        rect = cassette_art.button_rect(QRectF(opt.rect))
+        cassette_art.paint_cassette_button(
+            painter, rect, state, self._view.is_cassette_hovered(index),
+            opt.palette)
+
+
 def _format_size(size: int) -> str:
     if size <= 0:
         return ""
@@ -339,6 +367,9 @@ class TrackTableModel(QAbstractTableModel):
         self._with_index = with_index_column
         self._now_playing_id: int | None = None
         self._now_playing_active = False
+        # Optional Callable[[Track], QColor | None]: a per-row text color
+        # (friend mode greys songs I probably already have).
+        self.foreground_for = None
         self.set_visible_columns(["name", "artist", "album"])
 
     def set_now_playing(self, track_id: int | None, playing: bool):
@@ -472,6 +503,10 @@ class TrackTableModel(QAbstractTableModel):
             if role == Qt.ItemDataRole.DisplayRole:
                 return index.row() + 1
             return None
+        if field == CASSETTE_FIELD:
+            return None  # painted by the delegate
+        if role == Qt.ItemDataRole.ForegroundRole and self.foreground_for:
+            return self.foreground_for(track)
 
         if (role == Qt.ItemDataRole.DecorationRole and field == "name"
                 and track.track_id == self._now_playing_id):
@@ -569,6 +604,14 @@ class TrackTableView(QTableView):
         # itself reaching into the library.
         self.playlists_for_track = None  # Callable[[int], list[tuple[str,str]]]
 
+        # Friend sharing. read_only: someone else's songs — no playing, no
+        # editing, no dragging into my playlists (their ids aren't mine).
+        # cassette_hooks: (state_for(track id) -> "off"|"on"|None,
+        # toggled(track id)) — turns the cassette column on.
+        self.read_only = False
+        self.cassette_hooks = None
+        self._hover_cassette_index: QPersistentModelIndex | None = None
+
         # Drag and drop (default indicator off: we paint a glowing line)
         self.setDragEnabled(True)
         self.setAcceptDrops(True)
@@ -600,11 +643,43 @@ class TrackTableView(QTableView):
     def set_source_playlist(self, pid: str):
         self._source_playlist_id = pid
 
+    def set_read_only(self, read_only: bool):
+        self.read_only = read_only
+        self.setDragEnabled(not read_only)
+        self.setAcceptDrops(not read_only and self._content_editable)
+
+    def cassette_state_at(self, index):
+        if self.cassette_hooks is None or not index.isValid():
+            return None
+        track = self.model_.track_at(self.model_.source_row(index.row()))
+        return self.cassette_hooks[0](track.track_id)
+
+    def is_cassette_hovered(self, index) -> bool:
+        hover = self._hover_cassette_index
+        return (hover is not None and hover.isValid()
+                and hover.row() == index.row()
+                and hover.column() == index.column())
+
+    def _is_cassette_index(self, index) -> bool:
+        return (self.cassette_hooks is not None and index.isValid()
+                and self.model_.fields[index.column()] == CASSETTE_FIELD)
+
+    def _set_cassette_hover(self, index):
+        new = QPersistentModelIndex(index) if index is not None else None
+        old = self._hover_cassette_index
+        if new == old:
+            return
+        self._hover_cassette_index = new
+        for persistent in (old, new):
+            if persistent is not None and persistent.isValid():
+                self.viewport().update(self.visualRect(
+                    self.model_.index(persistent.row(), persistent.column())))
+
     def set_content_editable(self, editable: bool):
         """Smart playlists pass False: dropping, reordering, cut/paste and
         remove are all disabled (membership is derived from criteria)."""
         self._content_editable = editable
-        self.setAcceptDrops(editable)
+        self.setAcceptDrops(editable and not self.read_only)
 
     def context_id(self) -> str:
         """Identifies what this table is currently showing, so the now-playing
@@ -691,7 +766,7 @@ class TrackTableView(QTableView):
 
