feat: ant path rendering on cahnges

frontend/src/app/canvas/CanvasPage.tsx

@@ -66,6 +66,7 @@ import {
   getNodeType,
   isConnectionAllowed,
 } from '@/lib/nodeRegistry'
+import { getPathNodeIds } from '@/lib/graphPath'
 import type { AppNode, AppEdge } from '@/lib/nodeTypes'
 import { toast } from 'sonner'
 import {
@@ -77,6 +78,8 @@ import {
 
 const SNAP_GRID: [number, number] = [15, 15]
 const DUPLICATE_OFFSET = { x: 30, y: 30 }
+/** Minimum time (ms) the connection ant trail runs when a path update is in progress. */
+const CONNECTION_PATH_UPDATE_MIN_MS = 1500
 const snapToGrid = (x: number, y: number): { x: number; y: number } => ({
   x: Math.round(x / SNAP_GRID[0]) * SNAP_GRID[0],
   y: Math.round(y / SNAP_GRID[1]) * SNAP_GRID[1],
@@ -264,6 +267,75 @@ export function CanvasPage({ projectId }: CanvasPageProps) {
   const [isSelecting, setIsSelecting] = React.useState(false)
   const [ariaAnnouncement, setAriaAnnouncement] = React.useState<string | null>(null)
   const [fullscreenNodeId, setFullscreenNodeId] = React.useState<string | null>(null)
+  const [connectionPathUpdatingNodeIds, setConnectionPathUpdatingNodeIds] = React.useState<string[]>([])
+  const [connectionPathTriggerNodeIds, setConnectionPathTriggerNodeIds] = React.useState<string[]>([])
+  const pathUpdateNodeIdsRef = useRef<Set<string>>(new Set())
+  const pathUpdateStartTimeRef = useRef<number | null>(null)
+  const pathUpdateEndTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null)
+
+  const clearPathUpdateSession = useCallback(() => {
+    setConnectionPathUpdatingNodeIds([])
+    setConnectionPathTriggerNodeIds([])
+  }, [])
+
+  const startConnectionPathUpdate = useCallback((nodeId: string) => {
+    const ref = pathUpdateNodeIdsRef.current
+    ref.add(nodeId)
+    if (ref.size === 1) {
+      pathUpdateStartTimeRef.current = Date.now()
+      if (pathUpdateEndTimeoutRef.current != null) {
+        clearTimeout(pathUpdateEndTimeoutRef.current)
+        pathUpdateEndTimeoutRef.current = null
+      }
+    }
+    setConnectionPathUpdatingNodeIds(Array.from(ref))
+  }, [])
+
+  const endConnectionPathUpdate = useCallback((nodeId: string) => {
+    const ref = pathUpdateNodeIdsRef.current
+    ref.delete(nodeId)
+    if (ref.size > 0) {
+      setConnectionPathUpdatingNodeIds(Array.from(ref))
+      return
+    }
+    const startedAt = pathUpdateStartTimeRef.current ?? 0
+    const elapsed = Date.now() - startedAt
+    const remaining = Math.max(0, CONNECTION_PATH_UPDATE_MIN_MS - elapsed)
+    if (remaining === 0) {
+      clearPathUpdateSession()
+    } else {
+      pathUpdateEndTimeoutRef.current = setTimeout(() => {
+        pathUpdateEndTimeoutRef.current = null
+        clearPathUpdateSession()
+      }, remaining)
+    }
+  }, [clearPathUpdateSession])
+
+  const pathTriggerBatchRef = useRef<Set<string>>(new Set())
+  const pathTriggerScheduledRef = useRef(false)
+  const addConnectionPathTrigger = useCallback((nodeId: string) => {
+    pathTriggerBatchRef.current.add(nodeId)
+    if (pathTriggerScheduledRef.current) return
+    pathTriggerScheduledRef.current = true
+    requestAnimationFrame(() => {
+      pathTriggerScheduledRef.current = false
+      const batch = new Set(pathTriggerBatchRef.current)
+      pathTriggerBatchRef.current = new Set()
+      if (batch.size === 0) return
+      setConnectionPathTriggerNodeIds((prev) => {
+        const next = new Set(prev)
+        batch.forEach((id) => next.add(id))
+        return next.size === prev.length && prev.every((id) => next.has(id)) ? prev : Array.from(next)
+      })
+    })
+  }, [])
+
+  React.useEffect(() => () => {
+    if (pathUpdateEndTimeoutRef.current != null) {
+      clearTimeout(pathUpdateEndTimeoutRef.current)
+    }
+  }, [])
+
   const nodesRef = useRef(nodes)
   nodesRef.current = nodes
 
@@ -471,6 +543,11 @@ export function CanvasPage({ projectId }: CanvasPageProps) {
     flowActionsRef.current?.pasteAtViewportCenter?.()
   }, [])
 
+  const connectionPathNodeIds = useMemo(
+    () => getPathNodeIds(edges, connectionPathUpdatingNodeIds, connectionPathTriggerNodeIds),
+    [edges, connectionPathUpdatingNodeIds, connectionPathTriggerNodeIds]
+  )
+
   const flowContextValue = useMemo(
     () => ({
       nodes,
@@ -485,6 +562,12 @@ export function CanvasPage({ projectId }: CanvasPageProps) {
       flowActionsRef,
       fullscreenNodeId,
       setFullscreenNodeId,
+      connectionPathUpdatingNodeIds,
+      connectionPathTriggerNodeIds,
+      addConnectionPathTrigger,
+      connectionPathNodeIds,
+      startConnectionPathUpdate,
+      endConnectionPathUpdate,
     }),
     [
       nodes,
@@ -499,6 +582,12 @@ export function CanvasPage({ projectId }: CanvasPageProps) {
       flowActionsRef,
       fullscreenNodeId,
       setFullscreenNodeId,
+      connectionPathUpdatingNodeIds,
+      connectionPathTriggerNodeIds,
+      addConnectionPathTrigger,
+      connectionPathNodeIds,
+      startConnectionPathUpdate,
+      endConnectionPathUpdate,
     ]
   )