feat: replace ID-based URLs with slugs for songs and playlists

- Add `slug` column to `songs` and `playlists` tables via migrations 005 & 006
- Implement slug generation logic (lowercase, hyphenated, unique) in both services
- Backfill existing rows with auto-generated slugs on startup
- Update public routes to use `/songs/:slug` and `/playlists/:slug`
- Replace all view templates to link using slugs instead of numeric IDs

db/migrations/005_playlist_slug.sql

@@ -0,0 +1,2 @@
+ALTER TABLE playlists ADD COLUMN slug TEXT;
+CREATE UNIQUE INDEX playlists_slug_unique ON playlists (slug);

db/migrations/006_song_slug.sql

@@ -0,0 +1,2 @@
+ALTER TABLE songs ADD COLUMN slug TEXT;
+CREATE UNIQUE INDEX songs_slug_unique ON songs (slug);

src/routes/public.js

@@ -64,8 +64,8 @@ router.get('/songs', (req, res) => {
   });
 });
 
-router.get('/songs/:id', (req, res, next) => {
-  const song = songs.findById(Number(req.params.id));
+router.get('/songs/:slug', (req, res, next) => {
+  const song = songs.findBySlug(req.params.slug);
   if (!song) return next();
   if (!canView(song.visibility, song.uploadedBy, req.session.user?.id)) {
     return denyAccess(req, res, next, song.visibility);
@@ -78,17 +78,16 @@ router.get('/playlists', (req, res) => {
   res.render('public/playlists', { title: 'Playlists', playlists: playlists.listVisible(loggedIn) });
 });
 
-router.get('/playlists/:id', (req, res, next) => {
-  const id = Number(req.params.id);
-  const playlist = playlists.findById(id);
+router.get('/playlists/:slug', (req, res, next) => {
+  const playlist = playlists.findBySlug(req.params.slug);
   if (!playlist) return next();
   const userId = req.session.user?.id;
   // Use effective visibility (most restrictive of playlist + all its tracks).
-  const effectiveVisibility = playlists.getEffectiveVisibility(id);
+  const effectiveVisibility = playlists.getEffectiveVisibility(playlist.id);
   if (!canView(effectiveVisibility, playlist.createdBy, userId)) {
     return denyAccess(req, res, next, effectiveVisibility);
   }
-  const tracks = playlists.getTracks(id).filter(t => canView(t.visibility, t.uploadedBy, userId));
+  const tracks = playlists.getTracks(playlist.id).filter(t => canView(t.visibility, t.uploadedBy, userId));
   res.render('public/playlist', { title: playlist.title, playlist, tracks });
 });
 

src/services/playlists.js

@@ -86,11 +86,47 @@ const removeTrackStmt = db.prepare('DELETE FROM playlist_songs WHERE playlist_id
 const clearTracksStmt = db.prepare('DELETE FROM playlist_songs WHERE playlist_id = ?');
 const countStmt = db.prepare('SELECT COUNT(*) AS c FROM playlist_songs WHERE playlist_id = ?');
 const creatorNameStmt = db.prepare('SELECT display_name FROM users WHERE id = ?');
+const findBySlugIdStmt   = db.prepare('SELECT id FROM playlists WHERE slug = ?');
+const findBySlugExactStmt = db.prepare('SELECT * FROM playlists WHERE slug = ?');
+const updateSlugStmt     = db.prepare('UPDATE playlists SET slug = ? WHERE id = ?');
+
+function toSlug(title) {
+  return title
+    .toLowerCase()
+    .trim()
+    .replace(/[^a-z0-9\s-]/g, '')
+    .replace(/\s+/g, '-')
+    .replace(/-+/g, '-')
+    .replace(/^-|-$/g, '');
+}
+
+function generateUniqueSlug(title, excludeId = null) {
+  const base = toSlug(title) || 'playlist';
+  let candidate = base;
+  let n = 2;
+  // eslint-disable-next-line no-constant-condition
+  while (true) {
+    const row = findBySlugIdStmt.get(candidate);
+    if (!row || row.id === excludeId) return candidate;
+    candidate = `${base}-${n++}`;
+  }
+}
+
+// Backfill slugs for any rows missing one (runs once after migration 005).
+const _noSlugRows = db.prepare('SELECT id, title FROM playlists WHERE slug IS NULL').all();
+for (const row of _noSlugRows) {
+  updateSlugStmt.run(generateUniqueSlug(row.title, row.id), row.id);
+}
+
+function findBySlug(slug) {
+  return toView(findBySlugExactStmt.get(slug));
+}
 
