#include "SceneViewportMoveGizmo.h"

#include "Core/IUndoManager.h"
#include "SceneViewportMath.h"
#include "SceneViewportPicker.h"

#include <XCEngine/Components/GameObject.h>

namespace XCEngine {
namespace Editor {

namespace {

constexpr float kMoveGizmoHandleLengthPixels = 100.0f;
constexpr float kMoveGizmoHoverThresholdPixels = 10.0f;

Math::Vector3 GetAxisVector(SceneViewportGizmoAxis axis) {
    switch (axis) {
    case SceneViewportGizmoAxis::X:
        return Math::Vector3::Right();
    case SceneViewportGizmoAxis::Y:
        return Math::Vector3::Up();
    case SceneViewportGizmoAxis::Z:
        return Math::Vector3::Forward();
    case SceneViewportGizmoAxis::None:
    default:
        return Math::Vector3::Zero();
    }
}

Math::Color GetAxisBaseColor(SceneViewportGizmoAxis axis) {
    switch (axis) {
    case SceneViewportGizmoAxis::X:
        return Math::Color(0.91f, 0.09f, 0.05f, 1.0f);
    case SceneViewportGizmoAxis::Y:
        return Math::Color(0.45f, 1.0f, 0.12f, 1.0f);
    case SceneViewportGizmoAxis::Z:
        return Math::Color(0.11f, 0.29f, 1.0f, 1.0f);
    case SceneViewportGizmoAxis::None:
    default:
        return Math::Color::White();
    }
}

Math::Color WithAlpha(const Math::Color& color, float alpha) {
    return Math::Color(color.r, color.g, color.b, alpha);
}

SceneViewportGizmoPlane GetPlaneForIndex(size_t index) {
    switch (index) {
    case 0:
        return SceneViewportGizmoPlane::XY;
    case 1:
        return SceneViewportGizmoPlane::XZ;
    case 2:
        return SceneViewportGizmoPlane::YZ;
    default:
        return SceneViewportGizmoPlane::None;
    }
}

void GetPlaneAxes(
    SceneViewportGizmoPlane plane,
    Math::Vector3& outAxisA,
    Math::Vector3& outAxisB) {
    switch (plane) {
    case SceneViewportGizmoPlane::XY:
        outAxisA = Math::Vector3::Right();
        outAxisB = Math::Vector3::Up();
        return;
    case SceneViewportGizmoPlane::XZ:
        outAxisA = Math::Vector3::Right();
        outAxisB = Math::Vector3::Forward();
        return;
    case SceneViewportGizmoPlane::YZ:
        outAxisA = Math::Vector3::Up();
        outAxisB = Math::Vector3::Forward();
        return;
    case SceneViewportGizmoPlane::None:
    default:
        outAxisA = Math::Vector3::Zero();
        outAxisB = Math::Vector3::Zero();
        return;
    }
}

Math::Vector3 GetPlaneNormal(SceneViewportGizmoPlane plane) {
    switch (plane) {
    case SceneViewportGizmoPlane::XY:
        return Math::Vector3::Forward();
    case SceneViewportGizmoPlane::XZ:
        return Math::Vector3::Up();
    case SceneViewportGizmoPlane::YZ:
        return Math::Vector3::Right();
    case SceneViewportGizmoPlane::None:
    default:
        return Math::Vector3::Zero();
    }
}

Math::Color GetPlaneBaseColor(SceneViewportGizmoPlane plane) {
    switch (plane) {
    case SceneViewportGizmoPlane::XY:
        return GetAxisBaseColor(SceneViewportGizmoAxis::Z);
    case SceneViewportGizmoPlane::XZ:
        return GetAxisBaseColor(SceneViewportGizmoAxis::Y);
    case SceneViewportGizmoPlane::YZ:
        return GetAxisBaseColor(SceneViewportGizmoAxis::X);
    case SceneViewportGizmoPlane::None:
    default:
        return Math::Color::White();
    }
}

