What is RAG? Let a café chatbot read the right policy section

# Mộc café policies

## Opening hours and holidays
Mộc is open from 6:30 a.m. to 10 p.m. every day. For Tet, the Vietnamese Lunar New Year, the shop closes from the 28th day of the last lunar month through the 3rd day of the new year, and announces it on the home page a week ahead. On other public holidays the shop stays open, but home deliveries may be slower.

## Ordering and payment
Customers order on the website or by messaging the shop. The shop accepts bank transfer, e-wallets and cash on delivery. A bank-transfer order is made once the shop sees the money arrive in its account, which usually takes under two minutes.

## Delivery fee
Mộc delivers within 5 km for a fee of 15,000 đồng. Orders of 150,000 đồng or more get free delivery. Beyond 5 km the shop does not deliver, but customers can book a ride-hailing driver to pick the order up.

## Cancelling an order
Customers can cancel for free while the order is still in the "received" state. Once it moves to "being made", the shop cannot cancel because the ingredients are already used. A valid cancellation of a bank-transfer order is refunded in full, as described in the Refunds section.

## Replacing a wrong or badly made item
If the shop delivers the wrong item or makes it differently from the order, the customer should message within 30 minutes of receiving it, with a photo of what was delivered. The shop will remake the correct item and deliver it again for free, or refund the customer if they would rather not wait. An item that is more than half drunk cannot be replaced.

## Refunds
The shop refunds within three working days, to the same payment method the customer used. Cash orders are refunded by bank transfer to the account the customer provides. The refund covers the price of the item; the delivery fee is only refunded when the mistake was the shop's.

## Allergies and ingredients
Salt coffee and bac xiu contain milk. The egg banh mi contains gluten and egg. Customers with allergies should write a note in the order, and the shop will say whether it can accommodate them. The shop uses shared equipment, so it cannot completely guarantee that ingredients never mix.

## Promotions and discount codes
Each order can use one discount code. A code cannot be combined with the loyalty program in the same order. An expired code is not extended, and an order that has already been paid cannot have a code added.

## Loyalty points
Every 10,000 đồng earns one point. One hundred points can be exchanged for any drink priced up to 35,000 đồng. Points are valid for twelve months from the day they are earned. An order that is refunded loses the points it earned.

## Bulk orders
Orders of 20 cups or more must be placed one day ahead, and the shop will give a separate quote. Bulk orders do not get discount codes. The shop confirms by message before 5 p.m. the day before.

## Gift vouchers
Vouchers start at 100,000 đồng and are valid for six months. A voucher cannot be exchanged for cash and is not refundable after it is sold. One order can use several vouchers.

## Bring your own cup
Customers who bring their own cup get 3,000 đồng off each drink. The cup must be clean and hold at least 350 ml. The shop may refuse a cup that smells or is cracked.

## Customer privacy
The shop uses phone numbers and addresses only for delivery and order support. The shop does not sell or share customer information with third parties. A customer who wants their information deleted can message the shop.

## Contact
Customers message the shop during opening hours. In urgent cases, such as an allergic reaction after drinking, call the shop's hotline immediately.

import { readFileSync } from "node:fs";

export type Section = { title: string; body: string };

// Splits a Markdown document into sections: each "## ..." heading opens a new one.
export function splitSections(markdown: string): Section[] {
  return markdown
    .split(/^## /m)
    .slice(1) // whatever comes before the first "## " is just the document's overall title
    .map((block) => {
      const [title, ...lines] = block.split("\n");
      return { title: title.trim(), body: lines.join("\n").trim() };
    });
}

export function readPolicy(): Section[] {
  return splitSections(readFileSync(new URL("../policy.md", import.meta.url), "utf8"));
}

import type { Section } from "./split-sections.ts";

