Expose more private API so users can use the full power

Installed more private headers.
TabWidget_p.h was moved into widgets/ as the QtQuick impl won't
use that abstraction. Could even be folded into TabWidgetWidget.

Fixes #65

src/private/widgets/TabWidget_p.h

@@ -0,0 +1,184 @@
+/*
+  This file is part of KDDockWidgets.
+
+  SPDX-FileCopyrightText: 2019-2020 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
+  Author: Sérgio Martins <sergio.martins@kdab.com>
+
+  SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only
+
+  Contact KDAB at <info@kdab.com> for commercial licensing options.
+*/
+
+/**
+ * @file
+ * @brief Implements a QTabWidget derived class with support for docking and undocking
+ * KDockWidget::DockWidget as tabs .
+ *
+ * @author Sérgio Martins \<sergio.martins@kdab.com\>
+ */
+
+#ifndef KD_TAB_WIDGET_P_H
+#define KD_TAB_WIDGET_P_H
+
+#include "docks_export.h"
+#include "../Draggable_p.h"
+#include "../Frame_p.h"
+#include "DockWidgetBase.h"
+
+#include <QTabBar>
+#include <QVector>
+
+#include <memory>
+
+namespace KDDockWidgets {
+
+class DockWidgetBase;
+class TabWidget;
+
+///@brief a QTabBar derived class to be used by KDDockWidgets::TabWidget
+class DOCKS_EXPORT TabBar : public Draggable
+{
+public:
+    /**
+     * @brief Constructs a new TabBar
+     * @param parent The parent TabWidget
+     */
+    explicit TabBar(QWidgetOrQuick *thisWidget, TabWidget *parent = nullptr);
+
+    /**
+     * @brief returns the dock widgets at tab number @p index
+     * @param index the tab number from which we want the dock widget
+     * @return the dock widget at tab number @p index
+     */
+    DockWidgetBase *dockWidgetAt(int index) const;
+
+    ///@overload
+    DockWidgetBase *dockWidgetAt(QPoint localPos) const;
+
+    // Draggable
+    std::unique_ptr<WindowBeingDragged> makeWindow() override;
+
+    /**
+     * @brief detaches a dock widget and shows it as a floating dock widget
+     * The dock widget is morphed into a FloatingWindow for convenience.
+     * @param dockWidget the dock widget to detach
+     * @returns the created FloatingWindow
+     */
+    FloatingWindow *detachTab(DockWidgetBase *dockWidget);
+
+    void onMousePress(QPoint localPos);
+
+    ///@brief returns whether there's only 1 tab
+    bool hasSingleDockWidget() const;
+
+    virtual int numDockWidgets() const = 0;
+    virtual int tabAt(QPoint localPos) const = 0;
+
+
+    /**
+     * @brief Returns this class as a QWidget (if using QtWidgets) or QQuickItem
+     */
+    QWidgetOrQuick *asWidget() const;
+
+    DockWidgetBase *singleDockWidget() const override;
+
+private:
+    TabWidget *const m_tabWidget;
+    QPointer<DockWidgetBase> m_lastPressedDockWidget = nullptr;
+    QWidgetOrQuick *const m_thisWidget;
+};
+
+class DOCKS_EXPORT TabWidget : public Draggable
+{
+public:
+    /**
+     * @brief Constructs a new TabWidget, with @p frame as a parent
+     */
+    explicit TabWidget(QWidgetOrQuick *thisWidget, Frame *frame);
+
+    /**
+     * @brief returns the number of dock widgets in this TabWidget
+     */
+    virtual int numDockWidgets() const = 0;
+
+    /**
+     * @brief Removes a dock widget from the TabWidget
+     */
+    virtual void removeDockWidget(DockWidgetBase *) = 0;
+
+    /**
+     * @brief Returns the index of the dock widget, or -1 if it doesn't exist
+     */
+    virtual int indexOfDockWidget(DockWidgetBase *) const = 0;
+
+    /**
+     * @brief Sets the current dock widget index
+     */
+    virtual void setCurrentDockWidget(int index) = 0;
+    void setCurrentDockWidget(DockWidgetBase *);
+
+    virtual void insertDockWidget(int index, DockWidgetBase *, const QIcon&, const QString &title) = 0;
+
+    virtual void setTabBarAutoHide(bool) = 0;
+
+    /**
+     * @brief Returns the current index
+     */
+    virtual int currentIndex() const = 0;
+
+    ///@brief appends a dock widget into this TabWidget
+    void addDockWidget(DockWidgetBase *);
+
+    /**
+     * @brief Returns the dock widget tabbed at index @p index
+     */
+    virtual DockWidgetBase *dockwidgetAt(int index) const = 0;
+
+    /**
+     * @brief detaches a dock widget and shows it as a floating dock widget
+     * @param dockWidget the dock widget to detach
+     */
+    virtual void detachTab(DockWidgetBase *dockWidget) = 0;
+
+    /**
+     * @brief inserts @p dockwidget into the TabWidget, at @p index
+     * @param dockwidget the dockwidget to insert
+     * @param index The index to where to put it
+     */
+    void insertDockWidget(DockWidgetBase *dockwidget, int index);
+
+    /**
+     * @brief Returns whether dockwidget @p dw is contained in this tab widget
+     * Equivalent to indexOf(dw) != -1
+     */
+    bool contains(DockWidgetBase *dw) const;
+
+    /**
+     * @brief Returns the tab bar
+     */
+    virtual TabBar* tabBar() const = 0;
+
+    /**
+     * @brief Returns this class as a QWidget (if using QtWidgets) or QQuickItem
+     */
+    QWidgetOrQuick *asWidget() const;
+
+    ///@brief getter for the frame
+    Frame *frame() const;
+
+    // Draggable interface
+    std::unique_ptr<WindowBeingDragged> makeWindow() override;
+    DockWidgetBase *singleDockWidget() const override;
+
+protected:
+    void onTabInserted();
+    void onTabRemoved();
+
+private:
+    Frame *const m_frame;
+    QWidgetOrQuick *const m_thisWidget;
+    Q_DISABLE_COPY(TabWidget)
+};
+}
+
+#endif