     def copy_selection(self):
         ids = self.selected_track_ids()
-        if not ids:
+        if not ids or self.read_only:
             return
         QApplication.clipboard().setMimeData(make_tracks_mime(
             ids, self._source_playlist_id, self.selected_source_rows()))
@@ -700,6 +775,8 @@ class TrackTableView(QTableView):
         """Copy the selection, then — in a playlist — remove it immediately so
         it visibly leaves; a paste re-inserts it at the target. From the
         library there's nothing to remove, so this is just a copy."""
+        if self.read_only:
+            return
         ids = self.selected_track_ids()
         if not ids:
             return
@@ -742,7 +819,10 @@ class TrackTableView(QTableView):
     def _show_header_menu(self, pos):
         menu = QMenu(self)
         visible = [f for f in self.model_.fields if f != INDEX_FIELD]
-        for field, label, _w in ALL_COLUMNS:
+        columns = list(ALL_COLUMNS)
+        if self.cassette_hooks is not None:
+            columns = [(CASSETTE_FIELD, "Cassette", 30)] + columns
+        for field, label, _w in columns:
             action = menu.addAction(label)
             action.setCheckable(True)
             action.setChecked(field in visible)
@@ -754,7 +834,7 @@ class TrackTableView(QTableView):
         if chosen.isChecked():
             new_visible = visible + [field]
             # Preserve canonical column ordering
-            new_visible = [f for f, _l, _w in ALL_COLUMNS if f in new_visible]
+            new_visible = [f for f, _l, _w in columns if f in new_visible]
         else:
             new_visible = [f for f in visible if f != field]
             if not new_visible:
@@ -766,6 +846,9 @@ class TrackTableView(QTableView):
     def _show_context_menu(self, pos):
         if not self.selected_track_ids():
             return
+        if self.read_only:
+            self._show_read_only_menu(pos)
+            return
         menu = QMenu(self)
         info_action = menu.addAction("Get Info\tCtrl+I")
         copy_action = menu.addAction("Copy\tCtrl+C")
@@ -850,6 +933,17 @@ class TrackTableView(QTableView):
         elif chosen is delete_action:
             self.delete_from_library_requested.emit(self.selected_track_ids())
 
+    def _show_read_only_menu(self, pos):
+        """Someone else's songs: nothing here edits, plays or copies them."""
+        selected = self.selected_track_ids()
+        if len(selected) != 1:
+            return
+        menu = QMenu(self)
+        youtube_action = menu.addAction("lookup on youtube")
+        if menu.exec(self.viewport().mapToGlobal(pos)) is youtube_action:
+            track = self.model_.track_at(self.selected_source_rows()[0])
+            QDesktopServices.openUrl(youtube_search_url(track))
+
     # ---- rating hover / click ----
 
     def _is_rating_index(self, index) -> bool:
@@ -877,16 +971,27 @@ class TrackTableView(QTableView):
     def mouseMoveEvent(self, event):
         index = self.indexAt(event.position().toPoint())
         self._set_rating_hover(index if self._is_rating_index(index) else None)
+        self._set_cassette_hover(index if self._is_cassette_index(index) else None)
         super().mouseMoveEvent(event)
 
     def leaveEvent(self, event):
         self._set_rating_hover(None)
+        self._set_cassette_hover(None)
         super().leaveEvent(event)
 
     def mousePressEvent(self, event):
         if event.button() == Qt.MouseButton.LeftButton:
             pos = event.position().toPoint()
             index = self.indexAt(pos)
+            if self._is_cassette_index(index):
+                track = self.model_.track_at(self.model_.source_row(index.row()))
+                if self.cassette_state_at(index) is not None:
+                    self.cassette_hooks[1](track.track_id)
+                    self.viewport().update(self.visualRect(index))
+                return  # a cassette click never selects or starts a drag
+            if self.read_only and self._is_rating_index(index):
+                super().mousePressEvent(event)
+                return
             if self._is_rating_index(index):
                 track = self.model_.track_at(self.model_.source_row(index.row()))
                 slot = rating_slot_at(
@@ -900,6 +1005,8 @@ class TrackTableView(QTableView):
     # ---- playback ----
 
     def _on_double_click(self, index):
+        if self.read_only:
+            return  # browsing only: the audio isn't here
         ids = self.view_order_track_ids()
         if ids:
             self.play_requested.emit(ids, index.row())

