/*
    SPDX-FileCopyrightText: 2010 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.net>
    SPDX-FileContributor: Stephen Kelly <stephen@kdab.com>

    SPDX-License-Identifier: LGPL-2.0-or-later
*/

#ifndef KVIEWSTATESERIALIZER_H
#define KVIEWSTATESERIALIZER_H

#include <QObject>
#include <QPair>
#include <QStringList>
#include <memory>

#include "kwidgetsaddons_export.h"

class QAbstractItemView;
class QItemSelectionModel;
class QAbstractItemModel;
class QAbstractScrollArea;
class QModelIndex;

class KViewStateSerializerPrivate;

/**
  @class KViewStateSerializer kviewstateserializer.h KViewStateSerializer

  @brief Object for saving and restoring state in QTreeViews and QItemSelectionModels

  Implement the indexFromConfigString and indexToConfigString methods to handle
  the model in the view whose state is being saved. These implementations can be
  quite trivial:

  @code
    QModelIndex DynamicTreeStateSaver::indexFromConfigString(const QAbstractItemModel* model,
                                                             const QString& key) const
    {
        QModelIndexList list = model->match(model->index(0, 0),
                                            DynamicTreeModel::DynamicTreeModelId,
                                            key.toInt(), 1, Qt::MatchRecursive);
        if (list.isEmpty()) {
            return QModelIndex();
        }
        return list.first();
    }

    QString DynamicTreeStateSaver::indexToConfigString(const QModelIndex& index) const
    {
        return index.data(DynamicTreeModel::DynamicTreeModelId).toString();
    }
  @endcode

  It is possible to restore the state of a QTreeView (that is, the expanded state and
  selected state of all indexes as well as the horizontal and vertical scroll state) by
  using setView.

  If there is no tree view state to restore (for example if using QML), the selection
  state of a QItemSelectionModel can be saved or restored instead.

  The state of any QAbstractScrollArea can also be saved and restored.

  A KViewStateSerializer should be created on the stack when saving and on the heap
  when restoring. The model may be populated dynamically between several event loops,
  so it may not be immediate for the indexes that should be selected to be in the model.
  The saver should *not* be persisted as a member. The saver will destroy itself when it
  has completed the restoration specified in the config group, or a small amount of time
  has elapsed.

  @code
    MyWidget::MyWidget(Qobject *parent)
      : QWidget(parent)
    {
        ...

        m_view = new QTreeView(splitter);
        m_view->setModel(model);

        connect(model, &QAbstractItemModel::modelAboutToBeReset, this, [this]() { saveState(); });
        connect(model, &QAbstractItemModel::modelReset, [this]() { restoreState(); });
        connect(qApp, &QApplication::aboutToQuit, this, [this]() { saveState(); });

        restoreState();
    }

    void StateSaverWidget::saveState()
    {
        ConcreteStateSaver saver;
        saver.setView(m_view);

        KConfigGroup cfg(KSharedConfig::openConfig(), "ExampleViewState");
        saver.saveState(cfg);
        cfg.sync();
    }

    void StateSaverWidget::restoreState()
    {
        // Will delete itself.
        ConcreteTreeStateSaver *saver = new ConcreteStateSaver();
        saver->setView(m_view);
        KConfigGroup cfg(KSharedConfig::openConfig(), "ExampleViewState");
        saver->restoreState(cfg);
    }
  @endcode

  After creating a saver, the state can be saved using a KConfigGroup.

  It is also possible to save and restore state directly by using the restoreSelection,
  restoreExpanded etc methods. Note that the implementation of these methods should return
  strings that the indexFromConfigString implementation can handle.

  @code
    class DynamicTreeStateSaver : public KViewStateSerializer
    {
        Q_OBJECT
    public:
      // ...

        void selectItems(const QList<qint64> &items)
        {
            QStringList itemStrings;
            for (qint64 item : items) {
                itemStrings << QString::number(item);
            }
            restoreSelection(itemStrings);
        }

        void expandItems(const QList<qint64> &items)
        {
            QStringList itemStrings;
            for (qint64 item : items) {
                itemStrings << QString::number(item);
            }
            restoreSelection(itemStrings);
        }
    };
  @endcode

  Note that a single instance of this class should be used with only one widget.
  That is don't do this:

  @code
    saver->setView(treeView1);
    saver->setSelectionModel(treeView2->selectionModel());
    saver->setScrollArea(treeView3);
  @endcode

  To save the state of 3 different widgets, use three savers, even if they operate
  on the same root model.

  @code
    saver1->setView(treeView1);
    saver2->setSelectionModel(treeView2->selectionModel());
    saver3->setScrollArea(treeView3);
  @endcode

  @note The KViewStateSerializer does not take ownership of any widgets set on it.

  It is recommended to restore the state on application startup and after the
  model has been reset, and to save the state on application close and before
  the model has been reset.

  @see QAbstractItemModel::modelAboutToBeReset QAbstractItemModel::modelReset

  @author Stephen Kelly <stephen@kdab.com>
  @since 4.5
*/
class KWIDGETSADDONS_EXPORT KViewStateSerializer : public QObject
{
    Q_OBJECT
public:
    /**
     * Constructor
     */
    explicit KViewStateSerializer(QObject *parent = nullptr);

    /**
     * Destructor
     */
    ~KViewStateSerializer() override;

    /**
     * The view whose state is persisted.
     */
    QAbstractItemView *view() const;

    /**
     * Sets the view whose state is persisted.
     */
    void setView(QAbstractItemView *view);

    /**
     * The QItemSelectionModel whose state is persisted.
     */
    QItemSelectionModel *selectionModel() const;

    /**
     * Sets the QItemSelectionModel whose state is persisted.
     */
    void setSelectionModel(QItemSelectionModel *selectionModel);

    /**
     * Returns a QStringList describing the selection in the selectionModel.
     */
    QStringList selectionKeys() const;

    /**
     * Returns a QStringList representing the expanded indexes in the QTreeView.
     */
    QStringList expansionKeys() const;

    /**
     * Returns a QString describing the current index in the selection model.
     */
    QString currentIndexKey() const;

    /**
     * Returns the vertical and horizontal scroll of the QAbstractScrollArea.
     */
    QPair<int, int> scrollState() const;

    /**
     * Select the indexes described by @p indexStrings
     */
    void restoreSelection(const QStringList &indexStrings);

    /**
     * Make the index described by @p indexString the currentIndex in the selectionModel.
     */
    void restoreCurrentItem(const QString &indexString);

    /**
     * Expand the indexes described by @p indexStrings in the QTreeView.
     */
    void restoreExpanded(const QStringList &indexStrings);

    /**
     * Restores the scroll state of the QAbstractScrollArea to the @p verticalScoll
     * and @p horizontalScroll
     */
    void restoreScrollState(int verticalScoll, int horizontalScroll);

protected:
    /**
     * Reimplement to return an index in the @p model described by the unique key @p key
     */
    virtual QModelIndex indexFromConfigString(const QAbstractItemModel *model, const QString &key) const = 0;

    /**
     * Reimplement to return a unique string for the @p index.
     */
    virtual QString indexToConfigString(const QModelIndex &index) const = 0;

    void restoreState();

private:
    //@cond PRIVATE
    Q_DECLARE_PRIVATE(KViewStateSerializer)
    std::unique_ptr<KViewStateSerializerPrivate> const d_ptr;
    //@endcond
};

#endif