XCEngine/new_editor/include/XCEditor/Collections/UIEditorTreeDragDrop.h

#pragma once

#include <XCEditor/Collections/UIEditorDragDropInteraction.h>
#include <XCEditor/Collections/UIEditorTreeView.h>

#include <XCEngine/UI/Types.h>

#include <string>
#include <string_view>
#include <vector>

namespace XCEngine::UI::Editor::Collections::TreeDragDrop {

using ::XCEngine::UI::UIPoint;
using ::XCEngine::UI::UIRect;
using DragDropInteraction::kDefaultDragThreshold;
using Widgets::HitTestUIEditorTreeView;
using Widgets::UIEditorTreeViewHitTarget;
using Widgets::UIEditorTreeViewHitTargetKind;
using Widgets::UIEditorTreeViewInvalidIndex;

struct State : DragDropInteraction::State {
    bool dropToRoot = false;
};

struct ProcessResult : DragDropInteraction::ProcessResult {
    bool droppedToRoot = false;
};

inline void ResetTransientRequests(State& state) {
    DragDropInteraction::ResetTransientRequests(state);
}

inline bool HasActivePointerCapture(const State& state) {
    return DragDropInteraction::HasActivePointerCapture(state);
}

inline bool ContainsPoint(const UIRect& rect, const UIPoint& point) {
    return point.x >= rect.x &&
        point.x <= rect.x + rect.width &&
        point.y >= rect.y &&
        point.y <= rect.y + rect.height;
}

inline const Widgets::UIEditorTreeViewItem* ResolveHitItem(
    const Widgets::UIEditorTreeViewLayout& layout,
    const std::vector<Widgets::UIEditorTreeViewItem>& items,
    const UIPoint& point,
    UIEditorTreeViewHitTarget* hitTargetOutput = nullptr) {
    const UIEditorTreeViewHitTarget hitTarget = HitTestUIEditorTreeView(layout, point);
    if (hitTargetOutput != nullptr) {
        *hitTargetOutput = hitTarget;
    }

    if (hitTarget.itemIndex >= items.size()) {
        return nullptr;
    }

    return &items[hitTarget.itemIndex];
}

inline std::size_t FindVisibleIndexForItemId(
    const Widgets::UIEditorTreeViewLayout& layout,
    const std::vector<Widgets::UIEditorTreeViewItem>& items,
    std::string_view itemId) {
    for (std::size_t visibleIndex = 0u; visibleIndex < layout.visibleItemIndices.size(); ++visibleIndex) {
        const std::size_t itemIndex = layout.visibleItemIndices[visibleIndex];
        if (itemIndex < items.size() && items[itemIndex].itemId == itemId) {
            return visibleIndex;
        }
    }

    return UIEditorTreeViewInvalidIndex;
}

inline std::vector<DragDropInteraction::UIInputEvent> BuildInteractionInputEvents(
    const State& state,
    const Widgets::UIEditorTreeViewLayout& layout,
    const std::vector<Widgets::UIEditorTreeViewItem>& items,
    const std::vector<DragDropInteraction::UIInputEvent>& rawEvents,
    float dragThreshold = kDefaultDragThreshold) {
    auto resolveDraggableItem =
        [&layout, &items](const UIPoint& point) -> std::string {
        UIEditorTreeViewHitTarget hitTarget = {};
        const Widgets::UIEditorTreeViewItem* hitItem =
            ResolveHitItem(layout, items, point, &hitTarget);
        if (hitItem != nullptr &&
            hitTarget.kind == UIEditorTreeViewHitTargetKind::Row) {
            return hitItem->itemId;
        }

        return {};
    };

    DragDropInteraction::PreviewState preview =
        DragDropInteraction::BuildPreviewState(state);
    std::vector<DragDropInteraction::UIInputEvent> filteredEvents = {};
    filteredEvents.reserve(rawEvents.size());
    for (const DragDropInteraction::UIInputEvent& event : rawEvents) {
        if (!DragDropInteraction::ProcessPreviewEvent(
                preview,
                event,
                resolveDraggableItem,
                dragThreshold)) {
            filteredEvents.push_back(event);
        }
    }

    return filteredEvents;
}

template <typename Callbacks>
ProcessResult ProcessInputEvents(
    State& state,
    const Widgets::UIEditorTreeViewLayout& layout,
    const std::vector<Widgets::UIEditorTreeViewItem>& items,
    const std::vector<DragDropInteraction::UIInputEvent>& inputEvents,
    const UIRect& bounds,
    Callbacks& callbacks,
    float dragThreshold = kDefaultDragThreshold) {
    struct AdaptedCallbacks {
        const Widgets::UIEditorTreeViewLayout& layout;
        const std::vector<Widgets::UIEditorTreeViewItem>& items;
        const UIRect& bounds;
        Callbacks& callbacks;
        bool droppedToRoot = false;

        std::string ResolveDraggableItem(const UIPoint& point) const {
            UIEditorTreeViewHitTarget hitTarget = {};
            const Widgets::UIEditorTreeViewItem* hitItem =
                ResolveHitItem(layout, items, point, &hitTarget);
            if (hitItem != nullptr &&
                hitTarget.kind == UIEditorTreeViewHitTargetKind::Row) {
                return hitItem->itemId;
            }

            return {};
        }

        void ResetDropTarget(State& state) const {
            state.dropTargetItemId.clear();
            state.dropToRoot = false;
            state.validDropTarget = false;
        }

        void UpdateDropTarget(
            State& state,
            std::string_view draggedItemId,
            const UIPoint& point) const {
            UIEditorTreeViewHitTarget hitTarget = {};
            const Widgets::UIEditorTreeViewItem* hitItem =
                ResolveHitItem(layout, items, point, &hitTarget);
            if (hitItem != nullptr &&
                (hitTarget.kind == UIEditorTreeViewHitTargetKind::Row ||
                 hitTarget.kind == UIEditorTreeViewHitTargetKind::Disclosure)) {
                state.dropTargetItemId = hitItem->itemId;
                state.validDropTarget =
                    callbacks.CanDropOnItem(draggedItemId, state.dropTargetItemId);
                return;
            }

            if (ContainsPoint(bounds, point)) {
                state.dropToRoot = true;
                state.validDropTarget = callbacks.CanDropToRoot(draggedItemId);
            }
        }

        bool IsItemSelected(std::string_view itemId) const {
            return callbacks.IsItemSelected(itemId);
        }

        bool SelectDraggedItem(std::string_view itemId) const {
            return callbacks.SelectDraggedItem(itemId);
        }

        bool CommitDrop(State& state, DragDropInteraction::ProcessResult&) {
            droppedToRoot = state.dropToRoot;
            return state.dropToRoot
                ? callbacks.CommitDropToRoot(state.draggedItemId)
                : callbacks.CommitDropOnItem(
                    state.draggedItemId,
                    state.dropTargetItemId);
        }
    } adaptedCallbacks{ layout, items, bounds, callbacks };

    ProcessResult result = {};
    const DragDropInteraction::ProcessResult interactionResult =
        DragDropInteraction::ProcessInputEvents(
            state,
            inputEvents,
            adaptedCallbacks,
            dragThreshold);
    result.selectionForced = interactionResult.selectionForced;
    result.dropCommitted = interactionResult.dropCommitted;
    result.draggedItemId = interactionResult.draggedItemId;
    result.dropTargetItemId = interactionResult.dropTargetItemId;
    result.droppedToRoot = adaptedCallbacks.droppedToRoot;
    return result;
}

} // namespace XCEngine::UI::Editor::Collections::TreeDragDrop