 function toView(row) {
   if (!row) return null;
   return {
     id: row.id,
+    slug: row.slug,
     title: row.title,
     description: row.description,
     coverPath: row.cover_path,
@@ -123,6 +159,8 @@ function create(data) {
     visibility: data.visibility || 'logged_in',
     created_by: data.createdBy || null,
   });
+  const slug = generateUniqueSlug(data.title, info.lastInsertRowid);
+  updateSlugStmt.run(slug, info.lastInsertRowid);
   return toView(findByIdStmt.get(info.lastInsertRowid));
 }
 
@@ -133,6 +171,8 @@ function update(id, data) {
     description: data.description || null,
     visibility: data.visibility || 'logged_in',
   });
+  const slug = generateUniqueSlug(data.title, id);
+  updateSlugStmt.run(slug, id);
   return toView(findByIdStmt.get(id));
 }
 
@@ -199,7 +239,7 @@ function setOrder(playlistId, songIds) {
 }
 
 module.exports = {
-  create, update, setCover, setVisibility, remove, findById, getEffectiveVisibility,
+  create, update, setCover, setVisibility, remove, findById, findBySlug, getEffectiveVisibility,
   listVisible, listAll, listByUser, featured,
   getTracks, trackCount, addTrack, removeTrack, setOrder,
 };

src/services/songs.js

@@ -35,11 +35,53 @@ const listForManagementStmt = db.prepare(`
 const recentGuestStmt = db.prepare(`SELECT * FROM songs WHERE visibility = 'public' ORDER BY created_at DESC LIMIT ?`);
 const recentUserStmt = db.prepare(`SELECT * FROM songs WHERE visibility IN ('public', 'logged_in') ORDER BY created_at DESC LIMIT ?`);
 const uploaderNameStmt = db.prepare('SELECT display_name FROM users WHERE id = ?');
+const findBySlugIdStmt    = db.prepare('SELECT id FROM songs WHERE slug = ?');
+const findBySlugExactStmt = db.prepare('SELECT * FROM songs WHERE slug = ?');
+const updateSlugStmt      = db.prepare('UPDATE songs SET slug = ? WHERE id = ?');
+
+function toSlug(text) {
+  return (text || '')
+    .toLowerCase()
+    .trim()
+    .replace(/[^a-z0-9\s-]/g, '')
+    .replace(/\s+/g, '-')
+    .replace(/-+/g, '-')
+    .replace(/^-|-$/g, '');
+}
+
+function buildSongSlugBase(title, artist) {
+  const t = toSlug(title) || 'song';
+  const a = toSlug(artist);
+  return a ? `${t}-by-${a}` : t;
+}
+
+function generateUniqueSlug(title, artist, excludeId = null) {
+  const base = buildSongSlugBase(title, artist);
+  let candidate = base;
+  let n = 2;
+  // eslint-disable-next-line no-constant-condition
+  while (true) {
+    const row = findBySlugIdStmt.get(candidate);
+    if (!row || row.id === excludeId) return candidate;
+    candidate = `${base}-${n++}`;
+  }
+}
+
+// Backfill slugs for any rows missing one (runs once after migration 006).
+const _noSlugRows = db.prepare('SELECT id, title, artist FROM songs WHERE slug IS NULL').all();
+for (const row of _noSlugRows) {
+  updateSlugStmt.run(generateUniqueSlug(row.title, row.artist, row.id), row.id);
+}
+
+function findBySlug(slug) {
+  return toView(findBySlugExactStmt.get(slug));
+}
 
