Disable export until a system has components

The Overview share menu offered a wiring diagram and a full report even
for an empty system. Gate it on loads, batteries or chargers being
present (iOS + Android) and add UI tests for both states.

Cable/Loads/LoadsView.swift

@@ -56,6 +56,10 @@ struct LoadsView: View {
         allChargers.filter { $0.system == system }
     }
 
+    private var hasComponents: Bool {
+        !savedLoads.isEmpty || !savedBatteries.isEmpty || !savedChargers.isEmpty
+    }
+
     var body: some View {
         VStack(spacing: 0) {
             TabView(selection: $selectedComponentTab) {
@@ -174,6 +178,7 @@ struct LoadsView: View {
                         } label: {
                             Image(systemName: "square.and.arrow.up")
                         }
+                        .disabled(!hasComponents)
                         .accessibilityIdentifier("system-overview-share-button")
                     }
                 } else if showPrimary || showEditLoads || showEditBatteries || showEditChargers {

CableUITestsScreenshot/SystemExportButtonUITests.swift

@@ -0,0 +1,71 @@
+import XCTest
+
+/// Verifies that the Overview export/share menu is only available once the
+/// system actually contains something worth exporting.
+final class SystemExportButtonUITests: XCTestCase {
+
+    override func setUpWithError() throws {
+        try super.setUpWithError()
+        continueAfterFailure = false
+        XCUIDevice.shared.orientation = .portrait
+    }
+
+    @MainActor
+    func testExportIsDisabledForSystemWithoutComponents() throws {
+        let app = launch(arguments: ["--uitest-reset-data"])
+
+        let createSystemButton = app.buttons["create-system-button"]
+        XCTAssertTrue(createSystemButton.waitForExistence(timeout: 15))
+        createSystemButton.tap()
+
+        let shareButton = app.buttons["system-overview-share-button"]
+        XCTAssertTrue(shareButton.waitForExistence(timeout: 15))
+        XCTAssertFalse(
+            shareButton.isEnabled,
+            "Export must stay disabled while the system has no loads, batteries or chargers"
+        )
+    }
+
+    @MainActor
+    func testExportIsEnabledOnceComponentsExist() throws {
+        let app = launch(arguments: ["--uitest-reset-data", "--uitest-sample-data"])
+
+        openFirstSystem(in: app)
+
+        let shareButton = app.buttons["system-overview-share-button"]
+        XCTAssertTrue(shareButton.waitForExistence(timeout: 15))
+        XCTAssertTrue(
+            shareButton.isEnabled,
+            "Export must be available for a system that has components"
+        )
+    }
+
+    // MARK: - Helpers
+
+    private func launch(arguments: [String]) -> XCUIApplication {
+        let app = XCUIApplication()
+        app.launchArguments = arguments
+        app.launch()
+        return app
+    }
+
+    private func openFirstSystem(in app: XCUIApplication) {
+        let list: XCUIElement
+        if app.collectionViews["systems-list"].waitForExistence(timeout: 15) {
+            list = app.collectionViews["systems-list"]
+        } else {
+            list = app.collectionViews.firstMatch
+        }
+        XCTAssertTrue(list.waitForExistence(timeout: 15))
+
+        let firstCell = list.cells.element(boundBy: 0)
+        XCTAssertTrue(firstCell.waitForExistence(timeout: 10))
+
+        let cellButton = firstCell.buttons.firstMatch
+        if cellButton.exists {
+            cellButton.tap()
+        } else {
+            firstCell.coordinate(withNormalizedOffset: CGVector(dx: 0.5, dy: 0.5)).tap()
+        }
+    }
+}

android/app/src/main/java/app/voltplan/cable/ui/system/SystemDetailScreen.kt

@@ -157,7 +157,7 @@ fun SystemDetailScreen(
                                     strokeWidth = 2.dp,
                                 )
                             } else {
-                                IconButton(onClick = { showOverviewMenu = true }) {
+                                IconButton(onClick = { showOverviewMenu = true }, enabled = state.hasComponents) {
                                     Icon(Icons.Outlined.IosShare, contentDescription = stringResource(R.string.overview_share_pdf))
                                 }
                             }

android/app/src/main/java/app/voltplan/cable/ui/system/SystemDetailViewModel.kt

@@ -22,6 +22,9 @@ data class DetailState(
     val chargers: List<SavedCharger> = emptyList(),
 ) {
     val metrics: SystemMetrics get() = SystemMetrics(loads, batteries, chargers)
+
+    val hasComponents: Boolean
+        get() = loads.isNotEmpty() || batteries.isNotEmpty() || chargers.isNotEmpty()
 }
 
 class SystemDetailViewModel(