import { App } from '@modelcontextprotocol/ext-apps'
import { type z } from 'zod'
type AppInfo = {
name: string
version: string
}
type ConnectOptions = {
appInfo?: AppInfo
onToolInput?: (params: { arguments?: Record<string, unknown> }) => void
}
const DEFAULT_APP_INFO: AppInfo = {
name: 'calculator-widget',
version: '1.0.0',
}
let appInstance: App | null = null
let appPromise: Promise<App | null> | null = null
function hasHost() {
return typeof window !== 'undefined' && window.parent && window.parent !== window
}
export function connectMcpApp(options: ConnectOptions = {}) {
if (!hasHost()) {
return Promise.resolve(null)
}
if (!appInstance) {
appInstance = new App(options.appInfo ?? DEFAULT_APP_INFO)
}
if (options.onToolInput) {
appInstance.ontoolinput = options.onToolInput
}
if (!appPromise) {
appPromise = appInstance
.connect()
.then(() => appInstance)
.catch((error) => {
console.warn('[MCP Apps] Failed to connect to host', error)
return null
})
}
return appPromise
}
export function waitForToolInput<RenderData>(
schema?: z.ZodSchema<RenderData>,
): Promise<RenderData | null> {
if (!hasHost()) {
return Promise.resolve(null)
}
return new Promise((resolve, reject) => {
let resolved = false
void connectMcpApp({
onToolInput: (params) => {
if (resolved) return
resolved = true
const toolInput = (params?.arguments ?? {}) as RenderData
if (!schema) {
resolve(toolInput)
return
}
const parseResult = schema.safeParse(toolInput)
if (!parseResult.success) {
reject(parseResult.error)
return
}
resolve(parseResult.data)
},
})
})
}
export async function sendPromptMessage(prompt: string) {
const app = await connectMcpApp()
if (!app) {
console.warn('[MCP Apps] Host not available; prompt not sent.')
return null
}
try {
return await app.sendMessage({
role: 'user',
content: [{ type: 'text', text: prompt }],
})
} catch (error) {
console.warn('[MCP Apps] Failed to send message', error)
return null
}
}
