/*
 Copyright (c) 2011, Andre Somers
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
 modification, are permitted provided that the following conditions are met:
 * Redistributions of source code must retain the above copyright
 notice, this list of conditions and the following disclaimer.
 * Redistributions in binary form must reproduce the above copyright
 notice, this list of conditions and the following disclaimer in the
 documentation and/or other materials provided with the distribution.
 * Neither the name of the Rathenau Instituut, Andre Somers nor the
 names of its contributors may be used to endorse or promote products
 derived from this software without specific prior written permission.
 
 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 DISCLAIMED. IN NO EVENT SHALL ANDRE SOMERS BE LIABLE FOR ANY
 DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 LOSS OF USE, DATA, OR #######; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
#include "simplecrypt.h"
#include <QByteArray>
#include <QtDebug>
#include <QtGlobal>
#include <QDateTime>
#include <QCryptographicHash>
#include <QDataStream>

SimpleCrypt::SimpleCrypt():
m_key(0),
m_compressionMode(CompressionAuto),
m_protectionMode(ProtectionChecksum),
m_lastError(ErrorNoError)
{
    qsrand(uint(QDateTime::currentMSecsSinceEpoch() & 0xFFFF));
}

SimpleCrypt::SimpleCrypt(quint64 key):
m_key(key),
m_compressionMode(CompressionAuto),
m_protectionMode(ProtectionChecksum),
m_lastError(ErrorNoError)
{
    qsrand(uint(QDateTime::currentMSecsSinceEpoch() & 0xFFFF));
    splitKey();
}

void SimpleCrypt::setKey(quint64 key)
{
    m_key = key;
    splitKey();
}

void SimpleCrypt::splitKey()
{
    m_keyParts.clear();
    m_keyParts.resize(8);
    for (int i=0;i<8;i++) {
        quint64 part = m_key;
        for (int j=i; j>0; j--)
            part = part >> 8;
        part = part & 0xff;
        m_keyParts[i] = static_cast<char>(part);
    }
}

QByteArray SimpleCrypt::encryptToByteArray(const QString& plaintext)
{
    QByteArray plaintextArray = plaintext.toUtf8();
    return encryptToByteArray(plaintextArray);
}

QByteArray SimpleCrypt::encryptToByteArray(QByteArray plaintext)
{
    if (m_keyParts.isEmpty()) {
        qWarning() << "No key set.";
        m_lastError = ErrorNoKeySet;
        return QByteArray();
    }
    
    
    QByteArray ba = plaintext;
    
    CryptoFlags flags = CryptoFlagNone;
    if (m_compressionMode == CompressionAlways) {
        ba = qCompress(ba, 9); //maximum compression
        flags |= CryptoFlagCompression;
    } else if (m_compressionMode == CompressionAuto) {
        QByteArray compressed = qCompress(ba, 9);
        if (compressed.count() < ba.count()) {
            ba = compressed;
            flags |= CryptoFlagCompression;
        }
    }
    
    QByteArray integrityProtection;
    if (m_protectionMode == ProtectionChecksum) {
        flags |= CryptoFlagChecksum;
        QDataStream s(&integrityProtection, QIODevice::WriteOnly);
        s << qChecksum(ba.constData(), ba.length());
    } else if (m_protectionMode == ProtectionHash) {
        flags |= CryptoFlagHash;
        QCryptographicHash hash(QCryptographicHash::Sha1);
        hash.addData(ba);
        
        integrityProtection += hash.result();
    }
    
    //prepend a random char to the string
    char randomChar = char(qrand() & 0xFF);
    ba = randomChar + integrityProtection + ba;
    
    int pos(0);
    char lastChar(0);
    
    int cnt = ba.count();
    
    while (pos < cnt) {
        ba[pos] = ba.at(pos) ^ m_keyParts.at(pos % 8) ^ lastChar;
        lastChar = ba.at(pos);
        ++pos;
    }
    
