/*
 * Copyright (C) 2003-2008  Justin Karneges <justin@affinix.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301  USA
 *
 */

#include "qca_support.h"

#include "qca_safeobj.h"
#include <QDateTime>
#include <QDir>
#include <QFileInfo>
#include <QFileSystemWatcher>
#include <QList>

namespace QCA {

// this gets us DOR-SS and SR, provided we delete the object between uses.
// we assume QFileSystemWatcher complies to DS,NE.
class QFileSystemWatcherRelay : public QObject
{
    Q_OBJECT
public:
    QFileSystemWatcher *watcher;

    QFileSystemWatcherRelay(QFileSystemWatcher *_watcher, QObject *parent = nullptr)
        : QObject(parent)
        , watcher(_watcher)
    {
        connect(watcher,
                &QFileSystemWatcher::directoryChanged,
                this,
                &QFileSystemWatcherRelay::directoryChanged,
                Qt::QueuedConnection);
        connect(watcher,
                &QFileSystemWatcher::fileChanged,
                this,
                &QFileSystemWatcherRelay::fileChanged,
                Qt::QueuedConnection);
    }

Q_SIGNALS:
    void directoryChanged(const QString &path);
    void fileChanged(const QString &path);
};

//----------------------------------------------------------------------------
// DirWatch
//----------------------------------------------------------------------------
class DirWatch::Private : public QObject
{
    Q_OBJECT
public:
    DirWatch                *q;
    QFileSystemWatcher      *watcher;
    QFileSystemWatcherRelay *watcher_relay;
    QString                  dirName;

    Private(DirWatch *_q)
        : QObject(_q)
        , q(_q)
        , watcher(nullptr)
        , watcher_relay(nullptr)
    {
    }

public Q_SLOTS:
    void watcher_changed(const QString &path)
    {
        Q_UNUSED(path);
        emit q->changed();
    }
};

DirWatch::DirWatch(const QString &dir, QObject *parent)
    : QObject(parent)
{
    d = new Private(this);
    setDirName(dir);
}

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

QString DirWatch::dirName() const
{
    return d->dirName;
}

void DirWatch::setDirName(const QString &dir)
{
    if (d->watcher) {
        delete d->watcher;
        delete d->watcher_relay;
        d->watcher       = nullptr;
        d->watcher_relay = nullptr;
    }

    d->dirName = dir;

    if (!d->dirName.isEmpty() && QFileInfo(d->dirName).isDir()) {
        d->watcher       = new QFileSystemWatcher(this);
        d->watcher_relay = new QFileSystemWatcherRelay(d->watcher, this);
        connect(d->watcher_relay, &QFileSystemWatcherRelay::directoryChanged, d, &Private::watcher_changed);

        d->watcher->addPath(d->dirName);
    }
}

//----------------------------------------------------------------------------
// FileWatch
//----------------------------------------------------------------------------

class FileWatch::Private : public QObject
{
    Q_OBJECT
public:
    FileWatch               *q;
    QFileSystemWatcher      *watcher;
    QFileSystemWatcherRelay *watcher_relay;
    QString                  fileName; // file (optionally w/ path) as provided by user
    QString                  filePath; // absolute path of file, calculated by us
    bool                     fileExisted;

    Private(FileWatch *_q)
        : QObject(_q)
        , q(_q)
        , watcher(nullptr)
        , watcher_relay(nullptr)
    {
    }

    void start(const QString &_fileName)
    {
        fileName = _fileName;

        watcher       = new QFileSystemWatcher(this);
        watcher_relay = new QFileSystemWatcherRelay(watcher, this);
        connect(watcher_relay, &QFileSystemWatcherRelay::directoryChanged, this, &Private::dir_changed);
        connect(watcher_relay, &QFileSystemWatcherRelay::fileChanged, this, &Private::file_changed);

        QFileInfo fi(fileName);
        fi.makeAbsolute();
        filePath       = fi.filePath();
        const QDir dir = fi.dir();

        // we watch both the directory and the file itself.  the
        //   reason we watch the directory is so we can detect when
        //   the file is deleted/created

        // we don't bother checking for dir existence before adding,
        //   since there isn't an atomic way to do both at once.  if
        //   it turns out that the dir doesn't exist, then the
        //   monitoring will just silently not work at all.

        watcher->addPath(dir.path());

        // can't watch for non-existent directory
        if (!watcher->directories().contains(dir.path())) {
            stop();
            return;
        }

        // save whether or not the file exists
        fileExisted = fi.exists();

        // add only if file existent
        // if no it will be added on directoryChanged signal
        if (fileExisted)
            watcher->addPath(filePath);

        // TODO: address race conditions and think about error
        //   reporting instead of silently failing.  probably this
        //   will require a Qt API update.
    }

    void stop()
    {
        if (watcher) {
            delete watcher;
            delete watcher_relay;
            watcher       = nullptr;
            watcher_relay = nullptr;
        }

        fileName.clear();
        filePath.clear();
    }

private Q_SLOTS:
    void dir_changed(const QString &path)
    {
        Q_UNUSED(path);
        QFileInfo  fi(filePath);
        const bool exists = fi.exists();
        if (exists && !fileExisted) {
            // this means the file was created.  put a
            //   watch on it.
            fileExisted = true;
            watcher->addPath(filePath);
            emit q->changed();
        }
    }

    void file_changed(const QString &path)
    {
        Q_UNUSED(path);
        QFileInfo fi(filePath);
        if (!fi.exists() && !fileExisted) {
            // Got a file changed signal on a file that does not exist
            // and is not actively watched. This happens when we
            // previously watched a file but it was deleted and after
            // the original deletion changed-signal we get another one
            // (for example because of bad signal timing). In this scenario
            // we must ignore the change as the change, whatever it may
            // have been, is of no interest to us because we don't watch
            // the file and furthermore the file does not even exist.
            return;
        } else if (!fi.exists()) {
            fileExisted = false;
        };
        emit q->changed();
    }
};

FileWatch::FileWatch(const QString &file, QObject *parent)
    : QObject(parent)
{
    d = new Private(this);
    d->start(file);
}

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

QString FileWatch::fileName() const
{
    return d->fileName;
}

void FileWatch::setFileName(const QString &file)
{
    d->stop();
    d->start(file);
}

}

#include "dirwatch.moc"