source: backend/GlobeGuru-backend/src/main/java/AccountHandler.java@ cd64b06

import com.fasterxml.jackson.databind.ObjectMapper;
import com.google.api.client.googleapis.auth.oauth2.GoogleIdToken;
import com.google.api.client.googleapis.auth.oauth2.GoogleIdTokenVerifier;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.json.jackson2.JacksonFactory;
import com.sun.net.httpserver.HttpExchange;
import com.sun.net.httpserver.HttpHandler;

import java.io.IOException;
import java.security.GeneralSecurityException;
import java.sql.SQLException;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;

public class AccountHandler implements HttpHandler {
    private static final Map<String, String> sessions = new ConcurrentHashMap<>();
    private static final String CLIENT_ID = "376204422797-s8f05nn6drmec1cko2h4kg1nk24abgc9.apps.googleusercontent.com";

    @Override
    public void handle(HttpExchange exchange) throws IOException {
        String path = exchange.getRequestURI().getPath();
        String method = exchange.getRequestMethod();

        if ("POST".equalsIgnoreCase(method)) {
            switch (path) {
                case "/account/register":
                    handleRegister(exchange);
                    break;
                case "/account/login":
                    handleLogin(exchange);
                    break;
                case "/account/logout":
                    handleLogout(exchange);
                    break;
                case "/account/delete":
                    handleDeleteAccount(exchange);
                    break;
                default:
                    Server.sendResponse(exchange, 404, "Endpoint not found");
            }
        } else if ("GET".equalsIgnoreCase(method) && path.equalsIgnoreCase("/account/session")) {
            handleSession(exchange);
        } else {
            Server.sendResponse(exchange, 405, "Method not allowed");
        }
    }

    private void handleSession(HttpExchange exchange) throws IOException {
        String sessionId = getSessionId(exchange);
        ObjectMapper mapper = new ObjectMapper();
        Map<String, Object> response = new HashMap<>();
        if (sessionId != null && sessions.containsKey(sessionId)) {
            response.put("loggedIn", true);
            response.put("user", sessions.get(sessionId));
            try {
                response.put("isAdmin", DatabaseUtil.isAdmin(sessions.get(sessionId)));
            } catch (SQLException e) {
                e.printStackTrace();
                response.put("isAdmin", false);
            }
        } else {
            response.put("loggedIn", false);
        }

        String jsonResponse = mapper.writeValueAsString(response);
        Server.sendResponse(exchange, 200, jsonResponse);
    }

    private String getSessionId(HttpExchange exchange) {
        List<String> cookies = exchange.getRequestHeaders().get("Cookie");
        if (cookies != null) {
            for (String cookie : cookies) {
                if (cookie.contains("sessionId=")) {
                    return cookie.replaceAll("g_state=\\{\"i_l\":0\\}; sessionId=", "");
                }
            }
        }
        return null;
    }


    private void handleRegister(HttpExchange exchange) throws IOException {
        String requestBody = new String(exchange.getRequestBody().readAllBytes());
        ObjectMapper mapper = new ObjectMapper();
        Map<String, String> formData = mapper.readValue(requestBody, Map.class);
        String username = formData.get("username");
        String email = formData.get("email");
        String password = formData.get("password");

        try {
            if (DatabaseUtil.registerUser(username, email, password)) {
                Server.sendResponse(exchange, 200, "{\"message\": \"Registration successful!\"}");
            } else {
                Server.sendResponse(exchange, 400, "{\"message\": \"Registration failed! User may already exist.\"}");
            }
        } catch (SQLException e) {
            e.printStackTrace();
            Server.sendResponse(exchange, 500, "{\"message\": \"Internal server error\"}");
        }
    }

    private void handleLogin(HttpExchange exchange) throws IOException {
        String requestBody = new String(exchange.getRequestBody().readAllBytes());
        ObjectMapper mapper = new ObjectMapper();
        Map<String, String> formData = mapper.readValue(requestBody, Map.class);

        if (formData.containsKey("id_token")) {
            handleGoogleSignIn(exchange, formData.get("id_token"));
        } else {
            handleFormLogin(exchange, formData.get("email"), formData.get("password"));
        }
    }

    private void handleGoogleSignIn(HttpExchange exchange, String idTokenString) throws IOException {
        HttpTransport transport = new NetHttpTransport();
        JsonFactory jsonFactory = JacksonFactory.getDefaultInstance();