Math::Vector3 NormalizeVector3(const Math::Vector3& value, const Math::Vector3& fallback) {
    return value.SqrMagnitude() <= Math::EPSILON ? fallback : value.Normalized();
}

float Cross2D(const Math::Vector2& a, const Math::Vector2& b) {
    return a.x * b.y - a.y * b.x;
}

float PolygonAreaTwice(const std::array<Math::Vector2, 4>& corners) {
    float areaTwice = 0.0f;
    for (size_t index = 0; index < corners.size(); ++index) {
        const Math::Vector2& current = corners[index];
        const Math::Vector2& next = corners[(index + 1) % corners.size()];
        areaTwice += current.x * next.y - next.x * current.y;
    }
    return areaTwice;
}

bool PointInTriangle(
    const Math::Vector2& point,
    const Math::Vector2& a,
    const Math::Vector2& b,
    const Math::Vector2& c) {
    const float ab = Cross2D(b - a, point - a);
    const float bc = Cross2D(c - b, point - b);
    const float ca = Cross2D(a - c, point - c);
    const bool hasNegative = ab < 0.0f || bc < 0.0f || ca < 0.0f;
    const bool hasPositive = ab > 0.0f || bc > 0.0f || ca > 0.0f;
    return !(hasNegative && hasPositive);
}

bool PointInQuad(const Math::Vector2& point, const std::array<Math::Vector2, 4>& corners) {
    return PointInTriangle(point, corners[0], corners[1], corners[2]) ||
        PointInTriangle(point, corners[0], corners[2], corners[3]);
}

Math::Vector2 QuadCenter(const std::array<Math::Vector2, 4>& corners) {
    Math::Vector2 center = Math::Vector2::Zero();
    for (const Math::Vector2& corner : corners) {
        center += corner;
    }
    return center / 4.0f;
}

bool IsMouseInsideViewport(const SceneViewportMoveGizmoContext& context) {
    return context.mousePosition.x >= 0.0f &&
           context.mousePosition.y >= 0.0f &&
           context.mousePosition.x <= context.viewportSize.x &&
           context.mousePosition.y <= context.viewportSize.y;
}

float ComputeWorldUnitsPerPixel(
    const SceneViewportOverlayData& overlay,
    const Math::Vector3& worldPoint,
    float viewportHeight) {
    if (!overlay.valid || viewportHeight <= 1.0f) {
        return 0.0f;
    }

    const Math::Vector3 cameraForward = NormalizeVector3(overlay.cameraForward, Math::Vector3::Forward());
    const float depth = Math::Vector3::Dot(worldPoint - overlay.cameraPosition, cameraForward);
    if (depth <= Math::EPSILON) {
        return 0.0f;
    }

    return 2.0f * depth * std::tan(overlay.verticalFovDegrees * Math::DEG_TO_RAD * 0.5f) / viewportHeight;
}

} // namespace

void SceneViewportMoveGizmo::Update(const SceneViewportMoveGizmoContext& context) {
    BuildDrawData(context);
    if (m_dragMode == DragMode::None && IsMouseInsideViewport(context)) {
        m_hoveredAxis = HitTestAxis(context.mousePosition);
        m_hoveredPlane = m_hoveredAxis == SceneViewportGizmoAxis::None
            ? HitTestPlane(context.mousePosition)
            : SceneViewportGizmoPlane::None;
    } else if (m_dragMode == DragMode::None) {
        m_hoveredAxis = SceneViewportGizmoAxis::None;
        m_hoveredPlane = SceneViewportGizmoPlane::None;
    } else if (m_dragMode == DragMode::Axis) {
        m_hoveredAxis = m_activeAxis;
        m_hoveredPlane = SceneViewportGizmoPlane::None;
    } else {
        m_hoveredAxis = SceneViewportGizmoAxis::None;
        m_hoveredPlane = m_activePlane;
    }

    RefreshHandleState();
}

bool SceneViewportMoveGizmo::TryBeginDrag(const SceneViewportMoveGizmoContext& context, IUndoManager& undoManager) {
    if (m_dragMode != DragMode::None ||
        (m_hoveredAxis == SceneViewportGizmoAxis::None && m_hoveredPlane == SceneViewportGizmoPlane::None) ||
        context.selectedObject == nullptr ||
        !m_drawData.visible ||
        undoManager.HasPendingInteractiveChange()) {
        return false;
    }

