//
// Copyright (c) 2008-2020 the Urho3D project.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//

#pragma once

#include "../UI/UIElement.h"

namespace Urho3D
{

class BorderImage;
class ScrollBar;

/// Scrollable %UI element for showing a (possibly large) child element.
class URHO3D_API ScrollView : public UIElement
{
    URHO3D_OBJECT(ScrollView, UIElement);

public:
    /// Construct.
    explicit ScrollView(Context* context);
    /// Destruct.
    ~ScrollView() override;
    /// Register object factory.
    static void RegisterObject(Context* context);

    /// Perform UI element update.
    void Update(float timeStep) override;
    /// Apply attribute changes that can not be applied immediately.
    void ApplyAttributes() override;
    /// React to mouse wheel.
    void OnWheel(int delta, MouseButtonFlags buttons, QualifierFlags qualifiers) override;
    /// React to a key press.
    void OnKey(Key key, MouseButtonFlags buttons, QualifierFlags qualifiers) override;
    /// React to resize.
    void OnResize(const IntVector2& newSize, const IntVector2& delta) override;

    /// Return whether the element could handle wheel input.
    bool IsWheelHandler() const override { return true; }

    /// Set content element.
    /// @property
    void SetContentElement(UIElement* element);
    /// Set view offset from the top-left corner.
    /// @property
    void SetViewPosition(const IntVector2& position);
    /// Set view offset from the top-left corner.
    void SetViewPosition(int x, int y);
    /// Set scrollbars' visibility manually. Disables scrollbar autoshow/hide.
    void SetScrollBarsVisible(bool horizontal, bool vertical);
    /// Set horizontal scrollbar visibility manually. Disables scrollbar autoshow/hide.
    /// @property
    void SetHorizontalScrollBarVisible(bool visible);
    /// Set vertical scrollbar visibility manually. Disables scrollbar autoshow/hide.
    /// @property
    void SetVerticalScrollBarVisible(bool visible);
    /// Set whether to automatically show/hide scrollbars. Default true.
    /// @property
    void SetScrollBarsAutoVisible(bool enable);
    /// Set arrow key scroll step. Also sets it on the scrollbars.
    /// @property
    void SetScrollStep(float step);
    /// Set arrow key page step.
    /// @property
    void SetPageStep(float step);

    /// Set scroll deceleration.
    /// @property
    void SetScrollDeceleration(float deceleration) { scrollDeceleration_ = deceleration; }

    /// Set scroll snap epsilon.
    /// @property
    void SetScrollSnapEpsilon(float snap) { scrollSnapEpsilon_ = snap; }

    /// Set whether child elements should be disabled while touch scrolling.
    /// @property
    void SetAutoDisableChildren(bool disable) { autoDisableChildren_ = disable; };

    /// Set how much touch movement is needed to trigger child element disabling.
    /// @property
    void SetAutoDisableThreshold(float amount) { autoDisableThreshold_ = amount; };

    /// Return view offset from the top-left corner.
    /// @property
    const IntVector2& GetViewPosition() const { return viewPosition_; }

    /// Return content element.
    /// @property
    UIElement* GetContentElement() const { return contentElement_; }

    /// Return horizontal scroll bar.
    /// @property
    ScrollBar* GetHorizontalScrollBar() const { return horizontalScrollBar_; }

    /// Return vertical scroll bar.
    /// @property
    ScrollBar* GetVerticalScrollBar() const { return verticalScrollBar_; }

    /// Return scroll panel.
    /// @property
    BorderImage* GetScrollPanel() const { return scrollPanel_; }

    /// Return whether scrollbars are automatically shown/hidden.
    /// @property
    bool GetScrollBarsAutoVisible() const { return scrollBarsAutoVisible_; }

    /// Return whether the horizontal scrollbar is visible.
    /// @property
    bool GetHorizontalScrollBarVisible() const;

    /// Return whether the vertical scrollbar is visible.
    /// @property
    bool GetVerticalScrollBarVisible() const;