 function toView(row) {
   if (!row) return null;
   return {
     id: row.id,
+    slug: row.slug,
     title: row.title,
     artist: row.artist,
     album: row.album,
@@ -68,6 +110,8 @@ function create(data) {
     visibility: data.visibility || 'logged_in',
     uploaded_by: data.uploadedBy || null,
   });
+  const slug = generateUniqueSlug(data.title, data.artist, info.lastInsertRowid);
+  updateSlugStmt.run(slug, info.lastInsertRowid);
   return toView(findByIdStmt.get(info.lastInsertRowid));
 }
 
@@ -81,6 +125,8 @@ function update(id, data) {
     year: data.year || null,
     visibility: data.visibility || 'logged_in',
   });
+  const slug = generateUniqueSlug(data.title, data.artist, id);
+  updateSlugStmt.run(slug, id);
   return toView(findByIdStmt.get(id));
 }
 
@@ -129,4 +175,4 @@ function recent(n = 8, loggedIn = false) {
   return (loggedIn ? recentUserStmt : recentGuestStmt).all(n).map(toView);
 }
 
-module.exports = { create, update, setCover, remove, findById, list, listAll, listByUser, listForManagement, recent };
+module.exports = { create, update, setCover, remove, findById, findBySlug, list, listAll, listByUser, listForManagement, recent };

src/views/admin/playlists.ejs

@@ -16,7 +16,7 @@
     <tbody>
       <% playlists.forEach((p) => { %>
         <tr>
-          <td><a href="/playlists/<%= p.id %>"><%= p.title %></a></td>
+          <td><a href="/playlists/<%= p.slug %>"><%= p.title %></a></td>
           <td>
             <% if (p.visibility === 'logged_in') { %>
               <span class="badge badge-logged-in">Members</span>

src/views/admin/songs.ejs

@@ -16,7 +16,7 @@
     <tbody>
       <% songs.forEach((s) => { %>
         <tr>
-          <td><a href="/songs/<%= s.id %>"><%= s.title %></a></td>
+          <td><a href="/songs/<%= s.slug %>"><%= s.title %></a></td>
           <td><%= s.artist %></td>
           <td><%= s.album || '' %></td>
           <td>

src/views/partials/song_list.ejs

@@ -7,7 +7,7 @@
         <div class="song-cover cover-fallback">♪</div>
       <% } %>
       <div class="song-main">
-        <a class="song-title" href="/songs/<%= s.id %>"><%= s.title %></a>
+        <a class="song-title" href="/songs/<%= s.slug %>"><%= s.title %></a>
         <% if (s.visibility === 'logged_in') { %><span class="badge badge-logged-in">Members</span><% } %>
         <% if (s.visibility === 'private') { %><span class="badge badge-private">Private</span><% } %>
         <div class="muted small"><%= s.artist %><% if (s.album) { %> · <%= s.album %><% } %></div>

src/views/public/home.ejs

@@ -10,7 +10,7 @@
   <% } else { %>
     <div class="grid">
       <% featured.forEach((p) => { %>
-        <a class="card" href="/playlists/<%= p.id %>">
+        <a class="card" href="/playlists/<%= p.slug %>">
           <% if (p.coverPath) { %>
             <img src="/media/<%= p.coverPath %>" alt="" />
           <% } else { %>

src/views/public/playlists.ejs

@@ -4,7 +4,7 @@
 <% } else { %>
   <div class="grid">
     <% playlists.forEach((p) => { %>
-      <a class="card" href="/playlists/<%= p.id %>">
+      <a class="card" href="/playlists/<%= p.slug %>">
         <% if (p.coverPath) { %>
           <img src="/media/<%= p.coverPath %>" alt="" />
         <% } else { %>