    Math::Ray worldRay;
    if (!BuildSceneViewportRay(
            context.overlay,
            context.viewportSize,
            context.mousePosition,
            worldRay)) {
        return false;
    }

    const Math::Vector3 objectWorldPosition = context.selectedObject->GetTransform()->GetPosition();
    const Math::Vector3 pivotWorldPosition = context.selectedObject->GetTransform()->GetPosition();
    Math::Vector3 dragPlaneNormal = Math::Vector3::Zero();
    Math::Vector3 worldAxis = Math::Vector3::Zero();

    if (m_hoveredAxis != SceneViewportGizmoAxis::None) {
        worldAxis = GetAxisVector(m_hoveredAxis);
        if (!BuildSceneViewportAxisDragPlaneNormal(context.overlay, worldAxis, dragPlaneNormal)) {
            return false;
        }
    } else {
        dragPlaneNormal = GetPlaneNormal(m_hoveredPlane);
        if (dragPlaneNormal.SqrMagnitude() <= Math::EPSILON) {
            return false;
        }
    }

    const Math::Plane dragPlane = BuildSceneViewportPlaneFromPointNormal(pivotWorldPosition, dragPlaneNormal);
    float hitDistance = 0.0f;
    if (!worldRay.Intersects(dragPlane, hitDistance)) {
        return false;
    }

    undoManager.BeginInteractiveChange("Move Gizmo");
    if (!undoManager.HasPendingInteractiveChange()) {
        return false;
    }

    const Math::Vector3 hitPoint = worldRay.GetPoint(hitDistance);
    m_dragMode = m_hoveredAxis != SceneViewportGizmoAxis::None ? DragMode::Axis : DragMode::Plane;
    m_activeAxis = m_hoveredAxis;
    m_activePlane = m_hoveredPlane;
    m_activeEntityId = context.selectedObject->GetID();
    m_activeAxisDirection = worldAxis;
    m_activePlaneNormal = dragPlaneNormal;
    m_dragPlane = dragPlane;
    m_dragStartObjectWorldPosition = objectWorldPosition;
    m_dragStartPivotWorldPosition = pivotWorldPosition;
    m_dragStartHitWorldPosition = hitPoint;
    m_dragStartAxisScalar = Math::Vector3::Dot(hitPoint - pivotWorldPosition, worldAxis);
    RefreshHandleState();
    return true;
}

void SceneViewportMoveGizmo::UpdateDrag(const SceneViewportMoveGizmoContext& context) {
    if (m_dragMode == DragMode::None ||
        context.selectedObject == nullptr ||
        context.selectedObject->GetID() != m_activeEntityId) {
        return;
    }

    Math::Ray worldRay;
    if (!BuildSceneViewportRay(
            context.overlay,
            context.viewportSize,
            context.mousePosition,
            worldRay)) {
        return;
    }

    float hitDistance = 0.0f;
    if (!worldRay.Intersects(m_dragPlane, hitDistance)) {
        return;
    }

    const Math::Vector3 hitPoint = worldRay.GetPoint(hitDistance);
    if (m_dragMode == DragMode::Axis) {
        const float currentAxisScalar = Math::Vector3::Dot(hitPoint - m_dragStartPivotWorldPosition, m_activeAxisDirection);
        const float deltaScalar = currentAxisScalar - m_dragStartAxisScalar;
        context.selectedObject->GetTransform()->SetPosition(
            m_dragStartObjectWorldPosition + m_activeAxisDirection * deltaScalar);
        return;
    }

    if (m_dragMode == DragMode::Plane) {
        const Math::Vector3 planeDelta = Math::Vector3::ProjectOnPlane(
            hitPoint - m_dragStartHitWorldPosition,
            m_activePlaneNormal);
        context.selectedObject->GetTransform()->SetPosition(
            m_dragStartObjectWorldPosition + planeDelta);
    }
}

void SceneViewportMoveGizmo::EndDrag(IUndoManager& undoManager) {
    if (m_dragMode == DragMode::None) {
        return;
    }

    if (undoManager.HasPendingInteractiveChange()) {
        undoManager.FinalizeInteractiveChange();
    }

    m_dragMode = DragMode::None;
    m_activeAxis = SceneViewportGizmoAxis::None;
    m_activePlane = SceneViewportGizmoPlane::None;
    m_activeEntityId = 0;
    m_activeAxisDirection = Math::Vector3::Zero();
    m_activePlaneNormal = Math::Vector3::Zero();
    m_dragStartObjectWorldPosition = Math::Vector3::Zero();
    m_dragStartPivotWorldPosition = Math::Vector3::Zero();
    m_dragStartHitWorldPosition = Math::Vector3::Zero();
    m_dragStartAxisScalar = 0.0f;
    RefreshHandleState();
}

void SceneViewportMoveGizmo::CancelDrag(IUndoManager* undoManager) {
    if (undoManager != nullptr && undoManager->HasPendingInteractiveChange()) {
        undoManager->CancelInteractiveChange();
    }

