package com.selenium.course.pages;

import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.support.FindBy;
import org.openqa.selenium.support.PageFactory;

public class LoginPage {

    private WebDriver driver;

    // Locators via @FindBy annotations
    @FindBy(id = "username")
    private WebElement usernameInput;

    @FindBy(id = "password")
    private WebElement passwordInput;

    @FindBy(css = "button[type='submit']")
    private WebElement loginButton;

    @FindBy(css = ".error-message")
    private WebElement errorMessage;

    // Constructor — initializes PageFactory
    public LoginPage(WebDriver driver) {
        this.driver = driver;
        PageFactory.initElements(driver, this);
    }

    // Actions
    public LoginPage enterUsername(String username) {
        usernameInput.clear();
        usernameInput.sendKeys(username);
        return this;  // Fluent API — enables chaining
    }

    public LoginPage enterPassword(String password) {
        passwordInput.clear();
        passwordInput.sendKeys(password);
        return this;
    }

    public HomePage clickLogin() {
        loginButton.click();
        return new HomePage(driver);
    }

    public LoginPage clickLoginExpectingError() {
        loginButton.click();
        return this;
    }

    // Verifications
    public String getErrorMessage() {
        return errorMessage.getText();
    }

    public boolean isLoginButtonDisplayed() {
        return loginButton.isDisplayed();
    }

    // Fluent login shortcut
    public HomePage loginAs(String username, String password) {
        return enterUsername(username)
            .enterPassword(password)
            .clickLogin();
    }
}

package com.selenium.course.tests;

import com.selenium.course.base.BaseTest;
import com.selenium.course.pages.LoginPage;
import com.selenium.course.pages.HomePage;
import org.testng.Assert;
import org.testng.annotations.Test;

public class LoginTest extends BaseTest {

    @Test
    public void testSuccessfulLogin() {
        LoginPage loginPage = new LoginPage(driver);

        // Fluent API chaining
        HomePage homePage = loginPage
            .enterUsername("admin")
            .enterPassword("admin123")
            .clickLogin();

        Assert.assertTrue(homePage.isWelcomeDisplayed());
    }

    @Test
    public void testInvalidLogin() {
        LoginPage loginPage = new LoginPage(driver);

        loginPage.enterUsername("wrong")
            .enterPassword("wrong")
            .clickLoginExpectingError();

        Assert.assertEquals(
            loginPage.getErrorMessage(),
            "Invalid credentials");
    }

    @Test
    public void testFluentLogin() {
        // One-liner using the convenience method
        LoginPage loginPage = new LoginPage(driver);
        HomePage home = loginPage.loginAs("admin", "admin123");
        Assert.assertTrue(home.isWelcomeDisplayed());
    }
}

"""Login page object"""
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC


class LoginPage:

    # Locators
    USERNAME_INPUT = (By.ID, "username")
    PASSWORD_INPUT = (By.ID, "password")
    LOGIN_BUTTON = (By.CSS_SELECTOR, "button[type='submit']")
    ERROR_MESSAGE = (By.CSS_SELECTOR, ".error-message")

    def __init__(self, driver):
        self.driver = driver
        self.wait = WebDriverWait(driver, 10)

    # Actions
    def enter_username(self, username):
        el = self.wait.until(EC.visibility_of_element_located(
            self.USERNAME_INPUT))
        el.clear()
        el.send_keys(username)
        return self  # Fluent API

    def enter_password(self, password):
        el = self.driver.find_element(*self.PASSWORD_INPUT)
        el.clear()
        el.send_keys(password)
        return self

    def click_login(self):
        self.driver.find_element(*self.LOGIN_BUTTON).click()
        from pages.home_page import HomePage
        return HomePage(self.driver)

    def click_login_expecting_error(self):
        self.driver.find_element(*self.LOGIN_BUTTON).click()
        return self

    # Verifications
    def get_error_message(self):
        return self.driver.find_element(*self.ERROR_MESSAGE).text

    def is_login_button_displayed(self):
        return self.driver.find_element(*self.LOGIN_BUTTON).is_displayed()

    # Convenience method
    def login_as(self, username, password):
        return (self.enter_username(username)
                    .enter_password(password)
                    .click_login())

"""Login tests using Page Object Model"""
from pages.login_page import LoginPage
import pytest

def test_successful_login(driver):
    login_page = LoginPage(driver)

    home_page = (login_page
        .enter_username("admin")
        .enter_password("admin123")
        .click_login())

    assert home_page.is_welcome_displayed()

def test_invalid_login(driver):
    login_page = LoginPage(driver)

    (login_page
        .enter_username("wrong")
        .enter_password("wrong")
        .click_login_expecting_error())

    assert login_page.get_error_message() == "Invalid credentials"

def test_fluent_login(driver):
    login_page = LoginPage(driver)
    home = login_page.login_as("admin", "admin123")
    assert home.is_welcome_displayed()