feat: store playlists with a fixed favorites list for every account

db/migrations/00004_playlists.sql

@@ -0,0 +1,35 @@
+-- +goose Up
+CREATE TABLE playlists (
+    id uuid PRIMARY KEY DEFAULT uuidv7(),
+    owner_id uuid NOT NULL REFERENCES members ON DELETE CASCADE,
+    -- 每个账号恰好一个“我喜欢”：注册时创建，不能改名或删除。
+    kind text NOT NULL CHECK (kind IN ('favorites', 'custom')),
+    name text NOT NULL,
+    -- 新加入的曲目取 item_seq + 1 作为排序值，排在最前。
+    item_seq bigint NOT NULL DEFAULT 0,
+    created_at timestamptz NOT NULL DEFAULT now(),
+    -- 歌单改名或曲目增减的时间。
+    updated_at timestamptz NOT NULL DEFAULT now()
+);
+
+CREATE INDEX ON playlists (owner_id);
+CREATE UNIQUE INDEX ON playlists (owner_id) WHERE kind = 'favorites';
+
+-- 展示用的元数据存一份快照：歌单里的歌不一定准备过，tracks 表里可能没有。
+CREATE TABLE playlist_items (
+    playlist_id uuid NOT NULL REFERENCES playlists ON DELETE CASCADE,
+    source text NOT NULL,
+    track_id text NOT NULL,
+    title text NOT NULL,
+    artist text,
+    album text,
+    cover_url text,
+    cover_key text,
+    duration_ms bigint NOT NULL,
+    page_url text NOT NULL,
+    position bigint NOT NULL,
+    added_at timestamptz NOT NULL DEFAULT now(),
+    PRIMARY KEY (playlist_id, source, track_id)
+);
+
+CREATE INDEX ON playlist_items (playlist_id, position DESC);

db/queries/playlists.sql

@@ -0,0 +1,64 @@
+-- name: CreateFavorites :exec
+INSERT INTO playlists (owner_id, kind, name) VALUES (@owner_id, 'favorites', '我喜欢');
+
+-- name: MemberPlaylists :many
+SELECT p.id, p.kind, p.name, p.created_at, p.updated_at, count(i.track_id)::bigint AS track_count
+FROM playlists p
+LEFT JOIN playlist_items i ON i.playlist_id = p.id
+WHERE p.owner_id = @owner_id
+GROUP BY p.id
+ORDER BY p.kind = 'favorites' DESC, p.created_at, p.id;
+
+-- name: MemberPlaylistCovers :many
+SELECT DISTINCT ON (i.playlist_id) i.playlist_id, i.cover_url, i.cover_key
+FROM playlist_items i
+JOIN playlists p ON p.id = i.playlist_id
+WHERE p.owner_id = @owner_id AND (i.cover_url IS NOT NULL OR i.cover_key IS NOT NULL)
+ORDER BY i.playlist_id, i.position DESC;
+
+-- name: LockFavorites :exec
+-- 新建歌单前锁住这个账号的“我喜欢”：同一个账号并发新建时依次计数，不会越过上限。
+SELECT id FROM playlists WHERE owner_id = @owner_id AND kind = 'favorites' FOR UPDATE;
+
+-- name: CountPlaylists :one
+SELECT count(*) FROM playlists WHERE owner_id = @owner_id;
+
+-- name: CreatePlaylist :one
+INSERT INTO playlists (owner_id, kind, name) VALUES (@owner_id, 'custom', @name)
+RETURNING id, created_at, updated_at;
+
+-- name: PlaylistKind :one
+SELECT kind FROM playlists WHERE id = @id AND owner_id = @owner_id;
+
+-- name: RenamePlaylist :execrows
+UPDATE playlists SET name = @name, updated_at = now() WHERE id = @id AND owner_id = @owner_id AND kind = 'custom';
+
+-- name: DeletePlaylist :execrows
+DELETE FROM playlists WHERE id = @id AND owner_id = @owner_id AND kind = 'custom';
+
+-- name: LockPlaylist :one
+-- 改动曲目前锁住歌单：并发加入时依次检查上限、分配排序值。删除歌单先锁歌单行再级联删除曲目，其他操作也要先锁歌单再动曲目，否则会互相死锁。
+SELECT item_seq FROM playlists WHERE id = @id AND owner_id = @owner_id FOR UPDATE;
+
+-- name: PlaylistHasItem :one
+SELECT EXISTS (SELECT FROM playlist_items WHERE playlist_id = @playlist_id AND source = @source AND track_id = @track_id);
+
+-- name: CountPlaylistItems :one
+SELECT count(*) FROM playlist_items WHERE playlist_id = @playlist_id;
+
+-- name: InsertPlaylistItem :exec
+INSERT INTO playlist_items (playlist_id, source, track_id, title, artist, album, cover_url, cover_key, duration_ms, page_url, position)
+VALUES (@playlist_id, @source, @track_id, @title, @artist, @album, @cover_url, @cover_key, @duration_ms, @page_url, @position);
+
+-- name: SetPlaylistSeq :exec
+UPDATE playlists SET item_seq = @item_seq, updated_at = now() WHERE id = @id;
+
+-- name: PlaylistItems :many
+SELECT * FROM playlist_items WHERE playlist_id = @playlist_id ORDER BY position DESC;
+
+-- name: DeletePlaylistItem :exec
+WITH deleted AS (
+    DELETE FROM playlist_items WHERE playlist_id = @playlist_id AND source = @source AND track_id = @track_id
+    RETURNING playlist_id
+)
+UPDATE playlists SET updated_at = now() WHERE id IN (SELECT playlist_id FROM deleted);

internal/adapter/out/postgres/internal/query/models.go

@@ -18,6 +18,21 @@ type Member struct {
 	Email        *string
 }
 
+type PlaylistItem struct {
+	PlaylistID string
+	Source     string
+	TrackID    string
+	Title      string
+	Artist     *string
+	Album      *string
+	CoverURL   *string
+	CoverKey   *string
+	DurationMs int64
+	PageURL    string
+	Position   int64
+	AddedAt    time.Time
+}
+
 type Room struct {
 	ID           string
 	Kind         string

