import java.security.SecureRandom;
import java.util.Random;
import java.nio.charset.StandardCharsets;
import java.util.Base64;
import java.security.MessageDigest;

public class CheckLib {
    
    private static final Random random = new Random();
    private static final SecureRandom secureRandom = new SecureRandom();
    
    private static final String ALPHANUMERIC = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    private static final String ALPHA_LOWER = "abcdefghijklmnopqrstuvwxyz";
    private static final String ALPHA_UPPER = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private static final String NUMERIC = "0123456789";
    private static final String HEX = "0123456789abcdef";
    
    public static String rndString(int length) {
        return rndAlphanumeric(length);
    }
    
    public static String generateUsername() {
        return "user_" + timestampSec() + "_" + rndAlphaLower(6);
    }
    
    public static String generateUsername(String prefix) {
        return prefix + "_" + timestampSec() + "_" + rndAlphaLower(6);
    }
    
    public static String generatePassword() {
        return rndAlphanumeric(16);
    }
    
    public static String generatePassword(int length) {
        return rndAlphanumeric(length);
    }
    
    public static String rndAlphanumeric(int length) {
        return randomString(length, ALPHANUMERIC);
    }
    
    public static String rndAlphaLower(int length) {
        return randomString(length, ALPHA_LOWER);
    }
    
    public static String rndAlphaUpper(int length) {
        return randomString(length, ALPHA_UPPER);
    }
    
    public static String rndNumeric(int length) {
        return randomString(length, NUMERIC);
    }
    
    public static String rndHex(int length) {
        return randomString(length, HEX);
    }
    
    public static String randomString(int length, String charset) {
        StringBuilder sb = new StringBuilder(length);
        for (int i = 0; i < length; i++) {
            sb.append(charset.charAt(random.nextInt(charset.length())));
        }
        return sb.toString();
    }
    
    public static byte[] rndBytes(int length) {
        byte[] bytes = new byte[length];
        secureRandom.nextBytes(bytes);
        return bytes;
    }
    
    public static byte[] rndBytesFast(int length) {
        byte[] bytes = new byte[length];
        random.nextBytes(bytes);
        return bytes;
    }
    
    public static int rndInt(int min, int max) {
        return random.nextInt(max - min) + min;
    }
    
    public static int rndInt(int max) {
        return random.nextInt(max);
    }
    
    public static long rndLong() {
        return random.nextLong();
    }
    
    public static String toHex(byte[] bytes) {
        StringBuilder sb = new StringBuilder(bytes.length * 2);
        for (byte b : bytes) {
            sb.append(String.format("%02x", b));
        }
        return sb.toString();
    }
    
    public static byte[] fromHex(String hex) {
        int len = hex.length();
        byte[] data = new byte[len / 2];
        for (int i = 0; i < len; i += 2) {
            data[i / 2] = (byte) ((Character.digit(hex.charAt(i), 16) << 4)
                                + Character.digit(hex.charAt(i+1), 16));
        }
        return data;
    }
    
    public static String toBase64(byte[] bytes) {
        return Base64.getEncoder().encodeToString(bytes);
    }
    
    public static String toBase64(String str) {
        return Base64.getEncoder().encodeToString(str.getBytes(StandardCharsets.UTF_8));
    }
    
    public static byte[] fromBase64(String base64) {
        return Base64.getDecoder().decode(base64);
    }
    
    public static String fromBase64String(String base64) {
        return new String(Base64.getDecoder().decode(base64), StandardCharsets.UTF_8);
    }
    
    public static String toBase64Url(byte[] bytes) {
        return Base64.getUrlEncoder().withoutPadding().encodeToString(bytes);
    }
    
    public static byte[] fromBase64Url(String base64) {
        return Base64.getUrlDecoder().decode(base64);
    }
    
    public static String md5(String input) {
        return hash(input, "MD5");
    }
    
    public static String sha1(String input) {
        return hash(input, "SHA-1");
    }
    
    public static String sha256(String input) {
        return hash(input, "SHA-256");
    }
    
    public static String hash(String input, String algorithm) {
        try {
            MessageDigest md = MessageDigest.getInstance(algorithm);
            byte[] hash = md.digest(input.getBytes(StandardCharsets.UTF_8));
            return toHex(hash);
        } catch (Exception e) {
            throw new RuntimeException("Hash failed: " + e.getMessage(), e);
        }
    }
    
    public static byte[] hashBytes(byte[] input, String algorithm) {
        try {
            MessageDigest md = MessageDigest.getInstance(algorithm);
            return md.digest(input);
        } catch (Exception e) {
            throw new RuntimeException("Hash failed: " + e.getMessage(), e);
        }
    }
    
    public static long timestamp() {
        return System.currentTimeMillis();
    }
    
    public static long timestampSec() {
        return System.currentTimeMillis() / 1000;
    }
    
    public static void sleep(long ms) {
        try {
            Thread.sleep(ms);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
        }
    }
    
    public static void sleepSec(long seconds) {
        sleep(seconds * 1000);
    }
    
    public static String repeat(String str, int count) {
        return str.repeat(count);
    }
    
    public static String padLeft(String str, int length, char padChar) {
        if (str.length() >= length) return str;
        return String.valueOf(padChar).repeat(length - str.length()) + str;
    }
    
    public static String padRight(String str, int length, char padChar) {
        if (str.length() >= length) return str;
        return str + String.valueOf(padChar).repeat(length - str.length());
    }
    
    public static void info(String msg) {
        System.out.println("[*] " + msg);
    }
    
    public static void success(String msg) {
        System.out.println("[+] " + msg);
    }
    
    public static void error(String msg) {
        System.out.println("[-] " + msg);
    }
    
    public static void warn(String msg) {
        System.out.println("[!] " + msg);
    }
    
    public static void debug(String msg) {
        System.out.println("[DEBUG] " + msg);
    }
    
    public static void hexDump(byte[] data) {
        hexDump(data, 16);
    }
    
    public static void hexDump(byte[] data, int bytesPerLine) {
        for (int i = 0; i < data.length; i += bytesPerLine) {
            System.out.printf("%08x: ", i);
            
            for (int j = 0; j < bytesPerLine; j++) {
                if (i + j < data.length) {
                    System.out.printf("%02x ", data[i + j]);
                } else {
                    System.out.print("   ");
                }
            }
            
            System.out.print(" | ");
            
            for (int j = 0; j < bytesPerLine && i + j < data.length; j++) {
                byte b = data[i + j];
                if (b >= 32 && b < 127) {
                    System.out.print((char) b);
                } else {
                    System.out.print('.');
                }
            }
            
            System.out.println();
        }
    }
}