@RunWith(MockitoJUnitRunner.class)
public class LoginServletTest {

    private static final String USER_SERVICE_CONTEXT_ATTRIBUTE = "userService";
    private static final String WELCOME_PAGE_URL = "welcome";
    private static final String LOGIN_PAGE_URL = "login";
    private static final String EMAIL_ATTRIBUTE_NAME = "email";
    private static final String PASSWORD_ATTRIBUTE_NAME = "password";
    private static final String TEST_EMAIL = "test_email@gmail.com";
    private static final String TEST_PASSWORD = "test_password";
    private static final String WRONG_EMAIL = "wrong_email@gmail.com";
    private static final String LOGIN_ERROR_ATTRIBUTE_NAME = "loginError";
    private static final String LOGIN_DTO_ATTRIBUTE_NAME = "loginDTO";
    private static final String LOGIN_ERROR_MESSAGE = "Wrong credentials. Please try again.";
    private static final String USER_ATTRIBUTE = "user";

    private LoginServlet servlet = new LoginServlet();

    @Mock
    private ServletConfig servletConfig;
    @Mock
    private ServletContext servletContext;
    @Mock
    private HttpServletRequest request;
    @Mock
    private HttpServletResponse response;
    @Mock
    private HttpSession session;
    @Mock
    private RequestDispatcher requestDispatcher;
    @Mock
    private UserService userService;

    private User testUser;

    @Before
    public void setUp() throws Exception {
        when(servletConfig.getServletContext()).thenReturn(servletContext);
        when(servletContext.getAttribute(USER_SERVICE_CONTEXT_ATTRIBUTE)).thenReturn(userService);

        when(request.getServletContext()).thenReturn(servletContext);
        when(request.getRequestDispatcher(anyString())).thenReturn(requestDispatcher);
        when(request.getSession()).thenReturn(session);

        testUser = new User();
        testUser.setEmail(TEST_EMAIL);
        testUser.setPassword(TEST_PASSWORD);

        when(userService.loadUserByUsername(TEST_EMAIL)).thenReturn(testUser);
        when(userService.loadUserByUsername(WRONG_EMAIL)).thenReturn(null);
    }

    @Test
    public void testServletInit() throws Exception {
        servlet.init(servletConfig);
    }

    @Test
    public void testDoPostOnCorrectCredentials() throws Exception {
        servlet.init(servletConfig);
        mockGetRequestParams(TEST_EMAIL, TEST_PASSWORD);
        servlet.doPost(request, response);

        verify(session).setAttribute(USER_ATTRIBUTE, testUser);
        verify(response).sendRedirect(WELCOME_PAGE_URL);
    }

    @Test
    public void testDoPostOnWrongCredentials() throws Exception {
        servlet.init(servletConfig);
        mockGetRequestParams(WRONG_EMAIL, Strings.EMPTY);
        servlet.doPost(request, response);
        verify(session).setAttribute(LOGIN_ERROR_ATTRIBUTE_NAME, LOGIN_ERROR_MESSAGE);
        verify(session).setAttribute(LOGIN_DTO_ATTRIBUTE_NAME, WRONG_EMAIL);
        verify(response).sendRedirect(LOGIN_PAGE_URL);
    }

    private void mockGetRequestParams(String email, String password) {
        when(request.getParameter(EMAIL_ATTRIBUTE_NAME)).thenReturn(email);
        when(request.getParameter(PASSWORD_ATTRIBUTE_NAME)).thenReturn(password);
    }
}