git.stella-ops.org/src/__Libraries/StellaOps.ElkSharp/ElkEdgePostProcessor.BoundarySlots.Snap.cs

namespace StellaOps.ElkSharp;

internal static partial class ElkEdgePostProcessor
{
    private static List<ElkPoint>? TryBuildGatewaySourceBoundarySlotSkirtCandidate(
        IReadOnlyList<ElkPoint> currentPath,
        ElkPositionedNode sourceNode,
        ElkPoint boundaryPoint,
        IReadOnlyCollection<ElkPositionedNode> nodes,
        string? sourceNodeId,
        string? targetNodeId,
        double obstaclePadding)
    {
        if (!ElkShapeBoundaries.IsGatewayShape(sourceNode)
            || currentPath.Count < 3)
        {
            return null;
        }

        var firstExteriorIndex = FindFirstGatewayExteriorPointIndex(currentPath, sourceNode);
        var preferredContinuationIndex = FindGatewaySourceCurlRecoveryIndex(currentPath, firstExteriorIndex)
            ?? FindPreferredGatewayExitContinuationIndex(currentPath, sourceNode, firstExteriorIndex);
        var candidateIndices = new HashSet<int>
        {
            Math.Clamp(currentPath.Count - 2, 1, currentPath.Count - 1),
            Math.Clamp(preferredContinuationIndex, 1, currentPath.Count - 1),
        };

        List<ElkPoint>? bestCandidate = null;
        List<ElkPoint>? bestLaneRejoinCandidate = null;
        var bestScore = double.PositiveInfinity;
        var bestLaneRejoinScore = double.PositiveInfinity;
        foreach (var continuationIndex in candidateIndices.OrderBy(index => index))
        {
            var continuationPoint = currentPath[continuationIndex];
            var repairCandidates = new List<List<ElkPoint>>();
            var laneRejoinCandidate = TryBuildGatewaySourceBoundarySlotLaneRejoinCandidate(
                currentPath,
                sourceNode,
                boundaryPoint,
                continuationPoint,
                continuationIndex,
                nodes,
                sourceNodeId,
                targetNodeId);
            if (laneRejoinCandidate is not null && PathChanged(currentPath, laneRejoinCandidate))
            {
                var laneRejoinScore = ComputePathLength(laneRejoinCandidate) + (Math.Max(0, laneRejoinCandidate.Count - 2) * 4d);
                if (laneRejoinScore < bestLaneRejoinScore)
                {
                    bestLaneRejoinScore = laneRejoinScore;
                    bestLaneRejoinCandidate = laneRejoinCandidate;
                }
            }

            var continuationAnchoredCandidate = BuildGatewaySourceRepairPath(
                currentPath,
                sourceNode,
                boundaryPoint,
                continuationPoint,
                continuationIndex,
                continuationPoint,
                nodes,
                sourceNodeId,
                targetNodeId);
            if (PathChanged(currentPath, continuationAnchoredCandidate))
            {
                repairCandidates.Add(continuationAnchoredCandidate);
            }

            var prefixCandidate = TryBuildLocalObstacleSkirtBoundaryShortcut(
                currentPath,
                boundaryPoint,
                continuationPoint,
                nodes,
                sourceNodeId,
                targetNodeId,
                targetNode: null,
                obstaclePadding);
            if (prefixCandidate is not null && prefixCandidate.Count >= 2)
            {
                var rebuilt = new List<ElkPoint>(prefixCandidate);
                for (var i = continuationIndex + 1; i < currentPath.Count; i++)
                {
                    var point = currentPath[i];
                    if (!ElkEdgeRoutingGeometry.PointsEqual(rebuilt[^1], point))
                    {
                        rebuilt.Add(new ElkPoint { X = point.X, Y = point.Y });
                    }
                }

                var skirtCandidate = NormalizePathPoints(rebuilt);
                if (PathChanged(currentPath, skirtCandidate))
                {
                    repairCandidates.Add(skirtCandidate);
                }
            }

            foreach (var candidate in repairCandidates)
            {
                var score = ComputePathLength(candidate) + (Math.Max(0, candidate.Count - 2) * 4d);
                if (score >= bestScore)
                {
                    continue;
                }

