path: root/packages/meshbay-hub/src/meshbay_hub/static/playlists.js

import {
  MANIFEST_KIND, bodyKind, FAVORITES_ID,
  emptyManifest, emptyBody, mergeManifests, mergeBodies,
  toStored, fromStored, livePlaylists, repairTracks, indexTracks,
} from './playlist-merge.js';
import { derivePlaylistKey, seal, open } from './playlist-crypto.js';
import {
  session, _loadBundleKey, openDB, IDB_PLAYLISTS,
} from './hub-client.js';

/**
 * Playlists: the store, and putting it on nodes.
 *
 * `docs/playlists.md` §7 and §14. The rules live in `playlist-merge.js` and the
 * sealing in `playlist-crypto.js`, both of which are pure and both of which are
 * executed by their own tests. What is here is the part that cannot be: reading
 * and writing IndexedDB, and talking to nodes.
 *
 * **The client is the authority.** The merged state is what is in this
 * browser's IndexedDB, and every merge takes the maximum across the local copy
 * *plus* whatever each node answers. A node serving a stale copy, or a fresh
 * one it never received, can only lose the tie — it can never lower the merged
 * state, because the local copy is one of the inputs. That is what makes an
 * offline node a non-event rather than a hazard.
 *
 * **Nothing here dials.** Sync rides connections that were being opened anyway:
 * opening a group, the Search page's sweep, the music pool connecting to play a
 * track. A sweep of every group costs ten seconds per unreachable one, and
 * doing that at sign-in for a feature nobody has asked to use yet is exactly
 * what §7 refuses.
 */

// ── local identity ───────────────────────────────────────────────────────────

const DEVICE_KEY = 'meshbay_playlist_device';

/**
 * A stable id for *this browser*, for breaking merge ties and nothing else.
 *
 * Not an identity and not a secret: it never leaves the sealed blob, and two
 * devices needing different values is the whole requirement. Random rather than
 * derived from the account, because two browsers of one account must not
 * collide — which is the one case the tie-break exists for.
 */
function deviceId() {
  try {
    let id = localStorage.getItem(DEVICE_KEY);
    if (!id) {
      id = Array.from(crypto.getRandomValues(new Uint8Array(8)),
                      (b) => b.toString(16).padStart(2, '0')).join('');
      localStorage.setItem(DEVICE_KEY, id);
    }
    return id;
  } catch {
    // A private window with storage refused. A per-session id still breaks
    // ties correctly; it just stops being the *same* device next time, which
    // costs nothing but a different arbitrary winner on a tie.
    return 'ephemeral';
  }
}

// ── the key ──────────────────────────────────────────────────────────────────

let _key = null;
let _keyFor = null;

/**
 * The playlist key, derived once per sign-in from the HKDF handle that rides
 * alongside the bundle key (`keyderive.js`'s deriveBundleKeys).
 *
 * `v2hkdf` is absent when this browser's session predates it — a stored bundle
 * key from before the change, loaded out of IndexedDB. There is nothing to do
 * about that here and nothing to fall back to: the passphrase is not in memory
 * to re-derive from. Playlists stay local until the next sign-in, which is a
 * degradation rather than a failure and is reported as one.
 */
async function playlistKey(userId) {
  if (_key && _keyFor === userId) return _key;
  let bundleKey = session.bundleKey;
  if (!bundleKey) {
    bundleKey = await _loadBundleKey();
    if (bundleKey) session.bundleKey = bundleKey;
  }
  if (!bundleKey || !bundleKey.v2hkdf) return null;
  _key = await derivePlaylistKey(bundleKey.v2hkdf);
  _keyFor = userId;
  return _key;
}

/** Sign-out: the next account on this browser must not inherit this one's key. */
function forgetPlaylistKey() {
  _key = null;
  _keyFor = null;
  _state = null;
}

// ── local storage ────────────────────────────────────────────────────────────
//
// Plaintext in IndexedDB, exactly as the cached group indexes already are
// (`hub-client.js`'s `group_indexes`). What is sealed is the copy that leaves
// this browser; a second encryption layer over the local cache would protect
// against nothing the index cache is not already exposed to, and would need a
// key held in the same place.
//
// Keyed by `userId|kind`, not by `kind`. Two accounts on one browser is
// ordinary, and a sign-out that fails to run is ordinary too — so the
// separation is in the key rather than in a cleanup path that has to happen.

