// Daily "don't forget to read" reminders, sent via ntfy.sh (https://ntfy.sh) —
// a free pub/sub push service: POST a message to a topic URL, anyone
// subscribed to that topic (via the ntfy app or a browser) gets notified.
// No API keys or push-subscription plumbing needed.
import { getUsersWithRemindersEnabled, setLastReminderDate, getReadingProgress } from './db.js';

// A reminder still goes out if the server was briefly down (or restarting) at the
// exact minute — as long as it's within this window after the chosen time.
const GRACE_MINUTES = 180;
const SEND_TIMEOUT_MS = 10_000;

export function isValidTimeZone(tz) {
  if (!tz) return false;
  try { new Intl.DateTimeFormat('en-US', { timeZone: tz }); return true; } catch { return false; }
}

// The calendar date ("YYYY-MM-DD") and minutes-since-midnight in a timezone; the
// server's own timezone when none (or an invalid one) is saved.
export function zonedNow(date = new Date(), tz) {
  const timeZone = isValidTimeZone(tz) ? tz : undefined;
  const parts = Object.fromEntries(
    new Intl.DateTimeFormat('en-CA', {
      timeZone, hourCycle: 'h23', year: 'numeric', month: '2-digit', day: '2-digit', hour: '2-digit', minute: '2-digit',
    }).formatToParts(date).map((p) => [p.type, p.value]),
  );
  return { date: `${parts.year}-${parts.month}-${parts.day}`, minutes: Number(parts.hour) * 60 + Number(parts.minute) };
}

// Is this user's reminder due right now (and not already sent today)?
export function isDue(user, now = new Date()) {
  const match = /^([01]\d|2[0-3]):([0-5]\d)$/.exec(user.reminderTime ?? '');
  if (!match) return false;
  const target = Number(match[1]) * 60 + Number(match[2]);
  const local = zonedNow(now, user.reminderTz);
  if (user.lastReminderDate === local.date) return false;
  return local.minutes >= target && local.minutes < target + GRACE_MINUTES;
}

// POSTs one notification to the user's ntfy topic. Throws with a readable message on failure.
export async function sendNtfy(user, { title, body, tags = 'open_book' }) {
  const base = (user.ntfyUrl || 'https://ntfy.sh').replace(/\/+$/, '');
  const url = `${base}/${encodeURIComponent(user.ntfyTopic)}`;
  const headers = { Title: title, Tags: tags };
  if (process.env.APP_URL) headers.Click = process.env.APP_URL; // tapping the notification opens the app
  let res;
  try {
    res = await fetch(url, { method: 'POST', headers, body, signal: AbortSignal.timeout(SEND_TIMEOUT_MS) });
  } catch (err) {
    throw new Error(err.name === 'TimeoutError' ? `Timed out reaching ${base}` : `Could not reach ${base} (${err.cause?.code ?? err.message})`);
  }
  if (!res.ok) throw new Error(`ntfy responded ${res.status}`);
}

export function reminderBody(progress) {
  const active = (Array.isArray(progress?.progress) ? progress.progress : []).filter((p) => !p.completedAt).length;
  return active > 1 ? `Don't forget today's reading! You have ${active} plans in progress.` : "Don't forget today's reading!";
}

/** Sends a one-off notification so the user can confirm their topic/server work. */
export function sendTestReminder(user) {
  return sendNtfy(user, { title: 'Reading reminders are working', body: 'This is a test from Bible Study Project. Your daily reminder will arrive like this.', tags: 'white_check_mark' });
}

export async function checkReminders(now = new Date()) {
  for (const user of getUsersWithRemindersEnabled().filter((u) => isDue(u, now))) {
    try {
      const progress = getReadingProgress(user.id);
      const hasActivePlan = Array.isArray(progress?.progress) && progress.progress.some((p) => !p.completedAt);
      if (!hasActivePlan) continue; // nothing to nudge them about
      await sendNtfy(user, { title: 'Reading Plan Reminder', body: reminderBody(progress) });
      setLastReminderDate(user.id, zonedNow(now, user.reminderTz).date);
    } catch (err) {
      console.error(`Reading reminder failed for user ${user.id}:`, err.message);
    }
  }
}

/** Checks once a minute whether any user's reminder time has arrived. */
export function startReminderScheduler() {
  setInterval(() => {
    checkReminders().catch((err) => console.error('Reminder scheduler error:', err));
  }, 60 * 1000);
}