feat: select several playlist songs to remove, save or reorder them and drag songs into place

web/src/features/playlists/my-playlist-page.tsx

@@ -1,22 +1,32 @@
-import type { MyPlaylistItem, Track } from '@/core/realtime'
-import type { SongItem } from '@/shared/ui'
+import type { MovePlan } from './track-order'
+import type { MyPlaylist, MyPlaylistItem, Track } from '@/core/realtime'
+import type { SongAction } from '@/shared/ui'
 import { ArrowLeft, CirclePlus, ListMusic, ListPlus, Trash2 } from 'lucide-react'
 import { useEffect, useState } from 'react'
 import { api } from '@/core/api'
 import { errorMessage } from '@/core/errors'
-import { roomStore, sameTrack } from '@/core/room'
-import { enqueue, sourceName } from '@/features/queue'
+import { roomStore } from '@/core/room'
+import { enqueue } from '@/features/queue'
 import { bookTitle } from '@/shared/lib/book-title'
 import { useStore } from '@/shared/lib/use-store'
-import { EmptyState, Skeleton, SongList } from '@/shared/ui'
+import { EmptyState, Modal, Skeleton } from '@/shared/ui'
 import { FavoritesMark, PlaylistCover } from './playlist-cover'
 import { formatPlaylistDate } from './playlist-date'
 import { PlaylistMenu } from './playlist-menu'
+import { PlaylistTracks } from './playlist-tracks'
 import { playlistsStore, trackKey } from './playlists-store'
 import { saveToPlaylistLabel } from './save-label'
 import { SaveToPlaylistDialog } from './save-to-playlist'
+import { SelectionBar } from './selection-bar'
+import { TrackEdits } from './track-edits'
+import { dropAt } from './track-order'
+import { noSelection, retain, selectAll } from './track-selection'
 import './playlists.css'
 
+function keysOf(items: readonly MyPlaylistItem[]): string[] {
+  return items.map(item => trackKey(item.track))
+}
+
 export function MyPlaylistPage({ id, onBack }: { id: string, onBack: () => void }) {
   const playlist = useStore(playlistsStore, s => s.playlists?.find(p => p.id === id) ?? null)
   const listed = useStore(playlistsStore, s => s.playlists !== null)
@@ -26,34 +36,83 @@ export function MyPlaylistPage({ id, onBack }: { id: string, onBack: () => void
   const [items, setItems] = useState<MyPlaylistItem[] | null>(null)
   const [failed, setFailed] = useState<string | null>(null)
   const [attempt, setAttempt] = useState(0)
+  const [selection, setSelection] = useState(noSelection)
+  // 点了“选择”：没有选中项时也显示勾选框。有选中项时总是处于多选模式。
+  const [picking, setPicking] = useState(false)
   const [saving, setSaving] = useState<{ track: Track, title: string } | null>(null)
+  const [savingSelected, setSavingSelected] = useState(false)
+  const [confirmingRemoval, setConfirmingRemoval] = useState(false)
+  const [edits] = useState(() => new TrackEdits(() => setAttempt(n => n + 1)))
   // 歌单的更新时间变了就重新读取：加入、移出、移动和复制都会推进它，歌曲数不变时顺序也可能变了。
   useEffect(() => {
     let active = true
+    const usable = edits.read()
     api.listMyPlaylistItems(id).then(({ items }) => {
-      if (!active)
+      if (!active || !usable())
         return
       setItems(items)
       setFailed(null)
+      setSelection(selection => retain(selection, keysOf(items)))
     }, (error: unknown) => {
-      if (active)
+      if (active && usable())
         setFailed(errorMessage(error))
     })
     return () => {
       active = false
     }
-  }, [id, attempt, playlist?.updatedAtMs])
+  }, [id, attempt, playlist?.updatedAtMs, edits])
   useEffect(() => {
     const refresh = () => setAttempt(n => n + 1)
     window.addEventListener('focus', refresh)
     return () => window.removeEventListener('focus', refresh)
   }, [])
+  const selecting = picking || selection.keys.size > 0
+  // 对话框和菜单自己处理 Esc。
+  useEffect(() => {
+    if (!selecting)
+      return
+    const onKeyDown = (event: KeyboardEvent) => {
+      if (event.key !== 'Escape' || event.defaultPrevented || (event.target instanceof Element && event.target.closest('dialog, [popover]')))
+        return
+      setSelection(noSelection)
+      setPicking(false)
+    }
+    document.addEventListener('keydown', onKeyDown)
+    return () => document.removeEventListener('keydown', onKeyDown)
+  }, [selecting])
   const [now] = useState(Date.now)
   const name = playlist?.name ?? '歌单'
   // 读到了自己的歌单，里面却没有它：在别处删掉了，或者换了账号。
   const gone = listed && !playlist
   // 读不到时不再显示之前的曲目：它们可能已经不在了，也可能属于之前的账号。
   const shown = gone || failed ? null : items
+
+  const exitSelection = () => {
+    setSelection(noSelection)
+    setPicking(false)
+  }
+
+  const move = (target: MyPlaylist, current: MyPlaylistItem[], plan: MovePlan<string>) => {
+    const byKey = new Map(current.map(item => [trackKey(item.track), item]))
+    const trackOf = (key: string) => byKey.get(key)!.track
+    const tracks = plan.moved.map(trackOf)
+    const before = plan.before === undefined ? undefined : trackOf(plan.before)
+    setItems(plan.order.map(key => byKey.get(key)!))
+    void edits.run(() => playlistsStore.moveItems(target, tracks, before), () => setItems(current))
+  }
+
+  const remove = async (target: MyPlaylist, current: MyPlaylistItem[], tracks: Track[]) => {
+    const gone = new Set(tracks.map(trackKey))
+    const rest = current.filter(item => !gone.has(trackKey(item.track)))
+    const previousSelection = selection
+    setItems(rest)
+    setSelection(retain(selection, keysOf(rest)))
+    await edits.run(() => playlistsStore.removeItems(target, tracks), () => {
+      setItems(current)
+      setSelection(previousSelection)
+    })
+  }
+
   let body
   if (gone) {
     body = (
@@ -95,57 +154,53 @@ export function MyPlaylistPage({ id, onBack }: { id: string, onBack: () => void
     )
   }
   else {
+    const actions = ({ track, meta }: MyPlaylistItem): SongAction[] => {
+      const blocked = track.source === 'link' && ephemeral
+      return [
+        {
+          icon: CirclePlus,
+          label: blocked ? '临时房间不能点链接里的歌' : `点歌${bookTitle(meta.title)}`,
+          disabled: !connected || blocked,
+          run: async () => {
+            await enqueue(track)
+          },
+        },
+        {
