import * as functions from 'firebase-functions'
import * as admin from 'firebase-admin'

/**
 * Firestore trigger that notifies partners when a game session is created or completed.
 * 
 * Path: couples/{coupleId}/sessions/{sessionId}
 * Condition: onWrite (create, update, delete)
 */
export const onGameSessionUpdate = functions.firestore
  .document('couples/{coupleId}/sessions/{sessionId}')
  .onWrite(async (change, context) => {
    const { coupleId, sessionId } = context.params as { coupleId: string; sessionId: string }

    // The per-couple active-session lock lives at sessions/_active — it is a pointer, not a
    // game session, so it must never produce a partner notification.
    if (sessionId === '_active') return

    const db = admin.firestore()
    const messaging = admin.messaging()

    // Get the session document
    const sessionDoc = await db.collection('couples').doc(coupleId).collection('sessions').doc(sessionId).get()
    const session = sessionDoc.data()
    if (!session) {
      console.log(`[onGameSessionUpdate] session ${sessionId} not found, skipping`)
      return
    }

    // Get couple info
    const coupleDoc = await db.collection('couples').doc(coupleId).get()
    if (!coupleDoc.exists) {
      console.warn(`[onGameSessionUpdate] couple ${coupleId} not found`)
      return
    }

    const coupleData = coupleDoc.data() ?? {}
    const userIds = (coupleData.userIds ?? []) as string[]
    if (userIds.length !== 2) {
      console.warn(`[onGameSessionUpdate] invalid couple ${coupleId}: expected 2 users, got ${userIds.length}`)
      return
    }

    const partnerA = userIds[0]
    const partnerB = userIds[1]

    // Get user display names for notifications
    const userA = await db.collection('users').doc(partnerA).get()
    const userB = await db.collection('users').doc(partnerB).get()
    const partnerAName = userA.data()?.displayName ?? 'Partner A'
    const partnerBName = userB.data()?.displayName ?? 'Partner B'
    const avatarA = userA.data()?.photoUrl as string | undefined
    const avatarB = userB.data()?.photoUrl as string | undefined

    const currentData = change.after.data() ?? {}
    if (!change.after.exists) return // deletion — nothing to notify
    const status = currentData.status as string | undefined
    const sessionRef = db.collection('couples').doc(coupleId).collection('sessions').doc(sessionId)

    // Detect start/finish from the session's CURRENT state + a one-time flag, NOT from the
    // change.before→change.after status diff. The atomic session start (F-RACE-001) writes the
    // session doc AND the sessions/_active pointer in a single transaction; transactional writes
    // can be delivered to onWrite with change.before === change.after (the "Snapshot has no
    // readTime" path), which made the inactive→active edge unreliable and intermittently dropped
    // the partner_started_game push. Claiming a flag inside a transaction makes each notification
    // fire exactly once no matter how the event is delivered (and prevents double-sends).

    // ── New session started ──────────────────────────────────────────────
    if (status === 'active' && !currentData.startNotifiedAt) {
      const claimed = await db.runTransaction(async (tx) => {
        const fresh = await tx.get(sessionRef)
        const d = fresh.data()
        if (!fresh.exists || !d || d.status !== 'active' || d.startNotifiedAt) return false
        tx.update(sessionRef, { startNotifiedAt: admin.firestore.FieldValue.serverTimestamp() })
        return true
      })
      if (claimed) {
        const startedBy = currentData.startedByUserId
        const gameType = currentData.gameType ?? 'wheel'
        const recipientId = startedBy === partnerA ? partnerB : partnerA
        const starterName = startedBy === partnerA ? partnerAName : partnerBName
        const starterAvatar = startedBy === partnerA ? avatarA : avatarB
        await notifyPartner(
          db, messaging, recipientId, starterName, gameType,
          'partner_started_game', `${starterName} has started a game. Tap to join!`, coupleId,
          starterAvatar, sessionId
        )
      }
      return
    }