tests/test_round67.py

@@ -0,0 +1,298 @@
+"""Round 67: friend mode — browsing a friend's library and cassetting songs.
+
+* Matching is best effort: exact = artist + album + title + length within 2 s;
+  fuzzy = artist + title. Case, accents, punctuation, "feat." and a leading
+  "The" don't count.
+* The friend's library is read-only here: no playing, no editing, no
+  dragging their ids into my playlists.
+* Nothing is saved as you click. Save and Close writes requests.json;
+  Cancel drops everything; leaving any other way with changes asks.
+* The size readout goes orange when Syncthing would stall (its free-space
+  floor) and red when the songs won't fit.
+"""
+import json
+
+import pytest
+from PyQt6.QtCore import Qt
+
+from lintunes.cassette import matching, publish, requests as req, share, space
+from lintunes.cassette.friend_library import load_friend_library
+from lintunes.cassette.service import CassetteService
+from lintunes.cassette.state import Friend, Selection, in_dir, out_dir
+from lintunes.models import Playlist, Track
+from lintunes.models.library import Library
+
+
+def _t(tid, name, artist, album, ms=200_000, **kw):
+    return Track(track_id=tid, name=name, artist=artist, album=album,
+                 total_time=ms, size=5_000_000, **kw)
+
+
+# ---- matching ----
+
+class TestMatching:
+    def test_normalize(self):
+        assert matching.normalize("The Beatles") == "beatles"
+        assert matching.normalize("Beyoncé") == "beyonce"
+        assert matching.normalize("Crazy In Love (feat. Jay-Z)") == "crazy in love"
+        assert matching.normalize("Hey Jude - Remastered 2015") == "hey jude remastered 2015"
+        assert matching.normalize("Hey Jude (Remastered 2015)") == "hey jude"
+        assert matching.normalize("Simon & Garfunkel") == "simon and garfunkel"
+        assert matching.normalize("Song ft. Someone") == "song"
+
+    def test_exact_needs_album_and_length(self):
+        index = matching.LibraryIndex([_t(1, "Hey Jude", "The Beatles", "1")])
+        assert index.classify(_t(9, "hey jude", "Beatles", "1", ms=201_500)) == matching.EXACT
+        assert index.classify(_t(9, "Hey Jude", "The Beatles", "1", ms=210_000)) == matching.FUZZY
+        assert index.classify(_t(9, "Hey Jude", "The Beatles", "Past Masters")) == matching.FUZZY
+        assert index.classify(_t(9, "Let It Be", "The Beatles", "1")) is None
+
+    def test_album_artist_or_artist(self):
+        mine = _t(1, "Track", "Guest", "Comp", album_artist="Various Artists")
+        index = matching.LibraryIndex([mine])
+        assert index.classify(_t(9, "Track", "Guest", "Comp")) == matching.EXACT
+
+    def test_unknown_length_still_exact(self):
+        index = matching.LibraryIndex([_t(1, "A", "B", "C", ms=0)])
+        assert index.classify(_t(9, "A", "B", "C")) == matching.EXACT
+
+
+# ---- space ----
+
+class TestSpace:
+    def test_verdicts(self):
+        gb = 10**9
+        assert space.verdict(1 * gb, 50 * gb, 50 * gb, 1 * gb) == space.OK
+        assert space.verdict(49 * gb, 50 * gb, 50 * gb, 2 * gb) == space.TIGHT
+        assert space.verdict(60 * gb, 50 * gb, 500 * gb, 1 * gb) == space.FULL
+
+    def test_human(self):
+        assert space.human(740_000) == "740 KB"
+        assert space.human(1_200_000_000) == "1.2 GB"
+
+    def test_disk_usage_of_missing_path_uses_its_parent(self, tmp_path):
+        assert space.disk_usage(tmp_path / "not" / "yet") is not None
+
+
+# ---- requests & the friend's copy ----
+
+class TestFiles:
+    def test_requests_round_trip(self, tmp_path):
+        assert req.write_requests(tmp_path, [3, 1, 3])
+        assert json.loads((tmp_path / req.REQUESTS_FILE).read_text())["tracks"] == [1, 3]
+        assert not req.write_requests(tmp_path, {1, 3})
+        assert req.read_requests(tmp_path) == {1, 3}
+
+    def test_garbled_requests_is_empty(self, tmp_path):
+        (tmp_path / req.REQUESTS_FILE).write_text("{half a fi")
+        assert req.read_requests(tmp_path) == set()
+
+    def test_load_friend_library(self, tmp_path):
+        library = Library()
+        library.tracks[5] = _t(5, "Song", "Artist", "Album", rating=100)
+        library.playlists["P"] = Playlist(name="Mix", persistent_id="P",
+                                          track_ids=[5])
+        share.publish_share(tmp_path, library, Selection(all_library=True,
+                                                          all_playlists=True))
