const DB_COLLECTION = 'plank_data'
const ENV_ID = 'cloudbase-d1g56kl2q8f4f7d8a'
const { deleteAllPages } = require('./cloud-delete')

let _db = null
let _pushTimer = null
let _enabled = false
let _docId = null      // cache doc id after first successful push
let _openid = null     // cache openid from first successful add, used to
                      // re-locate our doc when _docId goes stale
                      // (e.g. user manually deleted the doc in the console)
let _openidPromise = null   // in-flight _fetchOpenid promise, prevents
                            // concurrent pushAll calls from racing the
                            // openid lookup (and each issuing an add())

const getDb = () => {
  if (!_enabled) return null
  if (!_db) {
    try { _db = wx.cloud.database({ env: ENV_ID }) } catch (e) { _enabled = false }
  }
  return _db
}

const init = () => {
  try {
    wx.cloud.init({ env: ENV_ID, traceUser: true })
    _enabled = true
    console.log('[cloud] init ok, env:', ENV_ID)
  } catch (e) {
    _enabled = false
    console.warn('[cloud] init failed — cloud sync disabled:', e.message || e)
  }
}

const pullAll = async () => {
  const db = getDb()
  if (!db) return null
  try {
    // Always need the openid to safely locate OUR doc under the custom
    // security rule. Cache it on first call so subsequent pulls are fast.
    if (!_openid) {
      _openid = await _fetchOpenid()
    }
    if (!_openid) return null  // cloud function call failed; bail

    // Locate our doc by _openid, ordered by updatedAt descending so
    // we always get the MOST RECENT doc. Without orderBy, limit(1)
    // returns the OLDEST doc (_id ascending), which causes data loss
    // when duplicate docs exist from the old cold-start-add() bug.
    const mine = await db.collection(DB_COLLECTION)
      .where({ _openid: _openid })
      .orderBy('updatedAt', 'desc')
      .limit(1)
      .get()
    if (mine && mine.data && mine.data.length > 0) {
      _docId = mine.data[0]._id
      return mine.data[0]
    }
    // No doc for us — that's a fresh install on a new device with no
    // history, or the user cleared their cloud data. Either way, nothing
    // to restore.
    _docId = null
    return null
  } catch (e) {
    return null
  }
}

// One-shot helper: call the getOpenid cloud function and return the
// openid string. Returns null on any failure (function not deployed,
// network error, etc.) — pullAll then bails cleanly.
const _fetchOpenid = async () => {
  try {
    const res = await wx.cloud.callFunction({ name: 'getOpenid' })
    if (res && res.result && res.result.openid) return res.result.openid
    console.warn('[cloud] getOpenid returned no openid:', JSON.stringify(res))
  } catch (e) {
    console.warn('[cloud] getOpenid call failed — cloud functions may not be deployed:', e.message || e)
  }
  return null
}

/**
 * Resolve and cache the user's openid exactly once per app session,
 * sharing a single in-flight promise across concurrent callers.
 *
 * Why this exists: pushAll() schedules _doPush() 2s later. Between the
 * schedule and the actual run, the module-level caches (_openid, _docId)
 * are null on every cold start. The original code would let _doPush fall
 * straight through to add() and create a brand-new cloud doc on every
 * cold start — which leaderboard then summed across N docs for the same
 * _openid. Pre-resolving openid here lets _doPush always locate the
 * existing doc (or skip the write if lookup fails) before considering
 * add().
 */
const _ensureOpenid = async () => {
  if (_openid) return _openid
  if (!_openidPromise) {
    _openidPromise = _fetchOpenid().then(o => {
      _openid = o
      _openidPromise = null
      return o
    }).catch(e => {
      _openidPromise = null
      return null
    })
  }
  return _openidPromise
}

const pushAll = () => {
  if (!_enabled) { console.log('[cloud] pushAll skipped (not enabled)'); return }
  console.log('[cloud] pushAll scheduled')
  // Pre-warm openid so _doPush never sees _openid=null on a cold start
  // (which used to bypass the locate-by-openid branch and call add(),
  // creating a duplicate cloud doc every cold start).
  _ensureOpenid().finally(() => {
    if (_pushTimer) clearTimeout(_pushTimer)
    _pushTimer = setTimeout(() => _doPush(), 2000)
  })
}

const cancelPendingPush = () => {
  if (_pushTimer) {
    clearTimeout(_pushTimer)
    _pushTimer = null
  }
}

const _markSynced = () => {
  try { wx.setStorageSync('_cloud_sync_at', Date.now()) } catch (e) {}
}

const _doPush = async () => {
  console.log('[cloud] _doPush starting...')
  const db = getDb()
  if (!db) { console.log('[cloud] _doPush aborted (no db)'); return }
  try {
    const storage = require('./storage')
    const themeMod = require('./theme')

    const data = {
      records: storage.getRecords(),
      settings: storage.getSettings(),
      streak: storage.getStreak(),
      customPlans: storage.getCustomPlans(),
      profile: storage.getProfile(),
      themeId: themeMod.getCurrentTheme().id,
      updatedAt: db.serverDate()
    }
    console.log('[cloud] _doPush records keys:', Object.keys(data.records || {}))

