const { getRedisClient } = require("./redis/client")
const userInterestProfileDb = require("../db/userInterestProfile.db")
const { getCategoryDealIndexKey } = require("./redis/categoryDealIndex.service")
const { getDealsByIdsFromRedis } = require("./redis/hotDealList.service")
const { getNewDealIds } = require("./redis/newDealList.service")

const FEED_KEY_PREFIX = "deals:lists:personalized:user:"
const FEED_TTL_SECONDS = Math.max(60, Number(process.env.PERSONAL_FEED_TTL_SECONDS) || 2 * 60 * 60)
const FEED_REBUILD_THRESHOLD_SECONDS = Math.max(
  60,
  Number(process.env.PERSONAL_FEED_REBUILD_THRESHOLD_SECONDS) || 60 * 60
)
const FEED_CANDIDATE_LIMIT = Math.max(20, Number(process.env.PERSONAL_FEED_CANDIDATE_LIMIT) || 120)
const FEED_MAX_CATEGORIES = Math.max(1, Number(process.env.PERSONAL_FEED_MAX_CATEGORIES) || 8)
const FEED_PER_CATEGORY_LIMIT = Math.max(5, Number(process.env.PERSONAL_FEED_PER_CATEGORY_LIMIT) || 40)
const FEED_LOOKBACK_DAYS = Math.max(1, Number(process.env.PERSONAL_FEED_LOOKBACK_DAYS) || 30)
const FEED_NOISE_MAX = Math.max(0, Number(process.env.PERSONAL_FEED_NOISE_MAX) || 50)
const FEED_PAGE_LIMIT = 20

function normalizePositiveInt(value) {
  const num = Number(value)
  if (!Number.isInteger(num) || num <= 0) return null
  return num
}

function normalizePagination({ page, limit }) {
  const rawPage = Number(page)
  const rawLimit = Number(limit)
  const safePage = Number.isInteger(rawPage) && rawPage > 0 ? rawPage : 1
  const safeLimit =
    Number.isInteger(rawLimit) && rawLimit > 0 ? Math.min(rawLimit, 50) : 20
  return { page: safePage, limit: safeLimit, skip: (safePage - 1) * safeLimit }
}

function getLatestKey(userId) {
  return `${FEED_KEY_PREFIX}${userId}:latest`
}

function getFeedKey(userId, feedId) {
  return `${FEED_KEY_PREFIX}${userId}:${feedId}`
}

function getFeedKeyMatchPattern(userId) {
  return `${FEED_KEY_PREFIX}${userId}:*`
}

function parseCategoryScores(rawScores) {
  if (!rawScores || typeof rawScores !== "object" || Array.isArray(rawScores)) return []
  const entries = []
  for (const [categoryIdRaw, scoreRaw] of Object.entries(rawScores)) {
    const categoryId = normalizePositiveInt(categoryIdRaw)
    const score = Number(scoreRaw)
    if (!categoryId || !Number.isFinite(score) || score <= 0) continue
    entries.push({ categoryId, score })
  }
  return entries.sort((a, b) => b.score - a.score)
}

function buildFallbackFeedIds(dealIds = []) {
  return Array.from(
    new Set(
      (Array.isArray(dealIds) ? dealIds : [])
        .map((id) => Number(id))
        .filter((id) => Number.isInteger(id) && id > 0)
    )
  ).slice(0, FEED_CANDIDATE_LIMIT)
}

function computePersonalScore({ categoryScore, dealScore }) {
  const safeCategory = Math.max(0, Number(categoryScore) || 0)
  const safeDealScore = Math.max(1, Number(dealScore) || 0)
  const noise = FEED_NOISE_MAX > 0 ? Math.floor(Math.random() * (FEED_NOISE_MAX + 1)) : 0
  return safeCategory * safeDealScore + noise
}

async function getFeedFromRedis(redis, userId) {
  const latestId = await redis.get(getLatestKey(userId))
  if (!latestId) return null
  const key = getFeedKey(userId, latestId)
  const raw = await redis.call("JSON.GET", key)
  const ttl = Number(await redis.ttl(key))
  if (!raw || ttl <= 0) return null
  try {
    const parsed = JSON.parse(raw)
    return {
      id: String(parsed.id || latestId),
      dealIds: buildFallbackFeedIds(parsed.dealIds || []),
      ttl,
    }
  } catch {
    return null
  }
}