+          icon: ListPlus,
+          label: saveToPlaylistLabel(meta.title),
+          secondary: true,
+          run: async () => setSaving({ track, title: meta.title }),
+        },
+        {
+          icon: Trash2,
+          label: `把${bookTitle(meta.title)}移出这个歌单`,
+          disabled: !playlist,
+          secondary: true,
+          run: async () => {
+            if (playlist)
+              await remove(playlist, items, [track])
+          },
+        },
+      ]
+    }
     body = (
-      <SongList
-        songs={items.map(({ track, meta }): SongItem => ({
-          key: trackKey(track),
-          title: meta.title,
-          artist: meta.artist || '未知艺术家',
-          album: meta.album,
-          coverUrl: meta.coverUrl,
-          durationMs: meta.durationMs,
-          sourceUrl: meta.pageUrl,
-          sourceName: sourceName(track),
-          playing: sameTrack(track, playing),
-        }))}
-        actions={(song, index) => {
-          const { track } = items[index]
-          const blocked = track.source === 'link' && ephemeral
-          return [
-            {
-              icon: CirclePlus,
-              label: blocked ? '临时房间不能点链接里的歌' : `点歌${bookTitle(song.title)}`,
-              disabled: !connected || blocked,
-              run: async () => {
-                await enqueue(track)
-              },
-            },
-            {
-              icon: ListPlus,
-              label: saveToPlaylistLabel(song.title),
-              secondary: true,
-              run: async () => setSaving({ track, title: song.title }),
-            },
-            {
-              icon: Trash2,
-              label: `把${bookTitle(song.title)}移出这个歌单`,
-              disabled: !playlist,
-              secondary: true,
-              run: async () => {
-                if (!playlist)
-                  return
-                // 失败时歌单可能已经在别处变了，重新读取。
-                if (await playlistsStore.removeItems(playlist, [track]))
-                  setItems(list => list?.filter(item => !sameTrack(item.track, track)) ?? list)
-                else
-                  setAttempt(n => n + 1)
-              },
-            },
-          ]
+      <PlaylistTracks
+        items={items}
+        playing={playing}
+        selection={selection}
+        selecting={selecting}
+        actions={actions}
+        onSelect={setSelection}
+        onMove={(plan) => {
+          if (playlist)
+            move(playlist, items, plan)
         }}
       />
     )
   }
+
+  const keys = items ? keysOf(items) : []
+  const selected = items?.filter(item => selection.keys.has(trackKey(item.track))).map(item => item.track) ?? []
   return (
     <section className="page-content my-playlist-page" aria-labelledby="my-playlist-title">
       <button type="button" className="button-ghost my-playlist-back text-ui-sm" aria-label="返回我的歌单" onClick={onBack}>
@@ -164,12 +219,65 @@ export function MyPlaylistPage({ id, onBack }: { id: string, onBack: () => void
               {`${playlist.trackCount} 首，更新于${formatPlaylistDate(playlist.updatedAtMs, now)}，创建于${formatPlaylistDate(playlist.createdAtMs, now)}`}
             </p>
           )}
-          {playlist && !playlist.favorites && <PlaylistMenu playlist={playlist} align="start" className="my-playlist-menu" onDeleted={onBack} />}
+          <div className="my-playlist-actions">
+            {shown && shown.length > 0 && (
+              <button type="button" className="button-secondary my-playlist-select" onClick={() => selecting ? exitSelection() : setPicking(true)}>
+                {selecting ? '完成' : '选择'}
+              </button>
+            )}
+            {playlist && !playlist.favorites && <PlaylistMenu playlist={playlist} align="start" className="my-playlist-menu" onDeleted={onBack} />}
+          </div>
         </div>
       </header>
       {body}
+      {/* 选中数的播报常驻在页面上：选择栏要等选中第一首才出现，跟着它出现的播报区域读屏软件不会播报。 */}
+      <p className="sr-only" role="status">{shown && selected.length > 0 ? `已选 ${selected.length} 首` : ''}</p>
       {!connected && shown?.length ? <p className="text-ui-caption muted my-playlist-hint">进入房间之后才能点歌。</p> : null}
+      {playlist && shown && selected.length > 0 && (
+        <SelectionBar
+          count={selected.length}
+          allSelected={selected.length === shown.length}
+          onSave={() => setSavingSelected(true)}
+          onTop={() => {
+            const plan = dropAt(keys, selection.keys, 0)
+            if (plan)
+              move(playlist, shown, plan)
+          }}
+          onBottom={() => {
+            const plan = dropAt(keys, selection.keys, keys.length)
+            if (plan)
+              move(playlist, shown, plan)
+          }}
+          onRemove={() => {
+            if (selected.length > 1)
+              setConfirmingRemoval(true)
+            else
+              void remove(playlist, shown, selected)
+          }}
+          onToggleAll={() => setSelection(selected.length === shown.length ? noSelection : selectAll(keys))}
+          onClose={exitSelection}
+        />
+      )}
       {saving && <SaveToPlaylistDialog track={saving.track} title={saving.title} onClose={() => setSaving(null)} />}
+      {playlist && savingSelected && <SaveToPlaylistDialog from={playlist} tracks={selected} onClose={() => setSavingSelected(false)} />}
+      {playlist && shown && confirmingRemoval && (
+        <Modal title="移出歌曲" onClose={() => setConfirmingRemoval(false)}>
+          <p className="text-ui-base muted">{`把 ${selected.length} 首歌移出这个歌单？`}</p>
+          <div className="dialog-actions">
+            <button type="button" className="button-secondary" onClick={() => setConfirmingRemoval(false)}>取消</button>
+            <button
+              type="button"
+              className="button-destructive"
+              onClick={() => {
+                setConfirmingRemoval(false)
+                void remove(playlist, shown, selected)
+              }}
+            >
+              移出
+            </button>
+          </div>
+        </Modal>
+      )}
     </section>
   )
 }