// Very common words that don't help tell one section from another.
const STOP_WORDS = new Set(["the", "a", "an", "and", "or", "of", "to", "is", "are", "be", "it", "for", "in", "on", "if", "i", "my", "me", "you", "your", "can", "do", "does", "how", "what", "when", "will", "with", "at", "by", "that", "this", "than", "so", "get", "got", "from", "has", "have", "was", "were", "not", "no", "any", "much", "many", "long", "shop", "moc", "cafe"]);

export function splitWords(text: string): string[] {
  return (text.toLowerCase().match(/\p{L}+|\d+/gu) ?? []).filter((word) => !STOP_WORDS.has(word));
}

export type SearchResult = { section: Section; score: number; matched: string[] };

// Keyword scoring: every word of the question that appears in a section earns points,
// and the rarer the word (the fewer sections contain it) the more points. The title counts along with the body.
export function findSections(question: string, sections: Section[], limit = 2): SearchResult[] {
  const wordsOfSection = sections.map((s) => new Set(splitWords(`${s.title} ${s.body}`)));
  const questionWords = [...new Set(splitWords(question))];
  const idf = (word: string) => Math.log(1 + sections.length / (1 + wordsOfSection.filter((set) => set.has(word)).length));

  return sections
    .map((section, i) => {
      const matched = questionWords.filter((word) => wordsOfSection[i].has(word));
      return { section, matched, score: Number(matched.reduce((total, word) => total + idf(word), 0).toFixed(2)) };
    })
    .filter((result) => result.score > 0)
    .sort((a, b) => b.score - a.score)
    .slice(0, limit);
}

// Prints the sections the search picks for each question, so you can see whether it's right before calling the model.
import { findSections } from "./find-sections.ts";
import { readPolicy } from "./split-sections.ts";

const SECTIONS = readPolicy();
console.log(`The document has ${SECTIONS.length} sections: ${SECTIONS.map((s) => s.title).join(" | ")}\n`);

const QUESTIONS = [
  "From what amount is delivery free?",
  "If the shop delivers the wrong item, how long until I get a refund?",
  "I cancelled my bank transfer order, how long until the money is back?",
  "My coffee was made wrong and I want the shop to compensate me",
  "I'm allergic to milk, what can I drink?",
];

for (const question of QUESTIONS) {
  console.log(`Customer: ${question}`);
  const results = findSections(question, SECTIONS);
  if (results.length === 0) console.log("  (no section matches)");
  for (const { section, score, matched } of results) console.log(`  ${score.toFixed(2)}  ${section.title}   [matched: ${matched.join(", ")}]`);
  console.log();
}

The document has 14 sections: Opening hours and holidays | Ordering and payment | Delivery fee | Cancelling an order | Replacing a wrong or badly made item | Refunds | Allergies and ingredients | Promotions and discount codes | Loyalty points | Bulk orders | Gift vouchers | Bring your own cup | Customer privacy | Contact

Customer: From what amount is delivery free?
  2.84  Delivery fee   [matched: delivery, free]
  1.50  Cancelling an order   [matched: free]

Customer: If the shop delivers the wrong item, how long until I get a refund?
  7.28  Replacing a wrong or badly made item   [matched: delivers, wrong, item, refund]
  3.47  Refunds   [matched: item, refund]

Customer: I cancelled my bank transfer order, how long until the money is back?
  5.96  Ordering and payment   [matched: bank, transfer, order, money]
  3.88  Cancelling an order   [matched: bank, transfer, order]

Customer: My coffee was made wrong and I want the shop to compensate me
  3.58  Replacing a wrong or badly made item   [matched: made, wrong]
  2.08  Allergies and ingredients   [matched: coffee]

Customer: I'm allergic to milk, what can I drink?
  2.08  Allergies and ingredients   [matched: milk]
  2.08  Contact   [matched: allergic]

import Anthropic from "@anthropic-ai/sdk";

import type { Section } from "./split-sections.ts";
import { splitWords } from "./find-sections.ts";

export const MODEL = "claude-opus-5-5";

export const SYSTEM = `You are a customer service assistant for Mộc café. Answer briefly and in a friendly tone, in English.
Answer only from the sections inside the <documents> tag. At the end of your answer, give the name of the section you used in square brackets.
If the sections don't contain the information needed, say the shop doesn't have that information yet. Don't guess.`;