async function listUserFeedKeys(redis, userId) {
  const pattern = getFeedKeyMatchPattern(userId)
  const keys = []
  let cursor = "0"

  do {
    const [nextCursor, batch] = await redis.scan(cursor, "MATCH", pattern, "COUNT", 100)
    cursor = String(nextCursor)
    if (Array.isArray(batch) && batch.length) {
      batch.forEach((key) => {
        if (String(key).endsWith(":latest")) return
        keys.push(String(key))
      })
    }
  } while (cursor !== "0")

  return Array.from(new Set(keys))
}

function extractFeedIdFromKey(userId, key) {
  const prefix = `${FEED_KEY_PREFIX}${userId}:`
  if (!String(key).startsWith(prefix)) return null
  const feedId = String(key).slice(prefix.length)
  return feedId || null
}

async function getBestFeedFromRedis(redis, userId) {
  const keys = await listUserFeedKeys(redis, userId)
  if (!keys.length) return null

  const pipeline = redis.pipeline()
  keys.forEach((key) => pipeline.ttl(key))
  keys.forEach((key) => pipeline.call("JSON.GET", key))
  const results = await pipeline.exec()
  if (!Array.isArray(results) || !results.length) return null

  const ttlResults = results.slice(0, keys.length)
  const jsonResults = results.slice(keys.length)

  let best = null
  keys.forEach((key, idx) => {
    try {
      const ttl = Number(ttlResults[idx]?.[1] ?? -1)
      if (!Number.isFinite(ttl) || ttl <= 0) return
      const raw = jsonResults[idx]?.[1]
      if (!raw) return
      const parsed = JSON.parse(raw)
      const dealIds = buildFallbackFeedIds(parsed?.dealIds || [])
      const feedId = extractFeedIdFromKey(userId, key) || String(parsed?.id || "")
      if (!feedId) return

      if (!best || ttl > best.ttl) {
        best = {
          id: feedId,
          dealIds,
          ttl,
        }
      }
    } catch {}
  })

  return best
}

async function setLatestPointer(redis, userId, feedId, ttlSeconds) {
  const ttl = Math.max(1, Number(ttlSeconds) || FEED_TTL_SECONDS)
  await redis.set(getLatestKey(userId), String(feedId), "EX", ttl)
}

async function collectCandidateIdsFromIndexes(redis, topCategories = []) {
  if (!topCategories.length) return new Map()
  const cutoffTs = Date.now() - FEED_LOOKBACK_DAYS * 24 * 60 * 60 * 1000
  const pipeline = redis.pipeline()
  const refs = []

  topCategories.forEach((entry) => {
    const key = getCategoryDealIndexKey(entry.categoryId)
    if (!key) return
    pipeline.zrevrangebyscore(key, "+inf", String(cutoffTs), "LIMIT", 0, FEED_PER_CATEGORY_LIMIT)
    refs.push(entry)
  })

  if (!refs.length) return new Map()
  const results = await pipeline.exec()
  const categoryByDealId = new Map()

  results.forEach((result, idx) => {
    const [, rawIds] = result || []
    const categoryEntry = refs[idx]
    const ids = Array.isArray(rawIds) ? rawIds : []
    ids.forEach((id) => {
      const dealId = Number(id)
      if (!Number.isInteger(dealId) || dealId <= 0) return
      if (!categoryByDealId.has(dealId)) {
        categoryByDealId.set(dealId, categoryEntry)
      }
    })
  })

  return categoryByDealId
}

async function buildPersonalizedFeedForUser(redis, userId) {
  const profile = await userInterestProfileDb.getUserInterestProfile(userId)
  const categories = parseCategoryScores(profile?.categoryScores).slice(0, FEED_MAX_CATEGORIES)

  if (!categories.length) {
    const fallback = await getNewDealIds({})
    return {
      id: String(Date.now()),
      dealIds: buildFallbackFeedIds(fallback?.dealIds || []),
    }
  }

