Newsletter reply agent

import OpenAI from 'openai';
import { Mcpmailer } from '@mcpmailer/sdk';

/* ── your provider: this block is the only part that changes ── */
const client = new OpenAI({ apiKey: process.env.OPENAI_API_KEY });

const MODEL = process.env.MODEL;
if (!MODEL) throw new Error('Set MODEL to the model name your provider expects, e.g. export MODEL=gpt-4o-mini');

/** The only provider-specific code in any of these examples. */
async function ask({ system, user, schema }: {
  system: string;
  user: string;
  schema?: object;
}) {
  const res = await client.chat.completions.create({
    model: MODEL,
    messages: [
      { role: 'system', content: system },
      { role: 'user', content: user }
    ],
    // A schema turns the answer into an object instead of prose, which is what
    // the branching examples want. Without one you get the text back.
    ...(schema
      ? { response_format: { type: 'json_schema', json_schema: { name: 'out', schema, strict: true } } }
      : {})
  });

  const text = res.choices[0].message.content ?? '';
  return schema ? JSON.parse(text) : text;
}

/* ── the agent ── */

const mm = new Mcpmailer();
const AUTHOR = 'ada@acme.com';
const ISSUE = await Bun.file('./issue-31.md').text();

const SORT = {
  type: 'object',
  properties: {
    pile: { type: 'string', enum: ['answer', 'forward', 'for-author', 'archive'] },
    reply: { type: 'string' },
    line: { type: 'string' },
    unsubscribe: { type: 'boolean' }
  },
  required: ['pile']
};

const forYou: string[] = [];
let answered = 0, forwarded = 0, archived = 0;

for (const reply of await mm.listMessages({ unreadOnly: true, limit: 200 })) {
  const [contact] = await mm.lookupContact(reply.from);

  const out = await ask({
    system: NEWSLETTER_PROMPT,
    user: `The issue they read:\n${ISSUE}

From: ${reply.from}${contact ? ' (known)' : ''}

${reply.body ?? reply.snippet}`,
    schema: SORT
  });

  // Unsubscribes outrank every other pile, immediately and without a question.
  if (out.unsubscribe) {
    await mm.addRule({ match: 'exact_email', value: reply.from, action: 'block' });
    await mm.reply(reply.id, 'Removed. You will not hear from us again.');
    await mm.archiveMessage(reply.id);
    continue;
  }

  if (out.pile === 'answer') { await mm.reply(reply.id, out.reply); answered++; }
  else if (out.pile === 'forward') {
    await mm.forward(reply.id, [AUTHOR], { body: out.line ?? '' });
    await mm.reply(reply.id, 'Passing this to Ada, who will come back to you here.');
    forwarded++;
  }
  // Left unread on purpose: a personal note deserves the author, not an assistant.
  else if (out.pile === 'for-author') forYou.push(`${reply.from}: ${out.line}`);
  else { await mm.archiveMessage(reply.id); archived++; }

  if (out.pile !== 'for-author') await mm.markUnread(reply.id, false);
}

await mm.send({
  to: [AUTHOR],
  subject: `${forYou.length} replies for you`,
  body: [
    `For you (${forYou.length})`,
    ...forYou.map((l) => `- ${l}`),
    '',
    `Answered ${answered}, forwarded ${forwarded}, archived ${archived}.`
  ].join('\n'),
  style: 'plain'
});