/*  This file is part of the KDE libraries
    Copyright (C) 2022 Ivailo Monev <xakepa10@gmail.com>

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License version 2, as published by the Free Software Foundation.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public License
    along with this library; see the file COPYING.LIB.  If not, write to
    the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
    Boston, MA 02110-1301, USA.
*/ 

#include "kpasswdstore.h"
#include "kstandarddirs.h"
#include "kconfiggroup.h"
#include "kpassworddialog.h"
#include "kmessagebox.h"
#include "klocale.h"
#include "kdebug.h"

#include <QApplication>
#include <QElapsedTimer>
#include <QCryptographicHash>

#if defined(HAVE_OPENSSL)
#  include <openssl/evp.h>
#  include <openssl/err.h>
#endif

static const int kpasswdstore_buffsize = 1024;
static const int kpasswdstore_passretries = 3;
static const int kpasswdstore_passtimeout = 30000;

// EVP_CIPHER_CTX_key_length() and EVP_CIPHER_CTX_iv_length() cannot be called
// prior to EVP_EncryptInit() and EVP_DecryptInit() so hardcoding these
static const int kpasswdstore_keylen = 32;
static const int kpasswdstore_ivlen = 16;

#if QT_VERSION >= 0x041200
static const QCryptographicHash::Algorithm kpasswdstore_algorithm = QCryptographicHash::KAT;
#else
static const QCryptographicHash::Algorithm kpasswdstore_algorithm = QCryptographicHash::Sha1;
#endif

static QWidget* widgetForWindowID(const qlonglong windowid)
{
    return QWidget::find(windowid);
}

class KPasswdStorePrivate
{
public:
    KPasswdStorePrivate();
    ~KPasswdStorePrivate();

    bool ensurePasswd(const qlonglong windowid, const bool showerror);
    bool hasPasswd() const;
    void clearPasswd();

    QString decryptPasswd(const QString &passwd, bool *ok);
    QString encryptPasswd(const QString &passwd, bool *ok);

    mutable bool cacheonly;
    QString storeid;
    QString passwdstore;
    mutable QMap<QByteArray, QString> cache;

private:
#if defined(HAVE_OPENSSL)
    static QByteArray genBytes(const QByteArray &data, const int length);
    static QString passwdHash(const QString &passwd);

    QByteArray m_passwd;
    QByteArray m_passwdiv;
    QElapsedTimer m_passwdtimer;
#endif
};

KPasswdStorePrivate::KPasswdStorePrivate()
    : cacheonly(false),
    storeid(QApplication::applicationName()),
    passwdstore(KStandardDirs::locateLocal("data", "kpasswdstore.ini"))
{
#if defined(HAVE_OPENSSL)
    ERR_load_ERR_strings();
    EVP_add_cipher(EVP_aes_256_cbc());
#endif
}

KPasswdStorePrivate::~KPasswdStorePrivate()
{
}

bool KPasswdStorePrivate::ensurePasswd(const qlonglong windowid, const bool showerror)
{
    Q_ASSERT(!cacheonly);

#if defined(HAVE_OPENSSL)
    if (!m_passwd.isEmpty() && m_passwdtimer.elapsed() >= kpasswdstore_passtimeout) {
        m_passwd.clear();
    }
    m_passwdtimer.restart();

    if (m_passwd.isEmpty()) {
        KPasswordDialog kpasswddialog(widgetForWindowID(windowid));
        kpasswddialog.setPrompt(i18n("Enter a password for <b>%1</b> password storage", storeid));
        if (showerror) {
            kpasswddialog.showErrorMessage(i18n("Incorrect password"));
        }
        if (!kpasswddialog.exec()) {
            return false;
        }
        const QByteArray kpasswddialogpass = kpasswddialog.password().toUtf8();
        if (kpasswddialogpass.isEmpty()) {
            kWarning() << "Password is empty";
            clearPasswd();
            return false;
        }
        m_passwd = KPasswdStorePrivate::genBytes(kpasswddialogpass, kpasswdstore_keylen);
        if (m_passwd.isEmpty()) {
            kWarning() << "Password bytes is empty";
            clearPasswd();
            return false;
        }
        m_passwdiv = KPasswdStorePrivate::genBytes(m_passwd.toHex(), kpasswdstore_ivlen);
        if (m_passwdiv.isEmpty()) {
            kWarning() << "Password initialization vector is empty";
            clearPasswd();
            return false;
        }