// The database, its version and its stores are `hub-client.js`'s: two modules
// opening one database at versions of their own is a `VersionError` thrown at
// whichever runs second, and the store this uses was added there at version 2
// (docs/playlists.md §14.2).

async function _idbGet(userId, kind) {
  try {
    const db = await openDB();
    const tx = db.transaction(IDB_PLAYLISTS, 'readonly');
    const req = tx.objectStore(IDB_PLAYLISTS).get(`${userId}|${kind}`);
    const value = await new Promise((res, rej) => {
      req.onsuccess = () => res(req.result);
      req.onerror = () => rej(req.error);
    });
    db.close();
    return value || null;
  } catch { return null; }
}

async function _idbPut(userId, kind, value) {
  try {
    const db = await openDB();
    const tx = db.transaction(IDB_PLAYLISTS, 'readwrite');
    tx.objectStore(IDB_PLAYLISTS).put(value, `${userId}|${kind}`);
    await new Promise((res, rej) => { tx.oncomplete = res; tx.onerror = rej; });
    db.close();
  } catch { /* a private window, or storage refused — the session still works */ }
}

// ── in-memory state ──────────────────────────────────────────────────────────

let _state = null;   // { userId, manifest, bodies: Map(id -> body) }

async function ensureLoaded(userId) {
  if (_state && _state.userId === userId) return _state;
  const manifest = (await _idbGet(userId, MANIFEST_KIND)) || emptyManifest();
  _state = { userId, manifest, bodies: new Map() };
  return _state;
}

async function _body(userId, id) {
  const st = await ensureLoaded(userId);
  if (st.bodies.has(id)) return st.bodies.get(id);
  const body = (await _idbGet(userId, bodyKind(id))) || emptyBody(id);
  st.bodies.set(id, body);
  return body;
}

async function _saveManifest(st) {
  // Its own counter, separate from the per-playlist revisions: it is what the
  // node's `rev` column carries, and what a listing compares without opening
  // anything.
  st.manifest.rev = (st.manifest.rev || 0) + 1;
  await _idbPut(st.userId, MANIFEST_KIND, st.manifest);
}

async function _saveBody(st, body) {
  st.bodies.set(body.id, body);
  await _idbPut(st.userId, bodyKind(body.id), body);
}

/** The manifest entry for `id`, materialised if this is Favourites. */
function _entry(st, id, name) {
  let e = st.manifest.playlists[id];
  if (!e) {
    e = {
      name: name || '', rev: 1, body_rev: 0, device: deviceId(),
      updated_at: Math.floor(Date.now() / 1000), deleted: false, count: 0,
    };
    st.manifest.playlists[id] = e;
  }
  return e;
}

// ── reading ──────────────────────────────────────────────────────────────────

/**
 * Every playlist a reader should see, Favourites first.
 *
 * Drawn from the manifest alone — names, counts, a few kilobytes — so the
 * "add to playlist" menu opens instantly with every node offline and no body
 * fetched. That is what the manifest is for.
 */
async function listPlaylists(userId) {
  const st = await ensureLoaded(userId);
  return livePlaylists(st.manifest);
}

/**
 * One playlist's tracks, in the shape the player consumes.
 *
 * `cachedIndexes` is optional and is `[{ groupId, entries }]`: given it, an
 * entry whose hash is no longer in its group's index but whose path is gets
 * its id rewritten, and the other way round. Repaired in memory and written
 * back, once, so the next read costs nothing.
 */
async function getPlaylistTracks(userId, id, cachedIndexes) {
  const body = await _body(userId, id);
  let tracks = body.tracks || [];
  if (cachedIndexes && cachedIndexes.length) {
    let changed = 0;
    for (const { groupId, entries } of cachedIndexes) {
      const res = repairTracks(tracks, groupId, indexTracks(entries));
      tracks = res.tracks;
      changed += res.repaired;
    }
    if (changed) {
      const st = await ensureLoaded(userId);
      await _saveBody(st, { ...body, tracks });
    }
  }
  return tracks.map(fromStored);
}

// ── writing ──────────────────────────────────────────────────────────────────

function _newId() {
  return (crypto.randomUUID && crypto.randomUUID())
    || Array.from(crypto.getRandomValues(new Uint8Array(16)),
                  (b) => b.toString(16).padStart(2, '0')).join('');
}