+        publish.publish_intro(tmp_path, "Sam", None)
+        friend = load_friend_library(tmp_path)
+        assert friend.name == "Sam"
+        assert friend.tracks[5].name == "Song"
+        assert friend.tracks[5].rating == 0     # never crossed over
+        assert friend.playlists[0].name == "Mix"
+        assert friend.playlists[0].track_ids == [5]
+
+    def test_missing_or_garbled_is_empty(self, tmp_path):
+        assert load_friend_library(tmp_path, "Sam").tracks == {}
+        (tmp_path / share.LIBRARY_FILE).write_text("[1, 2")
+        (tmp_path / share.PLAYLISTS_FILE).write_text(json.dumps(
+            {"playlists": [{"id": "P", "track_ids": ["x", 99]}]}))
+        friend = load_friend_library(tmp_path, "Sam")
+        assert friend.name == "Sam" and friend.tracks == {}
+        assert friend.playlists[0].track_ids == []
+
+
+# ---- read-only table and the cassette column ----
+
+class TestTable:
+    def test_read_only_never_plays_or_copies(self, qapp):
+        from lintunes.gui.track_table import TrackTableView
+        table = TrackTableView()
+        table.set_read_only(True)
+        table.set_tracks([_t(1, "A", "B", "C")])
+        played = []
+        table.play_requested.connect(lambda *a: played.append(a))
+        table._on_double_click(table.model_.index(0, 0))
+        assert played == []
+        assert not table.dragEnabled() and not table.acceptDrops()
+
+    def test_cassette_column_click_toggles(self, qapp):
+        from PyQt6.QtCore import QPointF
+        from PyQt6.QtGui import QMouseEvent
+        from lintunes.gui.track_table import CASSETTE_FIELD, TrackTableView
+        table = TrackTableView()
+        on = set()
+        table.cassette_hooks = (lambda tid: "on" if tid in on else "off",
+                                lambda tid: on.symmetric_difference_update({tid}))
+        table.model_.set_visible_columns([CASSETTE_FIELD, "name"])
+        table.set_tracks([_t(7, "A", "B", "C")])
+        table.resize(400, 200)
+        table.show()
+        rect = table.visualRect(table.model_.index(0, 0))
+        event = QMouseEvent(QMouseEvent.Type.MouseButtonPress,
+                            QPointF(rect.center()), QPointF(rect.center()),
+                            Qt.MouseButton.LeftButton, Qt.MouseButton.LeftButton,
+                            Qt.KeyboardModifier.NoModifier)
+        table.mousePressEvent(event)
+        assert on == {7}
+        assert table.cassette_state_at(table.model_.index(0, 0)) == "on"
+
+
+# ---- friend mode itself ----
+
+class _Window:
+    """What FriendMode touches on MainWindow, and nothing more."""
+
+    def __init__(self):
+        from PyQt6.QtWidgets import QMainWindow, QStackedWidget
+        from lintunes.gui.sidebar import SidebarPanel
+        from unittest.mock import MagicMock
+        self.main = QMainWindow()
+        self.content_stack = QStackedWidget()
+        self.main.setCentralWidget(self.content_stack)
+        manager = MagicMock()
+        manager.library.playlists = {}
+        player = MagicMock()
+        self.sidebar = SidebarPanel(manager, player)
+        self.shown_mine = 0
+
+    def statusBar(self):
+        return self.main.statusBar()
+
+    def show_my_library(self):
+        self.shown_mine += 1
+
+
+@pytest.fixture
+def visit(qapp, tmp_path):
+    from lintunes.gui.friend_mode import FriendMode
+    friend_lib = Library()
+    for tid, (name, artist, album) in enumerate(
+            [("Hey Jude", "The Beatles", "1"), ("Let It Be", "The Beatles", "1"),
+             ("Blackbird", "The Beatles", "White"), ("Doo Wop", "Lauryn Hill", "Mis")],
+            start=10):
+        friend_lib.tracks[tid] = _t(tid, name, artist, album)
+    friend_lib.playlists["P"] = Playlist(name="Road Trip", persistent_id="P",
+                                         track_ids=[13, 10])
+    service = CassetteService(root=tmp_path, config_loader=lambda: {})
+    service._state.friends["tok"] = Friend(token="tok", device_id="X", name="Sam",
+                                           in_folder="f-in")
+    share.publish_share(in_dir(tmp_path, "tok"), friend_lib,
+                        Selection(all_library=True, all_playlists=True))
+    mine = Library()
+    mine.tracks[1] = _t(1, "Hey Jude", "Beatles", "1")          # exact
+    mine.tracks[2] = _t(2, "Blackbird", "The Beatles", "Other")  # fuzzy
+    window = _Window()
+    mode = FriendMode(window.main, service, mine, tmp_path)
+    mode._window = window
