import { Resend } from 'resend'
import { state } from './state.js'
import { queuePodcastChecklistWrite, queueCalendarEventsWrite, queueStudyUsersWrite } from './data.js'
import { DEFAULT_RESEND_FROM, DEFAULT_RESEND_TO } from './config.js'
import { celebrationDateForYear } from './helpers.js'

function toDateKey(date) {
  return date.toISOString().slice(0, 10)
}

export function startReminderScheduler() {
  checkReminders()
  setInterval(checkReminders, 60 * 60 * 1000)
}

async function checkReminders() {
  const todayKey = toDateKey(new Date())

  // Episodes
  const episodes = state.podcastChecklist?.episodes
  if (Array.isArray(episodes)) {
    let changed = false
    for (const ep of episodes) {
      if (!ep.datePublished || !(ep.reminderDays > 0) || ep.reminderSentAt) continue
      const publish = new Date(ep.datePublished + 'T12:00:00Z')
      if (isNaN(publish.getTime())) continue
      const reminderDate = new Date(publish)
      reminderDate.setUTCDate(reminderDate.getUTCDate() - ep.reminderDays)
      if (todayKey === toDateKey(reminderDate)) {
        const sent = await sendReminderEmail({
          label: ep.episodeNumber ? `Episode ${ep.episodeNumber}` : 'Episode',
          title: ep.title || 'Untitled',
          series: ep.series,
          date: ep.datePublished,
          reminderDays: ep.reminderDays,
          type: 'episode',
        })
        if (sent) { ep.reminderSentAt = new Date().toISOString(); changed = true }
      }
    }
    if (changed) queuePodcastChecklistWrite()
  }

  // Calendar events
  const events = state.calendarEvents
  if (Array.isArray(events)) {
    let changed = false
    for (const ev of events) {
      if (!ev.date || !(ev.reminderDays > 0) || ev.reminderSentAt) continue
      const publish = new Date(ev.date + 'T12:00:00Z')
      if (isNaN(publish.getTime())) continue
      const reminderDate = new Date(publish)
      reminderDate.setUTCDate(reminderDate.getUTCDate() - ev.reminderDays)
      if (todayKey === toDateKey(reminderDate)) {
        const sent = await sendReminderEmail({
          label: ev.type.charAt(0).toUpperCase() + ev.type.slice(1),
          title: ev.title,
          series: null,
          date: ev.date,
          reminderDays: ev.reminderDays,
          type: ev.type,
        })
        if (sent) { ev.reminderSentAt = new Date().toISOString(); changed = true }
      }
    }
    if (changed) queueCalendarEventsWrite()
  }

  // Birthdays — fire on the student's celebration day, once per calendar year
  const users = state.studyUsers ?? []
  let birthdayUsersChanged = false
  const todayYear = new Date().getUTCFullYear()
  const birthdayKids = []

  for (const user of users) {
    if (!user.birthdayMonth || !user.birthdayDay) continue
    const celebDate = celebrationDateForYear(user, todayYear)
    if (!celebDate) continue
    if (todayKey !== celebDate) continue
    if (user.birthdayEmailSentYear === todayYear) continue
    birthdayKids.push({ name: user.displayName || user.username, birthdayMonth: user.birthdayMonth, birthdayDay: user.birthdayDay, hasAlternate: Boolean(user.birthdayAlternateMonth) })
    user.birthdayEmailSentYear = todayYear
    birthdayUsersChanged = true
  }

  if (birthdayKids.length > 0) {
    await sendBirthdayNotificationEmail(birthdayKids)
    if (birthdayUsersChanged) queueStudyUsersWrite()
  }
}

async function sendBirthdayNotificationEmail(kids) {
  if (!process.env.RESEND_API_KEY) return
  try {
    const resend = new Resend(process.env.RESEND_API_KEY)
    const from = process.env.RESEND_FROM ?? DEFAULT_RESEND_FROM
    const to = process.env.RESEND_TO ?? DEFAULT_RESEND_TO
    const MONTHS = ['January','February','March','April','May','June','July','August','September','October','November','December']

    const lines = kids.map(k => {
      const bdayStr = `${MONTHS[k.birthdayMonth - 1]} ${k.birthdayDay}`
      const alt = k.hasAlternate ? ' (celebrating on alternate date)' : ''
      return `<li style="margin-bottom:6px"><strong>${k.name}</strong> — birthday: ${bdayStr}${alt}</li>`
    }).join('')

    const subject = kids.length === 1
      ? `🎂 Birthday today: ${kids[0].name}`
      : `🎂 ${kids.length} student birthdays today`

    const html = `
      <div style="font-family:system-ui,sans-serif;max-width:540px;margin:0 auto;color:#222">
        <h2 style="color:#c8860a;margin-bottom:4px">🎂 Student Birthday Celebration</h2>
        <p>The following student${kids.length > 1 ? 's have' : ' has'} a birthday celebration today — consider sending a special message or acknowledging them in your study community!</p>
        <ul style="padding-left:1.2em">${lines}</ul>
        <hr style="border:none;border-top:1px solid #eee;margin:16px 0">
        <p style="color:#777;font-size:0.85rem">To edit birthday info, open the Study Users panel in your admin settings.</p>
      </div>
    `
    const { error } = await resend.emails.send({ from, to, subject, html })
    if (error) console.error('[birthday] send error:', error)
    else console.log(`[birthday] notification sent for ${kids.map(k => k.name).join(', ')}`)
  } catch (err) {
    console.error('[birthday] send exception:', err)
  }
}

const TYPE_ICONS = { episode: '📅', general: '📌', recording: '🎙️', social: '📱', task: '✅' }

async function sendReminderEmail({ label, title, series, date, reminderDays, type }) {
  if (!process.env.RESEND_API_KEY) return false

  try {
    const resend = new Resend(process.env.RESEND_API_KEY)
    const from = process.env.RESEND_FROM ?? DEFAULT_RESEND_FROM
    const to = process.env.RESEND_TO ?? DEFAULT_RESEND_TO

    const eventDate = new Date(date + 'T12:00:00Z')
    const msLeft = eventDate.getTime() - Date.now()
    const daysLeft = Math.max(0, Math.ceil(msLeft / (1000 * 60 * 60 * 24)))

    const seriesStr = series ? ` (${series})` : ''
    const daysText = daysLeft === 0 ? 'today' : daysLeft === 1 ? 'in 1 day' : `in ${daysLeft} days`
    const icon = TYPE_ICONS[type] ?? '📅'
    const subject = `Reminder: ${label}: ${title} — ${daysText}`

    const html = `
      <div style="font-family:system-ui,sans-serif;max-width:540px;margin:0 auto;color:#222">
        <h2 style="color:#c8860a;margin-bottom:4px">${icon} Calendar Reminder</h2>
        <p style="font-size:1.1rem;margin-bottom:16px">
          <strong>${label}: ${title}</strong>${seriesStr}<br>
          <span style="color:#555">Scheduled for <strong>${date}</strong> — ${daysText}</span>
        </p>
        <hr style="border:none;border-top:1px solid #eee;margin:16px 0">
        <p style="color:#777;font-size:0.85rem">
          This reminder was set ${reminderDays} day${reminderDays === 1 ? '' : 's'} before the date.
          To change or remove it, open the Calendar in your admin panel.
        </p>
      </div>
    `

    const { error } = await resend.emails.send({ from, to, subject, html })
    if (error) { console.error('[reminder] send error:', error); return false }
    console.log(`[reminder] sent for "${title}" (${date})`)
    return true
  } catch (err) {
    console.error('[reminder] send exception:', err)
    return false
  }
}