web/src/features/playlists/playlist-tracks.tsx

@@ -0,0 +1,177 @@
+import type { KeyboardEvent, MouseEvent } from 'react'
+import type { MovePlan } from './track-order'
+import type { Selection } from './track-selection'
+import type { MyPlaylistItem, Track } from '@/core/realtime'
+import type { SongAction } from '@/shared/ui'
+import { GripVertical } from 'lucide-react'
+import { useLayoutEffect, useRef } from 'react'
+import { createPortal } from 'react-dom'
+import { sameTrack } from '@/core/room'
+import { sourceName } from '@/features/queue'
+import { bookTitle } from '@/shared/lib/book-title'
+import { formatDuration } from '@/shared/lib/time'
+import { AsyncIconButton, PlayingBars, SongArtwork } from '@/shared/ui'
+import { trackKey } from './playlists-store'
+import { moveByOne } from './track-order'
+import { selectAll, selectRange, toggle } from './track-selection'
+import { useTrackDrag } from './use-track-drag'
+
+function rowOf(list: HTMLElement | null, key: string): Element | null {
+  return list?.querySelector(`[data-key="${CSS.escape(key)}"]`) ?? null
+}
+
+// 多选时焦点落在勾选框上，读屏软件才读得出这一行是否选中；平时落在行上。
+function focusRow(row: Element | null | undefined, selecting: boolean): void {
+  const target = selecting ? row?.querySelector('.playlist-track-check') : row
+  if (target instanceof HTMLElement)
+    target.focus()
+}
+
+export function PlaylistTracks({ items, playing, selection, selecting, actions, onSelect, onMove }: {
+  items: MyPlaylistItem[]
+  playing: Track | undefined
+  selection: Selection
+  selecting: boolean
+  actions: (item: MyPlaylistItem) => SongAction[]
+  onSelect: (selection: Selection) => void
+  onMove: (plan: MovePlan<string>) => void
+}) {
+  const listRef = useRef<HTMLOListElement>(null)
+  const lineRef = useRef<HTMLDivElement>(null)
+  const labelRef = useRef<HTMLDivElement>(null)
+  const focusAfterMoveRef = useRef<string | null>(null)
+  // 最后获得焦点的行。勾选框随多选出现和消失，焦点在它上面时会丢。
+  const focusedRef = useRef<string | null>(null)
+  const keys = items.map(item => trackKey(item.track))
+  const { dragging, onPointerDown } = useTrackDrag({
+    listRef,
+    lineRef,
+    labelRef,
+    keys,
+    selected: selection.keys,
+    onDrop: (plan) => {
+      if (plan)
+        onMove(plan)
+    },
+  })
+
+  // 重新排列时 React 可能把获得焦点的行移出再插回，焦点会丢。
+  useLayoutEffect(() => {
+    const key = focusAfterMoveRef.current
+    if (key === null)
+      return
+    focusAfterMoveRef.current = null
+    focusRow(rowOf(listRef.current, key), selecting)
+  }, [items, selecting])
+
+  // 进出多选时，焦点留在原来那一行，落到这一行在新模式下的位置。
+  useLayoutEffect(() => {
+    const key = focusedRef.current
+    const active = document.activeElement
+    if (key === null || (active !== null && active !== document.body && !active.matches('.playlist-track')))
+      return
+    focusRow(rowOf(listRef.current, key), selecting)
+  }, [selecting])
+
+  const onRowClick = (event: MouseEvent, key: string) => {
+    if ((event.target as Element).closest('button, a'))
+      return
+    if (event.shiftKey)
+      onSelect(selectRange(selection, keys, key))
+    else if (event.metaKey || event.ctrlKey || selecting)
+      onSelect(toggle(selection, key))
+  }
+
+  const onKeyDown = (event: KeyboardEvent<HTMLOListElement>) => {
+    if ((event.metaKey || event.ctrlKey) && !event.altKey && !event.shiftKey && event.key.toLowerCase() === 'a') {
+      event.preventDefault()
+      onSelect(selectAll(keys))
+      return
+    }
+    // 其余按键只在焦点落在行本身或它的勾选框上时处理，行里的按钮保持原来的行为。勾选框上的空格由浏览器切换。
+    const target = event.target as HTMLElement
+    const row = target.closest<HTMLElement>('[data-key]')
+    const key = row?.dataset.key
+    if (!row || key === undefined || (target !== row && !target.matches('.playlist-track-check')))
+      return
+    if (event.key === ' ' && selecting && target === row) {
+      event.preventDefault()
+      onSelect(toggle(selection, key))
+      return
+    }
+    if ((event.key !== 'ArrowUp' && event.key !== 'ArrowDown') || event.metaKey || event.ctrlKey || event.shiftKey)
+      return
+    event.preventDefault()
+    const delta = event.key === 'ArrowUp' ? -1 : 1
+    if (!event.altKey) {
+      focusRow(delta < 0 ? row.previousElementSibling : row.nextElementSibling, selecting)
+      return
+    }
+    const plan = moveByOne(keys, selection.keys.has(key) ? selection.keys : new Set([key]), delta)
+    if (!plan)
+      return
+    focusAfterMoveRef.current = key
+    onMove(plan)
+  }
+
+  let label = ''
+  if (dragging) {
+    const [first] = dragging
+    label = dragging.size > 1 ? `${dragging.size} 首` : items.find(item => trackKey(item.track) === first)?.meta.title ?? ''
+  }
+
+  return (
+    <div className="playlist-tracks" data-dragging={dragging ? true : undefined}>
+      <ol ref={listRef} className="song-list" onKeyDown={onKeyDown}>
+        {items.map((item, index) => {
+          const { track, meta } = item
+          const key = keys[index]
+          const selected = selection.keys.has(key)
+          const source = sourceName(track)
+          const isPlaying = sameTrack(track, playing)
+          return (
+            <li
+              key={key}
+              data-key={key}
+              className="song-row playlist-track"
+              tabIndex={selecting ? -1 : 0}
+              data-playing={isPlaying || undefined}
+              data-selected={selected || undefined}
+              data-dragging={dragging?.has(key) || undefined}
+              onClick={event => onRowClick(event, key)}
+              onFocus={() => {
+                focusedRef.current = key
+              }}
+              onPointerDown={event => onPointerDown(event, key)}
+              // 按住封面拖动时，浏览器会开始原生的图片拖拽并取消指针事件，排序的拖动随之中断。
+              onDragStart={event => event.preventDefault()}
+            >
+              {selecting
+                ? <input type="checkbox" className="playlist-track-check" checked={selected} readOnly aria-label={`选择${bookTitle(meta.title)}`} />
+                : <span className="song-index text-ui-sm muted">{String(index + 1).padStart(2, '0')}</span>}
+              {/* 多选时点封面也是切换选中，不打开音源页面。 */}
+              <SongArtwork coverUrl={meta.coverUrl} title={meta.title} href={selecting ? undefined : meta.pageUrl} sourceName={source} />
+              <div className="song-copy">
+                <span className="song-title">
+                  {isPlaying && <PlayingBars />}
+                  <strong className="text-ui-base truncate">{meta.title}</strong>
+                </span>
+                <span className="text-ui-sm muted truncate">{[meta.artist || '未知艺术家', source].filter(Boolean).join(' · ')}</span>
+              </div>
+              <span className="song-album text-ui-sm muted truncate">{meta.album}</span>
+              <span className="song-duration text-ui-sm muted">{meta.durationMs > 0 ? formatDuration(meta.durationMs) : ''}</span>
+              {actions(item).map(action => (
+                <AsyncIconButton key={action.label} icon={action.icon} className={action.secondary ? 'song-action song-action-secondary' : 'song-action'} label={action.label} disabled={action.disabled} onAction={action.run} />
+              ))}
+              <span className="playlist-track-handle" data-drag-handle aria-hidden="true">
+                <GripVertical size={18} strokeWidth={1.7} />
+              </span>
+            </li>
+          )
+        })}
+      </ol>
+      {dragging && <div ref={lineRef} className="playlist-drop-line" />}
+      {dragging && createPortal(<div ref={labelRef} className="playlist-drag-label text-ui-sm">{label}</div>, document.body)}
+    </div>
+  )
+}

web/src/features/playlists/playlists-store.test.ts

@@ -382,6 +382,30 @@ describe('playlistsStore', () => {
     expect(notificationStore.state.notifications.map(n => n.message)).toEqual([changed])
   })
 
+  // 详情页的用法：移动经过 TrackEdits 排队。CONFLICT 说明歌单在别处变了，排在后面的移动基于过时的顺序。
+  it('排队的移动遇到 CONFLICT：提示服务端的文案，回到这次移动之前，后面的不再发出，结束后重新读取', async () => {
+    const { playlistsStore } = await loaded()
+    const { notificationStore } = await import('@/shared/ui')
+    const { TrackEdits } = await import('./track-edits')
+    let rereads = 0
+    const edits = new TrackEdits(() => rereads++)
+    failMove = true
+    let shown = '第一次移动之后'
+    void edits.run(() => playlistsStore.moveItems(favorites, [rain], sunny), () => {
+      shown = '移动之前'
+    })
+    shown = '第二次移动之后'
+    const done = edits.run(() => playlistsStore.moveItems(favorites, [sunny]), () => {
+      shown = '第一次移动之后'
+    })
+    await settle()
+    await done
+    expect(writes()).toEqual(['POST /api/me/playlists/p1/moves'])
+    expect(shown).toBe('移动之前')
+    expect(rereads).toBe(1)
+    expect(notificationStore.state.notifications.map(n => n.message)).toEqual([changed])
+  })
+
   it('游客不读取歌单', async () => {
     const { playlistsStore } = await import('./playlists-store')
     playlistsStore.start()

web/src/features/playlists/playlists.css

@@ -107,9 +107,39 @@
 .my-playlist-info { display: flex; flex-direction: column; align-items: flex-start; gap: 8px; min-width: 0; }
 .my-playlist-name { display: flex; align-items: center; gap: 10px; max-width: 100%; font-size: calc(var(--text-ui-xl) + 8px); font-weight: 700; line-height: 1.2; }
 .my-playlist-name > span { display: -webkit-box; overflow: hidden; -webkit-line-clamp: 2; -webkit-box-orient: vertical; overflow-wrap: anywhere; }
-.my-playlist-menu { margin-top: 4px; border: 1px solid var(--color-border); border-radius: 50%; }
+.my-playlist-actions { display: flex; align-items: center; gap: 8px; margin-top: 4px; }
+.my-playlist-select { min-width: 64px; border-radius: 999px; }
+.my-playlist-menu { border: 1px solid var(--color-border); border-radius: 50%; }
 .my-playlist-hint { margin-top: 12px; }
 
