/* This file is part of Flowee
 *
 * Copyright (C) 2017 Nathan Osman
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * 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.
 *
 * For the full copy of the License see <http://www.gnu.org/licenses/>
 */

#include <QIODevice>
#include <QTimer>

#include "qiodevicecopier.h"

#include "qiodevicecopier_p.h"

using namespace HttpEngine;

// Default value for the bufferSize property
const qint64 DefaultBufferSize = 65536;

QIODeviceCopierPrivate::QIODeviceCopierPrivate(QIODeviceCopier *copier, QIODevice *srcDevice, QIODevice *destDevice)
    : QObject(copier),
      q(copier),
      src(srcDevice),
      dest(destDevice),
      bufferSize(DefaultBufferSize),
      rangeFrom(0),
      rangeTo(-1)
{
}

void QIODeviceCopierPrivate::onReadyRead()
{
    if (dest->write(src->readAll()) == -1) {
        Q_EMIT q->error(dest->errorString());
        src->close();
    }
}

void QIODeviceCopierPrivate::onReadChannelFinished()
{
    // Read any data that remains and signal the end of the operation
    if (src->bytesAvailable()) {
        onReadyRead();
    }

    Q_EMIT q->finished();
}

void QIODeviceCopierPrivate::nextBlock()
{
    // Attempt to read an amount of data up to the size of the buffer
    QByteArray data;
    data.resize(bufferSize);
    qint64 dataRead = src->read(data.data(), bufferSize);

    // If an error occurred during the read, emit an error
    if (dataRead == -1) {
        Q_EMIT q->error(src->errorString());
        Q_EMIT q->finished();
        return;
    }

    // If range is specified (rangeTo >= 0), check if end of range is reached;
    // if it is, send only part from buffer truncated by range end
    if (rangeTo != -1 && src->pos() > rangeTo) {
        dataRead -= src->pos() - rangeTo - 1;
    }

    // Write the data to the destination device
    if (dest->write(data.constData(), dataRead) == -1) {
        Q_EMIT q->error(dest->errorString());
        Q_EMIT q->finished();
        return;
    }

    // Check if the end of the device has been reached or if the end of
    // the requested range is reached - if so, emit the finished signal and
    // if not, continue to read data at the next iteration of the event loop
    if (src->atEnd() || (rangeTo != -1 && src->pos() > rangeTo)) {
        Q_EMIT q->finished();
    } else {
        QTimer::singleShot(0, this, &QIODeviceCopierPrivate::nextBlock);
    }
}

QIODeviceCopier::QIODeviceCopier(QIODevice *src, QIODevice *dest, QObject *parent)
    : QObject(parent),
      d(new QIODeviceCopierPrivate(this, src, dest))
{
    connect(src, &QIODevice::destroyed, this, &QIODeviceCopier::stop);
    connect(dest, &QIODevice::destroyed, this, &QIODeviceCopier::stop);
}

void QIODeviceCopier::setBufferSize(qint64 size)
{
    d->bufferSize = size;
}

void QIODeviceCopier::setRange(qint64 from, qint64 to)
{
    d->rangeFrom = from;
    d->rangeTo = to;
}

void QIODeviceCopier::start()
{
    if (!d->src->isOpen()) {
        if (!d->src->open(QIODevice::ReadOnly)) {
            Q_EMIT error(tr("Unable to open source device for reading"));
            Q_EMIT finished();
            return;
        }
    }

    if (!d->dest->isOpen()) {
        if (!d->dest->open(QIODevice::WriteOnly)) {
            Q_EMIT error(tr("Unable to open destination device for writing"));
            Q_EMIT finished();
            return;
        }
    }

    // If range is set and d->src is not sequential, seek to starting position
    if (d->rangeFrom > 0 && !d->src->isSequential()) {
        if (!d->src->seek(d->rangeFrom)) {
            Q_EMIT error(tr("Unable to seek source device for specified range"));
            Q_EMIT finished();
            return;
        }
    }

    // These signals cannot be connected in the constructor since they may
    // begin firing before the start() method is called

    // readyRead() and readChannelFinished() are only emitted for sequential
    // devices - for other types of devices, it is necessary to check atEnd()
    // in order to determine whether the end of the device has been reached
    connect(d->src, &QIODevice::readyRead, d, &QIODeviceCopierPrivate::onReadyRead);
    connect(d->src, &QIODevice::readChannelFinished, d, &QIODeviceCopierPrivate::onReadChannelFinished);

    // The first read from the device needs to be triggered
    QTimer::singleShot(0, d, d->src->isSequential() ?
            &QIODeviceCopierPrivate::onReadyRead :
            &QIODeviceCopierPrivate::nextBlock);
}

void QIODeviceCopier::stop()
{
    disconnect(d->src, &QIODevice::readyRead, d, &QIODeviceCopierPrivate::onReadyRead);
    disconnect(d->src, &QIODevice::readChannelFinished, d, &QIODeviceCopierPrivate::onReadChannelFinished);

    Q_EMIT finished();
}