const path = require('path')
const fs = require('fs-extra')
const MessageModel = require('../models/MessageModel')

const ALLOWED_SELF_DESTRUCT_SECONDS = [10, 30, 60, 300, 3600]
const DELETE_WINDOW_MS = 24 * 60 * 60 * 1000

function parseSelfDestructSeconds(raw) {
  if (raw == null || raw === '' || raw === '0' || raw === 0) return null
  const n = parseInt(String(raw), 10)
  if (!Number.isFinite(n) || !ALLOWED_SELF_DESTRUCT_SECONDS.includes(n)) return null
  return n
}

function buildExpiresAt(seconds) {
  if (!seconds) return undefined
  return new Date(Date.now() + seconds * 1000)
}

function activeMessageFilter(baseFilter) {
  return {
    $and: [
      baseFilter,
      {
        $or: [
          {
            selfDestructSeconds: { $exists: true, $ne: null },
            selfDestructStartedAt: { $exists: false }
          },
          {
            selfDestructSeconds: { $exists: true, $ne: null },
            selfDestructStartedAt: { $exists: true, $ne: null },
            $or: [
              { expiresAt: { $exists: false } },
              { expiresAt: null },
              { expiresAt: { $gt: new Date() } }
            ]
          },
          {
            $and: [
              {
                $or: [
                  { selfDestructSeconds: { $exists: false } },
                  { selfDestructSeconds: null }
                ]
              },
              {
                $or: [
                  { expiresAt: { $exists: false } },
                  { expiresAt: null },
                  { expiresAt: { $gt: new Date() } }
                ]
              }
            ]
          }
        ]
      }
    ]
  }
}

function isWithinDeleteWindow(createdAt) {
  if (!createdAt) return false
  return Date.now() - new Date(createdAt).getTime() <= DELETE_WINDOW_MS
}

async function removeMessageFiles(messages) {
  for (const msg of messages) {
    if (!msg.file) continue
    const relative = String(msg.file).replace(/^\//, '')
    const filePath = path.join(__dirname, '../storage', relative)
    if (fs.existsSync(filePath)) {
      await fs.remove(filePath).catch(() => {})
    }
  }
}

async function deleteMessagesAndNotify(io, messages, options = {}) {
  if (!messages?.length) return []

  await removeMessageFiles(messages)
  const deletedIds = messages.map((m) => String(m._id))
  await MessageModel.deleteMany({ _id: { $in: deletedIds } })

  if (io) {
    const byThread = new Map()
    messages.forEach((m) => {
      const s = String(m.senderId)
      const r = String(m.receiverId)
      const key = [s, r].sort().join(':')
      if (!byThread.has(key)) byThread.set(key, { s, r, ids: [] })
      byThread.get(key).ids.push(String(m._id))
    })

    byThread.forEach(({ s, r, ids }) => {
      io.to(`chat:${s}:${r}`)
        .to(`chat:${r}:${s}`)
        .emit('messagesDeleted', {
          messageIds: ids,
          deletedBy: options.deletedBy,
          reason: options.reason || (options.deletedBy ? 'manual' : 'expired')
        })
      io.to(`user:${s}`).to(`user:${r}`).emit('chatListUpdate', { senderId: s, receiverId: r })
    })
  }

  return deletedIds
}

async function purgeExpiredMessages(io) {
  try {
    const expired = await MessageModel.find({ expiresAt: { $lte: new Date() } })
    if (!expired.length) return []
    return deleteMessagesAndNotify(io, expired)
  } catch (err) {
    console.error('purgeExpiredMessages error:', err)
    return []
  }
}

const scheduledTimers = new Map()

function scheduleMessageExpiry(io, message) {
  if (!message?.expiresAt || !message._id) return

  const id = String(message._id)
  if (scheduledTimers.has(id)) {
    clearTimeout(scheduledTimers.get(id))
  }

  const ms = new Date(message.expiresAt).getTime() - Date.now()
  if (ms <= 0) {
    MessageModel.findById(id)
      .then((doc) => doc && deleteMessagesAndNotify(io, [doc]))
      .catch(() => {})
    return
  }

  const timer = setTimeout(async () => {
    scheduledTimers.delete(id)
    try {
      const doc = await MessageModel.findById(id)
      if (doc && doc.expiresAt && new Date(doc.expiresAt) <= new Date()) {
        await deleteMessagesAndNotify(io, [doc])
      }
    } catch (err) {
      console.error('scheduleMessageExpiry error:', err)
    }
  }, ms)

  scheduledTimers.set(id, timer)
}

async function startSelfDestructOnView(io, message, viewerId) {
  if (!message?.selfDestructSeconds || message.selfDestructStartedAt) {
    return message
  }

  const viewer = String(viewerId)
  const receiver = String(message.receiverId)
  if (viewer !== receiver) return message

  const expiresAt = buildExpiresAt(message.selfDestructSeconds)
  const updated = await MessageModel.findByIdAndUpdate(
    message._id,
    {
      $set: {
        selfDestructStartedAt: new Date(),
        expiresAt
      }
    },
    { new: true }
  )

  if (updated) {
    scheduleMessageExpiry(io, updated)
    if (io) {
      const sid = String(updated.senderId)
      const rid = String(updated.receiverId)
      io.to(`chat:${sid}:${rid}`)
        .to(`chat:${rid}:${sid}`)
        .emit('messageSelfDestructStarted', {
          messageId: String(updated._id),
          expiresAt: updated.expiresAt.toISOString(),
          selfDestructSeconds: updated.selfDestructSeconds
        })
    }
  }

  return updated || message
}

async function markSelfDestructViewed(io, messageId, viewerId) {
  const msg = await MessageModel.findById(messageId)
  if (!msg || !msg.selfDestructSeconds || msg.selfDestructStartedAt) {
    return { message: msg }
  }

  const updated = await startSelfDestructOnView(io, msg, viewerId)
  return {
    message: updated,
    expiresAt: updated?.expiresAt
      ? new Date(updated.expiresAt).toISOString()
      : undefined
  }
}

async function startPendingSelfDestructForViewer(io, viewerId, peerId) {
  const viewer = String(viewerId)
  const peer = String(peerId)
  const pending = await MessageModel.find({
    receiverId: viewer,
    senderId: peer,
    selfDestructSeconds: { $exists: true, $ne: null },
    selfDestructStartedAt: { $exists: false }
  })

  await Promise.all(
    pending.map((msg) => startSelfDestructOnView(io, msg, viewer))
  )
}

module.exports = {
  ALLOWED_SELF_DESTRUCT_SECONDS,
  DELETE_WINDOW_MS,
  parseSelfDestructSeconds,
  buildExpiresAt,
  activeMessageFilter,
  isWithinDeleteWindow,
  purgeExpiredMessages,
  scheduleMessageExpiry,
  deleteMessagesAndNotify,
  startSelfDestructOnView,
  markSelfDestructViewed,
  startPendingSelfDestructForViewer
}