                bestScore = score;
                bestCandidate = candidate;
            }
        }

        return bestLaneRejoinCandidate ?? bestCandidate;
    }

    private static List<ElkPoint>? TryBuildGatewaySourceBoundarySlotLaneRejoinCandidate(
        IReadOnlyList<ElkPoint> currentPath,
        ElkPositionedNode sourceNode,
        ElkPoint boundaryPoint,
        ElkPoint continuationPoint,
        int continuationIndex,
        IReadOnlyCollection<ElkPositionedNode> nodes,
        string? sourceNodeId,
        string? targetNodeId)
    {
        if (!ElkShapeBoundaries.IsGatewayShape(sourceNode)
            || currentPath.Count < 3)
        {
            return null;
        }

        var boundarySide = ElkEdgeRoutingGeometry.ResolveBoundarySide(boundaryPoint, sourceNode);
        var padding = 8d;
        ElkPoint rejoinExterior;
        switch (boundarySide)
        {
            case "left":
                rejoinExterior = new ElkPoint { X = sourceNode.X - padding, Y = continuationPoint.Y };
                break;
            case "right":
                rejoinExterior = new ElkPoint { X = sourceNode.X + sourceNode.Width + padding, Y = continuationPoint.Y };
                break;
            case "top":
                rejoinExterior = new ElkPoint { X = continuationPoint.X, Y = sourceNode.Y - padding };
                break;
            case "bottom":
                rejoinExterior = new ElkPoint { X = continuationPoint.X, Y = sourceNode.Y + sourceNode.Height + padding };
                break;
            default:
                return null;
        }

        if (ElkShapeBoundaries.IsInsideNodeBoundingBoxInterior(sourceNode, rejoinExterior)
            || !ElkShapeBoundaries.HasValidGatewayBoundaryAngle(sourceNode, boundaryPoint, rejoinExterior))
        {
            return null;
        }

        var rebuilt = new List<ElkPoint> { boundaryPoint };
        if (!ElkEdgeRoutingGeometry.PointsEqual(rebuilt[^1], rejoinExterior))
        {
            rebuilt.Add(rejoinExterior);
        }

        if (!ElkEdgeRoutingGeometry.PointsEqual(rebuilt[^1], continuationPoint))
        {
            rebuilt.Add(continuationPoint);
        }

        for (var i = continuationIndex + 1; i < currentPath.Count; i++)
        {
            var point = currentPath[i];
            if (!ElkEdgeRoutingGeometry.PointsEqual(rebuilt[^1], point))
            {
                rebuilt.Add(new ElkPoint { X = point.X, Y = point.Y });
            }
        }

        var candidate = NormalizePathPoints(rebuilt);
        if (!PathChanged(currentPath, candidate)
            || HasNodeObstacleCrossing(candidate, nodes, sourceNodeId, targetNodeId)
            || !HasAcceptableGatewayBoundaryPath(candidate, nodes, sourceNodeId, targetNodeId, sourceNode, fromStart: true)
            || !HasCleanGatewaySourceBandPath(candidate, sourceNode))
        {
            return null;
        }

        return candidate;
    }

    private static bool TrySelectImprovedBoundarySlotSourceCandidate(
        ElkRoutedEdge[] edges,
        ElkRoutedEdge[] processedEdges,
        int edgeIndex,
        ElkRoutedEdge edge,
        IReadOnlyList<ElkPoint> currentPath,
        IReadOnlyCollection<List<ElkPoint>> candidates,
        IReadOnlyCollection<ElkPositionedNode> nodes,
        out List<ElkPoint> selectedPath)
    {
        selectedPath = [];
        if (candidates.Count == 0)
        {
            return false;
        }

        var baselineLayout = BuildBoundarySlotEvaluationLayout(
            edges,
            processedEdges,
            edgeIndex,
            BuildSingleSectionEdge(edge, currentPath));
        var baselineScore = ElkEdgeRoutingScoring.ComputeScore(baselineLayout, nodes);
        var bestScore = baselineScore;
        List<ElkPoint>? bestPath = null;
        var seenSignatures = new HashSet<string>(StringComparer.Ordinal);

