import org.apache.commons.codec.binary.Hex;
import org.assertj.core.api.SoftAssertions;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.io.UnsupportedEncodingException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;


public class Test
{
    private static String region = "us-east-1";
    static byte[] HmacSHA256(String data, byte[] key) throws Exception {
        String algorithm="HmacSHA256";
        Mac mac = Mac.getInstance(algorithm);
        mac.init(new SecretKeySpec(key, algorithm));
        return mac.doFinal(data.getBytes("UTF8"));
    }

    public static byte[] justSha256(String data) throws NoSuchAlgorithmException, UnsupportedEncodingException {
        MessageDigest digest = MessageDigest.getInstance("SHA-256");
        byte[] hash = digest.digest(data.getBytes("UTF8"));
        return hash;
    }

    static byte[] getSigningKey(String key, String dateStamp, String regionName, String serviceName) throws Exception {
        byte[] kSecret = ("AWS4" + key).getBytes("UTF8");


        byte[] kDate = HmacSHA256(dateStamp, kSecret);

        byte[] kRegion = HmacSHA256(regionName, kDate);

        byte[] kService = HmacSHA256(serviceName, kRegion);

        byte[] kSigning = HmacSHA256("aws4_request", kService);

        return kSigning;
    }



    public static String getSimpleDate()
    {
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("YYYYMMdd");


        return LocalDate.now().format(formatter);
    }

    public static String getAMZDate()
    {
    /*DateTimeFormatter formatter = DateTimeFormatter.ofPattern("YYYYMMDDHHMMSS");
    String timeStamp = new SimpleDateFormat("YYMMDD'T'HHMMSS'Z'").format(Calendar.getInstance().getTime());*/


        TimeZone tz = TimeZone.getTimeZone("UTC");
        DateFormat df = new SimpleDateFormat("yyyyMMdd'T'HHmmss'Z'"); // Quoted "Z" to indicate UTC, no timezone offset
        df.setTimeZone(tz);
        String timeStamp = df.format(new Date());


        return timeStamp;
    }



    public static String createSigningString(String timeStamp, String simpleDate,String serviceName) throws UnsupportedEncodingException, NoSuchAlgorithmException {

      /*AWS4-HMAC-SHA256
      20150830T123600Z
      20150830/us-east-1/iam/aws4_request
      f536975d06c0309214f805bb90ccff089219ecd68b2577efef23edd43b7e1a59*/

        String algorithm = "AWS4-HMAC-SHA256\n";
        String amzDate = timeStamp+"\n";
        String simpleDateRegionServiceRequest = simpleDate+"/"+region+"/"+serviceName+"/"+"aws4_request\n";

        String canonicalHash = getCanonicalHash(getCanonicalString("GET","/","Action=ListUsers&Version=2010-05-08","20150830T123600Z",""));

        String signingString = algorithm+amzDate+simpleDateRegionServiceRequest+canonicalHash;



        return signingString;

    }

    public static String getCanonicalString(String method, String absolutePath, String queryString, String timeStamp, String payload) throws UnsupportedEncodingException, NoSuchAlgorithmException {

        String contentType = "Content-Type:application/x-www-form-urlencoded; charset=utf-8\n".toLowerCase();
        String hostUrl = "host:iam.amazonaws.com\n";
        String date = "x-amz-date:"+timeStamp+"\n";

        String signedHeader = "content-type;host;x-amz-date\n";

        String hashedPayload = Hex.encodeHexString(justSha256(payload)).toLowerCase();



        String canonicalString = method+"\n"+absolutePath+"\n"+queryString+"\n"+contentType+hostUrl+date+"\n"+signedHeader+hashedPayload;




        return canonicalString;
    }


    public static String getCanonicalHash(String canonicalString) throws UnsupportedEncodingException, NoSuchAlgorithmException {
        return Hex.encodeHexString(justSha256(canonicalString)).toLowerCase();
    }




    public static void main(String[] args) throws Exception {


        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("YYYYMMDDHHMMSS");
        String timeStamp = new SimpleDateFormat("YYYYMMDD'T'HHMMSS'Z'").format(Calendar.getInstance().getTime());


        String canonString;
        System.out.println( canonString = getCanonicalHash(getCanonicalString("GET","/","Action=ListUsers&Version=2010-05-08","20150830T123600Z","")));

        String signingString = createSigningString("20150830T123600Z","20150830","iam");

        String key = "wJalrXUtnFEMI/K7MDENG+bPxRfiCYEXAMPLEKEY";
        String dateStamp = "20120215";
        String regionName = "us-east-1";
        String serviceName = "iam";

        String signingKey = Hex.encodeHexString(getSigningKey(key,dateStamp,regionName,serviceName));

        SoftAssertions softly = new SoftAssertions();

        softly.assertThat(canonString).isEqualToIgnoringCase("f536975d06c0309214f805bb90ccff089219ecd68b2577efef23edd43b7e1a59");
        String copiedSigningString = "AWS4-HMAC-SHA256\n" +
                "20150830T123600Z\n" +
                "20150830/us-east-1/iam/aws4_request\n" +
                "f536975d06c0309214f805bb90ccff089219ecd68b2577efef23edd43b7e1a59";



        softly.assertThat(signingString).isEqualTo(copiedSigningString);



        softly.assertThat(signingKey).isEqualToIgnoringCase("f4780e2d9f65fa895f9c67b32ce1baf0b0d8a43505a000a1a9e090d414db404d");

        dateStamp ="20150830";

        signingKey = Hex.encodeHexString(getSigningKey(key,dateStamp,regionName,serviceName));

        softly.assertThat(signingKey).isEqualToIgnoringCase("c4afb1cc5771d871763a393e44b703571b55cc28424d1a5e86da6ed3c154a4b9");


        System.out.println("COPIED STRING : "+copiedSigningString);

        System.out.println("SIGNING KEY : "+signingKey);
        String signature = Hex.encodeHexString(HmacSHA256(signingKey.trim(),justSha256(copiedSigningString)));

        System.out.println("Signature : "+signature);

        softly.assertThat(signature).isEqualToIgnoringCase("5d672d79c15b13162d9279b0855cfba6789a8edb4c82c400e06b5924a6f2b5d7");

        softly.assertAll();

    }
}