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

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

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

async function checkReminders() {
  const episodes = state.podcastChecklist?.episodes
  if (!Array.isArray(episodes)) return

  const todayKey = toDateKey(new Date())
  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)
    const reminderKey = toDateKey(reminderDate)

    if (todayKey >= reminderKey && todayKey <= toDateKey(publish)) {
      const sent = await sendReminderEmail(ep)
      if (sent) {
        ep.reminderSentAt = new Date().toISOString()
        changed = true
      }
    }
  }

  if (changed) queuePodcastChecklistWrite()
}

async function sendReminderEmail(ep) {
  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 publishDate = new Date(ep.datePublished + 'T12:00:00Z')
    const msLeft = publishDate.getTime() - Date.now()
    const daysLeft = Math.max(0, Math.ceil(msLeft / (1000 * 60 * 60 * 24)))

    const label = ep.episodeNumber ? `Episode ${ep.episodeNumber}` : 'Episode'
    const title = ep.title || 'Untitled'
    const series = ep.series ? ` (${ep.series})` : ''
    const daysText = daysLeft === 0 ? 'today' : daysLeft === 1 ? 'in 1 day' : `in ${daysLeft} days`
    const subject = `Reminder: "${label}: ${title}" publishes ${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">📅 Release Reminder</h2>
        <p style="font-size:1.1rem;margin-bottom:16px">
          <strong>${label}: ${title}</strong>${series}<br>
          <span style="color:#555">Publishes <strong>${ep.datePublished}</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 ${ep.reminderDays} day${ep.reminderDays === 1 ? '' : 's'} before the publish 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 episode "${title}" (${ep.datePublished})`)
    return true
  } catch (err) {
    console.error('[reminder] send exception:', err)
    return false
  }
}