Easy Connect

import { Position, MarkerType, type XYPosition, type InternalNode } from '@xyflow/svelte';
 
// this helper function returns the intersection point
// of the line between the center of the intersectionNode and the target node
function getNodeIntersection(intersectionNode: InternalNode, targetNode: InternalNode) {
  // https://math.stackexchange.com/questions/1724792/an-algorithm-for-finding-the-intersection-point-between-a-center-of-vision-and-a
  const intersectionNodePosition = intersectionNode.internals.positionAbsolute || {
    x: 0,
    y: 0,
  };
  const targetPosition = targetNode.internals.positionAbsolute || {
    x: 0,
    y: 0,
  };
 
  const w = (intersectionNode.measured.width ?? 0) / 2;
  const h = (intersectionNode.measured.height ?? 0) / 2;
 
  const x2 = intersectionNodePosition.x + w;
  const y2 = intersectionNodePosition.y + h;
  const x1 = targetPosition.x + (targetNode.measured.width ?? 0) / 2;
  const y1 = targetPosition.y + (targetNode.measured.height ?? 0) / 2;
 
  const xx1 = (x1 - x2) / (2 * w) - (y1 - y2) / (2 * h);
  const yy1 = (x1 - x2) / (2 * w) + (y1 - y2) / (2 * h);
  const a = 1 / (Math.abs(xx1) + Math.abs(yy1));
  const xx3 = a * xx1;
  const yy3 = a * yy1;
  const x = w * (xx3 + yy3) + x2;
  const y = h * (-xx3 + yy3) + y2;
 
  return { x, y };
}
 
// returns the position (top,right,bottom or right) passed node compared to the intersection point
function getEdgePosition(node: InternalNode, intersectionPoint: XYPosition) {
  if (!node.measured.width || !node.measured.height) {
    return null;
  }
  const nx = Math.round(node.internals.positionAbsolute?.x ?? 0);
  const ny = Math.round(node.internals.positionAbsolute?.y ?? 0);
  const px = Math.round(intersectionPoint.x);
  const py = Math.round(intersectionPoint.y);
 
  if (px <= nx + 1) {
    return Position.Left;
  }
  if (px >= nx + node.measured.width - 1) {
    return Position.Right;
  }
  if (py <= ny + 1) {
    return Position.Top;
  }
  if (py >= ny + node.measured.height - 1) {
    return Position.Bottom;
  }
 
  return Position.Top;
}
 
// returns the parameters (sx, sy, tx, ty, sourcePos, targetPos) you need to create an edge
export function getEdgeParams(source: InternalNode, target: InternalNode) {
  const sourceIntersectionPoint = getNodeIntersection(source, target);
  const targetIntersectionPoint = getNodeIntersection(target, source);
 
  const sourcePos = getEdgePosition(source, sourceIntersectionPoint);
  const targetPos = getEdgePosition(target, targetIntersectionPoint);
 
  return {
    sx: sourceIntersectionPoint.x,
    sy: sourceIntersectionPoint.y,
    tx: targetIntersectionPoint.x,
    ty: targetIntersectionPoint.y,
    sourcePos,
    targetPos,
  };
}