internal/adapter/out/postgres/internal/query/playlists.sql.go

@@ -0,0 +1,345 @@
+// Code generated by sqlc. DO NOT EDIT.
+// versions:
+//   sqlc v1.31.1
+// source: playlists.sql
+
+package query
+
+import (
+	"context"
+	"time"
+)
+
+const countPlaylistItems = `-- name: CountPlaylistItems :one
+SELECT count(*) FROM playlist_items WHERE playlist_id = $1
+`
+
+func (q *Queries) CountPlaylistItems(ctx context.Context, playlistID string) (int64, error) {
+	row := q.db.QueryRow(ctx, countPlaylistItems, playlistID)
+	var count int64
+	err := row.Scan(&count)
+	return count, err
+}
+
+const countPlaylists = `-- name: CountPlaylists :one
+SELECT count(*) FROM playlists WHERE owner_id = $1
+`
+
+func (q *Queries) CountPlaylists(ctx context.Context, ownerID string) (int64, error) {
+	row := q.db.QueryRow(ctx, countPlaylists, ownerID)
+	var count int64
+	err := row.Scan(&count)
+	return count, err
+}
+
+const createFavorites = `-- name: CreateFavorites :exec
+INSERT INTO playlists (owner_id, kind, name) VALUES ($1, 'favorites', '我喜欢')
+`
+
+func (q *Queries) CreateFavorites(ctx context.Context, ownerID string) error {
+	_, err := q.db.Exec(ctx, createFavorites, ownerID)
+	return err
+}
+
+const createPlaylist = `-- name: CreatePlaylist :one
+INSERT INTO playlists (owner_id, kind, name) VALUES ($1, 'custom', $2)
+RETURNING id, created_at, updated_at
+`
+
+type CreatePlaylistParams struct {
+	OwnerID string
+	Name    string
+}
+
+type CreatePlaylistRow struct {
+	ID        string
+	CreatedAt time.Time
+	UpdatedAt time.Time
+}
+
+func (q *Queries) CreatePlaylist(ctx context.Context, arg CreatePlaylistParams) (CreatePlaylistRow, error) {
+	row := q.db.QueryRow(ctx, createPlaylist, arg.OwnerID, arg.Name)
+	var i CreatePlaylistRow
+	err := row.Scan(&i.ID, &i.CreatedAt, &i.UpdatedAt)
+	return i, err
+}
+
+const deletePlaylist = `-- name: DeletePlaylist :execrows
+DELETE FROM playlists WHERE id = $1 AND owner_id = $2 AND kind = 'custom'
+`
+
+type DeletePlaylistParams struct {
+	ID      string
+	OwnerID string
+}
+
+func (q *Queries) DeletePlaylist(ctx context.Context, arg DeletePlaylistParams) (int64, error) {
+	result, err := q.db.Exec(ctx, deletePlaylist, arg.ID, arg.OwnerID)
+	if err != nil {
+		return 0, err
+	}
+	return result.RowsAffected(), nil
+}
+
+const deletePlaylistItem = `-- name: DeletePlaylistItem :exec
+WITH deleted AS (
+    DELETE FROM playlist_items WHERE playlist_id = $1 AND source = $2 AND track_id = $3
+    RETURNING playlist_id
+)
+UPDATE playlists SET updated_at = now() WHERE id IN (SELECT playlist_id FROM deleted)
+`
+
+type DeletePlaylistItemParams struct {
+	PlaylistID string
+	Source     string
+	TrackID    string
+}
+
+func (q *Queries) DeletePlaylistItem(ctx context.Context, arg DeletePlaylistItemParams) error {
+	_, err := q.db.Exec(ctx, deletePlaylistItem, arg.PlaylistID, arg.Source, arg.TrackID)
+	return err
+}
+
+const insertPlaylistItem = `-- name: InsertPlaylistItem :exec
+INSERT INTO playlist_items (playlist_id, source, track_id, title, artist, album, cover_url, cover_key, duration_ms, page_url, position)
+VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11)
+`
+
+type InsertPlaylistItemParams struct {
+	PlaylistID string
+	Source     string
+	TrackID    string
+	Title      string
+	Artist     *string
+	Album      *string
+	CoverURL   *string
+	CoverKey   *string
+	DurationMs int64
+	PageURL    string
+	Position   int64
+}
+
+func (q *Queries) InsertPlaylistItem(ctx context.Context, arg InsertPlaylistItemParams) error {
+	_, err := q.db.Exec(ctx, insertPlaylistItem,
+		arg.PlaylistID,
+		arg.Source,
+		arg.TrackID,
+		arg.Title,
+		arg.Artist,
+		arg.Album,
+		arg.CoverURL,
+		arg.CoverKey,
+		arg.DurationMs,
+		arg.PageURL,
+		arg.Position,
+	)
+	return err
+}
+
+const lockFavorites = `-- name: LockFavorites :exec
+SELECT id FROM playlists WHERE owner_id = $1 AND kind = 'favorites' FOR UPDATE
+`
+
+// 新建歌单前锁住这个账号的“我喜欢”：同一个账号并发新建时依次计数，不会越过上限。
+func (q *Queries) LockFavorites(ctx context.Context, ownerID string) error {
+	_, err := q.db.Exec(ctx, lockFavorites, ownerID)
+	return err
+}
+
+const lockPlaylist = `-- name: LockPlaylist :one
+SELECT item_seq FROM playlists WHERE id = $1 AND owner_id = $2 FOR UPDATE
+`
+
+type LockPlaylistParams struct {
+	ID      string
+	OwnerID string
+}
+
+// 改动曲目前锁住歌单：并发加入时依次检查上限、分配排序值。删除歌单先锁歌单行再级联删除曲目，其他操作也要先锁歌单再动曲目，否则会互相死锁。
+func (q *Queries) LockPlaylist(ctx context.Context, arg LockPlaylistParams) (int64, error) {
+	row := q.db.QueryRow(ctx, lockPlaylist, arg.ID, arg.OwnerID)
+	var item_seq int64
+	err := row.Scan(&item_seq)
