Move MP3Gain into its own tab

Sources/ContentView.swift

@@ -14,6 +14,11 @@ struct ContentView: View {
                     Label("SD-Karte", systemImage: "sdcard")
                 }
 
+            MP3GainToolView()
+                .tabItem {
+                    Label("MP3Gain", systemImage: "waveform")
+                }
+
             ID3TagToolView()
                 .tabItem {
                     Label("ID3-Tags", systemImage: "tag")
@@ -301,13 +306,6 @@ private struct SDCardToolView: View {
                 }
                 .disabled(!canRun)
 
-                Button {
-                    normalizeMP3Gain()
-                } label: {
-                    Label("MP3Gain", systemImage: "waveform")
-                }
-                .disabled(!canRun)
-
                 Button {
                     cleanSDCard()
                 } label: {
@@ -394,15 +392,73 @@ private struct SDCardToolView: View {
         }
     }
 
+}
+
+private struct MP3GainToolView: View {
+    @State private var targetURL: URL?
+    @State private var messages: [ExportMessage] = []
+    @State private var isWorking = false
+
+    private var canRun: Bool {
+        targetURL != nil && !isWorking
+    }
+
+    var body: some View {
+        VStack(spacing: 0) {
+            HStack(spacing: 10) {
+                Button {
+                    chooseFolder(title: "Ordner für MP3Gain wählen") { url in
+                        targetURL = url
+                        messages = []
+                    }
+                } label: {
+                    Label("Ordner", systemImage: "folder")
+                }
+
+                Spacer()
+
+                Button {
+                    normalizeMP3Gain()
+                } label: {
+                    Label("MP3Gain ausführen", systemImage: "waveform")
+                }
+                .buttonStyle(.borderedProminent)
+                .disabled(!canRun)
+            }
+            .padding(12)
+
+            Divider()
+
+            VStack(alignment: .leading, spacing: 16) {
+                VStack(alignment: .leading, spacing: 8) {
+                    Text("MP3Gain Normalisierung")
+                        .font(.title2.weight(.semibold))
+                    PathRow(label: "Ordner", url: targetURL)
+                    Text("Verwendet rekursiv: mp3gain -r -k -d 4")
+                        .foregroundStyle(.secondary)
+                }
+
+                VStack(alignment: .leading, spacing: 10) {
+                    Text("Protokoll")
+                        .font(.headline)
+                    MessageList(messages: messages, emptyText: "Noch keine MP3-Dateien normalisiert.")
+                }
+
+                Spacer(minLength: 0)
+            }
+            .padding(16)
+            .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .topLeading)
+        }
+    }
+
     private func normalizeMP3Gain() {
-        guard let sdCardURL else { return }
+        guard let targetURL else { return }
 
         isWorking = true
         messages = [.info("MP3Gain gestartet: -r -k -d 4")]
 
         DispatchQueue.global(qos: .userInitiated).async {
-            var result = MP3GainNormalizer(fileManager: .default).normalize(rootURL: sdCardURL)
-            result.append(contentsOf: SDCardValidator(fileManager: .default).validate(rootURL: sdCardURL))
+            let result = MP3GainNormalizer(fileManager: .default).normalize(rootURL: targetURL)
 
             DispatchQueue.main.async {
                 messages = result