    /// Return arrow key scroll step.
    /// @property
    float GetScrollStep() const;

    /// Return arrow key page step.
    /// @property
    float GetPageStep() const { return pageStep_; }

    /// Return scroll deceleration.
    /// @property
    float GetScrollDeceleration() const { return scrollDeceleration_; }

    /// Return scroll snap epsilon.
    /// @property
    float GetScrollSnapEpsilon() const { return scrollSnapEpsilon_; }

    /// Return whether child element will be disabled while touch scrolling.
    /// @property
    bool GetAutoDisableChildren() const { return autoDisableChildren_; }

    /// Return how much touch movement is needed to trigger child element disabling.
    /// @property
    float GetAutoDisableThreshold() const { return autoDisableThreshold_; }

    /// Set view position attribute.
    void SetViewPositionAttr(const IntVector2& value);

protected:
    /// Filter implicit attributes in serialization process.
    bool FilterImplicitAttributes(XMLElement& dest) const override;
    /// Filter implicit attributes in serialization process for internal scroll bar.
    bool FilterScrollBarImplicitAttributes(XMLElement& dest, const String& name) const;
    /// Resize panel based on scrollbar visibility.
    void UpdatePanelSize();
    /// Recalculate view size, validate view position and update scrollbars.
    void UpdateViewSize();
    /// Update the scrollbars' ranges and positions.
    void UpdateScrollBars();
    /// Limit and update the view with a new position.
    void UpdateView(const IntVector2& position);

    /// Content element.
    SharedPtr<UIElement> contentElement_;
    /// Horizontal scroll bar.
    SharedPtr<ScrollBar> horizontalScrollBar_;
    /// Vertical scroll bar.
    SharedPtr<ScrollBar> verticalScrollBar_;
    /// Scroll panel element.
    SharedPtr<BorderImage> scrollPanel_;
    /// Current view offset from the top-left corner.
    IntVector2 viewPosition_;
    /// Total view size.
    IntVector2 viewSize_;
    /// View offset attribute.
    IntVector2 viewPositionAttr_;
    /// Accumulated touch scroll speed.
    Vector2 touchScrollSpeed_;
    /// Max touch scroll speed.
    Vector2 touchScrollSpeedMax_;
    /// Arrow key page step.
    float pageStep_;
    /// Automatically show/hide scrollbars flag.
    bool scrollBarsAutoVisible_;
    /// Ignore scrollbar events flag. Used to prevent possible endless loop when resizing.
    bool ignoreEvents_;
    /// Resize content widget width to match panel. Internal flag, used by the ListView class.
    bool resizeContentWidth_;
    /// Scroll deceleration.
    float scrollDeceleration_;
    /// Scroll snap epsilon.
    float scrollSnapEpsilon_;
    /// Used to trigger scroll smoothing when false.
    bool scrollTouchDown_;
    /// Used to prevent touch scroll - scroll bar conflict.
    bool barScrolling_;
    /// Used to determine if child elements should be disabled while touch scrolling, to prevent their trigger.
    bool autoDisableChildren_;
    /// Used to determine if children have been disabled.
    bool scrollChildrenDisable_;
    /// Distance moved with touch scrolling.
    float touchDistanceSum_;
    /// Threshold to trigger auto disable children.
    float autoDisableThreshold_;

private:
    /// Handle scrollbar value changed.
    void HandleScrollBarChanged(StringHash eventType, VariantMap& eventData);
    /// Handle scrollbar visibility changed.
    void HandleScrollBarVisibleChanged(StringHash eventType, VariantMap& eventData);
    /// Handle content element resized.
    void HandleElementResized(StringHash eventType, VariantMap& eventData);
    /// Handle touch move event for scrolling.
    void HandleTouchMove(StringHash eventType, VariantMap& eventData);
    /// Handle the scroll smoothing.
    void ScrollSmooth(float timeStep);
};

}