+	return item_seq, err
+}
+
+const memberPlaylistCovers = `-- name: MemberPlaylistCovers :many
+SELECT DISTINCT ON (i.playlist_id) i.playlist_id, i.cover_url, i.cover_key
+FROM playlist_items i
+JOIN playlists p ON p.id = i.playlist_id
+WHERE p.owner_id = $1 AND (i.cover_url IS NOT NULL OR i.cover_key IS NOT NULL)
+ORDER BY i.playlist_id, i.position DESC
+`
+
+type MemberPlaylistCoversRow struct {
+	PlaylistID string
+	CoverURL   *string
+	CoverKey   *string
+}
+
+func (q *Queries) MemberPlaylistCovers(ctx context.Context, ownerID string) ([]MemberPlaylistCoversRow, error) {
+	rows, err := q.db.Query(ctx, memberPlaylistCovers, ownerID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []MemberPlaylistCoversRow
+	for rows.Next() {
+		var i MemberPlaylistCoversRow
+		if err := rows.Scan(&i.PlaylistID, &i.CoverURL, &i.CoverKey); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const memberPlaylists = `-- name: MemberPlaylists :many
+SELECT p.id, p.kind, p.name, p.created_at, p.updated_at, count(i.track_id)::bigint AS track_count
+FROM playlists p
+LEFT JOIN playlist_items i ON i.playlist_id = p.id
+WHERE p.owner_id = $1
+GROUP BY p.id
+ORDER BY p.kind = 'favorites' DESC, p.created_at, p.id
+`
+
+type MemberPlaylistsRow struct {
+	ID         string
+	Kind       string
+	Name       string
+	CreatedAt  time.Time
+	UpdatedAt  time.Time
+	TrackCount int64
+}
+
+func (q *Queries) MemberPlaylists(ctx context.Context, ownerID string) ([]MemberPlaylistsRow, error) {
+	rows, err := q.db.Query(ctx, memberPlaylists, ownerID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []MemberPlaylistsRow
+	for rows.Next() {
+		var i MemberPlaylistsRow
+		if err := rows.Scan(
+			&i.ID,
+			&i.Kind,
+			&i.Name,
+			&i.CreatedAt,
+			&i.UpdatedAt,
+			&i.TrackCount,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const playlistHasItem = `-- name: PlaylistHasItem :one
+SELECT EXISTS (SELECT FROM playlist_items WHERE playlist_id = $1 AND source = $2 AND track_id = $3)
+`
+
+type PlaylistHasItemParams struct {
+	PlaylistID string
+	Source     string
+	TrackID    string
+}
+
+func (q *Queries) PlaylistHasItem(ctx context.Context, arg PlaylistHasItemParams) (bool, error) {
+	row := q.db.QueryRow(ctx, playlistHasItem, arg.PlaylistID, arg.Source, arg.TrackID)
+	var exists bool
+	err := row.Scan(&exists)
+	return exists, err
+}
+
+const playlistItems = `-- name: PlaylistItems :many
+SELECT playlist_id, source, track_id, title, artist, album, cover_url, cover_key, duration_ms, page_url, position, added_at FROM playlist_items WHERE playlist_id = $1 ORDER BY position DESC
+`
+
+func (q *Queries) PlaylistItems(ctx context.Context, playlistID string) ([]PlaylistItem, error) {
+	rows, err := q.db.Query(ctx, playlistItems, playlistID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var items []PlaylistItem
+	for rows.Next() {
+		var i PlaylistItem
+		if err := rows.Scan(
+			&i.PlaylistID,
+			&i.Source,
+			&i.TrackID,
+			&i.Title,
+			&i.Artist,
+			&i.Album,
+			&i.CoverURL,
+			&i.CoverKey,
+			&i.DurationMs,
+			&i.PageURL,
+			&i.Position,
+			&i.AddedAt,
+		); err != nil {
+			return nil, err
+		}
+		items = append(items, i)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, err
+	}
+	return items, nil
+}
+
+const playlistKind = `-- name: PlaylistKind :one
+SELECT kind FROM playlists WHERE id = $1 AND owner_id = $2
+`
+
+type PlaylistKindParams struct {
+	ID      string
+	OwnerID string
+}
+
+func (q *Queries) PlaylistKind(ctx context.Context, arg PlaylistKindParams) (string, error) {
+	row := q.db.QueryRow(ctx, playlistKind, arg.ID, arg.OwnerID)
+	var kind string
+	err := row.Scan(&kind)
+	return kind, err
+}
+
+const renamePlaylist = `-- name: RenamePlaylist :execrows
+UPDATE playlists SET name = $1, updated_at = now() WHERE id = $2 AND owner_id = $3 AND kind = 'custom'
+`
+
+type RenamePlaylistParams struct {
+	Name    string
+	ID      string
+	OwnerID string
+}
+
+func (q *Queries) RenamePlaylist(ctx context.Context, arg RenamePlaylistParams) (int64, error) {
+	result, err := q.db.Exec(ctx, renamePlaylist, arg.Name, arg.ID, arg.OwnerID)
+	if err != nil {
+		return 0, err
+	}
+	return result.RowsAffected(), nil
+}
+
+const setPlaylistSeq = `-- name: SetPlaylistSeq :exec
+UPDATE playlists SET item_seq = $1, updated_at = now() WHERE id = $2
+`
+
+type SetPlaylistSeqParams struct {
+	ItemSeq int64
+	ID      string
+}
+
+func (q *Queries) SetPlaylistSeq(ctx context.Context, arg SetPlaylistSeqParams) error {
+	_, err := q.db.Exec(ctx, setPlaylistSeq, arg.ItemSeq, arg.ID)
+	return err
+}

