package org.openslx.satellitedaemon;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;
import java.nio.charset.StandardCharsets;
import java.security.NoSuchAlgorithmException;
import java.security.PrivateKey;
import java.security.PublicKey;
import java.security.spec.InvalidKeySpecException;
import java.util.Properties;
import java.util.Random;

import org.apache.log4j.Logger;
import org.openslx.encryption.AsymKeyHolder;
import org.openslx.satellitedaemon.util.Util;

public class Identity
{
	private static Logger log = Logger.getLogger( Identity.class );
	private static final Properties properties = new Properties();

	private static String organizationName = null;
	private static BigInteger privExponent = null;
	private static BigInteger pubExponent = null;
	private static BigInteger modulus = null;

	private static AsymKeyHolder akh = null;

	public static String getOrganizationName()
	{
		return organizationName = properties.getProperty( "ORGANIZATION_NAME" );
	}

	private static BigInteger getModulus()
	{
		return modulus = toBigInt( properties.getProperty( "MODULUS" ) );
	}

	private static BigInteger getPublicExponent()
	{
		return pubExponent = toBigInt( properties.getProperty( "PUBLIC_EXPONENT" ) );
	}

	private static BigInteger getPrivateExponent()
	{
		return privExponent = toBigInt( properties.getProperty( "PRIVATE_EXPONENT" ) );
	}

	/**
	 * Load properties
	 */
	static {
		InputStreamReader stream = null;
		try {
			// Load all entries of the config file into properties
			stream = new InputStreamReader(
					new FileInputStream( "config/identity.properties" ), StandardCharsets.UTF_8 );
			properties.load( stream );
			stream.close();
		} catch ( IOException e ) {
			log.error( "Could not load identity.properties. Exiting." );
			System.exit( 2 );
		} finally {
			Util.streamClose( stream );
		}

		Util.notNullOrEmptyFatal( getOrganizationName(), "Organiziation Name must not be empty!" );
		try {
			akh = new AsymKeyHolder( getPrivateExponent(), getPublicExponent(), getModulus() );
		} catch ( InvalidKeySpecException e ) {
			log.error( "InvalidKeySpecException", e );
		} catch ( NoSuchAlgorithmException e ) {
			log.error( "NoSuchAlgorithmException", e );
		}
	}

	/**
	 * Get private key for this server. If none exists yet, create a new one.
	 * 
	 * @return
	 */
	public static PrivateKey getPrivateKey()
	{
		if ( akh != null ) {
			return akh.getPrivateKey();
		}
		akh = new AsymKeyHolder();
		return akh.getPrivateKey();
	}

	/**
	 * Get public key for this server. If none exists yet, create a new one.
	 * 
	 * @return
	 */
	public static PublicKey getPublicKey()
	{
		if ( akh != null )
			return akh.getPublicKey();
		akh = new AsymKeyHolder();
		return akh.getPublicKey();
	}

	/**
	 * Get bit - length of key.
	 * 
	 * @return
	 */
	public static int keySize( BigInteger modulus )
	{
		return modulus.bitLength();
	}

	/**
	 * Checks if given modulus, private exponent and public exponent are valid
	 * values for key pair. Idea is to encrypt and decrypt random text and compare
	 * the result with initial text.
	 * 
	 * @param mod
	 * @param privExp
	 * @param pubExp
	 * @return True, if mod, privExp and pubExp are valid values.
	 */
	public static boolean isValidKeyPair( BigInteger mod, BigInteger privExp, BigInteger pubExp )
	{
		// First check given values (modulus, privExp, pubExp).
		if ( ( mod == null ) || ( privExp == null ) || ( pubExp == null ) ) {
			log.error( "Given arguments not valid: got NULL for modulus, private or public exponent." );
			return false;
		}

		// Testing encryption and description with given public and private key.
		// Idea: creating random text for encrypting and decrypting again.
		Random rnd = new Random();
		int size = rnd.nextInt( keySize( mod ) - 1 );
		BigInteger text = new BigInteger( size, rnd );
		// Encrypt.
		BigInteger cipher = text.modPow( pubExp, mod );
		// Decrypt again.
		BigInteger decrypted = cipher.modPow( privExp, mod );
		boolean isPassed = text.equals( decrypted );
		return isPassed;
	}

	public static boolean generateIdentity( String organizationName )
	{
		Identity.organizationName = organizationName;
		// generate new key pair.
		Identity.akh = new AsymKeyHolder();
		Identity.modulus = akh.getModulus();
		Identity.privExponent = akh.getPrivateExponent();
		Identity.pubExponent = akh.getPublicExponent();

		return writeIdToFile(
				Identity.organizationName,
				Identity.modulus,
				Identity.privExponent,
				Identity.pubExponent );
	}

	private static boolean writeIdToFile( String organizationName, BigInteger modulus, BigInteger privateExp, BigInteger publicExp )
	{
		File configFile = new File( "config/identity.properties" );
		FileOutputStream stream = null;
		try {
			stream = new FileOutputStream( configFile );
		} catch ( FileNotFoundException e ) {
			log.error( "FileNotFoundException", e );
			return false;
		}
		
		// create strings for writing to file. 
		String orgNameString = "ORGANIZATION_NAME=" + organizationName + "\n";
		String modString = "MODULUS=" + modulus.toString() + "\n";
		String privExpString = "PRIVATE_EXPONENT=" + privateExp.toString() + "\n";
		String pubExpString = "PUBLIC_EXPONENT=" + publicExp.toString() + "\n";

		try {
			stream.write( orgNameString.getBytes() );
			stream.write( modString.getBytes() );
			stream.write( privExpString.getBytes() );
			stream.write( pubExpString.getBytes() );
			return true;
		} catch ( IOException e ) {
			log.error( "IOException", e );
			return false;
		} finally {
			try {
				stream.close();
			} catch ( IOException e ) {
			}
		}
	}

	/**
	 * Check modulus, privExp and pubExp for not being null.
	 * 
	 * @return
	 */
	private static boolean checkMembers()
	{
		return ( ( getModulus() != null ) &&
				( getPrivateExponent() != null ) && ( getPublicExponent() != null ) );
	}

	/**
	 * Get BigInteger of read String number.
	 * 
	 * @param str
	 * @return
	 */
	private static BigInteger toBigInt( String str )
	{
		try {
			return new BigInteger( str );
		} catch ( Exception e ) {
			return null;
		}
	}
}