        // the only reason to encrypt and decrypt passwords is to obscure them
        // for the naked eye, if one can overwrite, delete or otherwise alter
        // the password store then there are more possibilities for havoc
        KConfig kconfig(passwdstore);
        KConfigGroup kconfiggroup = kconfig.group("KPasswdStore");
        const QString passwdhash = kconfiggroup.readEntry(storeid, QString());
        if (passwdhash.isEmpty()) {
            kconfiggroup.writeEntry(storeid, KPasswdStorePrivate::passwdHash(m_passwd));
            return true;
        }
        if (KPasswdStorePrivate::passwdHash(m_passwd) != passwdhash) {
            clearPasswd();
            return false;
        }
        return true;
    }
    return hasPasswd();
#else
    // not used
    return true;
#endif
}

bool KPasswdStorePrivate::hasPasswd() const
{
    return !m_passwd.isEmpty();
}

void KPasswdStorePrivate::clearPasswd()
{
    m_passwd.clear();
    m_passwdiv.clear();
}

QString KPasswdStorePrivate::decryptPasswd(const QString &passwd, bool *ok)
{
#if defined(HAVE_OPENSSL)
    EVP_CIPHER_CTX *opensslctx = EVP_CIPHER_CTX_new();
    if (Q_UNLIKELY(!opensslctx)) {
        kWarning() << ERR_error_string(ERR_get_error(), NULL);
        return QString();
    }

    int opensslresult = EVP_DecryptInit(
        opensslctx, EVP_aes_256_cbc(),
        reinterpret_cast<const uchar*>(m_passwd.constData()),
        reinterpret_cast<const uchar*>(m_passwdiv.constData())
    );
    if (Q_UNLIKELY(opensslresult != 1)) {
        kWarning() << ERR_error_string(ERR_get_error(), NULL);
        EVP_CIPHER_CTX_free(opensslctx);
        return QString();
    }

    // qDebug() << Q_FUNC_INFO << EVP_CIPHER_CTX_key_length(opensslctx);
    // qDebug() << Q_FUNC_INFO << EVP_CIPHER_CTX_iv_length(opensslctx);
    Q_ASSERT(EVP_CIPHER_CTX_key_length(opensslctx) == kpasswdstore_keylen);
    Q_ASSERT(EVP_CIPHER_CTX_iv_length(opensslctx) == kpasswdstore_ivlen);

    const QByteArray passwdbytes = QByteArray::fromHex(passwd.toUtf8());
    const int opensslbuffersize = (kpasswdstore_buffsize * EVP_CIPHER_CTX_block_size(opensslctx));
    uchar opensslbuffer[opensslbuffersize];
    ::memset(opensslbuffer, 0, sizeof(opensslbuffer) * sizeof(uchar));
    int opensslbufferpos = 0;
    opensslresult = EVP_DecryptUpdate(
        opensslctx,
        opensslbuffer, &opensslbufferpos,
        reinterpret_cast<const uchar*>(passwdbytes.constData()), passwdbytes.size()
    );
    if (Q_UNLIKELY(opensslresult != 1)) {
        kWarning() << ERR_error_string(ERR_get_error(), NULL);
        EVP_CIPHER_CTX_free(opensslctx);
        return QString();
    }

    opensslresult = EVP_DecryptFinal(
        opensslctx,
        opensslbuffer + opensslbufferpos, &opensslbufferpos
    );
    if (Q_UNLIKELY(opensslresult != 1)) {
        kWarning() << ERR_error_string(ERR_get_error(), NULL);
        EVP_CIPHER_CTX_free(opensslctx);
        return QString();
    }

    const QString result = QString::fromLatin1(reinterpret_cast<char*>(opensslbuffer), opensslbufferpos);
    EVP_CIPHER_CTX_free(opensslctx);
    *ok = !result.isEmpty();
    return result;
#else
    const QByteArray decrypted = QByteArray::fromBase64(passwd.toUtf8());
    const QString result = QString::fromLatin1(decrypted.constData(), decrypted.size());
    *ok = !result.isEmpty();
    return result;
#endif
}

QString KPasswdStorePrivate::encryptPasswd(const QString &passwd, bool *ok)
{
#if defined(HAVE_OPENSSL)
    EVP_CIPHER_CTX *opensslctx = EVP_CIPHER_CTX_new();
    if (Q_UNLIKELY(!opensslctx)) {
        kWarning() << ERR_error_string(ERR_get_error(), NULL);
        return QString();
    }

    int opensslresult = EVP_EncryptInit(
        opensslctx, EVP_aes_256_cbc(),
        reinterpret_cast<const uchar*>(m_passwd.constData()),
        reinterpret_cast<const uchar*>(m_passwdiv.constData())
    );
    if (Q_UNLIKELY(opensslresult != 1)) {
        kWarning() << ERR_error_string(ERR_get_error(), NULL);
        EVP_CIPHER_CTX_free(opensslctx);
        return QString();
    }

