JSPF: Implemented export as loves and listens

pkg/jspf/extensions.go

@@ -1,5 +1,5 @@
 /*
-Copyright © 2023 Philipp Wolfer <phw@uploadedlobster.com>
+Copyright © 2023-2025 Philipp Wolfer <phw@uploadedlobster.com>
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -22,7 +22,28 @@ THE SOFTWARE.
 
 package jspf
 
-import "time"
+import (
+	"encoding/json"
+	"fmt"
+	"time"
+)
+
+// Represents a JSPF extension
+type Extension any
+
+// A map of JSPF extensions
+type ExtensionMap map[string]Extension
+
+// Parses the extension with the given ID and unmarshals it into "v".
+// If the extensions is not found or the data cannot be unmarshalled,
+// an error is returned.
+func (e ExtensionMap) Get(id string, v any) error {
+	ext, ok := e[id]
+	if !ok {
+		return fmt.Errorf("extension %q not found", id)
+	}
+	return unmarshalExtension(ext, v)
+}
 
 const (
 	// The identifier for the MusicBrainz / ListenBrainz JSPF playlist extension
@@ -83,3 +104,11 @@ type MusicBrainzTrackExtension struct {
 	// this document.
 	AdditionalMetadata map[string]any `json:"additional_metadata,omitempty"`
 }
+
+func unmarshalExtension(ext Extension, v any) error {
+	asJson, err := json.Marshal(ext)
+	if err != nil {
+		return err
+	}
+	return json.Unmarshal(asJson, v)
+}