internal/adapter/out/postgres/members.go

@@ -70,12 +70,19 @@ func (s *Store) AccountProfile(ctx context.Context, memberID string) (port.Accou
 }
 
 func (s *Store) Register(ctx context.Context, memberID, username, passwordHash string) error {
-	n, err := s.q.RegisterMember(ctx, query.RegisterMemberParams{ID: memberID, Username: &username, PasswordHash: &passwordHash})
+	err := pgx.BeginFunc(ctx, s.pool, func(tx pgx.Tx) error {
+		q := s.q.WithTx(tx)
+		n, err := q.RegisterMember(ctx, query.RegisterMemberParams{ID: memberID, Username: &username, PasswordHash: &passwordHash})
+		if err != nil {
+			return usernameError(err)
+		}
+		if n == 0 {
+			return port.ErrAlreadyRegistered
+		}
+		return q.CreateFavorites(ctx, memberID)
+	})
 	if err != nil {
-		return fmt.Errorf("注册成员 %s：%w", memberID, usernameError(err))
-	}
-	if n == 0 {
-		return fmt.Errorf("注册成员 %s：%w", memberID, port.ErrAlreadyRegistered)
+		return fmt.Errorf("注册成员 %s：%w", memberID, err)
 	}
 	return nil
 }

internal/adapter/out/postgres/playlists.go

@@ -0,0 +1,216 @@
+package postgres
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/jackc/pgx/v5"
+
+	"github.com/dihemoe/alisten/internal/adapter/out/postgres/internal/query"
+	"github.com/dihemoe/alisten/internal/app/port"
+	"github.com/dihemoe/alisten/internal/domain/track"
+)
+
+var _ port.Playlists = (*Store)(nil)
+
+const favoritesKind = "favorites"
+
+func (s *Store) MemberPlaylists(ctx context.Context, ownerID string) ([]port.PlaylistRecord, error) {
+	rows, err := s.q.MemberPlaylists(ctx, ownerID)
+	if err != nil {
+		return nil, fmt.Errorf("读取成员 %s 的歌单：%w", ownerID, err)
+	}
+	coverRows, err := s.q.MemberPlaylistCovers(ctx, ownerID)
+	if err != nil {
+		return nil, fmt.Errorf("读取成员 %s 的歌单封面：%w", ownerID, err)
+	}
+	covers := make(map[string]*port.Cover, len(coverRows))
+	for _, c := range coverRows {
+		covers[c.PlaylistID] = &port.Cover{URL: orEmpty(c.CoverURL), Key: track.ObjectKey(orEmpty(c.CoverKey))}
+	}
+	lists := make([]port.PlaylistRecord, len(rows))
+	for i, r := range rows {
+		lists[i] = port.PlaylistRecord{
+			ID:         r.ID,
+			Name:       r.Name,
+			Favorites:  r.Kind == favoritesKind,
+			TrackCount: int(r.TrackCount),
+			CreatedAt:  r.CreatedAt,
+			UpdatedAt:  r.UpdatedAt,
+			Cover:      covers[r.ID],
+		}
+	}
+	return lists, nil
+}
+
+func (s *Store) CreatePlaylist(ctx context.Context, ownerID, name string, limit int) (port.PlaylistRecord, error) {
+	var created query.CreatePlaylistRow
+	err := pgx.BeginFunc(ctx, s.pool, func(tx pgx.Tx) error {
+		q := s.q.WithTx(tx)
+		if err := q.LockFavorites(ctx, ownerID); err != nil {
+			return err
+		}
+		n, err := q.CountPlaylists(ctx, ownerID)
+		if err != nil {
+			return err
+		}
+		if n >= int64(limit) {
+			return port.ErrPlaylistLimit
+		}
+		created, err = q.CreatePlaylist(ctx, query.CreatePlaylistParams{OwnerID: ownerID, Name: name})
+		return err
+	})
+	if err != nil {
+		return port.PlaylistRecord{}, fmt.Errorf("成员 %s 新建歌单：%w", ownerID, err)
+	}
+	return port.PlaylistRecord{ID: created.ID, Name: name, CreatedAt: created.CreatedAt, UpdatedAt: created.UpdatedAt}, nil
+}
+
+func (s *Store) RenamePlaylist(ctx context.Context, ownerID, id, name string) error {
+	if !isUUID(id) {
+		return port.ErrPlaylistNotFound
+	}
+	n, err := s.q.RenamePlaylist(ctx, query.RenamePlaylistParams{ID: id, OwnerID: ownerID, Name: name})
+	if err == nil && n == 0 {
+		err = s.unchangeable(ctx, ownerID, id)
+	}
+	if err != nil {
+		return fmt.Errorf("歌单 %s 改名：%w", id, err)
+	}
+	return nil
+}
+
+func (s *Store) DeletePlaylist(ctx context.Context, ownerID, id string) error {
+	if !isUUID(id) {
+		return port.ErrPlaylistNotFound
+	}
+	n, err := s.q.DeletePlaylist(ctx, query.DeletePlaylistParams{ID: id, OwnerID: ownerID})
+	if err == nil && n == 0 {
+		err = s.unchangeable(ctx, ownerID, id)
+	}
+	if err != nil {
+		return fmt.Errorf("删除歌单 %s：%w", id, err)
+	}
+	return nil
+}
+
+// 改名或删除没有影响任何行：要么是“我喜欢”，要么歌单不属于这个成员。
+func (s *Store) unchangeable(ctx context.Context, ownerID, id string) error {
+	kind, err := s.q.PlaylistKind(ctx, query.PlaylistKindParams{ID: id, OwnerID: ownerID})
+	switch {
+	case errors.Is(err, pgx.ErrNoRows):
+		return port.ErrPlaylistNotFound
+	case err != nil:
+		return err
+	case kind == favoritesKind:
+		return port.ErrFavoritesFixed
+	}
+	return port.ErrPlaylistNotFound
+}
+
+func (s *Store) owned(ctx context.Context, ownerID, id string) error {
+	if !isUUID(id) {
+		return port.ErrPlaylistNotFound
+	}
+	_, err := s.q.PlaylistKind(ctx, query.PlaylistKindParams{ID: id, OwnerID: ownerID})
+	if errors.Is(err, pgx.ErrNoRows) {
+		return port.ErrPlaylistNotFound
+	}
+	return err
+}
+
+func (s *Store) PlaylistItems(ctx context.Context, ownerID, id string) ([]port.PlaylistItem, error) {
+	if err := s.owned(ctx, ownerID, id); err != nil {
+		return nil, fmt.Errorf("读取歌单 %s：%w", id, err)
+	}
+	rows, err := s.q.PlaylistItems(ctx, id)
+	if err != nil {
+		return nil, fmt.Errorf("读取歌单 %s 的曲目：%w", id, err)
+	}
+	items := make([]port.PlaylistItem, len(rows))
+	for i, r := range rows {
+		items[i] = port.PlaylistItem{
+			Track: track.Track{Source: track.Source(r.Source), ID: r.TrackID},
+			Meta: track.Meta{
+				Title:    r.Title,
+				Artist:   orEmpty(r.Artist),
+				Album:    orEmpty(r.Album),
+				CoverURL: orEmpty(r.CoverURL),
+				CoverKey: track.ObjectKey(orEmpty(r.CoverKey)),
+				PageURL:  r.PageURL,
+				Duration: time.Duration(r.DurationMs) * time.Millisecond,
+			},
+		}
+	}
+	return items, nil
+}
+
+func (s *Store) AddPlaylistItem(ctx context.Context, ownerID, id string, item port.PlaylistItem, limit int) error {
+	if !isUUID(id) {
+		return port.ErrPlaylistNotFound
+	}
+	t, m := item.Track, item.Meta
+	err := pgx.BeginFunc(ctx, s.pool, func(tx pgx.Tx) error {
+		q := s.q.WithTx(tx)
+		seq, err := q.LockPlaylist(ctx, query.LockPlaylistParams{ID: id, OwnerID: ownerID})
+		if errors.Is(err, pgx.ErrNoRows) {
+			return port.ErrPlaylistNotFound
+		}
+		if err != nil {
+			return err
+		}
+		has, err := q.PlaylistHasItem(ctx, query.PlaylistHasItemParams{PlaylistID: id, Source: string(t.Source), TrackID: t.ID})
+		if err != nil || has {
+			return err
+		}
+		n, err := q.CountPlaylistItems(ctx, id)
+		if err != nil {
+			return err
+		}
+		if n >= int64(limit) {
+			return port.ErrPlaylistLimit
+		}
+		seq++
+		if err := q.InsertPlaylistItem(ctx, query.InsertPlaylistItemParams{
+			PlaylistID: id,
+			Source:     string(t.Source),
+			TrackID:    t.ID,
+			Title:      m.Title,
+			Artist:     nullable(m.Artist),
+			Album:      nullable(m.Album),
+			CoverURL:   nullable(m.CoverURL),
+			CoverKey:   nullable(string(m.CoverKey)),
+			DurationMs: m.Duration.Milliseconds(),
+			PageURL:    m.PageURL,
+			Position:   seq,
+		}); err != nil {
+			return err
+		}
+		return q.SetPlaylistSeq(ctx, query.SetPlaylistSeqParams{ID: id, ItemSeq: seq})
+	})
+	if err != nil {
+		return fmt.Errorf("向歌单 %s 加入 %s/%s：%w", id, t.Source, t.ID, err)
+	}
+	return nil
+}
+
+func (s *Store) RemovePlaylistItem(ctx context.Context, ownerID, id string, t track.Track) error {
+	if !isUUID(id) {
+		return port.ErrPlaylistNotFound
+	}
+	err := pgx.BeginFunc(ctx, s.pool, func(tx pgx.Tx) error {
+		q := s.q.WithTx(tx)
+		if _, err := q.LockPlaylist(ctx, query.LockPlaylistParams{ID: id, OwnerID: ownerID}); errors.Is(err, pgx.ErrNoRows) {
+			return port.ErrPlaylistNotFound
+		} else if err != nil {
+			return err
+		}
+		return q.DeletePlaylistItem(ctx, query.DeletePlaylistItemParams{PlaylistID: id, Source: string(t.Source), TrackID: t.ID})
+	})
+	if err != nil {
+		return fmt.Errorf("从歌单 %s 移除 %s/%s：%w", id, t.Source, t.ID, err)
+	}
+	return nil
+}

