flowtrack/notify.js

#!/usr/bin/env node
// Web Push for Flowtrack: VAPID keys, payload encryption (RFC 8291) and the
// daily "period soon / late" check. Dependency-free: Node's own crypto and
// SQLite. The schema is owned by app.py, which always initializes it first.
"use strict";

const crypto = require("node:crypto");
const path = require("node:path");
const Cycle = require(path.join(__dirname, "static", "cycle.js"));

const b64url = {
  encode: bytes => Buffer.from(bytes).toString("base64url"),
  decode: text => Buffer.from(text, "base64url")
};
const formatDay = number =>
  new Date(number * 86400000).toLocaleDateString("en-GB", { weekday: "short", day: "numeric", month: "short", timeZone: "UTC" });
const localIso = () => {
  const now = new Date();
  return `${now.getFullYear()}-${String(now.getMonth() + 1).padStart(2, "0")}-${String(now.getDate()).padStart(2, "0")}`;
};

function openDatabase(file) {
  const { DatabaseSync } = require("node:sqlite");
  const db = new DatabaseSync(file);
  db.exec("PRAGMA busy_timeout=10000");
  return db;
}

const setting = (db, key) => {
  const row = db.prepare("SELECT value FROM settings WHERE key = ?").get(key);
  return row ? row.value : null;
};

// Generated once and kept in the database: browsers bind each subscription
// to this key, so replacing it would silently break every subscribed device.
function vapidKeys(db) {
  if (!setting(db, "vapid_private")) {
    const { privateKey } = crypto.generateKeyPairSync("ec", { namedCurve: "prime256v1" });
    const jwk = privateKey.export({ format: "jwk" });
    const insert = db.prepare("INSERT OR IGNORE INTO settings (key, value) VALUES (?, ?)");
    insert.run("vapid_private", JSON.stringify(jwk));
    insert.run("vapid_public", b64url.encode(Buffer.concat([Buffer.from([4]), b64url.decode(jwk.x), b64url.decode(jwk.y)])));
  }
  return {
    privateKey: crypto.createPrivateKey({ key: JSON.parse(setting(db, "vapid_private")), format: "jwk" }),
    publicKey: setting(db, "vapid_public")
  };
}

function vapidAuthorization(endpoint, keys, contact, now = Date.now()) {
  const header = b64url.encode(JSON.stringify({ typ: "JWT", alg: "ES256" }));
  const claims = b64url.encode(JSON.stringify({
    aud: new URL(endpoint).origin,
    exp: Math.floor(now / 1000) + 12 * 3600,
    sub: contact
  }));
  const signature = crypto.sign("sha256", Buffer.from(`${header}.${claims}`), { key: keys.privateKey, dsaEncoding: "ieee-p1363" });
  return `vapid t=${header}.${claims}.${b64url.encode(signature)}, k=${keys.publicKey}`;
}

// RFC 8291 "aes128gcm": one record holding the whole payload.
function encrypt(payload, subscriberKey, authSecret) {
  const receiver = b64url.decode(subscriberKey);
  const auth = b64url.decode(authSecret);
  const sender = crypto.createECDH("prime256v1");
  const senderKey = sender.generateKeys();
  const shared = sender.computeSecret(receiver);
  const keyInfo = Buffer.concat([Buffer.from("WebPush: info\0"), receiver, senderKey]);
  const ikm = Buffer.from(crypto.hkdfSync("sha256", shared, auth, keyInfo, 32));
  const salt = crypto.randomBytes(16);
  const cek = Buffer.from(crypto.hkdfSync("sha256", ikm, salt, Buffer.from("Content-Encoding: aes128gcm\0"), 16));
  const nonce = Buffer.from(crypto.hkdfSync("sha256", ikm, salt, Buffer.from("Content-Encoding: nonce\0"), 12));
  const cipher = crypto.createCipheriv("aes-128-gcm", cek, nonce);
  // 0x02 marks the last (and only) record.
  const body = Buffer.concat([cipher.update(Buffer.concat([Buffer.from(payload), Buffer.from([2])])), cipher.final(), cipher.getAuthTag()]);
  const header = Buffer.alloc(21);
  salt.copy(header, 0);
  header.writeUInt32BE(4096, 16);
  header.writeUInt8(senderKey.length, 20);
  return Buffer.concat([header, senderKey, body]);
}