+.playlist-tracks { position: relative; }
+.playlist-track { user-select: none; -webkit-user-select: none; }
+.playlist-track:is(:focus-visible, :has(> .playlist-track-check:focus-visible)) { outline: 2px solid var(--color-brand); outline-offset: -2px; }
+.playlist-track[data-selected], .playlist-track[data-selected]:hover { background: var(--color-selected); }
+.playlist-track[data-dragging] { opacity: .4; }
+.playlist-track-check { margin: 0 3px; }
+.playlist-track-handle { display: grid; place-items: center; flex-shrink: 0; width: 24px; height: 36px; margin-left: -4px; color: var(--color-foreground-subtlest); cursor: grab; touch-action: none; -webkit-touch-callout: none; }
+.playlist-tracks[data-dragging], .playlist-tracks[data-dragging] .playlist-track-handle { cursor: grabbing; }
+.playlist-tracks[data-dragging] .playlist-track:not([data-selected]):hover { background: transparent; }
+@media (hover: hover) {
+  .playlist-track-handle { opacity: 0; transition: opacity 120ms ease; }
+  .playlist-tracks:not([data-dragging]) .playlist-track:is(:hover, :focus-visible, :has(> .playlist-track-check:focus-visible)) .playlist-track-handle { opacity: 1; }
+}
+.playlist-drop-line { position: absolute; top: 0; left: 8px; right: 8px; height: 2px; margin-top: -1px; border-radius: 1px; background: var(--color-brand); pointer-events: none; visibility: hidden; }
+.playlist-drag-label { position: fixed; top: 0; left: 0; z-index: 40; max-width: 240px; padding: 4px 10px; overflow: hidden; border: 1px solid var(--color-border); border-radius: 999px; background: var(--color-popover); color: var(--color-foreground); box-shadow: 0 8px 24px var(--color-shadow); text-overflow: ellipsis; white-space: nowrap; pointer-events: none; visibility: hidden; }
+
+.playlist-selection-bar { position: sticky; bottom: 16px; z-index: 5; display: flex; align-items: center; gap: 2px; width: fit-content; max-width: 100%; margin: 20px auto 0; padding: 6px 6px 6px 16px; border: 1px solid var(--color-border); border-radius: 12px; background: var(--color-popover); box-shadow: 0 12px 32px var(--color-shadow); animation: selection-bar-in 200ms cubic-bezier(.2, .8, .2, 1) both; }
+.playlist-selection-count { margin-right: 8px; font-variant-numeric: tabular-nums; white-space: nowrap; }
+.playlist-bar-button { display: inline-flex; align-items: center; gap: 6px; min-height: 36px; padding: 6px 10px; border: 0; border-radius: 8px; background: transparent; color: var(--color-foreground); white-space: nowrap; }
+.playlist-bar-button:hover { background: var(--color-hover); }
+.playlist-bar-button > svg { color: var(--color-foreground-subtle); }
+.playlist-bar-close { margin-left: 4px; color: var(--color-foreground-subtle); }
+:root[data-performance='low'] .playlist-selection-bar { animation-name: fade-in; }
+@keyframes selection-bar-in {
+  from { opacity: 0; transform: translateY(8px); }
+  to { opacity: 1; transform: none; }
+}
+
 @container playlists (max-width: 720px) {
   .playlist-table { --playlist-columns: minmax(0, 1fr) 36px; }
   .playlist-table-head, .playlist-col-trackCount, .playlist-col-updatedAt, .playlist-col-createdAt { display: none; }
@@ -120,6 +150,10 @@
   .playlists-controls { justify-content: space-between; }
   .playlist-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 20px 12px; }
 }
+@container my-playlist (max-width: 640px) {
+  .playlist-bar-button { justify-content: center; width: 36px; padding: 0; }
+  .playlist-bar-button > span { display: none; }
+}
 @container my-playlist (max-width: 560px) {
   .my-playlist-header { flex-direction: column; align-items: flex-start; gap: 16px; padding-bottom: 20px; }
   .playlist-cover-lg { width: 176px; }

web/src/features/playlists/save-to-playlist.tsx

@@ -4,7 +4,7 @@ import { ListPlus, Plus } from 'lucide-react'
 import { useEffect, useRef, useState } from 'react'
 import { profileStore } from '@/features/settings'
 import { useStore } from '@/shared/lib/use-store'
-import { IconButton, Modal, Skeleton } from '@/shared/ui'
+import { IconButton, Modal, notificationStore, Skeleton } from '@/shared/ui'
 import { openAccountSettings } from './account-settings'
 import { CreatePlaylistForm } from './create-playlist-form'
 import { FavoritesMark, PlaylistCover } from './playlist-cover'
@@ -23,15 +23,28 @@ function arrange(playlists: readonly MyPlaylist[], order: readonly string[]): My
   return sortPlaylists(playlists, byUpdate).sort((a, b) => at(a) - at(b))
 }
 
-export function SaveToPlaylistDialog({ track, title, onClose }: { track: Track, title: string, onClose: () => void }) {
+function savedMessage(saved: readonly MyPlaylist[], skipped: number): string {
+  const where = saved.length === 1 ? `“${saved[0].name}”` : ` ${saved.length} 个歌单`
+  return `已保存到${where}${skipped > 0 ? `，其中 ${skipped} 首已经在里面` : ''}`
+}
+
+// 一首歌：勾选立即生效。歌单里选中的多首：勾好目标歌单后一起保存，来源歌单不在列表里。
+type SaveToPlaylistProps = { onClose: () => void } & ({ track: Track, title: string } | { from: MyPlaylist, tracks: Track[] })
+
+export function SaveToPlaylistDialog(props: SaveToPlaylistProps) {
+  const { onClose } = props
+  const track = 'track' in props ? props.track : null
+  const from = 'from' in props ? props.from : null
   const account = useStore(profileStore, s => s.account)
   const playlists = useStore(playlistsStore, s => s.playlists)
   const failed = useStore(playlistsStore, s => s.failed)
-  const included = useStore(playlistsStore, s => s.memberships.get(trackKey(track))) ?? none
+  const included = useStore(playlistsStore, s => track ? s.memberships.get(trackKey(track)) : undefined) ?? none
+  const [picked, setPicked] = useState<ReadonlySet<string>>(none)
   const [order, setOrder] = useState<string[] | null>(null)
   const [readFailed, setReadFailed] = useState(false)
   const [attempt, setAttempt] = useState(0)
   const [creating, setCreating] = useState(false)
+  const [saving, setSaving] = useState(false)
   const listRef = useRef<HTMLUListElement>(null)
   // 从新建页回到列表时要获得焦点的元素：取消时是“新建歌单”，建好之后是新歌单的勾选框，聚焦的同时把它滚进视野。
   const returnFocusRef = useRef<string | null>(null)
@@ -40,7 +53,7 @@ export function SaveToPlaylistDialog({ track, title, onClose }: { track: Track,
     if (!account)
       return
     let active = true
-    void Promise.all([playlistsStore.load(), playlistsStore.containing(track)]).then(([, read]) => {
+    void Promise.all([playlistsStore.load(), track ? playlistsStore.containing(track) : true]).then(([, read]) => {
       if (!active)
         return
       setReadFailed(!read)
@@ -57,10 +70,21 @@ export function SaveToPlaylistDialog({ track, title, onClose }: { track: Track,
     returnFocusRef.current = null
   }, [creating])
 
-  const rows = playlists && order ? arrange(playlists, order) : null
+  const rows = playlists && order ? arrange(playlists, order).filter(p => p.id !== from?.id) : null
 
   const choose = (playlist: MyPlaylist, checked: boolean) => {
-    void playlistsStore.setMembership(playlist, track, checked)
+    if (track) {
+      void playlistsStore.setMembership(playlist, track, checked)
+      return
+    }
+    setPicked((current) => {
+      const next = new Set(current)
+      if (checked)
+        next.add(playlist.id)
+      else
+        next.delete(playlist.id)
+      return next
+    })
   }
 
   const backToList = (focus: string) => {
@@ -68,6 +92,16 @@ export function SaveToPlaylistDialog({ track, title, onClose }: { track: Track,
     setCreating(false)
   }
 
