Model vocalist section assignments

Sources/MusicAssistantCore/Domain/SongProject.swift

@@ -169,6 +169,44 @@ public extension SongProject {
         }
     }
 
+    var vocalistIDs: Set<String> {
+        Set(vocalists.map(\.id))
+    }
+
+    func vocalist(for vocalistID: String) -> Vocalist? {
+        vocalists.first { $0.id == vocalistID }
+    }
+
+    func vocalistsAssigned(toSectionID sectionID: String) -> [Vocalist] {
+        vocalists.filter { $0.assignedSections.contains(sectionID) }
+    }
+
+    mutating func upsertVocalist(_ vocalist: Vocalist) {
+        var normalizedVocalist = vocalist
+        normalizedVocalist.assignedSections = Self.uniqueOrderedIDs(vocalist.assignedSections)
+
+        if let index = vocalists.firstIndex(where: { $0.id == vocalist.id }) {
+            vocalists[index] = normalizedVocalist
+        } else {
+            vocalists.append(normalizedVocalist)
+        }
+    }
+
+    mutating func removeVocalist(id vocalistID: String) {
+        vocalists.removeAll { $0.id == vocalistID }
+    }
+
+    mutating func assignSection(_ sectionID: String, toVocalistID vocalistID: String) {
+        guard let index = vocalists.firstIndex(where: { $0.id == vocalistID }) else { return }
+        guard !vocalists[index].assignedSections.contains(sectionID) else { return }
+        vocalists[index].assignedSections.append(sectionID)
+    }
+
+    mutating func unassignSection(_ sectionID: String, fromVocalistID vocalistID: String) {
+        guard let index = vocalists.firstIndex(where: { $0.id == vocalistID }) else { return }
+        vocalists[index].assignedSections.removeAll { $0 == sectionID }
+    }
+
     mutating func appendSection(_ section: SongSection) {
         var orderedSection = section
         orderedSection.order = nextSectionOrder
@@ -200,6 +238,11 @@ public extension SongProject {
             return orderedSection
         }
     }
+
+    private static func uniqueOrderedIDs(_ ids: [String]) -> [String] {
+        var seenIDs = Set<String>()
+        return ids.filter { seenIDs.insert($0).inserted }
+    }
 }
 
 public enum ConversationMode: String, Codable, Equatable, Sendable {