+    mode.enter("tok")
+    return mode, window, service
+
+
+class TestFriendMode:
+    def test_enter_shows_their_library_purple(self, visit):
+        mode, window, _ = visit
+        assert window.sidebar.friend_mode
+        assert window.sidebar.library_button.text() == "Sam's Library"
+        assert window.content_stack.currentWidget() is mode._view
+        assert mode._view.table.read_only
+        assert mode.matches[10] == matching.EXACT
+        assert mode.matches[12] == matching.FUZZY
+        assert mode.matches[13] is None
+
+    def test_artist_cassettes_down_the_tree(self, visit):
+        mode, _, _ = visit
+        ids = mode._view.group_track_ids("artist", "The Beatles")
+        mode.toggle(ids)
+        assert mode.cassetted == {10, 11, 12}
+        assert mode.state_of([10, 13]) == "partial"
+        mode.toggle(ids)
+        assert mode.cassetted == set()
+
+    def test_nothing_saved_until_save(self, visit, tmp_path):
+        mode, window, service = visit
+        mode.toggle([13])
+        mode._toggle_follow("P")
+        assert not (out_dir(tmp_path, "tok") / req.REQUESTS_FILE).exists()
+        assert service.state().friends["tok"].cassetted == []
+        assert mode.is_dirty()
+        mode.save_and_close()
+        friend = service.state().friends["tok"]
+        assert friend.cassetted == [13] and friend.followed == ["P"]
+        # the followed playlist's songs are asked for too
+        assert req.read_requests(out_dir(tmp_path, "tok")) == {10, 13}
+        assert not mode.active and not window.sidebar.friend_mode
+        assert window.shown_mine == 1
+
+    def test_cancel_discards(self, visit, tmp_path):
+        mode, _, service = visit
+        mode.toggle([13])
+        mode.cancel()
+        assert service.state().friends["tok"].cassetted == []
+        assert not (out_dir(tmp_path, "tok") / req.REQUESTS_FILE).exists()
+
+    def test_leaving_with_changes_asks(self, visit, monkeypatch):
+        from lintunes.gui import friend_mode
+        mode, _, service = visit
+        mode.toggle([11])
+        monkeypatch.setattr(friend_mode, "ask_save_changes", lambda parent: friend_mode.STAY)
+        assert not mode.confirm_leave() and mode.active
+        monkeypatch.setattr(friend_mode, "ask_save_changes", lambda parent: friend_mode.DISCARD)
+        assert mode.confirm_leave() and not mode.active
+        assert service.state().friends["tok"].cassetted == []
+
+    def test_leaving_clean_never_asks(self, visit, monkeypatch):
+        from lintunes.gui import friend_mode
+        mode, _, _ = visit
+        monkeypatch.setattr(friend_mode, "ask_save_changes",
+                            lambda parent: pytest.fail("asked"))
+        assert mode.confirm_leave()
+
+    def test_hide_tracks_i_have(self, visit):
+        mode, _, _ = visit
+        mode.hide_have.setChecked(True)
+        shown = {t.track_id for t in mode._view.table.model_.tracks}
+        assert 10 not in shown           # exact: hidden
+        assert {11, 12, 13} <= shown     # fuzzy stays (grey)
+        grey = mode._foreground(mode.library.tracks[12])
+        assert grey is not None
+
+    def test_their_playlist_in_order(self, visit):
+        mode, window, _ = visit
+        mode._show_playlist("P")
+        assert window.content_stack.currentWidget() is mode._pane
+        assert [t.track_id for t in mode._pane.table.model_.tracks] == [13, 10]
+        assert mode._pane.table.read_only
+
+    def test_space_turns_red(self, visit, monkeypatch):
+        mode, _, _ = visit
+        from collections import namedtuple
+        usage = namedtuple("usage", "total used free")
+        monkeypatch.setattr(space, "disk_usage",
+                            lambda path: usage(100_000_000, 99_000_000, 1_000_000))
+        mode.toggle([10, 11])
+        assert mode.space_state()[0] == space.FULL
+        assert "#d0342c" in mode.size_label.styleSheet()
+
+
+class TestSelector:
+    def test_hidden_until_there_is_a_friend(self, qapp):
+        from unittest.mock import MagicMock
+        from lintunes.gui.sidebar import SidebarPanel
+        manager = MagicMock()
+        manager.library.playlists = {}
+        sidebar = SidebarPanel(manager, MagicMock())
+        assert sidebar.friend_button.isHidden()
+        sidebar.set_friend_selector_visible(True)
+        assert not sidebar.friend_button.isHidden()
+        assert "border-top-right-radius: 0" in sidebar.library_button.styleSheet()