+  const save = async (source: MyPlaylist, tracks: Track[], targets: MyPlaylist[]) => {
+    setSaving(true)
+    const results = await Promise.all(targets.map(target => playlistsStore.copyItems(source, target, tracks)))
+    const saved = targets.filter((_, index) => results[index] !== null)
+    const skipped = results.reduce<number>((sum, added) => added === null ? sum : sum + tracks.length - added, 0)
+    if (saved.length > 0)
+      notificationStore.success(savedMessage(saved, skipped))
+    onClose()
+  }
+
   let body
   if (!account) {
     body = (
@@ -120,7 +154,7 @@ export function SaveToPlaylistDialog({ track, title, onClose }: { track: Track,
   else {
     body = (
       <>
-        <p className="save-playlist-subject text-ui-caption muted truncate">{title}</p>
+        <p className="save-playlist-subject text-ui-caption muted truncate">{'tracks' in props ? `已选 ${props.tracks.length} 首` : props.title}</p>
         <ul ref={listRef} className="save-playlist-list">
           {rows.map(playlist => (
             <li key={playlist.id}>
@@ -128,7 +162,8 @@ export function SaveToPlaylistDialog({ track, title, onClose }: { track: Track,
                 <input
                   type="checkbox"
                   value={playlist.id}
-                  checked={included.has(playlist.id)}
+                  checked={(track ? included : picked).has(playlist.id)}
+                  disabled={saving}
                   onChange={event => choose(playlist, event.target.checked)}
                 />
                 <PlaylistCover cover={playlist.coverUrl} favorites={playlist.favorites} size="sm" />
@@ -141,12 +176,24 @@ export function SaveToPlaylistDialog({ track, title, onClose }: { track: Track,
             </li>
           ))}
           <li>
-            <button type="button" className="save-playlist-row save-playlist-new" onClick={() => setCreating(true)}>
+            <button type="button" className="save-playlist-row save-playlist-new" disabled={saving} onClick={() => setCreating(true)}>
               <span className="save-playlist-new-tile"><Plus strokeWidth={1.7} aria-hidden="true" /></span>
               <span className="text-ui-base">新建歌单</span>
             </button>
           </li>
         </ul>
+        {'tracks' in props && (
+          <div className="dialog-actions">
+            <button
+              type="button"
+              className="button-primary"
+              disabled={saving || picked.size === 0}
+              onClick={() => void save(props.from, props.tracks, rows.filter(p => picked.has(p.id)))}
+            >
+              保存
+            </button>
+          </div>
+        )}
       </>
     )
   }

web/src/features/playlists/selection-bar.tsx

@@ -0,0 +1,36 @@
+import type { LucideIcon } from 'lucide-react'
+import { ArrowDownToLine, ArrowUpToLine, ListChecks, ListPlus, ListX, Trash2, X } from 'lucide-react'
+import { IconButton } from '@/shared/ui'
+
+// 窄屏只显示图标，按钮的名称要包含显示的文字。
+function BarButton({ icon: Icon, text, label, onClick }: { icon: LucideIcon, text: string, label: string, onClick: () => void }) {
+  return (
+    <button type="button" className="playlist-bar-button" aria-label={label} onClick={onClick}>
+      <Icon size={18} strokeWidth={1.7} aria-hidden="true" />
+      <span>{text}</span>
+    </button>
+  )
+}
+
+export function SelectionBar({ count, allSelected, onSave, onTop, onBottom, onRemove, onToggleAll, onClose }: {
+  count: number
+  allSelected: boolean
+  onSave: () => void
+  onTop: () => void
+  onBottom: () => void
+  onRemove: () => void
+  onToggleAll: () => void
+  onClose: () => void
+}) {
+  return (
+    <div className="playlist-selection-bar" role="toolbar" aria-label="选中的歌">
+      <span className="playlist-selection-count text-ui-sm">{`已选 ${count} 首`}</span>
+      <BarButton icon={ListPlus} text="保存到歌单" label="把选中的歌保存到歌单" onClick={onSave} />
+      <BarButton icon={ArrowUpToLine} text="移到最前" label="把选中的歌移到最前" onClick={onTop} />
+      <BarButton icon={ArrowDownToLine} text="移到最后" label="把选中的歌移到最后" onClick={onBottom} />
+      <BarButton icon={Trash2} text="移出" label="把选中的歌移出这个歌单" onClick={onRemove} />
+      <BarButton icon={allSelected ? ListX : ListChecks} text={allSelected ? '取消全选' : '全选'} label={allSelected ? '取消全选' : '全选'} onClick={onToggleAll} />
+      <IconButton icon={X} className="playlist-bar-close" label="退出选择" onClick={onClose} />
+    </div>
+  )
+}

web/src/features/playlists/track-edits.test.ts

@@ -0,0 +1,125 @@
+import { describe, expect, it } from 'vitest'
+import { TrackEdits } from './track-edits'
+
+// 由测试决定每个请求何时完成、成功与否。
+function requests() {
+  const pending: ((ok: boolean) => void)[] = []
+  const sent: string[] = []
+  const request = (name: string) => () => {
+    sent.push(name)
+    return new Promise<boolean>(resolve => pending.push(resolve))
+  }
+  const settle = async (ok: boolean) => {
+    await flush()
+    pending.shift()!(ok)
+    await flush()
+  }
+  return { request, sent, settle }
+}
+
+function flush() {
+  return new Promise(resolve => setTimeout(resolve, 0))
+}
+
+function setup() {
+  let rereads = 0
+  const edits = new TrackEdits(() => rereads++)
+  return { edits, rereads: () => rereads }
+}
+
+describe('trackEdits', () => {
+  it('没有修改时读到的结果可以用', () => {
+    const { edits } = setup()
+    const usable = edits.read()
+    expect(usable()).toBe(true)
+  })
+
+  it('修改进行中返回的读取不能用', async () => {
+    const { edits } = setup()
+    const { request, settle } = requests()
+    void edits.run(request('移出'), () => {})
+    const usable = edits.read()
+    expect(usable()).toBe(false)
+    await settle(true)
+    expect(usable()).toBe(false)
+  })
+
+  it('读取开始之后发起的修改，即使在读取返回前已经完成，读到的也不能用', async () => {
+    const { edits } = setup()
+    const { request, settle } = requests()
+    const usable = edits.read()
+    void edits.run(request('移动'), () => {})
+    await settle(true)
+    expect(usable()).toBe(false)
+  })
+
+  it('最后一个修改完成之后重新读取一次', async () => {
+    const { edits, rereads } = setup()
+    const { request, settle } = requests()
+    void edits.run(request('移出'), () => {})
+    void edits.run(request('移动'), () => {})
+    await settle(true)
+    expect(rereads()).toBe(0)
+    await settle(true)
+    expect(rereads()).toBe(1)
+    expect(edits.read()()).toBe(true)
+  })
+
+  it('修改按发起的先后逐个请求，前一个完成之后才发下一个', async () => {
+    const { edits } = setup()
+    const { request, sent, settle } = requests()
+    void edits.run(request('移到最前'), () => {})
+    void edits.run(request('移到最后'), () => {})
+    await flush()
+    expect(sent).toEqual(['移到最前'])
+    await settle(true)
+    expect(sent).toEqual(['移到最前', '移到最后'])
+  })
+
+  it('一次失败之后，排在后面的不再发出，列表回到失败的那次之前，结束后重新读取一次', async () => {
+    const { edits, rereads } = setup()
+    const { request, sent, settle } = requests()
+    const rolledBack: string[] = []
+    let shown = '第一次移动之后'
+    void edits.run(request('第一次移动'), () => {
+      rolledBack.push('第一次移动')
+      shown = '移动之前'
+    })
+    shown = '第二次移动之后'
+    const done = edits.run(request('第二次移动'), () => {
+      rolledBack.push('第二次移动')
+      shown = '第一次移动之后'
+    })
+    await settle(false)
+    await done
+    expect(sent).toEqual(['第一次移动'])
+    expect(rolledBack).toEqual(['第一次移动'])
+    expect(shown).toBe('移动之前')
+    expect(rereads()).toBe(1)
+  })
+
+  it('失败之后新发起的修改照常请求', async () => {
+    const { edits } = setup()
+    const { request, sent, settle } = requests()
+    void edits.run(request('移动'), () => {})
+    await settle(false)
+    void edits.run(request('移出'), () => {})
+    await flush()
+    expect(sent).toEqual(['移动', '移出'])
+  })
+
+  it('移出失败时回到移出之前，全部完成之后重新读取', async () => {
+    const { edits, rereads } = setup()
+    const { request, settle } = requests()
+    let items = ['晴天', '七里香']
+    const before = items
+    items = ['七里香']
+    const done = edits.run(request('移出'), () => {
+      items = before
+    })
+    await settle(false)
+    await done
+    expect(items).toEqual(['晴天', '七里香'])
+    expect(rereads()).toBe(1)
+  })
+})

