fix: implemented cycle check on isValidConnection (#8716)

* Implemented cycle check on isValidConnection

* Implemented loop check if the loop done results in a loopcomponent loop

src/frontend/src/utils/reactflowUtils.ts

@@ -329,10 +329,11 @@ export function unselectAllNodesEdges(nodes: Node[], edges: Edge[]) {
 }
 
 export function isValidConnection(
-  { source, target, sourceHandle, targetHandle }: Connection,
+  connection: Connection,
   nodes?: AllNodeType[],
   edges?: EdgeType[],
 ): boolean {
+  const { source, target, sourceHandle, targetHandle } = connection;
   if (source === target) {
     return false;
   }
@@ -342,6 +343,33 @@ export function isValidConnection(
 
   const targetHandleObject: targetHandleType = scapeJSONParse(targetHandle!);
   const sourceHandleObject: sourceHandleType = scapeJSONParse(sourceHandle!);
+
+  // Helper to find the edge between two nodes
+  function findEdgeBetween(srcId: string, tgtId: string) {
+    return edgesArray.find((e) => e.source === srcId && e.target === tgtId);
+  }
+
+  // Modified hasCycle to return the path of edges forming the loop
+  const findCyclePath = (
+    node: AllNodeType,
+    visited = new Set(),
+    path: EdgeType[] = [],
+  ): EdgeType[] | null => {
+    if (visited.has(node.id)) return null;
+    visited.add(node.id);
+    for (const outgoer of getOutgoers(node, nodesArray, edgesArray)) {
+      const edge = findEdgeBetween(node.id, outgoer.id);
+      if (!edge) continue;
+      if (outgoer.id === source) {
+        // This edge would close the loop
+        return [...path, edge];
+      }
+      const result = findCyclePath(outgoer, visited, [...path, edge]);
+      if (result) return result;
+    }
+    return null;
+  };
+
   if (
     targetHandleObject.inputTypes?.some(
       (n) => n === sourceHandleObject.dataType,
@@ -359,22 +387,43 @@ export function isValidConnection(
         t === targetHandleObject.type,
     )
   ) {
-    let targetNode = nodesArray.find((node) => node.id === target!)?.data?.node;
-    if (!targetNode) {
-      if (!edgesArray.find((e) => e.targetHandle === targetHandle)) {
+    let targetNode = nodesArray.find((node) => node.id === target!);
+    let targetNodeDataNode = targetNode?.data?.node;
+    if (
+      (!targetNodeDataNode &&
+        !edgesArray.find((e) => e.targetHandle === targetHandle)) ||
+      (targetNodeDataNode &&
+        targetHandleObject.output_types &&
+        !edgesArray.find((e) => e.targetHandle === targetHandle)) ||
+      (targetNodeDataNode &&
+        !targetHandleObject.output_types &&
+        ((!targetNodeDataNode.template[targetHandleObject.fieldName].list &&
+          !edgesArray.find((e) => e.targetHandle === targetHandle)) ||
+          targetNodeDataNode.template[targetHandleObject.fieldName].list))
+    ) {
+      // If the current target handle is a loop component, allow connection immediately
+      if (targetHandleObject.output_types) {
         return true;
       }
-    } else if (
-      targetHandleObject.output_types &&
-      !edgesArray.find((e) => e.targetHandle === targetHandle)
-    ) {
-      return true;
-    } else if (
-      !targetHandleObject.output_types &&
-      ((!targetNode.template[targetHandleObject.fieldName].list &&
-        !edgesArray.find((e) => e.targetHandle === targetHandle)) ||
-        targetNode.template[targetHandleObject.fieldName].list)
-    ) {
+      // Check for loop and if any edge in the loop is a loop component
+      let cyclePath: EdgeType[] | null = null;
+      if (targetNode) {
+        cyclePath = findCyclePath(targetNode);
+      }
+      if (cyclePath) {
+        // Check if any edge in the cycle path is a loop component
+        const hasLoopComponent = cyclePath.some((edge) => {
+          try {
+            const th = scapeJSONParse(edge.targetHandle!);
+            return !!th.output_types;
+          } catch {
+            return false;
+          }
+        });
+        if (!hasLoopComponent) {
+          return false;
+        }
+      }
       return true;
     }
   }