internal/adapter/out/postgres/playlists_test.go

@@ -0,0 +1,326 @@
+package postgres
+
+import (
+	"errors"
+	"slices"
+	"strconv"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/jackc/pgx/v5/pgconn"
+
+	"github.com/dihemoe/alisten/internal/app/port"
+	"github.com/dihemoe/alisten/internal/domain/member"
+	"github.com/dihemoe/alisten/internal/domain/track"
+)
+
+func registered(t *testing.T, store *Store, username string) member.Member {
+	t.Helper()
+	m := createMember(t, store, username, "游客-"+username)
+	if err := store.Register(t.Context(), m.ID, username, "hash"); err != nil {
+		t.Fatal(err)
+	}
+	return m
+}
+
+func favoritesOf(t *testing.T, store *Store, ownerID string) string {
+	t.Helper()
+	lists, err := store.MemberPlaylists(t.Context(), ownerID)
+	if err != nil || len(lists) == 0 || !lists[0].Favorites {
+		t.Fatalf("歌单 = %#v, %v，期望第一个是“我喜欢”", lists, err)
+	}
+	return lists[0].ID
+}
+
+var (
+	sunnyItem = port.PlaylistItem{Track: track.Track{Source: track.NetEase, ID: "186016"}, Meta: track.Meta{Title: "晴天", Artist: "周杰伦", Album: "叶惠美", CoverURL: "https://p1.music.126.net/a.jpg", PageURL: "https://music.163.com/#/song?id=186016", Duration: 269 * time.Second}}
+	clipItem  = port.PlaylistItem{Track: track.Track{Source: track.Link, ID: "https://example.com/a.mp3"}, Meta: track.Meta{Title: "a.mp3", CoverKey: "covers/abc", PageURL: "https://example.com/a.mp3", Duration: time.Minute}}
+)
+
+func TestRegisterCreatesFavorites(t *testing.T) {
+	store, _ := newStore(t)
+	alice := registered(t, store, "alice")
+	lists, err := store.MemberPlaylists(t.Context(), alice.ID)
+	if err != nil || len(lists) != 1 || !lists[0].Favorites || lists[0].Name != "我喜欢" || lists[0].TrackCount != 0 {
+		t.Fatalf("注册之后的歌单 = %#v, %v，期望只有一个空的“我喜欢”", lists, err)
+	}
+	guest := createMember(t, store, "guest", "游客-1a2b")
+	if lists, err := store.MemberPlaylists(t.Context(), guest.ID); err != nil || len(lists) != 0 {
+		t.Errorf("游客的歌单 = %#v, %v，期望没有", lists, err)
+	}
+}
+
+func TestPlaylistLifecycle(t *testing.T) {
+	store, _ := newStore(t)
+	alice := registered(t, store, "alice")
+	bob := registered(t, store, "bob")
+	favorites := favoritesOf(t, store, alice.ID)
+	commute, err := store.CreatePlaylist(t.Context(), alice.ID, "通勤", 50)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := store.RenamePlaylist(t.Context(), alice.ID, commute.ID, "上班路上"); err != nil {
+		t.Fatal(err)
+	}
+	lists, err := store.MemberPlaylists(t.Context(), alice.ID)
+	if err != nil || len(lists) != 2 || lists[1].ID != commute.ID || lists[1].Name != "上班路上" || lists[1].TrackCount != 0 || lists[1].Cover != nil {
+		t.Errorf("歌单 = %#v, %v，期望“我喜欢”之后是改名后的 %s", lists, err, commute.ID)
+	}
+	if err := store.RenamePlaylist(t.Context(), alice.ID, favorites, "别的名字"); !errors.Is(err, port.ErrFavoritesFixed) {
+		t.Errorf("“我喜欢”改名 = %v，期望 ErrFavoritesFixed", err)
+	}
+	if err := store.DeletePlaylist(t.Context(), alice.ID, favorites); !errors.Is(err, port.ErrFavoritesFixed) {
+		t.Errorf("删除“我喜欢” = %v，期望 ErrFavoritesFixed", err)
+	}
+	for _, id := range []string{commute.ID, "not-a-uuid", "00000000-0000-7000-8000-000000000000"} {
+		if err := store.RenamePlaylist(t.Context(), bob.ID, id, "x"); !errors.Is(err, port.ErrPlaylistNotFound) {
+			t.Errorf("别人或不存在的歌单 %s 改名 = %v，期望 ErrPlaylistNotFound", id, err)
+		}
+		if err := store.DeletePlaylist(t.Context(), bob.ID, id); !errors.Is(err, port.ErrPlaylistNotFound) {
+			t.Errorf("删除别人或不存在的歌单 %s = %v，期望 ErrPlaylistNotFound", id, err)
+		}
+		if _, err := store.PlaylistItems(t.Context(), bob.ID, id); !errors.Is(err, port.ErrPlaylistNotFound) {
+			t.Errorf("读取别人或不存在的歌单 %s = %v，期望 ErrPlaylistNotFound", id, err)
+		}
+	}
+	if err := store.DeletePlaylist(t.Context(), alice.ID, commute.ID); err != nil {
+		t.Fatal(err)
+	}
+	if lists, err := store.MemberPlaylists(t.Context(), alice.ID); err != nil || len(lists) != 1 {
+		t.Errorf("删除之后的歌单 = %#v, %v，期望只剩“我喜欢”", lists, err)
+	}
+}
+
+func TestDeletePlaylistRemovesItsItems(t *testing.T) {
+	store, pool := newStore(t)
+	alice := registered(t, store, "alice")
+	commute, err := store.CreatePlaylist(t.Context(), alice.ID, "通勤", 50)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := store.AddPlaylistItem(t.Context(), alice.ID, commute.ID, sunnyItem, 1000); err != nil {
+		t.Fatal(err)
+	}
+	if err := store.DeletePlaylist(t.Context(), alice.ID, commute.ID); err != nil {
+		t.Fatal(err)
+	}
+	var count int
+	if err := pool.QueryRow(t.Context(), `SELECT count(*) FROM playlist_items WHERE playlist_id = $1`, commute.ID).Scan(&count); err != nil || count != 0 {
+		t.Errorf("删除歌单之后的曲目数 = %d, %v，期望 0", count, err)
+	}
+}
+
+func TestAccountHasOneFavorites(t *testing.T) {
+	store, pool := newStore(t)
+	alice := registered(t, store, "alice")
+	_, err := pool.Exec(t.Context(), `INSERT INTO playlists (owner_id, kind, name) VALUES ($1, 'favorites', '我喜欢')`, alice.ID)
+	var pgErr *pgconn.PgError
+	if !errors.As(err, &pgErr) || pgErr.Code != uniqueViolation {
+		t.Errorf("第二个“我喜欢” = %v，期望唯一约束错误", err)
+	}
+}
+
+func TestPlaylistLimitCountsFavorites(t *testing.T) {
+	store, _ := newStore(t)
+	alice := registered(t, store, "alice")
+	if _, err := store.CreatePlaylist(t.Context(), alice.ID, "一", 2); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := store.CreatePlaylist(t.Context(), alice.ID, "二", 2); !errors.Is(err, port.ErrPlaylistLimit) {
+		t.Errorf("超过上限时 = %v，期望 ErrPlaylistLimit", err)
+	}
+}
+
+func TestPlaylistItems(t *testing.T) {
+	store, _ := newStore(t)
+	alice := registered(t, store, "alice")
+	bob := registered(t, store, "bob")
+	favorites := favoritesOf(t, store, alice.ID)
+	for _, item := range []port.PlaylistItem{sunnyItem, clipItem, sunnyItem} {
+		if err := store.AddPlaylistItem(t.Context(), alice.ID, favorites, item, 2); err != nil {
+			t.Fatal(err)
+		}
+	}
+	items, err := store.PlaylistItems(t.Context(), alice.ID, favorites)
+	if want := []port.PlaylistItem{clipItem, sunnyItem}; err != nil || !slices.Equal(items, want) {
+		t.Errorf("曲目 = %#v, %v，期望新加入的在前、重复加入不变 %#v", items, err, want)
+	}
+	if lists, _ := store.MemberPlaylists(t.Context(), alice.ID); lists[0].TrackCount != 2 {
+		t.Errorf("曲目数 = %d，期望 2", lists[0].TrackCount)
+	}
+	third := port.PlaylistItem{Track: track.Track{Source: track.NetEase, ID: "185811"}, Meta: track.Meta{Title: "七里香", PageURL: "https://music.163.com/#/song?id=185811"}}
+	if err := store.AddPlaylistItem(t.Context(), alice.ID, favorites, third, 2); !errors.Is(err, port.ErrPlaylistLimit) {
+		t.Errorf("歌单满了时 = %v，期望 ErrPlaylistLimit", err)
+	}
+	if err := store.AddPlaylistItem(t.Context(), bob.ID, favorites, third, 2); !errors.Is(err, port.ErrPlaylistNotFound) {
