// Copyright Epic Games, Inc. All Rights Reserved.

#include "DragTool_Measure.h"
#include "SceneView.h"
#include "EditorViewportClient.h"
#include "CanvasItem.h"
#include "Settings/LevelEditorViewportSettings.h"
#include "EngineGlobals.h"
#include "Editor.h"
#include "SnappingUtils.h"
#include "CanvasTypes.h"

///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
//
// FDragTool_Measure
//
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

FDragTool_Measure::FDragTool_Measure(FEditorViewportClient* InViewportClient)
    : FDragTool(InViewportClient->GetModeTools()), ViewportClient(InViewportClient)
{
    bUseSnapping  = true;
    bConvertDelta = false;
}

FVector2D FDragTool_Measure::GetSnappedPixelPos(FVector2D PixelPos)
{
    FSceneViewFamilyContext ViewFamily(FSceneViewFamily::ConstructionValues(
                                           ViewportClient->Viewport,
                                           ViewportClient->GetScene(),
                                           ViewportClient->EngineShowFlags)
                                           .SetRealtimeUpdate(ViewportClient->IsRealtime()));

    FSceneView* View = ViewportClient->CalcSceneView(&ViewFamily);

    // Put the mouse pos in world space
    FVector WorldPos = View->ScreenToWorld(View->PixelToScreen(PixelPos.X, PixelPos.Y, 0.5f));
    ;

    // Snap the world position
    const float GridSize = GEditor->GetGridSize();
    const FVector GridBase(GridSize, GridSize, GridSize);
    FSnappingUtils::SnapPointToGrid(WorldPos, GridBase);

    // And back into pixel-space (might fail, in which case we return the original)
    View->WorldToPixel(WorldPos, PixelPos);

    // The canvas we're going to render to factors in dpi scale to final position.
    // Since we're basing our position off mouse coordinates it will already be pixel accurate and therefore we must back out the scale the canvas will apply
    PixelPos /= ViewportClient->GetDPIScale();

    return PixelPos;
}

void FDragTool_Measure::StartDrag(FEditorViewportClient* InViewportClient, const FVector& InStart, const FVector2D& InStartScreen)
{
    FDragTool::StartDrag(InViewportClient, InStart, InStartScreen);
    PixelStart = GetSnappedPixelPos(InStartScreen);
    PixelEnd   = PixelStart;
}

void FDragTool_Measure::AddDelta(const FVector& InDelta)
{
    FDragTool::AddDelta(InDelta);

    FIntPoint MousePos;
    ViewportClient->Viewport->GetMousePos(MousePos);
    PixelEnd = GetSnappedPixelPos(FVector2D(MousePos));
}

void FDragTool_Measure::Render(const FSceneView* View, FCanvas* Canvas)
{
    const float OrthoUnitsPerPixel = ViewportClient->GetOrthoUnitsPerPixel(ViewportClient->Viewport);
    const float Length             = FMath::RoundToFloat((PixelEnd - PixelStart).Size() * OrthoUnitsPerPixel * ViewportClient->GetDPIScale());

    if (View != nullptr && Canvas != nullptr && Length >= 1.f)
    {
        FCanvasLineItem LineItem(PixelStart, PixelEnd);
        Canvas->DrawItem(LineItem);

        const FVector2D PixelMid = FVector2D(PixelStart + ((PixelEnd - PixelStart) / 2));

        // Calculate number of decimal places to display, based on the current viewport zoom
        float Divisor                = 1.0f;
        int DecimalPlaces            = 0;
        const float OrderOfMagnitude = FMath::LogX(10.0f, OrthoUnitsPerPixel);

        switch (GetDefault<ULevelEditorViewportSettings>()->MeasuringToolUnits)
        {
            case MeasureUnits_Meters:
                Divisor = 100.0f;
                // Max one decimal place allowed for meters.
                DecimalPlaces = FMath::Clamp(FMath::FloorToInt(1.5f - OrderOfMagnitude), 0, 1);
                break;

            case MeasureUnits_Kilometers:
                Divisor = 100000.0f;
                // Max two decimal places allowed for kilometers.
                DecimalPlaces = FMath::Clamp(FMath::FloorToInt(4.5f - OrderOfMagnitude), 0, 2);
                break;
        }

        FNumberFormattingOptions Options;
        Options.UseGrouping             = false;
        Options.MinimumFractionalDigits = DecimalPlaces;
        Options.MaximumFractionalDigits = DecimalPlaces;

        const FText LengthStr           = FText::AsNumber(Length / Divisor, &Options);

        FCanvasTextItem TextItem(FVector2D(FMath::FloorToFloat(PixelMid.X), FMath::FloorToFloat(PixelMid.Y)), LengthStr, GEngine->GetSmallFont(), FLinearColor::White);
        TextItem.bCentreX = true;
        Canvas->DrawItem(TextItem);
    }
}