SoulSync/docs/media-server-engine-refactor-plan.md

Media Server Engine Refactor Plan

Goal

Same playbook as the download engine refactor, applied to media servers. Replace 33 if active_server == 'plex' / 'jellyfin' / 'navidrome' / 'soulsync' dispatch sites in web_server.py with a central MediaServerEngine that owns server selection + cross-server query dispatch. Each per-server client stays as-is for its protocol-specific work (Plex API SDK, Jellyfin REST, Navidrome OpenSubsonic, SoulSync filesystem walk).

The smell: Adding a 5th server (recent SoulSync standalone showed how) requires hunting through 33 web_server.py dispatch sites + DatabaseUpdateWorker branching + UI sync-button visibility hacks. Plex assumptions had leaked into nominally generic code paths.

Architecture target

┌───────────┐                         ┌──────────────────┐
│  feature  │ ─search/scan/sync─▶ ┌──│ MediaServerEngine │ ─▶ Plex (PlexAPI SDK)
│           │ ◀── results ──────  │  │ ◆ active selection│ ─▶ Jellyfin (REST)
└───────────┘                     │  │ ◆ dispatch        │ ─▶ Navidrome (Subsonic)
                                  │  │ ◆ shared shape   │ ─▶ SoulSync (filesystem)
                                  │  └──────────────────┘
                                  │  (no need for per-server thread pool — server APIs
                                  │   are sync-call shaped, not stream-shaped like downloads)

What clients keep (per-server, legitimately)

• Auth — Plex token, Jellyfin API key + user ID + library ID, Navidrome user/pass + salt, SoulSync filesystem path
• Wire protocol — PlexAPI SDK objects vs Jellyfin REST /Items vs Navidrome XML/JSON Subsonic vs filesystem walk
• ID schemes — Plex ratingKey (int), Jellyfin GUID (hex), Navidrome string, SoulSync MD5
• Connection state — each client owns its session / token / connection object
• Cache strategy — Jellyfin's aggressive pre-cache, Navidrome's folder filter, SoulSync's 5-min TTL
• Wrapper objects — JellyfinTrack, NavidromeTrack, etc. stay in client modules

What moves into the engine

Today (web_server.py duplicated)	Tomorrow (MediaServerEngine, single dispatch site)
if active_server == 'plex': plex_client.X() elif 'jellyfin': jellyfin_client.X() ...	engine.X() — engine reads active_server once, routes
Status check 4-way branch	engine.is_connected()
Library scan trigger 3-way	engine.trigger_library_scan()
Search dispatch in 3 sites	engine.search_tracks(title, artist)
Play history 4-way	engine.get_play_history()
Metadata writeback 4-way (genre / poster / bio)	engine.update_artist_genres() etc. — engine routes, plugin no-ops where unsupported
DatabaseUpdateWorker.server_type branching	engine injected, no per-server branching

Plugin contract (ABC, narrower than the download contract)

class MediaServerClient(ABC):
    # Connection
    @abstractmethod
    def is_connected(self) -> bool: ...
    @abstractmethod
    def ensure_connection(self) -> bool: ...

    # Library reads (required)
    @abstractmethod
    def get_all_artists(self): ...
    @abstractmethod
    def get_all_album_ids(self): ...
    @abstractmethod
    def search_tracks(self, title, artist, limit=15): ...
    @abstractmethod
    def get_recently_added_albums(self, max_results=400): ...

    # Library writes (required for the scan endpoints — may no-op for SoulSync)
    @abstractmethod
    def trigger_library_scan(self) -> bool: ...
    @abstractmethod
    def is_library_scanning(self) -> bool: ...

    # Playlist sync (optional — Navidrome stub returns True)
    def create_playlist(self, name, tracks) -> bool: return True
    def update_playlist(self, name, tracks) -> bool: return True
    def copy_playlist(self, source, dest_name) -> bool: return True

    # Analytics (optional)
    def get_play_history(self, limit=500) -> list: return []
    def get_track_play_counts(self) -> dict: return {}

    # Metadata writeback (optional — clients no-op where API doesn't support it)
    def update_artist_genres(self, artist, genres) -> bool: return True
    def update_artist_poster(self, artist, image_data) -> bool: return True
    def update_album_poster(self, album, image_data) -> bool: return True
    def update_artist_biography(self, artist) -> bool: return True

Phased commit plan

Phase 0 — Foundation

• 0.1 Plugin contract (core/media_server/contract.py) + ABC
• 0.2 Registry + dispatch helpers (core/media_server/registry.py)
• 0.3 Conformance tests — every registered client satisfies the ABC

Phase A — Behavior pinning

• A1 Pin Plex client surface (status check, search, scan trigger, metadata writeback shape)
• A2 Pin Jellyfin client surface
• A3 Pin Navidrome client surface
• A4 Pin SoulSync standalone client surface

Phase B — Engine skeleton

• B1 MediaServerEngine skeleton — holds clients, exposes active_server selection
• B2 Engine dispatch methods (is_connected, search_tracks, trigger_library_scan, is_library_scanning, etc.)
• B3 Engine-level conformance tests

Phase C — Migrate web_server.py dispatch sites

Each commit migrates a logical cluster (status, scan, playlist, metadata, history) so the diff per commit is small + reviewable.

• C1 Status / connection-check sites
• C2 Library scan trigger + scanning-state polling
• C3 Search dispatch (3 sites)
• C4 Playlist sync / apply / suggest
• C5 Play history + track play counts
• C6 Metadata writeback (genres / posters / bio)

Phase D — DatabaseUpdateWorker

• D1 Inject engine into DatabaseUpdateWorker
• D2 Strip self.server_type branching (use engine.get_active_client_type() where shape genuinely differs)

Phase E — Cleanup + ship

• E1 Drop unused imports / dead code
• E2 WHATS_NEW + PR description

Total estimated: 15-18 commits. ~600 LOC moved, ~200 LOC deleted.

Risk profile

Low:

• Phase 0 (pure additive — new contract, no existing code touched)
• Phase A (tests only)
• Phase B (engine exists but nothing routes through it yet)

Medium:

• Phase C (each commit changes 5-10 dispatch sites in web_server.py — cross-cutting)
• Phase D (DatabaseUpdateWorker is a hot path during library refresh)

Mitigation:

• Phase A pinning catches per-client behavior drift
• Phase B engine tested in isolation before C wires it in
• Phase C commits are small + reversible (one cluster per commit)
• Suite green at every commit

What's NOT in this PR

• Unifying track ID schemes (Plex int vs Jellyfin GUID vs Navidrome string vs SoulSync MD5) — separate data model refactor
• Merging Plex/Jellyfin/Navidrome wrapper objects (each tied to its API)
• Extracting common metadata writeback logic — too server-specific
• Adding new server types (Subsonic, MusicBrainz local) — out of scope; this PR makes them easier later

Coordination with other work

• Independent of the download engine refactor (PR #494) — different subsystem
• Cin's metadata engine work also independent
• No collisions expected

Compatibility commitments

• All existing config keys preserved
• All existing API endpoints preserved
• Plex/Jellyfin/Navidrome/SoulSync clients keep their public methods (engine wraps, doesn't replace)
• Active-server config (server.active) unchanged
• DatabaseUpdateWorker.server_type available for external readers (deprecated but not removed)