        GoogleIdTokenVerifier verifier = new GoogleIdTokenVerifier.Builder(transport, jsonFactory)
                .setAudience(Collections.singletonList(CLIENT_ID)).build();

        try {
            GoogleIdToken idToken = verifier.verify(idTokenString);
            if (idToken != null) {
                GoogleIdToken.Payload payload = idToken.getPayload();
                String email = payload.getEmail();
                if (DatabaseUtil.userExists(email)) {
                    System.out.println("User exists, logging in");
                    handleFormLogin(exchange, email, null);
                } else {
                    System.out.println("User does not exist, creating new user");
                    String name = (String) payload.get("name");
                    DatabaseUtil.registerUser(name, email, null); // Password is null for Google login
                    String response = createSession(email);
                    Server.sendResponse(exchange, 200, response);
                }
            } else {
                String response = "{\"message\": \"Invalid ID token\"}";
                System.out.println(response);
                Server.sendResponse(exchange, 401, response);
            }
        } catch (SQLException e) {
            e.printStackTrace();
            String response = "{\"message\": \"Database error\"}";
            System.out.println(response);
            Server.sendResponse(exchange, 500, response);
        } catch (GeneralSecurityException e) {
            throw new RuntimeException(e);
        }
    }

    private void handleFormLogin(HttpExchange exchange, String email, String password) throws IOException {
        try {
            if (DatabaseUtil.userExists(email)) {
                if (DatabaseUtil.authenticateUser(email, password)) {
                    String response = createSession(email);
                    Server.sendResponse(exchange, 200, response);
                } else {
                    String response = "{\"message\": \"Invalid password\"}";
                    System.out.println(response);
                    Server.sendResponse(exchange, 401, response);
                }
            } else {
                String response = "{\"message\": \"User does not exist\"}";
                System.out.println(response);
                Server.sendResponse(exchange, 404, response);
            }
        } catch (SQLException e) {
            e.printStackTrace();
            String response = "{\"message\": \"Database error: " + e.getMessage() + "\"}";
            System.out.println(response);
            Server.sendResponse(exchange, 500, response);
        }
    }

    private void handleLogout(HttpExchange exchange) throws IOException {
        String sessionId = getSessionId(exchange);
        if (sessionId != null && sessions.containsKey(sessionId)) {
            sessions.remove(sessionId);
            Server.sendResponse(exchange, 200, "{\"message\": \"Logout successful\"}");
        } else {
            Server.sendResponse(exchange, 401, "{\"message\": \"Not logged in\"}");
        }
    }

    private void handleDeleteAccount(HttpExchange exchange) throws IOException {
        String userIdStr = new String(exchange.getRequestBody().readAllBytes()).replaceAll("\"", "");
        int userId = Integer.parseInt(userIdStr);
        Map<String, Object> response = new HashMap<>();
        try {
            boolean success = DatabaseUtil.deleteUser(userId);
            response.put("success", success);
            if (!success) {
                response.put("message", "User not found");
            }
        } catch (SQLException e) {
            e.printStackTrace();
            response.put("success", false);
            response.put("message", "Database error: " + e.getMessage());
        }

        String jsonResponse = new ObjectMapper().writeValueAsString(response);
        Server.sendResponse(exchange, 200, jsonResponse);
    }


    private String createSession(String email) throws SQLException {
        String sessionId = UUID.randomUUID().toString();
        sessions.put(sessionId, email);
        boolean isAdmin = DatabaseUtil.isAdmin(email);
        return "{\"message\": \"" + email + " logged in!\", \"sessionId\": \"" + sessionId + "\", \"isAdmin\": " + isAdmin + "}";
    }

}