    QByteArray resultArray;
    resultArray.append(char(0x03));  //version for future updates to algorithm
    resultArray.append(char(flags)); //encryption flags
    resultArray.append(ba);
    
    m_lastError = ErrorNoError;
    return resultArray;
}

QString SimpleCrypt::encryptToString(const QString& plaintext)
{
    QByteArray plaintextArray = plaintext.toUtf8();
    QByteArray cypher = encryptToByteArray(plaintextArray);
    QString cypherString = QString::fromLatin1(cypher.toBase64());
    return cypherString;
}

QString SimpleCrypt::encryptToString(QByteArray plaintext)
{
    QByteArray cypher = encryptToByteArray(plaintext);
    QString cypherString = QString::fromLatin1(cypher.toBase64());
    return cypherString;
}

QString SimpleCrypt::decryptToString(const QString &cyphertext)
{
    QByteArray cyphertextArray = QByteArray::fromBase64(cyphertext.toLatin1());
    QByteArray plaintextArray = decryptToByteArray(cyphertextArray);
    QString plaintext = QString::fromUtf8(plaintextArray, plaintextArray.size());
    
    return plaintext;
}

QString SimpleCrypt::decryptToString(QByteArray cypher)
{
    QByteArray ba = decryptToByteArray(cypher);
    QString plaintext = QString::fromUtf8(ba, ba.size());
    
    return plaintext;
}

QByteArray SimpleCrypt::decryptToByteArray(const QString& cyphertext)
{
    QByteArray cyphertextArray = QByteArray::fromBase64(cyphertext.toLatin1());
    QByteArray ba = decryptToByteArray(cyphertextArray);
    
    return ba;
}

QByteArray SimpleCrypt::decryptToByteArray(QByteArray cypher)
{
    if (m_keyParts.isEmpty()) {
        qWarning() << "No key set.";
        m_lastError = ErrorNoKeySet;
        return QByteArray();
    }
    
    QByteArray ba = cypher;
    
    if( cypher.count() < 3 )
        return QByteArray();
    
    char version = ba.at(0);
    
    if (version !=3) {  //we only work with version 3
        m_lastError = ErrorUnknownVersion;
        qWarning() << "Invalid version or not a cyphertext.";
        return QByteArray();
    }
    
    CryptoFlags flags = CryptoFlags(ba.at(1));
    
    ba = ba.mid(2);
    int pos(0);
    int cnt(ba.count());
    char lastChar = 0;
    
    while (pos < cnt) {
        char currentChar = ba[pos];
        ba[pos] = ba.at(pos) ^ lastChar ^ m_keyParts.at(pos % 8);
        lastChar = currentChar;
        ++pos;
    }
    
    ba = ba.mid(1); //chop off the random number at the start
    
    bool integrityOk(true);
    if (flags.testFlag(CryptoFlagChecksum)) {
        if (ba.length() < 2) {
            m_lastError = ErrorIntegrityFailed;
            return QByteArray();
        }
        quint16 storedChecksum;
        {
            QDataStream s(&ba, QIODevice::ReadOnly);
            s >> storedChecksum;
        }
        ba = ba.mid(2);
        quint16 checksum = qChecksum(ba.constData(), ba.length());
        integrityOk = (checksum == storedChecksum);
    } else if (flags.testFlag(CryptoFlagHash)) {
        if (ba.length() < 20) {
            m_lastError = ErrorIntegrityFailed;
            return QByteArray();
        }
        QByteArray storedHash = ba.left(20);
        ba = ba.mid(20);
        QCryptographicHash hash(QCryptographicHash::Sha1);
        hash.addData(ba);
        integrityOk = (hash.result() == storedHash);
    }
    
    if (!integrityOk) {
        m_lastError = ErrorIntegrityFailed;
        return QByteArray();
    }
    
    if (flags.testFlag(CryptoFlagCompression))
        ba = qUncompress(ba);
    
    m_lastError = ErrorNoError;
    return ba;
}