AmiReel/Models/SourceCropSelection.cs

namespace AmiReel.Models;

/// <summary>Edge insets, in source pixels, removed by a manual crop.</summary>
public readonly record struct PixelInsets(int Left, int Right, int Top, int Bottom)
{
    public bool IsEmpty => Left == 0 && Right == 0 && Top == 0 && Bottom == 0;
}

/// <summary>Which part of an existing crop rectangle a pointer is on.</summary>
public enum CropHit
{
    None,
    Move,
    North,
    South,
    East,
    West,
    NorthWest,
    NorthEast,
    SouthWest,
    SouthEast,
}

/// <summary>Maps a dragged display rectangle onto source-pixel crop insets.</summary>
public static class SourceCropSelection
{
    public const int MinimumSize = 16;

    public static (double OffsetX, double OffsetY, double DisplayWidth, double DisplayHeight) FitUniform(
        double containerWidth, double containerHeight, int pixelWidth, int pixelHeight)
    {
        if (containerWidth <= 0 || containerHeight <= 0 || pixelWidth <= 0 || pixelHeight <= 0)
            return (0, 0, 0, 0);

        double containerAspect = containerWidth / containerHeight;
        double imageAspect = pixelWidth / (double)pixelHeight;
        double displayWidth;
        double displayHeight;
        if (containerAspect > imageAspect)
        {
            displayHeight = containerHeight;
            displayWidth = containerHeight * imageAspect;
        }
        else
        {
            displayWidth = containerWidth;
            displayHeight = containerWidth / imageAspect;
        }

        return ((containerWidth - displayWidth) / 2, (containerHeight - displayHeight) / 2, displayWidth, displayHeight);
    }

    public static PixelInsets ToInsets(
        int pixelWidth,
        int pixelHeight,
        double displayWidth,
        double displayHeight,
        double x,
        double y,
        double width,
        double height)
    {
        if (pixelWidth <= 0 || pixelHeight <= 0 || displayWidth <= 0 || displayHeight <= 0)
            return default;

        Normalize(ref x, ref y, ref width, ref height);
        x = Math.Clamp(x, 0, displayWidth);
        y = Math.Clamp(y, 0, displayHeight);
        width = Math.Clamp(width, 0, displayWidth - x);
        height = Math.Clamp(height, 0, displayHeight - y);

        double scaleX = pixelWidth / displayWidth;
        double scaleY = pixelHeight / displayHeight;
        int left = ToEvenPixel(x * scaleX, pixelWidth - MinimumSize);
        int top = ToEvenPixel(y * scaleY, pixelHeight - MinimumSize);
        int cropWidth = ToEvenPixel(width * scaleX, pixelWidth - left);
        int cropHeight = ToEvenPixel(height * scaleY, pixelHeight - top);
        if (cropWidth < MinimumSize)
            cropWidth = Math.Min(MinimumSize, pixelWidth - left);
        if (cropHeight < MinimumSize)
            cropHeight = Math.Min(MinimumSize, pixelHeight - top);

        return new PixelInsets(left, pixelWidth - left - cropWidth, top, pixelHeight - top - cropHeight);
    }

    public static (double X, double Y, double Width, double Height) ToDisplayRect(
        int pixelWidth, int pixelHeight, double displayWidth, double displayHeight, PixelInsets insets)
    {
        if (pixelWidth <= 0 || pixelHeight <= 0 || displayWidth <= 0 || displayHeight <= 0)
            return (0, 0, Math.Max(0, displayWidth), Math.Max(0, displayHeight));

        double scaleX = displayWidth / pixelWidth;
        double scaleY = displayHeight / pixelHeight;
        double x = insets.Left * scaleX;
        double y = insets.Top * scaleY;
        double width = Math.Max(1, (pixelWidth - insets.Left - insets.Right) * scaleX);
        double height = Math.Max(1, (pixelHeight - insets.Top - insets.Bottom) * scaleY);
        return (x, y, width, height);
    }

    public static (double X, double Y) ClampToDisplay(double x, double y, double displayWidth, double displayHeight) =>
        (Math.Clamp(x, 0, Math.Max(0, displayWidth)), Math.Clamp(y, 0, Math.Max(0, displayHeight)));

    public static CropHit HitTest(
        double rectX, double rectY, double rectWidth, double rectHeight, double pointerX, double pointerY, double handleSize)
    {
        if (rectWidth <= 0 || rectHeight <= 0 || handleSize < 0)
            return CropHit.None;