// Puts the sections that were found into the customer's message. Each section has a name so the model can cite it.
export function buildPrompt(question: string, sections: Section[]): string {
  const documents = sections.map((s) => `<section name="${s.title}">\n${s.body}\n</section>`).join("\n");
  return `<documents>\n${documents}\n</documents>\n\nCustomer's question: ${question}`;
}

export function hasKey(): boolean {
  return Boolean(process.env.ANTHROPIC_API_KEY) && process.env.MOC_OFFLINE !== "1";
}

export async function answer(question: string, sections: Section[]): Promise<string> {
  if (!hasKey()) return offlineModel(question, sections);
  const client = new Anthropic();
  const response = await client.messages.create({
    model: MODEL,
    max_tokens: 16000,
    output_config: { effort: "low" },
    system: SYSTEM,
    messages: [{ role: "user", content: buildPrompt(question, sections) }],
  });
  return response.content.filter((b) => b.type === "text").map((b) => b.text).join("");
}

// A simulated model, not a real one: picks the sentences in the sections that share the most words with the question
// and reads them back word for word. It can only use words that are in the sections, so it shows clearly what the model "sees".
function offlineModel(question: string, sections: Section[]): string {
  const questionWords = new Set(splitWords(question));
  const sentences = sections.flatMap((s) =>
    s.body.split(/(?<=\.)\s+/).map((sentence) => ({ sentence, title: s.title, matches: splitWords(sentence).filter((word) => questionWords.has(word)).length })),
  );
  const best = sentences.filter((s) => s.matches >= 2).sort((a, b) => b.matches - a.matches).slice(0, 2);
  if (best.length === 0) return "Sorry, Mộc doesn't have that information yet.";
  return `${best.map((s) => s.sentence).join(" ")} [${[...new Set(best.map((s) => s.title))].join("; ")}]`;
}

// The full RAG flow: find sections, build the prompt, ask the model. Compared with sending the whole document on every call.
import { answer, buildPrompt } from "./answer.ts";
import { findSections } from "./find-sections.ts";
import { readPolicy } from "./split-sections.ts";

const SECTIONS = readPolicy();
const QUESTIONS = process.argv.slice(2).length ? [process.argv.slice(2).join(" ")] : [
  "From what amount is delivery free?",
  "I cancelled my bank transfer order, how long until the money is back?",
];

const charsForWholeDocument = buildPrompt("", SECTIONS).length;
for (const question of QUESTIONS) {
  const chosen = findSections(question, SECTIONS).map((result) => result.section);
  console.log(`Customer: ${question}`);
  console.log(`  sent: ${chosen.map((s) => s.title).join(" + ")}`);
  console.log(`  ${buildPrompt(question, chosen).length} characters (sending the whole document: ${charsForWholeDocument} characters)`);
  console.log(`Mộc: ${await answer(question, chosen)}\n`);
}

Customer: From what amount is delivery free?
  sent: Delivery fee + Cancelling an order
  657 characters (sending the whole document: 4011 characters)
Mộc: Orders of 150,000 đồng or more get free delivery. [Delivery fee]

Customer: I cancelled my bank transfer order, how long until the money is back?
  sent: Ordering and payment + Cancelling an order
  735 characters (sending the whole document: 4011 characters)
Mộc: A bank-transfer order is made once the shop sees the money arrive in its account, which usually takes under two minutes. A valid cancellation of a bank-transfer order is refunded in full, as described in the Refunds section. [Ordering and payment; Cancelling an order]

Customer: My coffee was made wrong and I want the shop to compensate me
  sent: Replacing a wrong or badly made item + Allergies and ingredients
  869 characters (sending the whole document: 4011 characters)
Mộc: Sorry, Mộc doesn't have that information yet.