    Q_ASSERT(EVP_CIPHER_CTX_key_length(opensslctx) == kpasswdstore_keylen);
    Q_ASSERT(EVP_CIPHER_CTX_iv_length(opensslctx) == kpasswdstore_ivlen);

    const QByteArray passwdbytes = passwd.toUtf8();
    const int opensslbuffersize = (kpasswdstore_buffsize * EVP_CIPHER_CTX_block_size(opensslctx));
    uchar opensslbuffer[opensslbuffersize];
    ::memset(opensslbuffer, 0, sizeof(opensslbuffer) * sizeof(uchar));
    int opensslbufferpos = 0;
    opensslresult = EVP_EncryptUpdate(
        opensslctx,
        opensslbuffer, &opensslbufferpos,
        reinterpret_cast<const uchar*>(passwdbytes.constData()), passwdbytes.size()
    );
    if (Q_UNLIKELY(opensslresult != 1)) {
        kWarning() << ERR_error_string(ERR_get_error(), NULL);
        EVP_CIPHER_CTX_free(opensslctx);
        return QString();
    }

    opensslresult = EVP_EncryptFinal(
        opensslctx,
        opensslbuffer + opensslbufferpos, &opensslbufferpos
    );
    if (Q_UNLIKELY(opensslresult != 1)) {
        kWarning() << ERR_error_string(ERR_get_error(), NULL);
        EVP_CIPHER_CTX_free(opensslctx);
        return QString();
    }

    const QString result = QString::fromLatin1(QByteArray(reinterpret_cast<char*>(opensslbuffer), opensslbufferpos).toHex());
    EVP_CIPHER_CTX_free(opensslctx);
    *ok = !result.isEmpty();
    return result;
#else
    const QString result = passwd.toUtf8().toBase64();
    *ok = !result.isEmpty();
    return result;
#endif
}

#if defined(HAVE_OPENSSL)
QByteArray KPasswdStorePrivate::genBytes(const QByteArray &data, const int length)
{
    const QByteArray result = QCryptographicHash::hash(data, kpasswdstore_algorithm).toHex();
    Q_ASSERT(result.size() >= length);
    return result.mid(length);
}

QString KPasswdStorePrivate::passwdHash(const QString &passwd)
{
    return QCryptographicHash::hash(passwd.toUtf8(), QCryptographicHash::Sha512).toHex();
}
#endif

KPasswdStore::KPasswdStore(QObject *parent)
    : QObject(parent),
    d(new KPasswdStorePrivate())
{
}

KPasswdStore::~KPasswdStore()
{
    delete d;
}

void KPasswdStore::setStoreID(const QString &id)
{
    d->storeid = id;
    d->clearPasswd();
}

void KPasswdStore::setCacheOnly(const bool cacheonly)
{
    d->cacheonly = cacheonly;
    d->cache.clear();
}

bool KPasswdStore::cacheOnly() const
{
    return d->cacheonly;
}

bool KPasswdStore::hasPasswd(const QByteArray &key, const qlonglong windowid)
{
    return !getPasswd(key, windowid).isEmpty();
}

QString KPasswdStore::getPasswd(const QByteArray &key, const qlonglong windowid) const
{
    if (d->cacheonly) {
        return d->cache.value(key, QString());
    }

    int retry = kpasswdstore_passretries;
    while (retry > 0 && !d->ensurePasswd(windowid, retry < kpasswdstore_passretries)) {
        retry--;
    }
    if (!d->hasPasswd()) {
        KMessageBox::error(nullptr, i18n("The storage could not be open, no passwords will be permanently stored"));
        d->cacheonly = true;
        d->cache.clear();
        return QString();
    }

    bool ok = false;
    KConfig kconfig(d->passwdstore);
    const QString passwd = kconfig.group(d->storeid).readEntry(key.constData(), QString());
    return d->decryptPasswd(passwd, &ok);
}

bool KPasswdStore::storePasswd(const QByteArray &key, const QString &passwd, const qlonglong windowid)
{
    if (d->cacheonly) {
        d->cache.insert(key, passwd);
        return true;
    }

    int retry = kpasswdstore_passretries;
    while (retry > 0 && !d->ensurePasswd(windowid, retry < kpasswdstore_passretries)) {
        retry--;
    }
    if (!d->hasPasswd()) {
        KMessageBox::error(widgetForWindowID(windowid), i18n("The storage could not be open, no passwords will be permanently stored"));
        setCacheOnly(true);
        return storePasswd(key, passwd);
    }

    bool ok = false;
    KConfig kconfig(d->passwdstore);
    KConfigGroup kconfiggroup = kconfig.group(d->storeid);
    kconfiggroup.writeEntry(key.constData(), d->encryptPasswd(passwd, &ok));
    kconfiggroup.sync();
    return ok;
}

QByteArray KPasswdStore::makeKey(const QString &string)
{
    return QCryptographicHash::hash(string.toUtf8(), kpasswdstore_algorithm).toHex();
}