web/src/features/playlists/track-edits.ts

@@ -0,0 +1,39 @@
+// 详情页对曲目的修改（移动、移出）先在本地改好再请求。请求按发起的先后逐个发出，每次都基于上一次修改之后的顺序；
+// 一次失败之后，排在它后面的不再发出，由失败的那次回到它之前的样子。
+// 修改进行中读到的列表可能是修改之前的，不能用；最后一个修改结束之后再读一次，以服务端为准。
+export class TrackEdits {
+  readonly #reread: () => void
+  #tail: Promise<void> = Promise.resolve()
+  #generation = 0
+  #pending = 0
+  #started = 0
+
+  constructor(reread: () => void) {
+    this.#reread = reread
+  }
+
+  // request 失败时返回 false，不抛出。
+  run(request: () => Promise<boolean>, rollback: () => void): Promise<void> {
+    const generation = this.#generation
+    this.#pending++
+    this.#started++
+    const done = this.#tail.then(async () => {
+      if (this.#generation !== generation || await request())
+        return
+      this.#generation++
+      rollback()
+    }).finally(() => {
+      if (--this.#pending === 0)
+        this.#reread()
+    })
+    this.#tail = done
+    return done
+  }
+
+  // 读取开始时调用，返回的函数在读取返回时判断读到的列表能不能用。
+  read(): () => boolean {
+    const idle = this.#pending === 0
+    const started = this.#started
+    return () => idle && this.#started === started
+  }
+}

web/src/features/playlists/track-order.test.ts

@@ -0,0 +1,97 @@
+import { describe, expect, it } from 'vitest'
+import { dropAt, moveByOne, moveTracks } from './track-order'
+
+const order = ['a', 'b', 'c', 'd', 'e']
+
+// 与 internal/domain/playlist/order_test.go 的 TestMove 逐条对应。
+describe('moveTracks', () => {
+  const cases: { name: string, moved: string[], before?: string, want?: string[], error?: string }[] = [
+    { name: '移到最前', moved: ['d'], before: 'a', want: ['d', 'a', 'b', 'c', 'e'] },
+    { name: '移到最后', moved: ['b'], want: ['a', 'c', 'd', 'e', 'b'] },
+    { name: '移到中间', moved: ['a'], before: 'd', want: ['b', 'c', 'a', 'd', 'e'] },
+    { name: '多首保持给定先后', moved: ['e', 'b'], before: 'd', want: ['a', 'c', 'e', 'b', 'd'] },
+    { name: '多首移到最后保持给定先后', moved: ['c', 'a'], want: ['b', 'd', 'e', 'c', 'a'] },
+    { name: '忽略不存在的歌', moved: ['x', 'c', 'y'], before: 'a', want: ['c', 'a', 'b', 'd', 'e'] },
+    { name: '重复的歌只算一次', moved: ['c', 'c', 'b'], want: ['a', 'd', 'e', 'c', 'b'] },
+    { name: 'before 紧跟在移动的歌之后', moved: ['b'], before: 'c', want: order },
+    { name: 'before 是被移动的歌', moved: ['b', 'c'], before: 'c', error: 'before 不能是要移动的歌' },
+    { name: 'before 是不存在的被移动的歌', moved: ['x'], before: 'x', error: 'before 不能是要移动的歌' },
+    { name: 'before 不存在', moved: ['b'], before: 'x', error: '歌单已经变了，刷新之后再试' },
+    { name: '空移动', moved: [], before: 'c', want: order },
+    { name: '移动的歌都不存在', moved: ['x'], before: 'y', want: order },
+  ]
+  for (const { name, moved, before, want, error } of cases) {
+    it(name, () => {
+      const copy = [...order]
+      if (error)
+        expect(() => moveTracks(copy, moved, before)).toThrow(error)
+      else
+        expect(moveTracks(copy, moved, before)).toEqual(want)
+      expect(copy).toEqual(order)
+    })
+  }
+})
+
+describe('dropAt', () => {
+  it('插入位置之后第一首不移动的歌作为 before', () => {
+    expect(dropAt(order, new Set(['d']), 1)).toEqual({ order: ['a', 'd', 'b', 'c', 'e'], moved: ['d'], before: 'b' })
+  })
+
+  it('插入位置紧跟着要移动的歌时，跳过它们找 before', () => {
+    expect(dropAt(order, new Set(['b', 'e']), 1)).toEqual({ order: ['a', 'b', 'e', 'c', 'd'], moved: ['b', 'e'], before: 'c' })
+  })
+
+  it('放到最后时不传 before', () => {
+    expect(dropAt(order, new Set(['a', 'c']), 5)).toEqual({ order: ['b', 'd', 'e', 'a', 'c'], moved: ['a', 'c'], before: undefined })
+  })
+
+  it('多首按当前顺序一起移动', () => {
+    expect(dropAt(order, new Set(['e', 'b']), 0)).toEqual({ order: ['b', 'e', 'a', 'c', 'd'], moved: ['b', 'e'], before: 'a' })
+  })
+
+  it('拖回原位置不必发请求', () => {
+    expect(dropAt(order, new Set(['c']), 2)).toBeNull()
+    expect(dropAt(order, new Set(['c']), 3)).toBeNull()
+    expect(dropAt(order, new Set(['b', 'c']), 2)).toBeNull()
+  })
+
+  it('全选时什么也不做', () => {
+    expect(dropAt(order, new Set(order), 0)).toBeNull()
+    expect(dropAt(order, new Set(order), 5)).toBeNull()
+  })
+})
+
+describe('moveByOne', () => {
+  it('上移和下移一首', () => {
+    expect(moveByOne(order, new Set(['c']), -1)).toEqual({ order: ['a', 'c', 'b', 'd', 'e'], moved: ['c'], before: 'b' })
+    expect(moveByOne(order, new Set(['c']), 1)).toEqual({ order: ['a', 'b', 'd', 'c', 'e'], moved: ['c'], before: 'e' })
+  })
+
+  it('下移到最后时不传 before', () => {
+    expect(moveByOne(order, new Set(['d']), 1)).toEqual({ order: ['a', 'b', 'c', 'e', 'd'], moved: ['d'], before: undefined })
+  })
+
+  it('相连的多首一起移动', () => {
+    expect(moveByOne(order, new Set(['b', 'c']), -1)).toEqual({ order: ['b', 'c', 'a', 'd', 'e'], moved: ['b', 'c'], before: 'a' })
+    expect(moveByOne(order, new Set(['b', 'c']), 1)).toEqual({ order: ['a', 'd', 'b', 'c', 'e'], moved: ['b', 'c'], before: 'e' })
+  })
+
+  it('不相连的多首先收拢', () => {
+    expect(moveByOne(order, new Set(['b', 'd']), -1)).toEqual({ order: ['b', 'd', 'a', 'c', 'e'], moved: ['b', 'd'], before: 'a' })
+    expect(moveByOne(order, new Set(['b', 'd']), 1)).toEqual({ order: ['a', 'c', 'e', 'b', 'd'], moved: ['b', 'd'], before: undefined })
+  })
+
+  it('已经在最前时上移只收拢', () => {
+    expect(moveByOne(order, new Set(['a', 'c']), -1)).toEqual({ order: ['a', 'c', 'b', 'd', 'e'], moved: ['a', 'c'], before: 'b' })
+  })
+
+  it('已经到头时不动', () => {
+    expect(moveByOne(order, new Set(['a', 'b']), -1)).toBeNull()
+    expect(moveByOne(order, new Set(['e']), 1)).toBeNull()
+    expect(moveByOne(order, new Set(order), 1)).toBeNull()
+  })
+
+  it('要移动的歌都不在列表里时不动', () => {
+    expect(moveByOne(order, new Set(['x']), -1)).toBeNull()
+  })
+})

