01
type AgentName = 'general' | 'travel'
02

03
type ChatState = {
04
  activeAgent: AgentName
05
  messages: Array<{ role: 'user' | 'assistant'; content: string }>
06
}
07

08
const initialState: ChatState = {
09
  activeAgent: 'general',
10
  messages: [],
11
}

01
import {
02
  StateGraph,
03
  StateSchema,
04
  ReducedValue,
05
  START,
06
  END,
07
  Command,
08
} from '@langchain/langgraph'
09
import type { GraphNode, ConditionalEdgeRouter } from '@langchain/langgraph'
10
import { z } from 'zod'
11

12
const appendMessages = (
13
  current: Array<{ role: 'user' | 'assistant'; content: string }>,
14
  update: Array<{ role: 'user' | 'assistant'; content: string }>,
15
) => {
16
  return [...current, ...update]
17
}
18

19
const State = new StateSchema({
20
  activeAgent: z.enum(['general', 'travel']).default('general'),
21
  messages: new ReducedValue(
22
    z.array(
23
      z.object({
24
        role: z.enum(['user', 'assistant']),
25
        content: z.string(),
26
      }),
27
    ).default([]),
28
    { reducer: appendMessages },
29
  ),
30
})
31

32
const generalAgent: GraphNode<typeof State> = (state) => {
33
  const lastMessage = state.messages.at(-1)?.content ?? ''
34

35
  // 如果用户已经明确在聊旅行，这里就不继续硬接了
36
  if (lastMessage.includes('旅行') || lastMessage.includes('机票') || lastMessage.includes('酒店')) {
37
    return new Command({
38
      update: {
39
        activeAgent: 'travel',
40
        messages: [{
41
          role: 'assistant',
42
          content: '接下来由旅行助理继续帮你安排行程。',
43
        }],
44
      },
45
      goto: 'travelAgent',
46
    })
47
  }
48

49
  return {
50
    messages: [{
51
      role: 'assistant',
52
      content: '我先帮你判断一下需求方向，如果是旅行规划，我会把对话切给旅行助理。',
53
    }],
54
  }
55
}
56

57
const travelAgent: GraphNode<typeof State> = (state) => {
58
  const lastMessage = state.messages.at(-1)?.content ?? ''
59

60
  // 这里假设控制权已经切到了旅行角色，
61
  // 所以后面的回复会直接站在旅行助理的视角继续往下接
62
  return {
63
    messages: [{
64
      role: 'assistant',
65
      content: `旅行助理已接手，当前收到的新要求是：${lastMessage}`,
66
    }],
67
  }
68
}
69

70
const shouldContinue: ConditionalEdgeRouter<typeof State> = (state) => {
71
  if (state.activeAgent === 'travel') return 'travelAgent'
72
  return END
73
}
74

75
const graph = new StateGraph(State)
76
  .addNode('generalAgent', generalAgent, { ends: ['travelAgent'] })
77
  .addNode('travelAgent', travelAgent)
78
  .addEdge(START, 'generalAgent')
79
  .addConditionalEdges('generalAgent', shouldContinue, ['travelAgent'])
80
  .addEdge('travelAgent', END)
81
  .compile()

1
activeAgent: 'travel'

01
let state = await graph.invoke({
02
  messages: [{ role: 'user', content: '我想做一个日本旅行规划。' }],
03
})
04

05
console.log(state.activeAgent)
06
// → travel
07

08
state = await graph.invoke({
09
  // 这里把当前活跃角色继续传回去，
10
  // 所以下一轮不会再回到 generalAgent 重新判断
11
  activeAgent: state.activeAgent,
12
  messages: [{ role: 'user', content: '预算尽量控制在五千以内。' }],
13
})
14

15
console.log(state.messages.at(-1)?.content)
16
// → 旅行助理已接手，当前收到的新要求是：预算尽量控制在五千以内。