Feature: Draggable edge

src/utils/graph.ts

@@ -67,6 +67,37 @@ export const addEdge = (edgeParams: Edge | Connection, elements: Elements): Elem
   return elements.concat(edge);
 };
 
+export const updateEdge = (oldEdge: Edge, newConnection: Connection, elements: Elements): Elements => {
+  if (!newConnection.source || !newConnection.target) {
+    throw new Error("Can't create new edge. An edge needs a source and a target.");
+  }
+
+  // make sure that there is node with the target and one with the source id
+  [newConnection.source, newConnection.target].forEach((id) => {
+    const nodeId = id.includes('__') ? id.split('__')[0] : id;
+
+    if (!elements.find((e) => isNode(e) && e.id === nodeId)) {
+      throw new Error(`Can't create edge. Node with id=${nodeId} does not exist.`);
+    }
+  });
+  
+  const foundEdge = elements.find(e => isEdge(e) && e.id === oldEdge.id) as Edge;
+  if (!foundEdge) {
+    throw new Error(`The old edge with id=${oldEdge.id} does not exist.`);
+  }
+
+  // Remove old edge and create the new edge with parameters of old edge.
+  const edge = {
+    ...oldEdge,
+    id: getEdgeId(newConnection),
+    source: newConnection.source,
+    target: newConnection.target,
+  } as Edge;
+
+  return elements.filter(e => e.id !== oldEdge.id).concat(edge);
+};
+
+
 export const pointToRendererPoint = (
   { x, y }: XYPosition,
   [tx, ty, tScale]: Transform,