Implement snapshot version history

Sources/MusicAssistantCore/Domain/SongProject.swift

@@ -324,6 +324,25 @@ public extension SongProject {
         vocalists[index].assignedSections.removeAll { $0 == sectionID }
     }
 
+    mutating func createVersion(
+        id: String = UUID().uuidString,
+        label: String,
+        createdAt: Date = Date()
+    ) -> SongVersion {
+        let version = SongVersion(
+            id: id,
+            label: label,
+            snapshot: SongProjectSnapshot(project: self),
+            createdAt: createdAt
+        )
+        versions.append(version)
+        return version
+    }
+
+    func version(id versionID: String) -> SongVersion? {
+        versions.first { $0.id == versionID }
+    }
+
     mutating func appendSection(_ section: SongSection) {
         var orderedSection = section
         orderedSection.order = nextSectionOrder

Tests/MusicAssistantCoreTests/SongProjectModelTests.swift

@@ -89,6 +89,36 @@ final class SongProjectModelTests: XCTestCase {
         XCTAssertEqual(version.snapshot.instruments, project.instruments)
     }
 
+    func testVersionHistoryStoresIndependentSnapshots() {
+        var project = SongProject(
+            id: "versioned-project",
+            title: "First Title",
+            idea: "Original idea",
+            genres: [GenreStyle(id: "folk", name: "Folk")]
+        )
+        let createdAt = Date(timeIntervalSince1970: 500)
+
+        let version = project.createVersion(
+            id: "version-1",
+            label: "Initial snapshot",
+            createdAt: createdAt
+        )
+
+        project.title = "Changed Title"
+        project.idea = "Changed idea"
+        project.selectGenreStyle(GenreStyle(id: "electronic", name: "Electronic"))
+
+        XCTAssertEqual(project.versions.count, 1)
+        XCTAssertEqual(project.version(id: "version-1"), version)
+        XCTAssertEqual(project.versions.first?.label, "Initial snapshot")
+        XCTAssertEqual(project.versions.first?.createdAt, createdAt)
+        XCTAssertEqual(project.versions.first?.snapshot.title, "First Title")
+        XCTAssertEqual(project.versions.first?.snapshot.idea, "Original idea")
+        XCTAssertEqual(project.versions.first?.snapshot.genres, [GenreStyle(id: "folk", name: "Folk")])
+        XCTAssertEqual(project.title, "Changed Title")
+        XCTAssertEqual(project.genres.map(\.id), ["folk", "electronic"])
+    }
+
     func testGenreStylesAreModeledAsMultiSelect() {
         let arabicPop = GenreStyle(id: "arabic-pop", name: "Arabic Pop")
         let synthwave = GenreStyle(id: "synthwave", name: "Synthwave")

docs/TASKS.md

@@ -34,7 +34,7 @@ requirement is missing and blocks implementation, record it in
 
 -   [x] Create new/open/save song projects locally.
 -   [x] Implement project list.
--   [ ] Implement immutable or snapshot-based version history.
+-   [x] Implement immutable or snapshot-based version history.
 -   [ ] Restore a previous version without destroying later versions.
 -   [ ] Add autosave strategy that does not create excessive versions.