        foreach (var candidate in candidates)
        {
            var normalizedCandidate = NormalizePathPoints(candidate);
            if (!PathChanged(currentPath, normalizedCandidate)
                || !seenSignatures.Add(CreatePathSignature(normalizedCandidate)))
            {
                continue;
            }

            var candidateLayout = (ElkRoutedEdge[])baselineLayout.Clone();
            candidateLayout[edgeIndex] = BuildSingleSectionEdge(edge, normalizedCandidate);
            var candidateScore = ElkEdgeRoutingScoring.ComputeScore(candidateLayout, nodes);
            if (!IsBetterBoundarySlotSourceCandidate(baselineScore, bestScore, candidateScore))
            {
                continue;
            }

            bestScore = candidateScore;
            bestPath = normalizedCandidate;
        }

        if (bestPath is null)
        {
            return false;
        }

        selectedPath = bestPath;
        return true;
    }

    private static ElkRoutedEdge[] BuildBoundarySlotEvaluationLayout(
        ElkRoutedEdge[] edges,
        ElkRoutedEdge[] processedEdges,
        int edgeIndex,
        ElkRoutedEdge currentEdge)
    {
        var layout = new ElkRoutedEdge[edges.Length];
        for (var i = 0; i < edges.Length; i++)
        {
            layout[i] = i < edgeIndex ? processedEdges[i] : edges[i];
        }

        layout[edgeIndex] = currentEdge;
        return layout;
    }

    private static bool IsBetterBoundarySlotSourceCandidate(
        EdgeRoutingScore baselineScore,
        EdgeRoutingScore currentBestScore,
        EdgeRoutingScore candidateScore)
    {
        if (candidateScore.BoundarySlotViolations >= baselineScore.BoundarySlotViolations
            || HasBlockingBoundarySlotSourceCandidateRegression(
                baselineScore,
                candidateScore,
                allowTemporarySoftTrade: candidateScore.BoundarySlotViolations < baselineScore.BoundarySlotViolations))
        {
            return false;
        }

        if (currentBestScore.BoundarySlotViolations >= baselineScore.BoundarySlotViolations)
        {
            return true;
        }

        if (candidateScore.BoundarySlotViolations != currentBestScore.BoundarySlotViolations)
        {
            return candidateScore.BoundarySlotViolations < currentBestScore.BoundarySlotViolations;
        }

        if (candidateScore.Value > currentBestScore.Value + 0.5d)
        {
            return true;
        }

        if (candidateScore.Value + 0.5d < currentBestScore.Value)
        {
            return false;
        }

        return candidateScore.TotalPathLength < currentBestScore.TotalPathLength - 0.5d;
    }

    private static bool HasBlockingBoundarySlotSourceCandidateRegression(
        EdgeRoutingScore baselineScore,
        EdgeRoutingScore candidateScore,
        bool allowTemporarySoftTrade)
    {
        return candidateScore.NodeCrossings > baselineScore.NodeCrossings
            || candidateScore.BelowGraphViolations > baselineScore.BelowGraphViolations
            || candidateScore.UnderNodeViolations > baselineScore.UnderNodeViolations
            || candidateScore.LongDiagonalViolations > baselineScore.LongDiagonalViolations
            || candidateScore.EntryAngleViolations > baselineScore.EntryAngleViolations
            || candidateScore.GatewaySourceExitViolations > baselineScore.GatewaySourceExitViolations
            || candidateScore.RepeatCollectorCorridorViolations > baselineScore.RepeatCollectorCorridorViolations
            || candidateScore.RepeatCollectorNodeClearanceViolations > baselineScore.RepeatCollectorNodeClearanceViolations
            || (!allowTemporarySoftTrade
                && candidateScore.TargetApproachJoinViolations > baselineScore.TargetApproachJoinViolations)
            || candidateScore.TargetApproachBacktrackingViolations > baselineScore.TargetApproachBacktrackingViolations
            || (!allowTemporarySoftTrade
                && candidateScore.SharedLaneViolations > baselineScore.SharedLaneViolations);
    }
}