platform/MUSIC_API.md

# Music API (`/api/music/*`)

Platform API the mobile app uses to **stream music** and **sync a server-built library index**, so the
app no longer pre-downloads whole tracks or walks/ID3-parses the library on-device.

- **Source of truth for the code:** `src/servers/sidecar/music/index.ts` (the `officer-music` sidecar owns
  all of this; the platform `/api/music/*` route is a transparent auth-ing proxy).
- **Music root:** `~/Music` on the server. All `path` values are **home-relative** (e.g.
  `Music/Albums/AC-DC/[1980] Back in Black/01 Hells Bells.mp3`), identical to `/api/file-browser/raw`.
- **`<rel>`:** an album folder path **relative to the `Music` root** (e.g. `Albums/AC-DC/[1980] Back in Black`).

## Auth

Every endpoint is behind the standard user auth. Two ways to pass the JWT:

- **Header:** `Authorization: Bearer <jwt>` (normal fetches).
- **Query:** `?token=<jwt>` — for media elements / native players that can't set headers (audio, images).

`401` = no token · `403` = invalid/expired token.

---

## 1. Playback — stream a track

```
GET /api/music/stream?path=<home-relative>&token=<jwt>
```

Byte-range streaming so the player can **seek without downloading the whole file**.

| Case | Status | Headers |
|---|---|---|
| No `Range` | `200` | `Content-Type`, `Content-Length`, `Accept-Ranges: bytes`, `X-Audio-Duration` |
| With `Range: bytes=…` | `206` | `Content-Range`, `Content-Length`, `Accept-Ranges: bytes`, `Content-Type`, `X-Audio-Duration` |

- **`X-Audio-Duration`**: track duration in **seconds** (ffprobe-derived). Read this to set the player's
  duration up front — it's the fix for AVPlayer reporting an *indefinite* duration on progressively-streamed
  VBR MP3s. No need to scan the file.
- Errors: `400` invalid/missing path · `404` not found · `416` bad range.

```
curl -H "Authorization: Bearer $JWT" -H "Range: bytes=0-1023" \
  "$BASE/api/music/stream?path=Music/Albums/AC-DC/[1980]%20Back%20in%20Black/01%20Hells%20Bells.mp3" -D -
```

---

## 2. Library index — the synced cache

The server maintains a cache tree that **mirrors the library**, one entry per album folder. The app syncs
this instead of walking + ID3-parsing the library itself.

Each album has a **version stamp `v`** (hash of the album's source files' names/sizes/mtimes + its cover).
`v` changes **iff the album's content changed** → it's the whole basis of the diff: *unchanged `v` ⇒ skip*.

### 2.1 Manifest — one call, whole library

```
GET /api/music/manifest
```
```jsonc
{
  "version": 1,
  "generatedAt": 1785034701973,          // ms; when the index was last built
  "albums": {
    "Albums/AC-DC/[1980] Back in Black": { "v": "50856380f1ca8f9", "cover": true, "tracks": 10 },
    "DJ Sets/Dave Clarke":              { "v": "a1b2c3d4e5f6a7b", "cover": false, "tracks": 3 },
    "Albums/AC-DC":                     { "v": "c0ffee1234567890", "cover": true, "tracks": 0, "disco": true }
    // …
  }
}
```
`404` if the index has never been built (see §3). Entries with **`tracks: 0`** are container folders (e.g. an
**artist** folder). An entry with **`disco: true`** is an artist folder that has a discography — fetch its
grouping via `/discography` (§2.4).

### 2.2 Album metadata

```
GET /api/music/meta?path=<rel>
```
Returns the album's `meta.json`. Sends `ETag: <v>`; a request with `If-None-Match: <v>` returns `304`.
```jsonc
{
  "path": "Albums/AC-DC/[1980] Back in Black",
  "cover": "cover.jpg",                    // present only if a cover exists
  "tracks": [
    {
      "file": "01 Hells Bells.mp3",        // filename within the album folder
      "title": "Hells Bells",
      "artist": "AC/DC",
      "albumArtist": "AC/DC",
      "album": "Back in Black",
      "track": "1",
      "year": "1980",
      "durationSec": 312
    }
    // …
  ]
}
```
All track fields except `file` are optional (absent when the tag is missing).
To stream a track: `GET /api/music/stream?path=Music/<rel>/<file>`.

### 2.3 Cover

```
GET /api/music/cover?path=<rel>
```
Compressed JPEG (≤600px on the long edge, ~30–80 KB). Sends `ETag: <v>`; `If-None-Match: <v>` → `304`.
Only meaningful when the manifest entry has `"cover": true`.