web/src/features/playlists/track-order.ts

@@ -0,0 +1,50 @@
+// 与后端的 playlist.Move 一致：order 是显示顺序，把 moved 按给出的先后放到 before 之前，没有 before 时放到最后。
+// moved 里不在 order 中的忽略，重复的只算一次；都不在 order 中时原样返回，此时不检查 before 是否还在。
+export function moveTracks<T>(order: readonly T[], moved: readonly T[], before?: T): T[] {
+  if (before !== undefined && moved.includes(before))
+    throw new Error('before 不能是要移动的歌')
+  const present = new Set(order)
+  const block = [...new Set(moved)].filter(item => present.has(item))
+  if (block.length === 0)
+    return [...order]
+  const blocked = new Set(block)
+  const rest = order.filter(item => !blocked.has(item))
+  const at = before === undefined ? rest.length : rest.indexOf(before)
+  if (at < 0)
+    throw new Error('歌单已经变了，刷新之后再试')
+  return [...rest.slice(0, at), ...block, ...rest.slice(at)]
+}
+
+// 一次移动请求：把 moved 按 order 中的先后放到 before 之前，结果是 order。
+export interface MovePlan<T> {
+  order: T[]
+  moved: T[]
+  before: T | undefined
+}
+
+// 把 moved 收拢成一段，放在其余的歌中第 at 首之前；顺序不变时返回 null，不必发请求。
+function place<T>(order: readonly T[], moved: ReadonlySet<T>, at: number): MovePlan<T> | null {
+  const block = order.filter(item => moved.has(item))
+  const before = order.filter(item => !moved.has(item))[at]
+  const next = moveTracks(order, block, before)
+  if (next.every((item, index) => item === order[index]))
+    return null
+  return { order: next, moved: block, before }
+}
+
+// index 是插入位置，取 0 到 order.length，表示放在 order[index] 之前。before 取插入位置之后第一首不移动的歌。
+export function dropAt<T>(order: readonly T[], moved: ReadonlySet<T>, index: number): MovePlan<T> | null {
+  return place(order, moved, order.slice(0, index).filter(item => !moved.has(item)).length)
+}
+
+// 上移时整段放到第一首要移动的歌前面那首之前，下移时放到最后一首要移动的歌后面那首之后。
+// 不相连的歌会先收拢到一起，与拖动多首时一致，所以一次请求就能完成。
+export function moveByOne<T>(order: readonly T[], moved: ReadonlySet<T>, delta: -1 | 1): MovePlan<T> | null {
+  const indexes = order.flatMap((item, index) => moved.has(item) ? [index] : [])
+  if (indexes.length === 0)
+    return null
+  const edge = delta < 0 ? indexes[0] : indexes[indexes.length - 1]
+  const restBefore = edge - indexes.filter(index => index < edge).length
+  const restCount = order.length - indexes.length
+  return place(order, moved, Math.min(restCount, Math.max(0, restBefore + delta)))
+}

web/src/features/playlists/track-selection.test.ts

@@ -0,0 +1,58 @@
+import type { Selection } from './track-selection'
+import { describe, expect, it } from 'vitest'
+import { noSelection, retain, selectAll, selectRange, toggle } from './track-selection'
+
+const order = ['a', 'b', 'c', 'd', 'e']
+
+function keys(selection: Selection): string[] {
+  return [...selection.keys].sort()
+}
+
+describe('track-selection', () => {
+  it('单击和 ⌘ 点击逐首切换，并把这首作为锚点', () => {
+    const one = toggle(noSelection, 'b')
+    expect(keys(one)).toEqual(['b'])
+    expect(one.anchor).toBe('b')
+    const two = toggle(one, 'd')
+    expect(keys(two)).toEqual(['b', 'd'])
+    const back = toggle(two, 'b')
+    expect(keys(back)).toEqual(['d'])
+    expect(back.anchor).toBe('b')
+  })
+
+  it('shift 点击把锚点到这首的一段加入选择，锚点不变', () => {
+    const selection = selectRange(toggle(toggle(noSelection, 'e'), 'b'), order, 'd')
+    expect(keys(selection)).toEqual(['b', 'c', 'd', 'e'])
+    expect(selection.anchor).toBe('b')
+  })
+
+  it('shift 点击锚点之前的歌时向上选', () => {
+    expect(keys(selectRange(toggle(noSelection, 'd'), order, 'b'))).toEqual(['b', 'c', 'd'])
+  })
+
+  it('没有锚点时 shift 点击只切换这首', () => {
+    const selection = selectRange(noSelection, order, 'c')
+    expect(keys(selection)).toEqual(['c'])
+    expect(selection.anchor).toBe('c')
+  })
+
+  it('锚点已经不在列表里时 shift 点击只切换这首', () => {
+    expect(keys(selectRange(toggle(noSelection, 'x'), order, 'c'))).toEqual(['c', 'x'])
+  })
+
+  it('全选和清空', () => {
+    expect(keys(selectAll(order))).toEqual(order)
+    expect(keys(noSelection)).toEqual([])
+  })
+
+  it('列表变化后去掉不存在的歌和锚点', () => {
+    const selection = retain(toggle(toggle(noSelection, 'a'), 'c'), ['a', 'b'])
+    expect(keys(selection)).toEqual(['a'])
+    expect(selection.anchor).toBeNull()
+  })
+
+  it('列表变化不影响选择时返回原对象', () => {
+    const selection = toggle(noSelection, 'c')
+    expect(retain(selection, order)).toBe(selection)
+  })
+})

web/src/features/playlists/track-selection.ts

@@ -0,0 +1,38 @@
+export interface Selection {
+  keys: ReadonlySet<string>
+  // Shift 点击从这里选起：最后一次逐首切换的那首。
+  anchor: string | null
+}
+
+export const noSelection: Selection = { keys: new Set(), anchor: null }
+
+export function toggle(selection: Selection, key: string): Selection {
+  const keys = new Set(selection.keys)
+  if (!keys.delete(key))
+    keys.add(key)
+  return { keys, anchor: key }
+}
+
+// 把锚点到 key 的一段加入选择；没有锚点，或者锚点已经不在列表里时，只切换 key。
+export function selectRange(selection: Selection, order: readonly string[], key: string): Selection {
+  const from = selection.anchor === null ? -1 : order.indexOf(selection.anchor)
+  const to = order.indexOf(key)
+  if (from < 0 || to < 0)
+    return toggle(selection, key)
+  const range = order.slice(Math.min(from, to), Math.max(from, to) + 1)
+  return { keys: new Set([...selection.keys, ...range]), anchor: selection.anchor }
+}
+
+export function selectAll(order: readonly string[]): Selection {
+  return { keys: new Set(order), anchor: null }
+}
+
+// 列表重新读取之后去掉已经不在里面的歌；没有变化时返回原对象。
+export function retain(selection: Selection, order: readonly string[]): Selection {
+  const present = new Set(order)
+  const keys = [...selection.keys].filter(key => present.has(key))
+  const anchor = selection.anchor !== null && present.has(selection.anchor) ? selection.anchor : null
+  if (keys.length === selection.keys.size && anchor === selection.anchor)
+    return selection
+  return { keys: new Set(keys), anchor }
+}