+		t.Errorf("加入别人的歌单 = %v，期望 ErrPlaylistNotFound", err)
+	}
+	for range 2 {
+		if err := store.RemovePlaylistItem(t.Context(), alice.ID, favorites, sunnyItem.Track); err != nil {
+			t.Fatal(err)
+		}
+	}
+	if items, err := store.PlaylistItems(t.Context(), alice.ID, favorites); err != nil || !slices.Equal(items, []port.PlaylistItem{clipItem}) {
+		t.Errorf("移除之后的曲目 = %#v, %v", items, err)
+	}
+	if err := store.RemovePlaylistItem(t.Context(), bob.ID, favorites, clipItem.Track); !errors.Is(err, port.ErrPlaylistNotFound) {
+		t.Errorf("从别人的歌单移除 = %v，期望 ErrPlaylistNotFound", err)
+	}
+}
+
+func TestConcurrentPlaylistAddsRespectLimit(t *testing.T) {
+	store, pool := newStore(t)
+	alice := registered(t, store, "alice")
+	favorites := favoritesOf(t, store, alice.ID)
+	var wg sync.WaitGroup
+	for i := range 10 {
+		wg.Go(func() {
+			item := port.PlaylistItem{Track: track.Track{Source: track.NetEase, ID: strconv.Itoa(i)}, Meta: track.Meta{Title: "歌", PageURL: "https://music.163.com/"}}
+			_ = store.AddPlaylistItem(t.Context(), alice.ID, favorites, item, 5)
+		})
+	}
+	wg.Wait()
+	if items, err := store.PlaylistItems(t.Context(), alice.ID, favorites); err != nil || len(items) != 5 {
+		t.Errorf("并发加入之后有 %d 首, %v，期望正好 5 首", len(items), err)
+	}
+	var distinct, seq int64
+	var largest int64
+	if err := pool.QueryRow(t.Context(), `SELECT count(DISTINCT i.position), max(i.position), max(p.item_seq)
+FROM playlist_items i JOIN playlists p ON p.id = i.playlist_id WHERE i.playlist_id = $1`, favorites).Scan(&distinct, &largest, &seq); err != nil {
+		t.Fatal(err)
+	}
+	if distinct != 5 || largest > seq {
+		t.Errorf("排序值有 %d 种、最大 %d，歌单的 item_seq 是 %d，期望 5 首的排序值两两不同且都不大于 item_seq", distinct, largest, seq)
+	}
+}
+
+func TestConcurrentPlaylistCreatesRespectLimit(t *testing.T) {
+	store, _ := newStore(t)
+	alice := registered(t, store, "alice")
+	var wg sync.WaitGroup
+	for i := range 10 {
+		wg.Go(func() {
+			_, _ = store.CreatePlaylist(t.Context(), alice.ID, "歌单"+strconv.Itoa(i), 5)
+		})
+	}
+	wg.Wait()
+	if lists, err := store.MemberPlaylists(t.Context(), alice.ID); err != nil || len(lists) != 5 {
+		t.Errorf("并发新建之后有 %d 个歌单, %v，期望正好 5 个（含“我喜欢”）", len(lists), err)
+	}
+}
+
+func TestPlaylistTimestamps(t *testing.T) {
+	store, _ := newStore(t)
+	alice := registered(t, store, "alice")
+	created, err := store.CreatePlaylist(t.Context(), alice.ID, "通勤", 50)
+	if err != nil || created.CreatedAt.IsZero() || created.UpdatedAt.IsZero() || created.Cover != nil {
+		t.Fatalf("新建 = %#v, %v，期望带创建和更新时间、没有封面", created, err)
+	}
+	read := func() port.PlaylistRecord {
+		t.Helper()
+		lists, err := store.MemberPlaylists(t.Context(), alice.ID)
+		if err != nil || len(lists) != 2 {
+			t.Fatalf("歌单 = %#v, %v", lists, err)
+		}
+		return lists[1]
+	}
+	before := read()
+	if !before.CreatedAt.Equal(created.CreatedAt) || !before.UpdatedAt.Equal(created.UpdatedAt) {
+		t.Errorf("读出的时间 %v/%v，期望与新建时一致 %v/%v", before.CreatedAt, before.UpdatedAt, created.CreatedAt, created.UpdatedAt)
+	}
+	steps := []struct {
+		name    string
+		do      func() error
+		changed bool
+	}{
+		{"改名", func() error { return store.RenamePlaylist(t.Context(), alice.ID, created.ID, "上班路上") }, true},
+		{"加入新曲目", func() error { return store.AddPlaylistItem(t.Context(), alice.ID, created.ID, sunnyItem, 10) }, true},
+		{"重复加入", func() error { return store.AddPlaylistItem(t.Context(), alice.ID, created.ID, sunnyItem, 10) }, false},
+		{"移除曲目", func() error { return store.RemovePlaylistItem(t.Context(), alice.ID, created.ID, sunnyItem.Track) }, true},
+		{"移除不存在的曲目", func() error { return store.RemovePlaylistItem(t.Context(), alice.ID, created.ID, sunnyItem.Track) }, false},
+	}
+	for _, step := range steps {
+		if err := step.do(); err != nil {
+			t.Fatalf("%s：%v", step.name, err)
+		}
+		after := read()
+		if got := after.UpdatedAt.After(before.UpdatedAt); got != step.changed {
+			t.Errorf("%s之后更新时间推进 = %v，期望 %v", step.name, got, step.changed)
+		}
+		if !after.CreatedAt.Equal(before.CreatedAt) {
+			t.Errorf("%s之后创建时间变了：%v -> %v", step.name, before.CreatedAt, after.CreatedAt)
+		}
+		before = after
+	}
+}
+
+func TestPlaylistCoverIsTheFirstSongWithOne(t *testing.T) {
+	store, _ := newStore(t)
+	alice := registered(t, store, "alice")
+	favorites := favoritesOf(t, store, alice.ID)
+	add := func(source track.Source, id, coverURL string, coverKey track.ObjectKey) {
+		t.Helper()
+		item := port.PlaylistItem{
+			Track: track.Track{Source: source, ID: id},
+			Meta:  track.Meta{Title: id, CoverURL: coverURL, CoverKey: coverKey, PageURL: "https://example.com/" + id},
+		}
+		if err := store.AddPlaylistItem(t.Context(), alice.ID, favorites, item, 100); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for i := range 3 {
+		add(track.NetEase, strconv.Itoa(i), "https://img.example/"+strconv.Itoa(i)+".jpg", "")
+	}
+	add(track.Link, "https://example.com/a.mp3", "", "covers/a.jpg")
+	add(track.NetEase, "no-cover", "", "")
+	lists, err := store.MemberPlaylists(t.Context(), alice.ID)
+	if err != nil || len(lists) != 1 {
+		t.Fatalf("歌单 = %#v, %v", lists, err)
+	}
+	if got, want := lists[0].Cover, (port.Cover{Key: "covers/a.jpg"}); got == nil || *got != want {
+		t.Errorf("封面 = %+v，期望跳过没有封面的歌，取排在最前的 %+v", got, want)
+	}
+}
+
+func TestConcurrentRemovalsAndDeletesDoNotDeadlock(t *testing.T) {
+	store, pool := newStore(t)
+	alice := registered(t, store, "alice")
+	lists := make([]string, 20)
+	for i := range lists {
+		p, err := store.CreatePlaylist(t.Context(), alice.ID, "歌单"+strconv.Itoa(i), 50)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if err := store.AddPlaylistItem(t.Context(), alice.ID, p.ID, sunnyItem, 1000); err != nil {
+			t.Fatal(err)
+		}
+		lists[i] = p.ID
+	}
+	removed, deleted := make(chan error, len(lists)), make(chan error, len(lists))
+	var wg sync.WaitGroup
+	for _, list := range lists {
+		wg.Go(func() { removed <- store.RemovePlaylistItem(t.Context(), alice.ID, list, sunnyItem.Track) })
+		wg.Go(func() { deleted <- store.DeletePlaylist(t.Context(), alice.ID, list) })
+	}
+	wg.Wait()
+	close(removed)
+	close(deleted)
+	for err := range removed {
+		if err != nil && !errors.Is(err, port.ErrPlaylistNotFound) {
+			t.Errorf("与删除歌单并发移出 = %v，期望成功或 ErrPlaylistNotFound", err)
+		}
+	}
+	for err := range deleted {
+		if err != nil {
+			t.Errorf("与移出并发删除歌单 = %v，期望成功", err)
+		}
+	}
+	if lists, err := store.MemberPlaylists(t.Context(), alice.ID); err != nil || len(lists) != 1 {
+		t.Errorf("删除之后的歌单 = %#v, %v，期望只剩“我喜欢”", lists, err)
+	}
+	var count int
+	if err := pool.QueryRow(t.Context(), `SELECT count(*) FROM playlist_items`).Scan(&count); err != nil || count != 0 {
+		t.Errorf("删除歌单之后还有 %d 首曲目, %v，期望 0", count, err)
+	}
+}

