TilesheetDefinitionValidator.cs

using Gondwana.Physics.Collisions;
 
namespace Gondwana.Drawing.Tilesheets.GTS;

public static class TilesheetDefinitionValidator
{
    public static IReadOnlyList<string> Validate(TilesheetDefinition definition, int? imageWidth = null, int? imageHeight = null)
    {
        ArgumentNullException.ThrowIfNull(definition);
        var errors = new List<string>();
        var names = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
        foreach (var region in definition.Regions ?? [])
        {
            if (region is null) { errors.Add("Regions contains a null entry."); continue; }
            var label = $"Region '{region.Name}'";
            if (string.IsNullOrWhiteSpace(region.Name)) errors.Add($"{label}: name is empty.");
            if (!names.Add(region.Name)) errors.Add($"{label}: duplicate name.");
            if (region.Area.Width <= 0 || region.Area.Height <= 0 || region.TileSize.Width <= 0 || region.TileSize.Height <= 0)
            {
                errors.Add($"{label}: area and tile dimensions must be positive.");
                continue;
            }
            if (region.Area.X < 0 || region.Area.Y < 0 ||
                (imageWidth.HasValue && (long)region.Area.X + region.Area.Width > imageWidth) ||
                (imageHeight.HasValue && (long)region.Area.Y + region.Area.Height > imageHeight)) errors.Add($"{label}: area is outside the source image.");
            if (Negative(region.TilePadding)) errors.Add($"{label}: tile padding cannot be negative.");
            if (region.RegionMargin.Left < 0 || region.RegionMargin.Top < 0 ||
                region.RegionMargin.Right < -region.TilePadding.Right ||
                region.RegionMargin.Bottom < -region.TilePadding.Bottom)
                errors.Add($"{label}: leading margins cannot be negative; trailing margins may only cancel trailing tile padding.");
            if (Negative(region.Overhang)) errors.Add($"{label}: overhang cannot be negative.");
            var (columns, rows) = GridSize(region);
            if (columns <= 0 || rows <= 0) errors.Add($"{label}: layout contains no complete frames.");
            CheckCollision(region.CollisionAdjust, region, label, errors);
            if (!Enum.IsDefined(region.CollisionType)) errors.Add($"{label}: unknown collision type.");
            var coordinates = new HashSet<(int, int)>();
            foreach (var frame in region.Frames ?? [])
            {
                if (frame is null) { errors.Add($"{label}: null frame metadata."); continue; }
                var frameLabel = $"{label}, frame ({frame.XTile}, {frame.YTile})";
                if (!coordinates.Add((frame.XTile, frame.YTile))) errors.Add($"{frameLabel}: duplicate frame metadata.");
                if (frame.XTile < 0 || frame.YTile < 0 || frame.XTile >= columns || frame.YTile >= rows) errors.Add($"{frameLabel}: coordinates are outside the frame grid.");
                if (frame.CollisionAdjust is { } adjust) CheckCollision(adjust, region, frameLabel, errors);
                if (frame.CollisionType is { } type && !Enum.IsDefined(type)) errors.Add($"{frameLabel}: unknown collision type.");
            }
        }
        return errors;
    }

    public static (long Columns, long Rows) GridSize(TilesheetRegionDefinition region)
    {
        long width = (long)region.TileSize.Width + region.TilePadding.Left + region.TilePadding.Right;
        long height = (long)region.TileSize.Height + region.TilePadding.Top + region.TilePadding.Bottom;
        return (width <= 0 ? 0 : Math.Max(0, ((long)region.Area.Width - region.RegionMargin.Left - region.RegionMargin.Right) / width),
            height <= 0 ? 0 : Math.Max(0, ((long)region.Area.Height - region.RegionMargin.Top - region.RegionMargin.Bottom) / height));
    }
 
    private static bool Negative(Spacing spacing) => spacing.Left < 0 || spacing.Right < 0 || spacing.Top < 0 || spacing.Bottom < 0;
    private static void CheckCollision(CollisionAdjust adjust, TilesheetRegionDefinition region, string label, List<string> errors)
    {
        // Negative adjustments intentionally expand collision bounds. Only inverted
        // geometry is impossible; zero-sized collision areas may disable collisions.
        if ((long)adjust.Left + adjust.Right > region.TileSize.Width || (long)adjust.Top + adjust.Bottom > region.TileSize.Height)
            errors.Add($"{label}: collision adjustments invert the frame's collision rectangle.");
    }
}