linker/README.md

# Reddit → Spotify / Bandcamp linker

A Firefox extension that, while you browse a Reddit thread, finds **artist / band
names** in the comments (and the post body) and turns them into inline links to
**Spotify** and **Bandcamp** — so a recommendation thread like
[this one](https://www.reddit.com/r/SlamDeathMetal/comments/1txh2r1/) becomes a
list of clickable artists instead of names you have to copy-paste into search.

The hard part is *"which words are artists and which aren't?"*. Rather than guess
with client-side rules, the extension hands candidate names to a tiny local
**resolver service** that checks each one against a real music database and only
links the names that actually match an artist.

```
 reddit page                 content script                 resolver service
 ───────────                 ──────────────                 ────────────────
 comment text  ──extract──>  candidate names  ──POST /resolve──>  Spotify API  (direct links)
                                                                     or
 <a> links     <──rewrite──  confirmed links  <─────────────────  MusicBrainz  (zero-setup)
```

## Layout

```
service/      tiny Node.js resolver (one file, zero npm deps)
  resolver.js
  package.json
  .env.example
extension/    Firefox MV2 extension
  manifest.json
  background.js   (does the resolver fetch; talks to the content script)
  content.js
  styles.css
  icon.svg
```

## 1. Run the resolver service

Requirements: **Node 18+** (uses the built-in `fetch`). No `npm install` needed —
there are no dependencies.

```sh
cd service
node resolver.js
# resolver listening on http://localhost:8787  (provider: musicbrainz)
```

That's it. With no configuration the resolver validates names against
**MusicBrainz** (no account required). When MusicBrainz knows an artist's official
links (its `url-relations`), you get **direct** Spotify and Bandcamp artist pages;
otherwise it falls back to Spotify/Bandcamp **search** URLs.

### Optional: direct Spotify links

For **direct artist links** (instead of Spotify search), give the service Spotify
API credentials:

1. Create a free app at <https://developer.spotify.com/dashboard> and copy its
   **Client ID** and **Client Secret**.
2. `cp .env.example .env` and fill them in (the `.env` file is gitignored):

   ```
   SPOTIFY_CLIENT_ID=your_id
   SPOTIFY_CLIENT_SECRET=your_secret
   ```
3. Restart the service. It will report `provider: spotify` on startup.

(Bandcamp has no public API; direct Bandcamp links come from MusicBrainz
`url-relations` when present, else a Bandcamp search URL.)

Quick check that it works:

```sh
curl -s localhost:8787/resolve \
  -H 'content-type: application/json' \
  -d '{"candidates":["Cerebral Bore","Devourment","Notarealband Xyzzy"]}'
# {"Cerebral Bore":{...},"Devourment":{...},"Notarealband Xyzzy":null}
```

## 2. Install the extension in Firefox

The extension is unpacked / unsigned, so load it as a **temporary add-on**:

1. Open `about:debugging#/runtime/this-firefox`.
2. **Load Temporary Add-on…**
3. Select `extension/manifest.json`.

It's now active until you restart Firefox. (To keep it permanently you'd sign it
via [AMO](https://addons.mozilla.org/developers/) or use Firefox Developer/ESR
with `xpinstall.signatures.required = false`.)

## 3. Use it

1. Make sure the resolver service is running.
2. Open any Reddit comments thread (a URL with `/comments/` in it).
3. Artist names become a single link — to **Spotify** if the artist is on Spotify,
   otherwise to **Bandcamp** — colour-coded (green = Spotify, teal = Bandcamp). New
   comments loaded as you scroll are linked automatically.
4. The toolbar icon shows the extension is active; its badge shows how many links were
   added on the current page.

## Troubleshooting

If nothing gets linked:

1. Confirm the resolver is running — `curl localhost:8787/health` should return
   `{"ok":true,...}`.
2. On the reddit thread, open the browser console (F12) and look for `[rsl]` logs: they
   report the root element, candidate count, and resolver responses on each scan. A
   `resolve failed` line means the background script can't reach the resolver (is it on
   `:8787`?); `candidates found: 0` means the comment text wasn't matched (please report
   the thread).
3. The content script reaches the resolver **through the extension's background script**
   — a page-context fetch to `http://localhost` is blocked by reddit's CSP — so make sure
   the add-on loaded without errors in `about:debugging`.

## Configuration

The resolver URL is the constant `RESOLVER_URL` at the top of
`extension/content.js` (default `http://localhost:8787`). If you change the host
or port, update **both** that constant **and** the matching entry in
`extension/manifest.json` → `permissions` (Firefox needs the host listed there to
let the content script reach it).

## Limitations (MVP)

- **Detection is capitalization-based.** Names written in lowercase, or split
  across formatting (e.g. **bold** in the middle of a name), can be missed. The
  resolver's exact-name match keeps false *positives* low; the trade-off is some
  false *negatives*.
- **Links are direct when MusicBrainz has the artist's `url-relations`** (official
  Bandcamp / Spotify pages); otherwise they fall back to a search URL. (Each
  confirmed artist costs one extra throttled MusicBrainz lookup, cached after.)
- The resolver caches results in memory; it resets when you restart it.
- Without Spotify credentials the MusicBrainz path is rate-limited to ~1 lookup/
  second, so the first scan of a large thread fills in gradually (cached after).
- Built and tested as a Firefox MV2 extension.

## License

Personal project — do as you like.