package utils.security;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;

import java.io.UnsupportedEncodingException;
import java.net.URL;
import java.net.URLEncoder;
import java.net.URLDecoder;
import java.util.TreeMap;
import java.util.Map;
import java.util.Iterator;

import org.apache.commons.codec.binary.Base64;

public class SigHelper
{
	private static final String HMAC_SHA1_ALGORITHM = "HmacSHA1";
	
	public static String getSignedUrl(String url, String key) throws Exception
	{
		return url + "&Signature=" + URLEncoder.encode(getSignature(url, key), "UTF-8");
	}

	public static String getSignature(String url, String key) throws Exception
	{
		URL u = new URL(url);
		return computeSignature(key, makeParamMap(u.getQuery()));
	}

	private static String computeSignature(String callerSecretKey, TreeMap<String, String> sortedMap) throws Exception
	{
		StringBuffer strToSign = new StringBuffer("");

		// Raise exception if caller key unknown
		if (callerSecretKey == null || callerSecretKey.equals(""))
			throw new RuntimeException("Invalid callid for computeSignature");

		for (Iterator i = sortedMap.entrySet().iterator(); i.hasNext();)
		{
			Map.Entry e = (Map.Entry) i.next();
			String key = (String) e.getKey();
			String[] value = (String[]) e.getValue();
			for (int j = 0; j < value.length; j++)
			{
				System.out.println("SigHelper.java: From parameter '" + key	+ "' adding " + " value '" + value[j] + "'");
				strToSign.append(key);
				strToSign.append(value[j]);
			}
		}

		System.out.println("SigHelper.java: Attempting to sign string '" + strToSign.toString());

		return calculateSig(callerSecretKey, strToSign.toString());
	}

	private static String calculateSig(String secretKey, String parametersToHash)
	{
		String result;

		try
		{
			SecretKeySpec signingKey = new SecretKeySpec(secretKey.getBytes(), HMAC_SHA1_ALGORITHM);

			Mac mac = Mac.getInstance(HMAC_SHA1_ALGORITHM);
			mac.init(signingKey);

			byte[] rawHmac = mac.doFinal(parametersToHash.getBytes());

			String encodedHMac = new String (Base64.encodeBase64Chunked (rawHmac));	

			// The following API behaves differently on windows and Linux
			if (System.getProperty("os.name").startsWith("Windows"))
				result = encodedHMac.substring(0, encodedHMac.length() - 2);
			else 
				result = encodedHMac.substring(0, encodedHMac.length() - 2);
		} catch (Exception e)
		{
			throw new RuntimeException("Error Calculating Hmac", e);
		}

		return result;
	}

	private static TreeMap<String, String> makeParamMap(String queryString) throws UnsupportedEncodingException
	{
		TreeMap hmp = new TreeMap(String.CASE_INSENSITIVE_ORDER);
		String[] param = queryString.split("&");
		for (int i = 0; i < param.length; i++)
		{
			int index = param[i].indexOf("=");
			String key = param[i].substring(0, index);
			String value = param[i].substring(index + 1);
			System.out.println("SigHelper.java: Adding " + key + " = " + value);
			if (hmp.get(key) == null)
				hmp.put(key, new String[] { URLDecoder.decode(value, "UTF-8") });
			else
			{
				// Very Rare Case
				String[] arr = (String[]) hmp.get(key);
				String[] arrNew = new String[arr.length + 1];
				arrNew[arr.length] = URLDecoder.decode(value, "UTF-8");
				for (int j = 0; j < arr.length; j++)
					arrNew[j] = arr[j];
			}
		}
		return hmp;
	}
}