    m_dragMode = DragMode::None;
    m_activeAxis = SceneViewportGizmoAxis::None;
    m_activePlane = SceneViewportGizmoPlane::None;
    m_activeEntityId = 0;
    m_activeAxisDirection = Math::Vector3::Zero();
    m_activePlaneNormal = Math::Vector3::Zero();
    m_dragStartObjectWorldPosition = Math::Vector3::Zero();
    m_dragStartPivotWorldPosition = Math::Vector3::Zero();
    m_dragStartHitWorldPosition = Math::Vector3::Zero();
    m_dragStartAxisScalar = 0.0f;
    m_hoveredAxis = SceneViewportGizmoAxis::None;
    m_hoveredPlane = SceneViewportGizmoPlane::None;
    RefreshHandleState();
}

bool SceneViewportMoveGizmo::IsHoveringHandle() const {
    return m_hoveredAxis != SceneViewportGizmoAxis::None ||
        m_hoveredPlane != SceneViewportGizmoPlane::None;
}

bool SceneViewportMoveGizmo::IsActive() const {
    return m_dragMode != DragMode::None;
}

uint64_t SceneViewportMoveGizmo::GetActiveEntityId() const {
    return m_activeEntityId;
}

const SceneViewportMoveGizmoDrawData& SceneViewportMoveGizmo::GetDrawData() const {
    return m_drawData;
}

void SceneViewportMoveGizmo::BuildDrawData(const SceneViewportMoveGizmoContext& context) {
    m_drawData = {};
    m_drawData.pivotRadius = 5.0f;

    const Components::GameObject* selectedObject = context.selectedObject;
    if (selectedObject == nullptr ||
        !context.overlay.valid ||
        context.viewportSize.x <= 1.0f ||
        context.viewportSize.y <= 1.0f) {
        return;
    }

    const Math::Vector3 gizmoWorldOrigin = selectedObject->GetTransform()->GetPosition();
    const SceneViewportProjectedPoint projectedPivot = ProjectSceneViewportWorldPoint(
        context.overlay,
        context.viewportSize.x,
        context.viewportSize.y,
        gizmoWorldOrigin);
    if (!projectedPivot.visible) {
        return;
    }

    m_drawData.visible = true;
    m_drawData.pivot = projectedPivot.screenPosition;
    const float worldUnitsPerPixel = ComputeWorldUnitsPerPixel(
        context.overlay,
        gizmoWorldOrigin,
        context.viewportSize.y);
    if (worldUnitsPerPixel <= Math::EPSILON) {
        m_drawData = {};
        return;
    }

    const float axisLengthWorld = worldUnitsPerPixel * kMoveGizmoHandleLengthPixels;
    const float planeInsetWorld = axisLengthWorld * 0.02f;
    const float planeExtentWorld = axisLengthWorld * 0.36f;

    const SceneViewportGizmoAxis axes[] = {
        SceneViewportGizmoAxis::X,
        SceneViewportGizmoAxis::Y,
        SceneViewportGizmoAxis::Z
    };
    for (size_t index = 0; index < m_drawData.handles.size(); ++index) {
        SceneViewportMoveGizmoHandleDrawData& handle = m_drawData.handles[index];
        handle.axis = axes[index];
        handle.start = projectedPivot.screenPosition;

        const Math::Vector3 axisEndWorld =
            gizmoWorldOrigin + GetAxisVector(handle.axis) * axisLengthWorld;
        const SceneViewportProjectedPoint projectedEnd = ProjectSceneViewportWorldPoint(
            context.overlay,
            context.viewportSize.x,
            context.viewportSize.y,
            axisEndWorld);
        if (projectedEnd.ndcDepth < 0.0f || projectedEnd.ndcDepth > 1.0f) {
            continue;
        }

        if ((projectedEnd.screenPosition - projectedPivot.screenPosition).SqrMagnitude() <= Math::EPSILON) {
            continue;
        }

        handle.end = projectedEnd.screenPosition;
        handle.visible = true;
        handle.color = GetAxisBaseColor(handle.axis);
    }

    for (size_t index = 0; index < m_drawData.planes.size(); ++index) {
        SceneViewportMoveGizmoPlaneDrawData& plane = m_drawData.planes[index];
        plane.plane = GetPlaneForIndex(index);