### 2.4 Discography (artist album grouping)

For artist folders (manifest entry with `"disco": true`), this returns a map of **album folder → release
type**, so the player can split an artist's album list into sections (Studio, Live, Compilation, Single, EP…).

```
GET /api/music/discography?path=<artist rel>      e.g. path=Albums/AC-DC
```
Sends `ETag: <v>`; `If-None-Match: <v>` → `304`.
```jsonc
{
  "artist": "Anthrax",
  "albums": {
    "[1984] Fistful Of Metal": "Studio",
    "[1985] Armed And Dangerous": "EP",
    "[1994] The Island Years": "Live",
    "[1991] Attack Of The Killer B's": "Compilation"
    // …
  }
}
```
- Keys are **album folder names** (`[year] title`) — they map 1:1 to the artist's album folders, i.e. the
  last path segment of that album's manifest `<rel>`. Group the artist's albums by looking each up here.
- **Types** are a normalized set: `Studio`, `Live`, `Compilation`, `Single`, `EP`, `Soundtrack`, `Remix`,
  `DJ-Mix`, `Demo`, `Mixtape`, `Bootleg`, `Other` (unknown values pass through as-is). The player defines
  section order.
- An album folder **not present** here has no classification → put it in an "Other"/uncategorized section.
- Source of truth is each artist's `_discography.md` (author-maintained); this JSON is derived from it and
  re-generated whenever that file changes (its `v` bumps independently of the albums' `meta`/`cover`).

---

## 3. Building / refreshing the index

The index is built **on demand** (nothing is pre-built or scheduled). A build is **incremental** — albums
whose `v` is unchanged are skipped — and it **prunes** albums removed from the library.

### 3.1 Trigger

```
POST /api/music/reindex          → returns IndexStatus (running: true)
GET  /api/music/reindex/status   → IndexStatus snapshot
```

`IndexStatus`:
```jsonc
{
  "running": true,
  "startedAt": 1785034701973, "finishedAt": null,
  "foldersScanned": 45, "albumsBuilt": 12, "albumsSkipped": 3,
  "tracksIndexed": 320, "coversSaved": 12, "discographies": 3,
  "currentPath": "Albums/AC-DC/[1980] Back in Black",
  "error": null
}
```

### 3.2 Live progress — SSE

```
GET /api/music/reindex/stream
```
- **Triggers a build if none is running.** Pass `?trigger=0` to **watch only** (subscribe without starting one).
- Emits `event: progress` (an `IndexStatus`) throttled to ~200 ms, then a single `event: done` (an
  `IndexReport`) and **closes** the stream.

```
event: progress
data: {"running":true,"foldersScanned":45,"tracksIndexed":320,"albumsBuilt":12,"albumsSkipped":3,"coversSaved":12,"currentPath":"Albums/AC-DC/[1980] Back in Black", …}

event: done
data: {"albums":15,"built":12,"skipped":3,"foldersScanned":45,"tracksIndexed":320,"coversSaved":12,"elapsedSec":37.2,"error":null}
```

`IndexReport` (the `done` payload):
```jsonc
{ "albums": 15, "built": 12, "skipped": 3, "foldersScanned": 45,
  "tracksIndexed": 320, "coversSaved": 12, "discographies": 3, "elapsedSec": 37.2, "error": null }
```

> First build of a large library takes a few minutes; re-runs are near-instant (unchanged albums skip via `v`).

---

## 4. Recommended resync algorithm (app side)

Keep the last `manifest.albums` you synced. On resync:

1. `GET /api/music/manifest`.
2. For each `<rel>` in the new manifest:
   - **new**, or **`v` differs** from your stored copy → fetch `GET /meta?path=<rel>` (+ `GET /cover?path=<rel>`
     if `cover:true`, + `GET /discography?path=<rel>` if `disco:true`); store them under your local `<rel>/`.
   - **`v` unchanged** → **skip** (no download).
3. For each `<rel>` you have locally that's **absent** from the new manifest → delete it.
4. Save the new manifest as your baseline.

Optionally trigger a fresh server build first via `GET /reindex/stream` (and show progress from its
`progress`/`done` events) so the manifest reflects the latest library before you diff.

Result: a resync after adding one album = 1 manifest fetch + that one album's `meta` + `cover`. Nothing else moves.

---

## Notes

- **Covers are server-compressed** (≤600px / q5) — sync them as-is; no client-side resizing needed.
- **Durations are exact** (ffprobe) in both `X-Audio-Duration` and `meta.json`'s `durationSec` (seconds).
- **Playback still goes through `/stream`** — the index is metadata + covers only. (Server-managed *offline
  audio files* is a separate, later feature.)
- **Errors** are plain HTTP: `503` if the music sidecar isn't connected, `502` if it's unreachable.