git.stella-ops.org/src/__Libraries/StellaOps.ElkSharp/ElkEdgeRouterIterative.LocalRepair.ShortestPaths.cs

using System.Collections.Concurrent;
using System.Diagnostics;
using System.Globalization;

namespace StellaOps.ElkSharp;

internal static partial class ElkEdgeRouterIterative
{
    private static List<ElkPoint>? TryBuildPreferredSideShortcut(
        ElkPositionedNode sourceNode,
        ElkPositionedNode targetNode,
        IReadOnlyCollection<ElkPositionedNode> nodes,
        string sourceId,
        string targetId)
    {
        var sourceCenterX = sourceNode.X + (sourceNode.Width / 2d);
        var sourceCenterY = sourceNode.Y + (sourceNode.Height / 2d);
        var targetCenterX = targetNode.X + (targetNode.Width / 2d);
        var targetCenterY = targetNode.Y + (targetNode.Height / 2d);
        var deltaX = targetCenterX - sourceCenterX;
        var deltaY = targetCenterY - sourceCenterY;
        var absDx = Math.Abs(deltaX);
        var absDy = Math.Abs(deltaY);
        if (absDx < 16d && absDy < 16d)
        {
            return null;
        }

        var horizontalDominant = absDx >= absDy;
        var preferredSourceSide = horizontalDominant
            ? deltaX >= 0d ? "right" : "left"
            : deltaY >= 0d ? "bottom" : "top";
        var preferredTargetSide = horizontalDominant
            ? deltaX >= 0d ? "left" : "right"
            : deltaY >= 0d ? "top" : "bottom";
        var start = BuildPreferredBoundaryPoint(sourceNode, preferredSourceSide, targetNode);
        var end = BuildPreferredBoundaryPoint(targetNode, preferredTargetSide, sourceNode);
        return TryBuildShortestOrthogonalPath(start, end, nodes, sourceId, targetId, targetNode, 0d);
    }

    private static ElkPoint BuildPreferredBoundaryPoint(
        ElkPositionedNode node,
        string side,
        ElkPositionedNode otherNode)
    {
        var horizontalInset = Math.Min(24d, Math.Max(12d, node.Width / 4d));
        var verticalInset = Math.Min(24d, Math.Max(12d, node.Height / 4d));
        var otherCenterX = otherNode.X + (otherNode.Width / 2d);
        var otherCenterY = otherNode.Y + (otherNode.Height / 2d);

        var boundary = side switch
        {
            "left" => new ElkPoint
            {
                X = node.X,
                Y = Math.Clamp(otherCenterY, node.Y + verticalInset, (node.Y + node.Height) - verticalInset),
            },
            "right" => new ElkPoint
            {
                X = node.X + node.Width,
                Y = Math.Clamp(otherCenterY, node.Y + verticalInset, (node.Y + node.Height) - verticalInset),
            },
            "top" => new ElkPoint
            {
                X = Math.Clamp(otherCenterX, node.X + horizontalInset, (node.X + node.Width) - horizontalInset),
                Y = node.Y,
            },
            _ => new ElkPoint
            {
                X = Math.Clamp(otherCenterX, node.X + horizontalInset, (node.X + node.Width) - horizontalInset),
                Y = node.Y + node.Height,
            },
        };

        if (!ElkShapeBoundaries.IsGatewayShape(node))
        {
            return boundary;
        }

        var referencePoint = side switch
        {
            "left" => new ElkPoint { X = node.X - Math.Max(24d, node.Width / 3d), Y = boundary.Y },
            "right" => new ElkPoint { X = node.X + node.Width + Math.Max(24d, node.Width / 3d), Y = boundary.Y },
            "top" => new ElkPoint { X = boundary.X, Y = node.Y - Math.Max(24d, node.Height / 3d) },
            _ => new ElkPoint { X = boundary.X, Y = node.Y + node.Height + Math.Max(24d, node.Height / 3d) },
        };

        var projected = ElkShapeBoundaries.ProjectOntoShapeBoundary(node, referencePoint);
        return ElkShapeBoundaries.PreferGatewayEdgeInteriorBoundary(node, projected, referencePoint);
    }

    private static List<ElkPoint>? TryBuildShortestOrthogonalPath(
        ElkPoint start,
        ElkPoint end,
        IReadOnlyCollection<ElkPositionedNode> nodes,
        string sourceId,
        string targetId,
        ElkPositionedNode? targetNode,
        double obstaclePadding)
    {
        var rawObstacles = nodes.Select(node => (
            Left: node.X - obstaclePadding,
            Top: node.Y - obstaclePadding,
            Right: node.X + node.Width + obstaclePadding,
            Bottom: node.Y + node.Height + obstaclePadding,
            Id: node.Id)).ToArray();