internal/app/port/member.go

@@ -38,7 +38,7 @@ type Members interface {
 	// name、avatarHash 或 email 为 nil 时保持原值，email 为空字符串表示清除。游客的 email 不保存。
 	UpdateMember(ctx context.Context, id string, name, avatarHash, email *string) (member.Member, error)
 	AccountProfile(ctx context.Context, memberID string) (AccountProfile, error)
-	// 用户名已属于其他成员时返回 ErrUsernameTaken，成员已经注册过时返回 ErrAlreadyRegistered。
+	// 用户名已属于其他成员时返回 ErrUsernameTaken，成员已经注册过时返回 ErrAlreadyRegistered。同时为这个账号创建“我喜欢”。
 	Register(ctx context.Context, memberID, username, passwordHash string) error
 	AccountByUsername(ctx context.Context, username string) (Account, error)
 	// 在同一个事务中删除 oldTokenHash 的会话，给 memberID 创建 newTokenHash 的会话。oldTokenHash 的会话已经不存在时返回

internal/app/port/playlist.go

@@ -0,0 +1,54 @@
+package port
+
+import (
+	"context"
+	"errors"
+	"time"
+
+	"github.com/dihemoe/alisten/internal/domain/track"
+)
+
+var (
+	ErrPlaylistNotFound = errors.New("歌单不存在")
+	ErrFavoritesFixed   = errors.New("“我喜欢”不能重命名或删除")
+	ErrPlaylistLimit    = errors.New("歌单或歌单里的歌已达上限")
+)
+
+type PlaylistRecord struct {
+	ID         string
+	Name       string
+	Favorites  bool
+	TrackCount int
+	CreatedAt  time.Time
+	UpdatedAt  time.Time
+	Cover      *Cover
+}
+
+// 链接曲目的封面在对象存储中，只有对象键。
+type Cover struct {
+	URL string
+	Key track.ObjectKey
+}
+
+type PlaylistItem struct {
+	Track track.Track
+	Meta  track.Meta
+}
+
+// 所有方法都按 ownerID 过滤：别人的歌单和不存在的歌单一样，返回 ErrPlaylistNotFound。“我喜欢”由 Members.Register 创建。
+type Playlists interface {
+	// “我喜欢”在最前，其余按创建的先后。Cover 是歌单里排在最前、有封面的那首歌的封面，没有时为 nil。
+	MemberPlaylists(ctx context.Context, ownerID string) ([]PlaylistRecord, error)
+	// 已有 limit 个歌单（含“我喜欢”）时返回 ErrPlaylistLimit。
+	CreatePlaylist(ctx context.Context, ownerID, name string, limit int) (PlaylistRecord, error)
+	// “我喜欢”返回 ErrFavoritesFixed。
+	RenamePlaylist(ctx context.Context, ownerID, id, name string) error
+	// “我喜欢”返回 ErrFavoritesFixed。
+	DeletePlaylist(ctx context.Context, ownerID, id string) error
+	// 新加入的在前。
+	PlaylistItems(ctx context.Context, ownerID, id string) ([]PlaylistItem, error)
+	// 已经在歌单里时什么也不做；已有 limit 首时返回 ErrPlaylistLimit。
+	AddPlaylistItem(ctx context.Context, ownerID, id string, item PlaylistItem, limit int) error
+	// 不在歌单里时什么也不做。
+	RemovePlaylistItem(ctx context.Context, ownerID, id string, t track.Track) error
+}

internal/app/port/porttest/store.go

@@ -16,6 +16,7 @@ import (
 	"github.com/dihemoe/alisten/internal/app/port"
 	"github.com/dihemoe/alisten/internal/domain/member"
 	"github.com/dihemoe/alisten/internal/domain/room"
+	"github.com/dihemoe/alisten/internal/domain/track"
 )
 
 // Store 的行为与 postgres 适配器一致，包括它会拒绝的输入。
@@ -33,6 +34,7 @@ type Store struct {
 	cookies            map[string]string
 	brandName          string
 	registrationClosed bool
+	playlists          []*storedPlaylist
 }
 
 type storedMember struct {
@@ -57,6 +59,7 @@ var (
 	_ port.Credentials     = (*Store)(nil)
 	_ port.APIKeys         = (*Store)(nil)
 	_ port.Site            = (*Store)(nil)
+	_ port.Playlists       = (*Store)(nil)
 )
 
 func New() *Store {
@@ -175,6 +178,8 @@ func (s *Store) Register(_ context.Context, memberID, username, passwordHash str
 		return port.ErrUsernameTaken
 	}
 	m.username, m.passwordHash = username, passwordHash
+	now := time.Now()
+	s.playlists = append(s.playlists, &storedPlaylist{id: s.newID(), owner: memberID, name: "我喜欢", favorites: true, created: now, updated: now})
 	return nil
 }
 