        bool nearLeft = Math.Abs(pointerX - rectX) <= handleSize;
        bool nearRight = Math.Abs(pointerX - (rectX + rectWidth)) <= handleSize;
        bool nearTop = Math.Abs(pointerY - rectY) <= handleSize;
        bool nearBottom = Math.Abs(pointerY - (rectY + rectHeight)) <= handleSize;
        bool alongX = pointerX >= rectX - handleSize && pointerX <= rectX + rectWidth + handleSize;
        bool alongY = pointerY >= rectY - handleSize && pointerY <= rectY + rectHeight + handleSize;

        if (nearTop && nearLeft)
            return CropHit.NorthWest;
        if (nearTop && nearRight)
            return CropHit.NorthEast;
        if (nearBottom && nearLeft)
            return CropHit.SouthWest;
        if (nearBottom && nearRight)
            return CropHit.SouthEast;
        if (nearTop && alongX)
            return CropHit.North;
        if (nearBottom && alongX)
            return CropHit.South;
        if (nearLeft && alongY)
            return CropHit.West;
        if (nearRight && alongY)
            return CropHit.East;
        if (pointerX >= rectX && pointerX <= rectX + rectWidth && pointerY >= rectY && pointerY <= rectY + rectHeight)
            return CropHit.Move;
        return CropHit.None;
    }

    public static (double X, double Y, double Width, double Height) AdjustRect(
        double x,
        double y,
        double width,
        double height,
        CropHit hit,
        double deltaX,
        double deltaY,
        double displayWidth,
        double displayHeight)
    {
        const double minSize = 8;
        double left = x;
        double top = y;
        double right = x + width;
        double bottom = y + height;

        if (hit == CropHit.Move)
        {
            left = Math.Clamp(left + deltaX, 0, Math.Max(0, displayWidth - width));
            top = Math.Clamp(top + deltaY, 0, Math.Max(0, displayHeight - height));
            return (left, top, width, height);
        }

        if (hit is CropHit.West or CropHit.NorthWest or CropHit.SouthWest)
            left = Math.Clamp(left + deltaX, 0, right - minSize);
        if (hit is CropHit.East or CropHit.NorthEast or CropHit.SouthEast)
            right = Math.Clamp(right + deltaX, left + minSize, displayWidth);
        if (hit is CropHit.North or CropHit.NorthWest or CropHit.NorthEast)
            top = Math.Clamp(top + deltaY, 0, bottom - minSize);
        if (hit is CropHit.South or CropHit.SouthWest or CropHit.SouthEast)
            bottom = Math.Clamp(bottom + deltaY, top + minSize, displayHeight);

        return (left, top, Math.Max(minSize, right - left), Math.Max(minSize, bottom - top));
    }

    public static PixelInsets Nudge(PixelInsets insets, int pixelWidth, int pixelHeight, int deltaX, int deltaY)
    {
        int width = pixelWidth - insets.Left - insets.Right;
        int height = pixelHeight - insets.Top - insets.Bottom;
        if (width < MinimumSize || height < MinimumSize)
            return insets;

        int left = ToEvenPixel(insets.Left + deltaX, pixelWidth - width);
        int top = ToEvenPixel(insets.Top + deltaY, pixelHeight - height);
        return new PixelInsets(left, pixelWidth - left - width, top, pixelHeight - top - height);
    }

    public static PixelInsets NudgeEdge(
        PixelInsets insets, int pixelWidth, int pixelHeight, int dLeft, int dTop, int dRight, int dBottom)
    {
        int left = ToEvenPixel(insets.Left + dLeft, pixelWidth - MinimumSize);
        int top = ToEvenPixel(insets.Top + dTop, pixelHeight - MinimumSize);
        int right = ToEvenPixel(insets.Right + dRight, pixelWidth - MinimumSize - left);
        int bottom = ToEvenPixel(insets.Bottom + dBottom, pixelHeight - MinimumSize - top);
        if (pixelWidth - left - right < MinimumSize)
            right = Math.Max(0, pixelWidth - left - MinimumSize);
        if (pixelHeight - top - bottom < MinimumSize)
            bottom = Math.Max(0, pixelHeight - top - MinimumSize);
        return new PixelInsets(left, right, top, bottom);
    }

    private static void Normalize(ref double x, ref double y, ref double width, ref double height)
    {
        if (width < 0)
        {
            x += width;
            width = -width;
        }

        if (height < 0)
        {
            y += height;
            height = -height;
        }
    }

    private static int ToEvenPixel(double value, int max)
    {
        int rounded = (int)Math.Round(value, MidpointRounding.AwayFromZero);
        int clamped = Math.Clamp(rounded, 0, Math.Max(0, max));
        return (clamped / 2) * 2;
    }
}