web/src/features/playlists/use-track-drag.ts

@@ -0,0 +1,180 @@
+import type { PointerEvent as ReactPointerEvent, RefObject } from 'react'
+import type { MovePlan } from './track-order'
+import { useEffect, useLayoutEffect, useRef, useState } from 'react'
+import { dropAt } from './track-order'
+
+// 按下之后移动超过这个距离才算拖动，否则是点击。
+const dragThreshold = 4
+const scrollZone = 56
+const maxScrollStep = 18
+
+function scrollParent(element: HTMLElement): HTMLElement {
+  for (let node = element.parentElement; node; node = node.parentElement) {
+    const { overflowY } = getComputedStyle(node)
+    if (overflowY === 'auto' || overflowY === 'scroll')
+      return node
+  }
+  return document.documentElement
+}
+
+// 插入位置：指针在第几行的上半部分之上，取 0 到行数。
+function insertionIndex(rows: readonly HTMLElement[], y: number): number {
+  let low = 0
+  let high = rows.length
+  while (low < high) {
+    const middle = (low + high) >> 1
+    const rect = rows[middle].getBoundingClientRect()
+    if (y < rect.top + rect.height / 2)
+      high = middle
+    else
+      low = middle + 1
+  }
+  return low
+}
+
+// 拖动结束时，按下和松开的位置不在同一行，浏览器仍会派发 click：吞掉它，免得切换选中。
+function swallowNextClick(): void {
+  const swallow = (event: MouseEvent) => {
+    event.stopPropagation()
+    event.preventDefault()
+  }
+  window.addEventListener('click', swallow, { capture: true, once: true })
+  setTimeout(() => window.removeEventListener('click', swallow, { capture: true }), 0)
+}
+
+// 鼠标按住行的任意位置都能拖，触屏只能拖把手，行的其余部分留给滚动。
+// 插入线和指针旁的标签每一帧直接改样式，不经过 React，拖动时整张列表不会重新渲染。
+export function useTrackDrag({ listRef, lineRef, labelRef, keys, selected, onDrop }: {
+  listRef: RefObject<HTMLElement | null>
+  lineRef: RefObject<HTMLElement | null>
+  labelRef: RefObject<HTMLElement | null>
+  keys: readonly string[]
+  selected: ReadonlySet<string>
+  onDrop: (plan: MovePlan<string> | null) => void
+}) {
+  const [dragging, setDragging] = useState<ReadonlySet<string> | null>(null)
+  const latestRef = useRef({ keys, selected, onDrop })
+  useLayoutEffect(() => {
+    latestRef.current = { keys, selected, onDrop }
+  })
+  const stopRef = useRef<(() => void) | null>(null)
+  useEffect(() => () => stopRef.current?.(), [])
+
+  const onPointerDown = (event: ReactPointerEvent<HTMLElement>, key: string) => {
+    const target = event.target as Element
+    if (event.button !== 0 || stopRef.current || target.closest('button, a'))
+      return
+    if (event.pointerType !== 'mouse' && !target.closest('[data-drag-handle]'))
+      return
+    const list = listRef.current
+    if (!list)
+      return
+    const { pointerId } = event
+    const scroller = scrollParent(list)
+    const start = { x: event.clientX, y: event.clientY }
+    const pointer = { ...start }
+    let moved: ReadonlySet<string> | null = null
+    let frame = 0
+
+    const rows = () => [...list.querySelectorAll<HTMLElement>('[data-key]')]
+
+    const autoScroll = () => {
+      const rect = scroller === document.documentElement ? new DOMRect(0, 0, innerWidth, innerHeight) : scroller.getBoundingClientRect()
+      const top = Math.max(rect.top, 0)
+      const bottom = Math.min(rect.bottom, innerHeight)
+      const into = pointer.y < top + scrollZone ? pointer.y - top - scrollZone : pointer.y > bottom - scrollZone ? pointer.y - bottom + scrollZone : 0
+      if (into !== 0)
+        scroller.scrollTop += Math.max(-1, Math.min(1, into / scrollZone)) * maxScrollStep
+    }
+
+    const paint = () => {
+      autoScroll()
+      const all = rows()
+      const index = insertionIndex(all, pointer.y)
+      const line = lineRef.current
+      if (line && all.length > 0) {
+        const plan = moved && dropAt(latestRef.current.keys, moved, index)
+        const edge = index < all.length ? all[index].getBoundingClientRect().top : all[all.length - 1].getBoundingClientRect().bottom
+        line.style.transform = `translateY(${edge - list.getBoundingClientRect().top}px)`
+        line.style.visibility = plan ? 'visible' : 'hidden'
+      }
+      const label = labelRef.current
+      if (label) {
+        label.style.transform = `translate(${pointer.x + 14}px, ${pointer.y + 12}px)`
+        label.style.visibility = 'visible'
+      }
+      frame = requestAnimationFrame(paint)
+    }
+
+    function onMove(move: PointerEvent) {
+      if (move.pointerId !== pointerId)
+        return
+      pointer.x = move.clientX
+      pointer.y = move.clientY
+      if (moved || Math.hypot(pointer.x - start.x, pointer.y - start.y) <= dragThreshold)
+        return
+      const { selected } = latestRef.current
+      moved = selected.has(key) ? selected : new Set([key])
+      setDragging(moved)
+      window.addEventListener('keydown', onKey, true)
+      frame = requestAnimationFrame(paint)
+    }
+
+    function endVisuals() {
+      cancelAnimationFrame(frame)
+      window.removeEventListener('keydown', onKey, true)
+      setDragging(null)
+    }
+
+    function onUp(up: PointerEvent) {
+      if (up.pointerId !== pointerId)
+        return
+      const dropped = moved
+      stop()
+      if (!dropped)
+        return
+      swallowNextClick()
+      latestRef.current.onDrop(dropAt(latestRef.current.keys, dropped, insertionIndex(rows(), up.clientY)))
+    }
+
+    function onCancel(cancel: PointerEvent) {
+      if (cancel.pointerId === pointerId)
+        stop()
+    }
+
+    // 按 Esc 取消之后指针仍然按着，松开时的 click 同样要吞掉。
+    function onKey(keyboard: KeyboardEvent) {
+      if (keyboard.key !== 'Escape')
+        return
+      keyboard.preventDefault()
+      keyboard.stopPropagation()
+      endVisuals()
+      document.removeEventListener('pointermove', onMove)
+      document.removeEventListener('pointerup', onUp)
+      document.addEventListener('pointerup', onCancelledUp)
+    }
+
+    function onCancelledUp(up: PointerEvent) {
+      if (up.pointerId !== pointerId)
+        return
+      stop()
+      swallowNextClick()
+    }
+
+    function stop() {
+      endVisuals()
+      document.removeEventListener('pointermove', onMove)
+      document.removeEventListener('pointerup', onUp)
+      document.removeEventListener('pointerup', onCancelledUp)
+      document.removeEventListener('pointercancel', onCancel)
+      stopRef.current = null
+    }
+
+    document.addEventListener('pointermove', onMove)
+    document.addEventListener('pointerup', onUp)
+    document.addEventListener('pointercancel', onCancel)
+    stopRef.current = stop
+  }
+
+  return { dragging, onPointerDown }
+}