    // Fast path: cached _docId update
    if (_docId) {
      try {
        await db.collection(DB_COLLECTION).doc(_docId).update({ data })
        console.log('[cloud] _doPush update ok')
        _markSynced()
        return
      } catch (e) {
        // Most commonly: doc was deleted out from under us (user cleared
        // the collection in the console). The custom write rule evaluates
        // `doc._openid == auth.openid` → `undefined == openid` → false,
        // so this surfaces as -502003 rather than "not found". Either way,
        // fall through and re-locate the doc via openid.
        console.log('[cloud] _doPush cached _docId stale, clearing:', e.message)
        _docId = null
      }
    }

    // Required path: always try to locate OUR doc by _openid before any
    // add(). pushAll() pre-warms _openid via _ensureOpenid, so by the time
    // we reach this branch on a cold start _openid is populated and we'll
    // hit the update branch instead of falling through to add(). This is
    // the fix for the "leaderboard data increases on its own" bug.
    const openid = await _ensureOpenid()
    if (openid) {
      const existing = await db.collection(DB_COLLECTION)
        .where({ _openid: openid })
        .orderBy('updatedAt', 'desc')   // 与 pullAll 一致,避免命中最旧文档
        .limit(1)
        .get()
      if (existing && existing.data && existing.data.length > 0) {
        _docId = existing.data[0]._id
        try {
          await db.collection(DB_COLLECTION).doc(_docId).update({ data })
          console.log('[cloud] _doPush update ok (re-located by _openid)')
          _markSynced()
          return
        } catch (e) {
          // If even the freshly-located doc rejects our update (custom
          // permission rule, race with another tab, etc.), DO NOT fall
          // through to add() — that would silently create a duplicate
          // cloud doc for the same user. Bail and let the next push retry.
          console.log('[cloud] _doPush update-by-openid failed, aborting:', e.message)
          _docId = null
          return
        }
      }
    }  // else: openid is null — skip locate+update, go straight to add()

    // Reached when: (a) openid exists but no doc found, OR (b) openid is
    // null (getOpenid not deployed). In both cases add() is safe — CloudBase
    // auto-populates _openid on document creation.
    console.log('[cloud] _doPush adding new doc (openid=' + (openid || 'null') + ')')
    const res = await db.collection(DB_COLLECTION).add({ data })
    if (res && res._id) _docId = res._id
    if (res && res._openid) _openid = res._openid
    console.log('[cloud] _doPush add ok, docId=', _docId)
    _markSynced()
  } catch (e) {
    console.log('[cloud] _doPush error:', e.message || e)
  }
}

const clearAll = async () => {
  const db = getDb()
  if (!db) throw new Error('云端服务不可用')

  // Ensure _openid is cached before trying to delete — without it we
  // can't reliably locate the user's doc (add() only returns _id).
  if (!_openid) {
    _openid = await _fetchOpenid()
  }
  if (!_openid) {
    console.log('[cloud] clearAll: cannot fetch openid, giving up')
    throw new Error('无法识别当前用户')
  }

  // Repeatedly fetch the first page and delete it. This avoids skip()'s
  // shifting-offset bug and removes legacy duplicate docs as well.
  await deleteAllPages(
    async () => {
      const mine = await db.collection(DB_COLLECTION)
        .where({ _openid: _openid })
        .limit(100)
        .get()
      return (mine && mine.data) || []
    },
    async (id) => {
      await db.collection(DB_COLLECTION).doc(id).remove()
      console.log('[cloud] clearAll: removed doc', id)
    }
  )

  // Invalidate cached ids so the next _doPush starts fresh.
  _docId = null
}

module.exports = {
  init, pullAll, pushAll, clearAll, cancelPendingPush,
  get enabled() { return _enabled },
  get syncStatus() {
    if (!_enabled) return 'disabled'
    if (!_openid) return 'unauthenticated'
    return 'ok'
  }
}