Tool loop in TypeScript

// loop.ts
import OpenAI from 'openai'
import type { ChatCompletionMessageParam, ChatCompletionTool } from 'openai/resources/chat/completions'
 
const client = new OpenAI({ baseURL: 'https://app.syntic.ai/v1', apiKey: process.env.SYNTIC_API_KEY })
 
// --- Your functions ---------------------------------------------------------
type Book = { title: string; copies: number; onLoan: number; dueBack: string | null }
const LIBRARY: Record<string, Book> = {
  '978-0141439518': { title: 'Pride and Prejudice', copies: 3, onLoan: 3, dueBack: '2026-10-19' },
  '978-0007119318': { title: 'The Hobbit', copies: 2, onLoan: 1, dueBack: null },
}
 
const functions: Record<string, (args: any) => unknown> = {
  find_book: ({ query }: { query: string }) => ({
    results: Object.entries(LIBRARY)
      .filter(([, b]) => b.title.toLowerCase().includes(String(query).toLowerCase()))
      .map(([isbn, b]) => ({ isbn, title: b.title })),
  }),
  availability: ({ isbn }: { isbn: string }) => {
    const b = LIBRARY[isbn]
    if (!b) return { error: `no book with ISBN ${isbn}` }
    const free = b.copies - b.onLoan
    return { available: free, next_due_back: free ? null : b.dueBack }
  },
}
 
// --- How they are described to the model ----------------------------------
const tools: ChatCompletionTool[] = [
  {
    type: 'function',
    function: {
      name: 'find_book',
      description: 'Search the catalogue by title words. Returns ISBNs.',
      parameters: { type: 'object', properties: { query: { type: 'string' } }, required: ['query'] },
    },
  },
  {
    type: 'function',
    function: {
      name: 'availability',
      description: 'Copies available now for an ISBN, and when the next one is due back.',
      parameters: { type: 'object', properties: { isbn: { type: 'string' } }, required: ['isbn'] },
    },
  },
]
 
// --- The loop ----------------------------------------------------------------
export async function run(question: string, maxRounds = 8): Promise<string> {
  const messages: ChatCompletionMessageParam[] = [
    { role: 'system', content: `You help members of a town library. Today is ${new Date().toISOString().slice(0, 10)}. Use the tools; never guess availability.` },
    { role: 'user', content: question },
  ]
  for (let round = 0; round < maxRounds; round++) {
    const reply = await client.chat.completions.create({
      model: 'Amara S1.2', stream: false, max_tokens: 800, tools, messages,
    })
    const msg = reply.choices[0].message
    if (!msg.tool_calls?.length) return msg.content ?? ''
    messages.push(msg) // the assistant turn, unchanged
    for (const call of msg.tool_calls) {
      let result: unknown
      try {
        const fn = functions[call.function.name]
        if (!fn) throw new Error(`unknown tool ${call.function.name}`)
        result = fn(JSON.parse(call.function.arguments || '{}'))
      } catch (err) {
        result = { error: (err as Error).message }
      }
      messages.push({ role: 'tool', tool_call_id: call.id, content: JSON.stringify(result) })
    }
  }
  return "Sorry, I couldn't finish that request."
}
 
console.log(await run('Can I borrow Pride and Prejudice today? If not, when?'))