import java.io.Console;
import java.util.Map;
import java.util.HexFormat;
import java.util.stream.Collectors;
import java.nio.file.Path;
import java.nio.file.Files;
import java.security.MessageDigest;

public class Auth {
    private static final byte[] INVALID_HASH = "----------------------------------------------------------------".getBytes();

    public static void main(String[] args) {
        try {
            Map<String, byte[]> passwd = Files.readAllLines(Path.of("passwd"))
                .stream()
                .filter(line -> line.indexOf(":") > 1 && line.length() > 3)
                .collect(Collectors.toMap(
                    line -> line.substring(0, line.indexOf(':')),
                    line -> HexFormat.of().parseHex(line.substring(line.indexOf(':') + 1))
                ));

            System.out.println("Chocolate Factory SCADA Command Line Interface v2.2.144");
            System.out.println();
            System.out.println("Please, enter your authentication credentials.");
            System.out.println();

            Console cons = System.console();

            String username;
            String password;

            long timeout = 500;
            while (true) {
                username = cons.readLine("> Username: ");
                password = new String(cons.readPassword("> Password: "));

                MessageDigest digest = MessageDigest.getInstance("SHA-256");
                byte[] encodedHash = digest.digest(password.getBytes());

                // constant time comparison to prevent timing attacks
                if (MessageDigest.isEqual(
                    passwd.getOrDefault(username, INVALID_HASH),
                    encodedHash
                )) {
                    System.out.println();
                    System.out.printf("Welcome %s!%n", username);
                    Thread.sleep(150);
                    break;
                } else {
                    // exponential timeout to prevent brute force attacks
                    System.out.println("Incorrect username and/or password.");
                    Thread.sleep(timeout);
                    timeout *= 2;
                }
            }

            printSystemStatus();
            printSecretRecipe();
        } catch (Exception e) {
            // ignore
        }
    }

    private static void printSystemStatus() throws Exception {
        // TOP SECRET
    }

    private static void printSecretRecipe() throws Exception {
        // TOP SECRET
    }
}