  const categoryByDealId = await collectCandidateIdsFromIndexes(redis, categories)
  const candidateIds = Array.from(categoryByDealId.keys()).slice(0, FEED_CANDIDATE_LIMIT * 3)

  if (!candidateIds.length) {
    const fallback = await getNewDealIds({})
    return {
      id: String(Date.now()),
      dealIds: buildFallbackFeedIds(fallback?.dealIds || []),
    }
  }

  const deals = await getDealsByIdsFromRedis(candidateIds, userId)
  const scored = deals
    .filter((deal) => String(deal?.status || "").toUpperCase() === "ACTIVE")
    .map((deal) => {
      const entry = categoryByDealId.get(Number(deal.id))
      const categoryScore = Number(entry?.score || 0)
      return {
        id: Number(deal.id),
        score: computePersonalScore({
          categoryScore,
          dealScore: Number(deal.score || 0),
        }),
      }
    })
    .filter((item) => Number.isInteger(item.id) && item.id > 0)

  scored.sort((a, b) => b.score - a.score)

  const rankedIds = Array.from(new Set(scored.map((item) => item.id))).slice(0, FEED_CANDIDATE_LIMIT)
  if (!rankedIds.length) {
    const fallback = await getNewDealIds({})
    return {
      id: String(Date.now()),
      dealIds: buildFallbackFeedIds(fallback?.dealIds || []),
    }
  }

  return {
    id: String(Date.now()),
    dealIds: rankedIds,
  }
}

async function cacheFeed(redis, userId, feed) {
  const feedId = String(feed?.id || Date.now())
  const dealIds = buildFallbackFeedIds(feed?.dealIds || [])
  const key = getFeedKey(userId, feedId)
  const payload = {
    id: feedId,
    createdAt: new Date().toISOString(),
    total: dealIds.length,
    dealIds,
  }
  await redis.call("JSON.SET", key, "$", JSON.stringify(payload))
  await redis.expire(key, FEED_TTL_SECONDS)
  await setLatestPointer(redis, userId, feedId, FEED_TTL_SECONDS)
  return { id: feedId, dealIds, ttl: FEED_TTL_SECONDS }
}

async function getOrBuildFeedIds(userId) {
  const uid = normalizePositiveInt(userId)
  if (!uid) return { id: null, dealIds: [] }
  const redis = getRedisClient()

  try {
    const best = (await getBestFeedFromRedis(redis, uid)) || (await getFeedFromRedis(redis, uid))
    if (best && best.ttl >= FEED_REBUILD_THRESHOLD_SECONDS) {
      await setLatestPointer(redis, uid, best.id, best.ttl)
      return best
    }
    if (best && best.ttl > 0) {
      // Keep current feed as fallback while creating a fresh one.
      const built = await buildPersonalizedFeedForUser(redis, uid)
      const cached = await cacheFeed(redis, uid, built)
      return cached?.dealIds?.length ? cached : best
    }
  } catch {}

  try {
    const built = await buildPersonalizedFeedForUser(redis, uid)
    return cacheFeed(redis, uid, built)
  } catch {
    const fallback = await getNewDealIds({})
    const dealIds = buildFallbackFeedIds(fallback?.dealIds || [])
    const payload = { id: String(Date.now()), dealIds, ttl: 0 }
    try {
      return cacheFeed(redis, uid, payload)
    } catch {
      return payload
    }
  }
}

async function getPersonalizedDeals({
  userId,
  page = 1,
} = {}) {
  const uid = normalizePositiveInt(userId)
  if (!uid) return { page: 1, total: 0, totalPages: 0, results: [], personalizedListId: null }

  const pagination = normalizePagination({ page, limit: FEED_PAGE_LIMIT })
  const feed = await getOrBuildFeedIds(uid)
  const ids = Array.isArray(feed?.dealIds) ? feed.dealIds : []
  const pageIds = ids.slice(pagination.skip, pagination.skip + pagination.limit)
  const deals = await getDealsByIdsFromRedis(pageIds, uid)

  return {
    page: pagination.page,
    total: ids.length,
    totalPages: ids.length ? Math.ceil(ids.length / pagination.limit) : 0,
    results: deals,
    personalizedListId: feed?.id || null,
  }
}

module.exports = {
  getPersonalizedDeals,
}