final class TabComponentViewController: UIViewController, TabComponent {
    let tabItem: TabItem
    
    init(title: String) {
        tabItem = TabItem(title: title)
        
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

final class TabItemViewControllerRouterTests: XCTestCase {
    let tabComponent1 = TabComponentViewController(title: "1")
    
    let tabComponent2 = TabComponentViewController(title: "2")
    
    let parentViewController = UIViewController()

    func testNoViewControllerParentsByDetault() {
        let _ = TabItemViewControllerRouter(tabComponents: [tabComponent1, tabComponent2], parentViewController: parentViewController,
                                               viewHierarchyUpdater: { _ in })
        
        XCTAssertNil(tabComponent1.parentViewController)
        XCTAssertNil(tabComponent2.parentViewController)
    }
    
    func testSelectingTabBarItemAddsViewControllerToParent() {
        let router = TabItemViewControllerRouter(tabComponents: [tabComponent1, tabComponent2], parentViewController: parentViewController,
                                                    viewHierarchyUpdater: { _ in })
        router.selectTabItem(tabComponent1.tabItem)
        
        XCTAssertEqual(tabComponent1.parentViewController, parentViewController)
    }
    
    func testSelectingTwoTabBarItemAddsViewControllerToParentAndRemovesPreviousController() {
        let router = TabItemViewControllerRouter(tabComponents: [tabComponent1, tabComponent2], parentViewController: parentViewController,
                                                    viewHierarchyUpdater: { _ in })
        router.selectTabItem(tabComponent1.tabItem)
        router.selectTabItem(tabComponent2.tabItem)
        
        XCTAssertNil(tabComponent1.parentViewController)
        XCTAssertEqual(tabComponent2.parentViewController, parentViewController)
    }
    
    func testSelectionInvokesHierarchyUpdaterWithCorrectView() {
        let expectation = expectationWithDescription("View hierarchy will be updated")
        
        let router = TabItemViewControllerRouter(tabComponents: [tabComponent1, tabComponent2], parentViewController: parentViewController, viewHierarchyUpdater: { view in
            XCTAssertEqual(view, self.tabComponent1.view)
            expectation.fulfill()
        })
        router.selectTabItem(tabComponent1.tabItem)
        
        waitForExpectationsWithTimeout(2) { error in
            if let _ = error {
                XCTFail()
            }
        }
    }
}