async function sendAll(db, contact, message) {
  const keys = vapidKeys(db);
  const subscriptions = db.prepare("SELECT endpoint, p256dh, auth FROM push_subscriptions").all();
  const result = { sent: 0, failed: 0, removed: 0, errors: [] };
  const payload = JSON.stringify(message);
  for (const subscription of subscriptions) {
    try {
      const response = await fetch(subscription.endpoint, {
        method: "POST",
        headers: {
          Authorization: vapidAuthorization(subscription.endpoint, keys, contact),
          "Content-Encoding": "aes128gcm",
          "Content-Type": "application/octet-stream",
          TTL: String(message.ttl || 86400),
          Urgency: "normal"
        },
        body: encrypt(payload, subscription.p256dh, subscription.auth),
        signal: AbortSignal.timeout(20000)
      });
      if (response.ok) {
        result.sent += 1;
      } else if (response.status === 404 || response.status === 410) {
        // The device unsubscribed or the app was removed from the home screen.
        db.prepare("DELETE FROM push_subscriptions WHERE endpoint = ?").run(subscription.endpoint);
        result.removed += 1;
      } else {
        result.failed += 1;
        result.errors.push(`${new URL(subscription.endpoint).host}: ${response.status} ${(await response.text()).slice(0, 200)}`);
      }
    } catch (error) {
      result.failed += 1;
      result.errors.push(`${new URL(subscription.endpoint).host}: ${error.message}`);
    }
  }
  return result;
}

// Which reminder, if any, is due today. Each kind is sent at most once per
// cycle (keyed on the cycle's start date), so a missed timer run or a second
// run on the same day never repeats it.
function dueReminder(summary, remindDays) {
  const { current, predictions, late, today } = summary;
  if (!current || current.onPeriod) return null;
  const cycle = Cycle.toIso(current.start);
  if (late > 0) {
    return {
      kind: "late",
      cycle,
      title: "Period is late",
      body: `It was expected on ${formatDay(today - late)}. Log it in Flowtrack when it starts.`
    };
  }
  const next = predictions[0];
  const until = next.start - today;
  if (until < 1 || until > remindDays) return null;
  return {
    kind: "soon",
    cycle,
    title: "Period expected soon",
    body: until === 1
      ? `Your period is expected tomorrow, ${formatDay(next.start)}.`
      : `Your period is expected in about ${until} days, around ${formatDay(next.start)}.`
  };
}

async function daily(db, contact, todayIso) {
  const days = {};
  for (const row of db.prepare("SELECT day, flow, symptoms FROM days").all()) {
    days[row.day] = { flow: row.flow, symptoms: JSON.parse(row.symptoms) };
  }
  const remindDays = Number(setting(db, "remind_days")) || 2;
  const reminder = dueReminder(Cycle.summarize(days, todayIso), remindDays);
  if (!reminder) return { due: null };
  if (db.prepare("SELECT 1 FROM notifications_sent WHERE kind = ? AND cycle = ?").get(reminder.kind, reminder.cycle)) {
    return { due: reminder.kind, alreadySent: true };
  }
  const result = await sendAll(db, contact, { title: reminder.title, body: reminder.body, tag: reminder.kind, url: "/" });
  // Only mark it sent once a device got it, so subscribing later the same
  // day still delivers it on the next run.
  if (result.sent) {
    db.prepare("INSERT OR IGNORE INTO notifications_sent (kind, cycle, sent_at) VALUES (?, ?, ?)")
      .run(reminder.kind, reminder.cycle, new Date().toISOString());
  }
  return { due: reminder.kind, ...result };
}

function parseArgs(argv) {
  const [command, ...rest] = argv;
  const options = { command };
  for (let index = 0; index < rest.length; index += 2) {
    if (!rest[index].startsWith("--")) throw new Error(`Unexpected argument ${rest[index]}`);
    options[rest[index].slice(2)] = rest[index + 1];
  }
  return options;
}

async function main(argv) {
  const options = parseArgs(argv);
  if (!options.database) throw new Error("--database is required");
  const db = openDatabase(options.database);
  try {
    if (options.command === "init") return { publicKey: vapidKeys(db).publicKey };
    if (!options.contact) throw new Error("--contact is required");
    if (options.command === "test") {
      return await sendAll(db, options.contact, {
        title: "Flowtrack",
        body: "Test notification: reminders will arrive like this.",
        tag: "test",
        url: "/",
        ttl: 600
      });
    }
    if (options.command === "daily") return await daily(db, options.contact, options.today || localIso());
    throw new Error("usage: flowtrack-notify init|test|daily --database DB [--contact URL] [--today YYYY-MM-DD]");
  } finally {
    db.close();
  }
}

if (require.main === module) {
  main(process.argv.slice(2)).then(
    result => { console.log(JSON.stringify(result)); },
    error => { console.error(error.message); process.exitCode = 1; }
  );
}

module.exports = { b64url, encrypt, vapidKeys, vapidAuthorization, dueReminder, main };