/**
 * Create a playlist under a name that is not already taken.
 *
 * Case- and accent-folded, because "Soirée" and "soiree" being two playlists
 * is not something anyone wants and is very easy to do by accident.
 */
async function createPlaylist(userId, name) {
  const st = await ensureLoaded(userId);
  const wanted = String(name || '').trim();
  if (!wanted) throw new Error('empty name');
  const fold = (s) => s.normalize('NFD').replace(/[̀-ͯ]/g, '').toLowerCase();
  for (const p of livePlaylists(st.manifest)) {
    if (fold(p.name) === fold(wanted)) throw new Error('duplicate name');
  }
  const id = _newId();
  _entry(st, id, wanted);
  await _saveManifest(st);
  await _saveBody(st, emptyBody(id));
  return id;
}

async function renamePlaylist(userId, id, name) {
  const st = await ensureLoaded(userId);
  const e = _entry(st, id);
  e.name = String(name || '').trim();
  e.rev += 1;
  e.device = deviceId();
  e.updated_at = Math.floor(Date.now() / 1000);
  await _saveManifest(st);
}

/**
 * Tombstone a playlist. Favourites is refused outright.
 *
 * Refusing rather than special-casing is what keeps the tombstone rule free of
 * an exception: a tombstone on the reserved id would have to be ignored by
 * every reader, and a tombstone rule with an exception is how the resurrection
 * defect ships.
 */
async function deletePlaylist(userId, id) {
  if (id === FAVORITES_ID) throw new Error('favorites cannot be deleted');
  const st = await ensureLoaded(userId);
  const e = _entry(st, id);
  e.deleted = true;
  e.rev += 1;
  e.device = deviceId();
  e.updated_at = Math.floor(Date.now() / 1000);
  await _saveManifest(st);
  st.bodies.delete(id);
  await _idbPut(st.userId, bodyKind(id), null);
}

/**
 * Append entries to a playlist, creating it if this is Favourites' first use.
 *
 * Duplicates are allowed in an ordinary playlist — real ones have them — and
 * refused in Favourites, where the gesture is a toggle rather than an append.
 * Returns how many were actually added, so the caller can say so.
 */
async function addTracks(userId, id, entries, groupId, name) {
  const st = await ensureLoaded(userId);
  const e = _entry(st, id, id === FAVORITES_ID ? (name || 'Favorites') : name);
  const body = await _body(userId, id);
  const existing = new Set(body.tracks.map((tr) => tr.id));
  const incoming = entries
    .map((entry) => toStored(entry, groupId))
    .filter((tr) => (id === FAVORITES_ID ? !existing.has(tr.id) : true));
  if (!incoming.length) return 0;

  const next = {
    ...body,
    rev: (body.rev || 0) + 1,
    device: deviceId(),
    tracks: [...body.tracks, ...incoming],
  };
  await _saveBody(st, next);
  e.body_rev = next.rev;
  e.count = next.tracks.length;
  e.updated_at = Math.floor(Date.now() / 1000);
  await _saveManifest(st);
  return incoming.length;
}

async function removeTrackAt(userId, id, at) {
  const st = await ensureLoaded(userId);
  const body = await _body(userId, id);
  if (at < 0 || at >= body.tracks.length) return false;
  const next = {
    ...body,
    rev: (body.rev || 0) + 1,
    device: deviceId(),
    tracks: [...body.tracks.slice(0, at), ...body.tracks.slice(at + 1)],
  };
  await _saveBody(st, next);
  const e = _entry(st, id);
  e.body_rev = next.rev;
  e.count = next.tracks.length;
  e.updated_at = Math.floor(Date.now() / 1000);
  await _saveManifest(st);
  return true;
}

/**
 * The current queue as a new playlist.
 *
 * The caller passes the tracks in **play order** — what the queue panel is
 * showing — rather than in the order they were added, because that is what
 * "save what I am listening to" means, shuffle included.
 */
async function saveQueueAsPlaylist(userId, name, entries) {
  const id = await createPlaylist(userId, name);
  await addTracks(userId, id, entries, null);
  return id;
}

// ── sync ─────────────────────────────────────────────────────────────────────

/**
 * Reconcile with one node, over a connection that was open anyway.
 *
 * Manifest first, always; bodies only when the merged manifest says this
 * browser's copy is behind, or when the node's is. A reader with forty
 * playlists who only ever plays two never transfers the other thirty-eight.
 *
 * Every failure is swallowed and reported in the return value rather than
 * thrown: this rides someone else's connection, and a playlist that could not
 * be reconciled must never break whatever that connection was opened for.
 */
async function syncWith(transport, userId) {
  const result = { ok: false, pulled: 0, pushed: 0, reason: null };
  if (!transport || !transport.connected) {
    result.reason = 'offline';
    return result;
  }
  const key = await playlistKey(userId);
  if (!key) {
    // No HKDF handle: a session from before it existed. Nothing to fall back
    // to, and silently doing nothing would be the worse answer.
    result.reason = 'no_key';
    return result;
  }
  const st = await ensureLoaded(userId);