    // ── Session completed (reveal ready for both) ────────────────────────
    if (status === 'completed' && !currentData.finishNotifiedAt) {
      const claimed = await db.runTransaction(async (tx) => {
        const fresh = await tx.get(sessionRef)
        const d = fresh.data()
        if (!fresh.exists || !d || d.status !== 'completed' || d.finishNotifiedAt) return false
        tx.update(sessionRef, { finishNotifiedAt: admin.firestore.FieldValue.serverTimestamp() })
        return true
      })
      if (claimed) {
        const gt = currentData.gameType ?? 'wheel'
        // Notify BOTH partners, each naming the OTHER.
        await notifyPartner(
          db, messaging, partnerA, partnerBName, gt,
          'partner_finished_game', `${partnerBName} finished — tap to see your results!`, coupleId,
          avatarB, sessionId
        )
        await notifyPartner(
          db, messaging, partnerB, partnerAName, gt,
          'partner_finished_game', `${partnerAName} finished — tap to see your results!`, coupleId,
          avatarA, sessionId
        )
      }
      return
    }
  })

/**
 * Send notification to partner via FCM and write to notification_queue.
 */
async function notifyPartner(
  db: admin.firestore.Firestore,
  messaging: admin.messaging.Messaging,
  partnerId: string,
  partnerName: string,
  gameType: string,
  notificationType: string,
  body: string,
  coupleId: string,
  senderAvatarUrl?: string,
  sessionId?: string
): Promise<void> {
  const title =
    notificationType === 'partner_finished_game'
      ? `${partnerName} finished the game`
      : `${partnerName} is playing`
  const notificationPayload = {
    type: notificationType,
    title,
    body: body,
  }

  // Write an in-app notification record for the partner
  await db
    .collection('users')
    .doc(partnerId)
    .collection('notification_queue')
    .add({
      ...notificationPayload,
      read: false,
      createdAt: admin.firestore.FieldValue.serverTimestamp(),
    })

  // Collect the partner's FCM tokens
  const tokens: string[] = []
  const partnerUserDoc = await db.collection('users').doc(partnerId).get()
  
  if (partnerUserDoc.exists) {
    const legacyToken = partnerUserDoc.data()?.fcmToken
    if (typeof legacyToken === 'string' && legacyToken.length > 0) {
      tokens.push(legacyToken)
    }
  }

  const tokenSnapshot = await db
    .collection('users')
    .doc(partnerId)
    .collection('fcmTokens')
    .get()
  tokenSnapshot.docs.forEach((doc) => {
    const t = doc.data()?.token
    if (typeof t === 'string' && t.length > 0 && !tokens.includes(t)) {
      tokens.push(t)
    }
  })

  if (tokens.length === 0) {
    console.log(`[notifyPartner] no FCM tokens for ${partnerId}`)
    return
  }

  const fcmMessage: admin.messaging.Message = {
    token: tokens[0],
    notification: {
      title: notificationPayload.title,
      body: notificationPayload.body,
    },
    // Put backgrounded notifications on the Games channel instead of the FCM fallback channel,
    // so importance/sound and the per-category toggle apply. E-OBS.
    android: { notification: { channelId: 'game_activity' } },
    data: {
      type: notificationPayload.type,
      couple_id: coupleId,
      game_type: gameType,
      // Lets the client deep link a results-ready push to the per-session results/replay screen
      // (a completed session isn't returned by getActiveSession). E-003 results-ready.
      ...(sessionId ? { game_session_id: sessionId } : {}),
      ...(senderAvatarUrl && senderAvatarUrl.length > 0
        ? { sender_avatar_url: senderAvatarUrl }
        : {}),
    },
  }

  const sendResults = await Promise.allSettled(
    tokens.map((token) => messaging.send({ ...fcmMessage, token }))
  )

  const failures: string[] = []
  sendResults.forEach((result, index) => {
    if (result.status === 'rejected') {
      failures.push(`${tokens[index]}: ${String(result.reason)}`)
    }
  })

  if (failures.length > 0) {
    console.error(`[notifyPartner] some notifications failed:`, failures)
  } else {
    console.log(`[notifyPartner] notified ${partnerId} (${notificationType})`)
  }
}