        bool SegmentIsClear(ElkPoint from, ElkPoint to) =>
            !ElkEdgePostProcessor.SegmentCrossesObstacle(from, to, rawObstacles, sourceId, targetId);

        if (Math.Abs(start.X - end.X) < 0.5d || Math.Abs(start.Y - end.Y) < 0.5d)
        {
            return SegmentIsClear(start, end)
                ? [start, end]
                : null;
        }

        foreach (var pivot in EnumerateOrthogonalShortcutPivots(start, end, targetNode))
        {
            if (!SegmentIsClear(start, pivot) || !SegmentIsClear(pivot, end))
            {
                continue;
            }

            return NormalizePolyline([start, pivot, end]);
        }

        return null;
    }

    private static IEnumerable<ElkPoint> EnumerateOrthogonalShortcutPivots(
        ElkPoint start,
        ElkPoint end,
        ElkPositionedNode? targetNode)
    {
        var targetSide = targetNode is null
            ? string.Empty
            : ElkEdgeRoutingGeometry.ResolveBoundarySide(end, targetNode);
        var preferred = targetSide is "left" or "right"
            ? new ElkPoint { X = start.X, Y = end.Y }
            : new ElkPoint { X = end.X, Y = start.Y };
        var alternate = targetSide is "left" or "right"
            ? new ElkPoint { X = end.X, Y = start.Y }
            : new ElkPoint { X = start.X, Y = end.Y };

        yield return preferred;
        if (!ElkEdgeRoutingGeometry.PointsEqual(preferred, alternate))
        {
            yield return alternate;
        }
    }

    private static IEnumerable<ElkPoint> EnumerateShortestRepairEndpoints(
        ElkPoint start,
        ElkPoint currentEnd,
        ElkPositionedNode? targetNode)
    {
        var endpoints = new List<ElkPoint>();

        void AddCandidate(ElkPoint candidate)
        {
            if (!endpoints.Any(existing => ElkEdgeRoutingGeometry.PointsEqual(existing, candidate)))
            {
                endpoints.Add(candidate);
            }
        }

        AddCandidate(currentEnd);
        if (targetNode is null)
        {
            return endpoints;
        }

        if (ElkShapeBoundaries.IsGatewayShape(targetNode))
        {
            if (ElkShapeBoundaries.TryProjectGatewayBoundarySlot(targetNode, "left", start.Y, out var left))
            {
                AddCandidate(left);
            }

            if (ElkShapeBoundaries.TryProjectGatewayBoundarySlot(targetNode, "right", start.Y, out var right))
            {
                AddCandidate(right);
            }

            if (ElkShapeBoundaries.TryProjectGatewayBoundarySlot(targetNode, "top", start.X, out var top))
            {
                AddCandidate(top);
            }

            if (ElkShapeBoundaries.TryProjectGatewayBoundarySlot(targetNode, "bottom", start.X, out var bottom))
            {
                AddCandidate(bottom);
            }

            return endpoints;
        }

        var horizontalInset = Math.Min(24d, Math.Max(12d, targetNode.Width / 4d));
        var verticalInset = Math.Min(24d, Math.Max(12d, targetNode.Height / 4d));
        var candidateEndpoints = new[]
        {
            new ElkPoint
            {
                X = targetNode.X,
                Y = Math.Clamp(start.Y, targetNode.Y + verticalInset, (targetNode.Y + targetNode.Height) - verticalInset),
            },
            new ElkPoint
            {
                X = targetNode.X + targetNode.Width,
                Y = Math.Clamp(start.Y, targetNode.Y + verticalInset, (targetNode.Y + targetNode.Height) - verticalInset),
            },
            new ElkPoint
            {
                X = Math.Clamp(start.X, targetNode.X + horizontalInset, (targetNode.X + targetNode.Width) - horizontalInset),
                Y = targetNode.Y,
            },
            new ElkPoint
            {
                X = Math.Clamp(start.X, targetNode.X + horizontalInset, (targetNode.X + targetNode.Width) - horizontalInset),
                Y = targetNode.Y + targetNode.Height,
            },
        };

        foreach (var candidate in candidateEndpoints)
        {
            AddCandidate(candidate);
        }

        return endpoints;
    }

}