refactor: capabilities registration

Signed-off-by: Deluan <deluan@navidrome.org>

plugins/capabilities.go

@@ -4,41 +4,13 @@ package plugins
 // Capabilities are detected by checking which functions a plugin exports.
 type Capability string
 
-const (
-	// CapabilityMetadataAgent indicates the plugin can provide artist/album metadata.
-	// Detected when the plugin exports at least one of the metadata agent functions.
-	CapabilityMetadataAgent Capability = "MetadataAgent"
-
-	// CapabilityScrobbler indicates the plugin can receive scrobble events.
-	// Detected when the plugin exports at least one of the scrobbler functions.
-	CapabilityScrobbler Capability = "Scrobbler"
-
-	// CapabilityScheduler indicates the plugin can receive scheduled event callbacks.
-	// Detected when the plugin exports the scheduler callback function.
-	CapabilityScheduler Capability = "Scheduler"
-)
-
 // capabilityFunctions maps each capability to its required/optional functions.
 // A plugin has a capability if it exports at least one of these functions.
-var capabilityFunctions = map[Capability][]string{
-	CapabilityMetadataAgent: {
-		FuncGetArtistMBID,
-		FuncGetArtistURL,
-		FuncGetArtistBiography,
-		FuncGetSimilarArtists,
-		FuncGetArtistImages,
-		FuncGetArtistTopSongs,
-		FuncGetAlbumInfo,
-		FuncGetAlbumImages,
-	},
-	CapabilityScrobbler: {
-		FuncScrobblerIsAuthorized,
-		FuncScrobblerNowPlaying,
-		FuncScrobblerScrobble,
-	},
-	CapabilityScheduler: {
-		FuncSchedulerCallback,
-	},
+var capabilityFunctions = map[Capability][]string{}
+
+// registerCapability registers a capability with its associated functions.
+func registerCapability(cap Capability, functions ...string) {
+	capabilityFunctions[cap] = functions
 }
 
 // functionExistsChecker is an interface for checking if a function exists in a plugin.

plugins/host_scheduler.go

@@ -12,8 +12,19 @@ import (
 	"github.com/navidrome/navidrome/scheduler"
 )
 
+// CapabilityScheduler indicates the plugin can receive scheduled event callbacks.
+// Detected when the plugin exports the scheduler callback function.
+const CapabilityScheduler Capability = "Scheduler"
+
 const FuncSchedulerCallback = "nd_scheduler_callback"
 
+func init() {
+	registerCapability(
+		CapabilityScheduler,
+		FuncSchedulerCallback,
+	)
+}
+
 // timeAfterFunc is a variable for time.AfterFunc, allowing tests to override it.
 var timeAfterFunc = time.AfterFunc
 

plugins/metadata_agent.go

@@ -7,6 +7,10 @@ import (
 	"github.com/navidrome/navidrome/core/agents"
 )
 
+// CapabilityMetadataAgent indicates the plugin can provide artist/album metadata.
+// Detected when the plugin exports at least one of the metadata agent functions.
+const CapabilityMetadataAgent Capability = "MetadataAgent"
+
 // Export function names (snake_case as per design)
 const (
 	FuncGetArtistMBID      = "nd_get_artist_mbid"
@@ -19,6 +23,20 @@ const (
 	FuncGetAlbumImages     = "nd_get_album_images"
 )
 
+func init() {
+	registerCapability(
+		CapabilityMetadataAgent,
+		FuncGetArtistMBID,
+		FuncGetArtistURL,
+		FuncGetArtistBiography,
+		FuncGetSimilarArtists,
+		FuncGetArtistImages,
+		FuncGetArtistTopSongs,
+		FuncGetAlbumInfo,
+		FuncGetAlbumImages,
+	)
+}
+
 // MetadataAgent is an adapter that wraps an Extism plugin and implements
 // the agents interfaces for metadata retrieval.
 type MetadataAgent struct {

plugins/scrobbler_adapter.go

@@ -9,6 +9,10 @@ import (
 	"github.com/navidrome/navidrome/model/request"
 )
 
+// CapabilityScrobbler indicates the plugin can receive scrobble events.
+// Detected when the plugin exports at least one of the scrobbler functions.
+const CapabilityScrobbler Capability = "Scrobbler"
+
 // Scrobbler function names (snake_case as per design)
 const (
 	FuncScrobblerIsAuthorized = "nd_scrobbler_is_authorized"
@@ -16,6 +20,15 @@ const (
 	FuncScrobblerScrobble     = "nd_scrobbler_scrobble"
 )
 
+func init() {
+	registerCapability(
+		CapabilityScrobbler,
+		FuncScrobblerIsAuthorized,
+		FuncScrobblerNowPlaying,
+		FuncScrobblerScrobble,
+	)
+}
+
 // ScrobblerPlugin is an adapter that wraps an Extism plugin and implements
 // the scrobbler.Scrobbler interface for scrobbling to external services.
 type ScrobblerPlugin struct {