  // What this node holds, and at what revision — kinds and numbers, no
  // payloads, one message. Without it there is no way to tell "the node is
  // behind" from "the node is up to date", and the first version of this
  // pushed every body on every sync because it could not tell the difference.
  const have = new Map();
  try {
    for (const b of await transport.listUserBlobs()) have.set(b.kind, b.rev);
  } catch (err) {
    // A node too old to know these messages at all. Nothing to reconcile with,
    // and nothing lost: the local copy is the authority and the next node this
    // browser reaches will take the writes.
    result.reason = err.message || 'unsupported';
    return result;
  }

  let theirs = null;
  if (have.has(MANIFEST_KIND)) {
    try {
      const row = await transport.fetchUserBlob(MANIFEST_KIND);
      if (row && row.blob_enc) {
        theirs = await open(row.blob_enc, MANIFEST_KIND, userId, key);
      }
    } catch (err) {
      result.reason = err.message || 'fetch failed';
      return result;
    }
  }

  const merged = mergeManifests(st.manifest, theirs || emptyManifest());
  merged.rev = Math.max(st.manifest.rev || 0, (theirs && theirs.rev) || 0);
  const grew = JSON.stringify(merged.playlists) !== JSON.stringify(st.manifest.playlists);
  if (grew) {
    st.manifest = merged;
    await _idbPut(userId, MANIFEST_KIND, merged);
    result.pulled += 1;
  }

  // Bodies, compared against what *this node* holds rather than against the
  // merged watermark: the watermark is the highest revision anybody has seen,
  // which says nothing about whether this particular node has it.
  //
  // A body is fetched only when this node is ahead, and pushed only when it is
  // behind. A reader with forty playlists who only ever plays two never
  // transfers the other thirty-eight, and a sync with nothing to do writes
  // nothing at all.
  for (const p of livePlaylists(merged)) {
    const local = await _body(userId, p.id);
    const kind = bodyKind(p.id);
    const nodeRev = have.has(kind) ? (have.get(kind) || 0) : -1;
    const localRev = local.rev || 0;

    if (nodeRev > localRev) {
      try {
        const row = await transport.fetchUserBlob(kind);
        if (row && row.blob_enc) {
          const remote = await open(row.blob_enc, kind, userId, key);
          const best = mergeBodies(local, remote);
          if (best && (best.rev || 0) > localRev) {
            await _saveBody(st, best);
            result.pulled += 1;
          }
        }
      } catch { /* one body failing must not stop the rest */ }
    } else if (localRev > nodeRev && localRev > 0) {
      try {
        await transport.storeUserBlob(
          kind, localRev, await seal(local, kind, userId, key));
        result.pushed += 1;
      } catch { /* a cap, or a node that went away mid-sweep */ }
    }
  }

  // A tombstoned playlist's body is dropped from every node as it is reached.
  // The tombstone in the manifest is what has to survive, not the tracks —
  // and without this the body of every playlist ever deleted stays on every
  // node for ever, filling the account's quota with graves.
  for (const [id, e] of Object.entries(merged.playlists)) {
    if (!e.deleted) continue;
    const kind = bodyKind(id);
    if (!have.has(kind)) continue;
    try { await transport.deleteUserBlob(kind); } catch { /* next time round */ }
  }

  // The manifest goes last, so a node never advertises a body it has not been
  // given: a reader on a third device would fetch a watermark, ask for the
  // body behind it and be told there is none.
  const mine = JSON.stringify(st.manifest.playlists);
  if (!theirs || mine !== JSON.stringify(theirs.playlists)) {
    try {
      await transport.storeUserBlob(
        MANIFEST_KIND, st.manifest.rev || 1,
        await seal(st.manifest, MANIFEST_KIND, userId, key));
      result.pushed += 1;
    } catch (err) {
      result.reason = err.message || 'store failed';
      return result;
    }
  }

  result.ok = true;
  return result;
}

export {
  FAVORITES_ID,
  deviceId, playlistKey, forgetPlaylistKey, ensureLoaded,
  listPlaylists, getPlaylistTracks,
  createPlaylist, renamePlaylist, deletePlaylist,
  addTracks, removeTrackAt, saveQueueAsPlaylist,
  syncWith,
};