/*
 * Copyright 2002-2014 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.security.crypto.keygen;

import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.security.SecureRandom;

import org.springframework.security.crypto.keygen.BytesKeyGenerator;

/**
 * A KeyGenerator that uses SecureRandom to generate byte array-based keys. Defaults to 8 byte keys produced by the
 * SHA1PRNG algorithm developed by the BouncyCastle Provider.
 * 
 * @author Keith Donald
 * @author Roy Clarkson
 * @since 1.0
 */
final class AndroidSecureRandomBytesKeyGenerator implements BytesKeyGenerator {

	private final SecureRandom random;

	private final int keyLength;

	/**
	 * Creates a secure random key generator using the defaults.
	 */
	public AndroidSecureRandomBytesKeyGenerator() {
		this(DEFAULT_ALGORITHM, DEFAULT_PROVIDER, DEFAULT_KEY_LENGTH);
	}

	/**
	 * Creates a secure random key generator with a custom key length.
	 */
	public AndroidSecureRandomBytesKeyGenerator(int keyLength) {
		this(DEFAULT_ALGORITHM, DEFAULT_PROVIDER, keyLength);
	}

	public int getKeyLength() {
		return keyLength;
	}

	public byte[] generateKey() {
		byte[] bytes = new byte[keyLength];
		random.nextBytes(bytes);
		return bytes;
	}

	// internal helpers

	/**
	 * Creates a secure random key generator that is fully customized.
	 */
	private AndroidSecureRandomBytesKeyGenerator(String algorithm, String provider, int keyLength) {
		this.random = createSecureRandom(algorithm, provider, keyLength);
		this.keyLength = keyLength;
	}

	private SecureRandom createSecureRandom(String algorithm, String provider, int keyLength) {
		try {
			SecureRandom random = SecureRandom.getInstance(algorithm, provider);
			random.setSeed(random.generateSeed(keyLength));
			return random;
		} catch (NoSuchAlgorithmException e) {
			throw new IllegalArgumentException("Not a supported SecureRandom key generation algorithm", e);
		} catch (NoSuchProviderException e) {
			throw new IllegalArgumentException("Not a supported SecureRandom key provider", e);
		}
	}

	private static final String DEFAULT_ALGORITHM = "SHA1PRNG";

	private static final String DEFAULT_PROVIDER = "Crypto";

	private static final int DEFAULT_KEY_LENGTH = 8;

}