        Math::Vector3 axisA = Math::Vector3::Zero();
        Math::Vector3 axisB = Math::Vector3::Zero();
        GetPlaneAxes(plane.plane, axisA, axisB);
        if (axisA.SqrMagnitude() <= Math::EPSILON || axisB.SqrMagnitude() <= Math::EPSILON) {
            continue;
        }

        const Math::Vector3 worldCorners[] = {
            gizmoWorldOrigin + axisA * planeInsetWorld + axisB * planeInsetWorld,
            gizmoWorldOrigin + axisA * planeExtentWorld + axisB * planeInsetWorld,
            gizmoWorldOrigin + axisA * planeExtentWorld + axisB * planeExtentWorld,
            gizmoWorldOrigin + axisA * planeInsetWorld + axisB * planeExtentWorld
        };

        bool valid = true;
        for (size_t cornerIndex = 0; cornerIndex < plane.corners.size(); ++cornerIndex) {
            const SceneViewportProjectedPoint projectedCorner = ProjectSceneViewportWorldPoint(
                context.overlay,
                context.viewportSize.x,
                context.viewportSize.y,
                worldCorners[cornerIndex]);
            if (projectedCorner.ndcDepth < 0.0f || projectedCorner.ndcDepth > 1.0f) {
                valid = false;
                break;
            }

            plane.corners[cornerIndex] = projectedCorner.screenPosition;
        }

        if (!valid || std::abs(PolygonAreaTwice(plane.corners)) <= 4.0f) {
            continue;
        }

        plane.visible = true;
        const Math::Color baseColor = GetPlaneBaseColor(plane.plane);
        plane.fillColor = WithAlpha(baseColor, 0.16f);
        plane.outlineColor = WithAlpha(baseColor, 0.88f);
    }
}

void SceneViewportMoveGizmo::RefreshHandleState() {
    for (SceneViewportMoveGizmoHandleDrawData& handle : m_drawData.handles) {
        if (!handle.visible) {
            continue;
        }

        handle.hovered = handle.axis == m_hoveredAxis;
        handle.active = handle.axis == m_activeAxis;
        handle.color = (handle.hovered || handle.active)
            ? Math::Color::Yellow()
            : GetAxisBaseColor(handle.axis);
    }

    for (SceneViewportMoveGizmoPlaneDrawData& plane : m_drawData.planes) {
        if (!plane.visible) {
            continue;
        }

        plane.hovered = plane.plane == m_hoveredPlane;
        plane.active = plane.plane == m_activePlane;
        const Math::Color baseColor = plane.hovered || plane.active
            ? Math::Color::Yellow()
            : GetPlaneBaseColor(plane.plane);
        plane.fillColor = WithAlpha(baseColor, plane.active ? 0.34f : (plane.hovered ? 0.26f : 0.16f));
        plane.outlineColor = WithAlpha(baseColor, plane.active ? 1.0f : (plane.hovered ? 0.95f : 0.82f));
    }
}

SceneViewportGizmoAxis SceneViewportMoveGizmo::HitTestAxis(const Math::Vector2& mousePosition) const {
    if (!m_drawData.visible) {
        return SceneViewportGizmoAxis::None;
    }

    const float hoverThresholdSq = kMoveGizmoHoverThresholdPixels * kMoveGizmoHoverThresholdPixels;
    SceneViewportGizmoAxis bestAxis = SceneViewportGizmoAxis::None;
    float bestDistanceSq = hoverThresholdSq;

    for (const SceneViewportMoveGizmoHandleDrawData& handle : m_drawData.handles) {
        if (!handle.visible) {
            continue;
        }

        const float distanceSq = DistanceToSegmentSquared(mousePosition, handle.start, handle.end);
        if (distanceSq > bestDistanceSq) {
            continue;
        }

        bestDistanceSq = distanceSq;
        bestAxis = handle.axis;
    }

    return bestAxis;
}

SceneViewportGizmoPlane SceneViewportMoveGizmo::HitTestPlane(const Math::Vector2& mousePosition) const {
    if (!m_drawData.visible) {
        return SceneViewportGizmoPlane::None;
    }

    SceneViewportGizmoPlane bestPlane = SceneViewportGizmoPlane::None;
    float bestDistanceSq = Math::FLOAT_MAX;
    for (const SceneViewportMoveGizmoPlaneDrawData& plane : m_drawData.planes) {
        if (!plane.visible || !PointInQuad(mousePosition, plane.corners)) {
            continue;
        }

        const float distanceSq = (QuadCenter(plane.corners) - mousePosition).SqrMagnitude();
        if (distanceSq >= bestDistanceSq) {
            continue;
        }

        bestDistanceSq = distanceSq;
        bestPlane = plane.plane;
    }

    return bestPlane;
}

} // namespace Editor
} // namespace XCEngine