@@ -526,3 +531,160 @@ func (s *Store) slugOwner(slug string) *port.RoomRecord {
 	}
 	return nil
 }
+
+type storedPlaylist struct {
+	id, owner, name  string
+	favorites        bool
+	items            []port.PlaylistItem
+	created, updated time.Time
+}
+
+func (p *storedPlaylist) cover() *port.Cover {
+	for i := len(p.items) - 1; i >= 0; i-- {
+		if m := p.items[i].Meta; m.CoverURL != "" || m.CoverKey != "" {
+			return &port.Cover{URL: m.CoverURL, Key: m.CoverKey}
+		}
+	}
+	return nil
+}
+
+// 调用方持有 s.mu。
+func (s *Store) playlist(ownerID, id string) *storedPlaylist {
+	for _, p := range s.playlists {
+		if p.id == id && p.owner == ownerID {
+			return p
+		}
+	}
+	return nil
+}
+
+func (s *Store) MemberPlaylists(_ context.Context, ownerID string) ([]port.PlaylistRecord, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	var lists []port.PlaylistRecord
+	for _, p := range s.playlists {
+		if p.owner != ownerID {
+			continue
+		}
+		r := port.PlaylistRecord{
+			ID:         p.id,
+			Name:       p.name,
+			Favorites:  p.favorites,
+			TrackCount: len(p.items),
+			CreatedAt:  p.created,
+			UpdatedAt:  p.updated,
+			Cover:      p.cover(),
+		}
+		if p.favorites {
+			lists = append([]port.PlaylistRecord{r}, lists...)
+		} else {
+			lists = append(lists, r)
+		}
+	}
+	return lists, nil
+}
+
+func (s *Store) CreatePlaylist(_ context.Context, ownerID, name string, limit int) (port.PlaylistRecord, error) {
+	if err := checkText(name); err != nil {
+		return port.PlaylistRecord{}, err
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	n := 0
+	for _, p := range s.playlists {
+		if p.owner == ownerID {
+			n++
+		}
+	}
+	if n >= limit {
+		return port.PlaylistRecord{}, port.ErrPlaylistLimit
+	}
+	now := time.Now()
+	p := &storedPlaylist{id: s.newID(), owner: ownerID, name: name, created: now, updated: now}
+	s.playlists = append(s.playlists, p)
+	return port.PlaylistRecord{ID: p.id, Name: name, CreatedAt: now, UpdatedAt: now}, nil
+}
+
+func (s *Store) RenamePlaylist(_ context.Context, ownerID, id, name string) error {
+	if err := checkText(name); err != nil {
+		return err
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	p := s.playlist(ownerID, id)
+	switch {
+	case p == nil:
+		return port.ErrPlaylistNotFound
+	case p.favorites:
+		return port.ErrFavoritesFixed
+	}
+	p.name = name
+	p.updated = time.Now()
+	return nil
+}
+
+func (s *Store) DeletePlaylist(_ context.Context, ownerID, id string) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	p := s.playlist(ownerID, id)
+	switch {
+	case p == nil:
+		return port.ErrPlaylistNotFound
+	case p.favorites:
+		return port.ErrFavoritesFixed
+	}
+	s.playlists = slices.DeleteFunc(s.playlists, func(other *storedPlaylist) bool { return other == p })
+	return nil
+}
+
+func (s *Store) PlaylistItems(_ context.Context, ownerID, id string) ([]port.PlaylistItem, error) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	p := s.playlist(ownerID, id)
+	if p == nil {
+		return nil, port.ErrPlaylistNotFound
+	}
+	items := make([]port.PlaylistItem, 0, len(p.items))
+	for i := len(p.items) - 1; i >= 0; i-- {
+		items = append(items, p.items[i])
+	}
+	return items, nil
+}
+
+func (s *Store) AddPlaylistItem(_ context.Context, ownerID, id string, item port.PlaylistItem, limit int) error {
+	m := item.Meta
+	if err := checkText(item.Track.ID, m.Title, m.Artist, m.Album, m.CoverURL, string(m.CoverKey), m.PageURL); err != nil {
+		return err
+	}
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	p := s.playlist(ownerID, id)
+	if p == nil {
+		return port.ErrPlaylistNotFound
+	}
+	if slices.ContainsFunc(p.items, func(i port.PlaylistItem) bool { return i.Track == item.Track }) {
+		return nil
+	}
+	if len(p.items) >= limit {
+		return port.ErrPlaylistLimit
+	}
+	item.Meta.Duration = item.Meta.Duration.Truncate(time.Millisecond)
+	p.items = append(p.items, item)
+	p.updated = time.Now()
+	return nil
+}
+
+func (s *Store) RemovePlaylistItem(_ context.Context, ownerID, id string, t track.Track) error {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	p := s.playlist(ownerID, id)
+	if p == nil {
+		return port.ErrPlaylistNotFound
+	}
+	n := len(p.items)
+	p.items = slices.DeleteFunc(p.items, func(i port.PlaylistItem) bool { return i.Track == t })
+	if len(p.items) < n {
+		p.updated = time.Now()
+	}
+	return nil
+}

internal/app/port/porttest/store_test.go

@@ -1,6 +1,12 @@
 package porttest
 
-import "testing"
+import (
+	"testing"
+	"time"
+
+	"github.com/dihemoe/alisten/internal/app/port"
+	"github.com/dihemoe/alisten/internal/domain/track"
+)
 
 func TestUpdateMemberRejectsTextPostgreSQLCannotStore(t *testing.T) {
 	store := New()
@@ -13,3 +19,29 @@ func TestUpdateMemberRejectsTextPostgreSQLCannotStore(t *testing.T) {
 		t.Error("含 NUL 的邮箱应报错")
 	}
 }
+
+func TestAddPlaylistItemKeepsMilliseconds(t *testing.T) {
+	store := New()
+	m, err := store.CreateMember(t.Context(), []byte("token"), "甲")
+	if err != nil {
+		t.Fatal(err)
+	}
+	list, err := store.CreatePlaylist(t.Context(), m.ID, "歌单", 10)
+	if err != nil {
+		t.Fatal(err)
+	}
+	item := port.PlaylistItem{
+		Track: track.Track{Source: "netease", ID: "1"},
+		Meta:  track.Meta{Title: "歌", Duration: 3*time.Minute + 1234*time.Microsecond + 567*time.Nanosecond},
+	}
+	if err := store.AddPlaylistItem(t.Context(), m.ID, list.ID, item, 10); err != nil {
+		t.Fatal(err)
+	}
+	items, err := store.PlaylistItems(t.Context(), m.ID, list.ID)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want := 3*time.Minute + time.Millisecond; items[0].Meta.Duration != want {
+		t.Errorf("Duration = %v，期望 %v", items[0].Meta.Duration, want)
+	}
+}