/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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.apache.commons.compress.archivers.sevenz;

import java.io.IOException;
import java.io.InputStream;
import java.security.GeneralSecurityException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import org.apache.commons.compress.PasswordRequiredException;

class AES256SHA256Decoder extends CoderBase {
    @Override
    InputStream decode(final String archiveName, final InputStream in, final long uncompressedLength,
            final Coder coder, final byte[] passwordBytes, final int maxMemoryLimitInKb) {
        return new InputStream() {
            private boolean isInitialized;
            private CipherInputStream cipherInputStream;

            private CipherInputStream init() throws IOException {
                if (isInitialized) {
                    return cipherInputStream;
                }
                if (coder.properties == null) {
                    throw new IOException("Missing AES256 properties in " + archiveName);
                }
                if (coder.properties.length < 2) {
                    throw new IOException("AES256 properties too short in " + archiveName);
                }
                final int byte0 = 0xff & coder.properties[0];
                final int numCyclesPower = byte0 & 0x3f;
                final int byte1 = 0xff & coder.properties[1];
                final int ivSize = ((byte0 >> 6) & 1) + (byte1 & 0x0f);
                final int saltSize = ((byte0 >> 7) & 1) + (byte1 >> 4);
                if (2 + saltSize + ivSize > coder.properties.length) {
                    throw new IOException("Salt size + IV size too long in " + archiveName);
                }
                final byte[] salt = new byte[saltSize];
                System.arraycopy(coder.properties, 2, salt, 0, saltSize);
                final byte[] iv = new byte[16];
                System.arraycopy(coder.properties, 2 + saltSize, iv, 0, ivSize);

                if (passwordBytes == null) {
                    throw new PasswordRequiredException(archiveName);
                }
                final byte[] aesKeyBytes;
                if (numCyclesPower == 0x3f) {
                    aesKeyBytes = new byte[32];
                    System.arraycopy(salt, 0, aesKeyBytes, 0, saltSize);
                    System.arraycopy(passwordBytes, 0, aesKeyBytes, saltSize,
                                     Math.min(passwordBytes.length, aesKeyBytes.length - saltSize));
                } else {
                    final MessageDigest digest;
                    try {
                        digest = MessageDigest.getInstance("SHA-256");
                    } catch (final NoSuchAlgorithmException noSuchAlgorithmException) {
                        throw new IOException("SHA-256 is unsupported by your Java implementation",
                            noSuchAlgorithmException);
                    }
                    final byte[] extra = new byte[8];
                    for (long j = 0; j < (1L << numCyclesPower); j++) {
                        digest.update(salt);
                        digest.update(passwordBytes);
                        digest.update(extra);
                        for (int k = 0; k < extra.length; k++) {
                            ++extra[k];
                            if (extra[k] != 0) {
                                break;
                            }
                        }
                    }
                    aesKeyBytes = digest.digest();
                }

                final SecretKey aesKey = new SecretKeySpec(aesKeyBytes, "AES");
                try {
                    final Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
                    cipher.init(Cipher.DECRYPT_MODE, aesKey, new IvParameterSpec(iv));
                    cipherInputStream = new CipherInputStream(in, cipher);
                    isInitialized = true;
                    return cipherInputStream;
                } catch (final GeneralSecurityException generalSecurityException) {
                    throw new IOException("Decryption error " +
                        "(do you have the JCE Unlimited Strength Jurisdiction Policy Files installed?)",
                        generalSecurityException);
                    }
            }

            @Override
            public int read() throws IOException {
                return init().read();
            }

            @Override
            public int read(final byte[] b, final int off, final int len) throws IOException {
                return init().read(b, off, len);
            }

            @Override
            public void close() throws IOException {
                if (cipherInputStream != null) {
                    cipherInputStream.close();
                }
            }
        };
    }
}
