import java.math.BigInteger;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.text.SimpleDateFormat;
import java.util.regex.*;
import java.util.*;

public class UrlAuth {

    private static String getHashString(String algorithm, String text) {
        MessageDigest hash = null;
        try {
            hash = MessageDigest.getInstance(algorithm);
        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
        hash.update(StandardCharsets.UTF_8.encode(text));
        return String.format("%x", new BigInteger(1, hash.digest()));
    }

    private static String getRandomString(int length) {
        int leftLimit = 48; // numeral '0'
        int rightLimit = 122; // letter 'z'
        Random random = new Random();
        String str = random.ints(leftLimit, rightLimit + 1)
                .filter(i -> (i <= 57 || i >= 65) && (i <= 90 || i >= 97))
                .limit(length)
                .collect(StringBuilder::new, StringBuilder::appendCodePoint, StringBuilder::append)
                .toString();
        return str;
    }

    private static Map<String, String> splitUrl(String url) {
        String pattern = "^(http://|https://)?([^/?]+)(/[^?]*)?(\\?.*)?$";
        Pattern r = Pattern.compile(pattern);
        Matcher m = r.matcher(url);
        Map<String, String> result = new HashMap<>();
        String scheme = "", domain = "", uri = "", args = "";
        if (m.find()) {
            scheme = m.group(1) == null ? "http://" : m.group(1);
            domain = m.group(2) == null ? "" : m.group(2);
            uri = m.group(3) == null ? "/" : m.group(3);
            args = m.group(4) == null ? "" : m.group(4);
        }
        result.put("scheme", scheme);
        result.put("domain", domain);
        result.put("uri", uri);
        result.put("args", args);
        return result;
    }

    private static String genUrl(String url, String key, long ts) {
        Map<String, String> uriInfo = splitUrl(url);
        String scheme = uriInfo.get("scheme"), domain = uriInfo.get("domain"), uri = uriInfo.get("uri"), args = uriInfo.get("args");
        String rand = getRandomString(10);
        String text = String.format("%s-%d-%s-%s", uri, ts, rand, key);
        String hash = getHashString("MD5", text);
        String authArg = String.format("auth_key=%d-%s-%s", ts, rand, hash);
        if (Objects.equals(args, ""))
            return String.format("%s%s%s?%s", scheme, domain, uri, authArg);
        else
            return String.format("%s%s%s%s&%s", scheme, domain, uri, args, authArg);
    }


    public static void main(String[] args) {
        String url = "http://www.test.com/a.txt?a=b&c=d";
        String secretKey = "secretKey";
        long ts = System.currentTimeMillis() / 1000;

        System.out.println("OriginUrl: " + url);
        System.out.printf("AuthUrl: %s\n", genUrl(url, secretKey, ts));
    }
}