const UserFollowModel = require('../models/UserFollowModel')
const NEAR_ME_RADIUS_METERS = 5000
const PostBookmarkModel = require('../models/PostBookmarkModel')
const PostModel = require('../models/PostModel')
const UserModel = require('../models/UserModel')
const LikeModel = require('../models/LikeModel')
const ExploreInteractionModel = require('../models/ExploreInteractionModel')
const { getBlockerUserIds } = require('./blockVisibility')
const { filterPostsByDistance } = require('./nearbyPosts')
const { postStatusFilter } = require('./moderationStatus')
const { buildUnifiedInterestScore } = require('./exploreAlgorithm')

async function getSuggestedFollowUsers(userId, limit = 15) {
  const viewer = await UserModel.findById(userId)
    .select('expertise blocked_users')
    .lean()

  const following = await UserFollowModel.find({ followerId: userId })
    .select('followingId')
    .lean()
  const excludeIds = new Set(
    following.map((f) => String(f.followingId)).concat(String(userId))
  )

  const blockerIds = new Set(
    (await getBlockerUserIds(UserModel, userId)).map(String)
  )

  const [interactions, likedPosts, interestWeights] = await Promise.all([
    ExploreInteractionModel.find({ viewerId: userId })
      .sort({ createdAt: -1 })
      .limit(40)
      .select('targetId authorId action')
      .lean(),
    LikeModel.find({ userId })
      .sort({ createdAt: -1 })
      .limit(30)
      .select('postId')
      .lean(),
    // شخصی‌سازی متقابل: علایقی که کاربر توی فروشگاه/آموزش/بیلبورد نشون داده هم اینجا اثر بذاره
    buildUnifiedInterestScore(userId),
  ])

  const interactedAuthorIds = new Set()
  interactions.forEach((row) => {
    if (row.authorId) interactedAuthorIds.add(String(row.authorId))
  })

  const likedPostIds = likedPosts.map((l) => l.postId).filter(Boolean)
  if (likedPostIds.length) {
    const likedPostsData = await PostModel.find({ _id: { $in: likedPostIds } })
      .select('user_id')
      .lean()
    likedPostsData.forEach((p) => interactedAuthorIds.add(String(p.user_id)))
  }

  let preferredExpertises = new Set()
  if (viewer?.expertise) preferredExpertises.add(viewer.expertise)

  if (interactedAuthorIds.size) {
    const authors = await UserModel.find({
      _id: { $in: [...interactedAuthorIds] },
    })
      .select('expertise')
      .lean()
    authors.forEach((a) => {
      if (a.expertise) preferredExpertises.add(a.expertise)
    })
  }

  const candidates = await UserModel.find({
    _id: { $nin: [...excludeIds] },
    user_name: { $nin: [null, ''] },
  })
    .select(
      '_id user_name first_name last_name expertise profile_image user_level'
    )
    .limit(120)
    .lean()

  const filtered = candidates.filter(
    (u) => !blockerIds.has(String(u._id)) && !excludeIds.has(String(u._id))
  )

  if (!filtered.length) return []

  const candidateIds = filtered.map((u) => u._id)
  const recentPosts = await PostModel.find({
    user_id: { $in: candidateIds },
    status: postStatusFilter(),
    is_archived: { $ne: true },
  })
    .sort({ createdAt: -1 })
    .lean()

  const postByUser = {}
  for (const p of recentPosts) {
    const uid = String(p.user_id)
    if (!postByUser[uid]) postByUser[uid] = p
  }

  const scored = filtered
    .filter((u) => postByUser[String(u._id)])
    .map((u) => {
      let score = Math.random() * 2
      if (preferredExpertises.has(u.expertise)) score += 8
      if (interactedAuthorIds.has(String(u._id))) score += 12
      if (u.expertise && interestWeights[u.expertise]) {
        score += Math.min(20, interestWeights[u.expertise])
      }
      const post = postByUser[String(u._id)]
      score += (post.likes?.length || 0) * 0.15
      return { user: u, score, previewPost: postByUser[String(u._id)] }
    })
    .sort((a, b) => b.score - a.score)
    .slice(0, limit)

  return scored.map(({ user, previewPost }) => ({
    _id: user._id,
    user_name: user.user_name,
    first_name: user.first_name,
    last_name: user.last_name,
    expertise: user.expertise,
    user_level: user.user_level,
    profile_image: user.profile_image,
    previewPost: {
      _id: previewPost._id,
      type: previewPost.type,
      // مدل واقعی مدیا رو با post_images/post_video برمی‌گردونه، نه همیشه files —
      // بدون این دو تا، فرانت‌اند (RN/وب) نمی‌تونست فایلِ پیش‌نمایش رو پیدا کنه و
      // کارت کاملاً خالی می‌موند
      post_images: previewPost.post_images,
      post_video: previewPost.post_video,
      files: previewPost.files,
      caption: previewPost.caption,
    },
    is_following: false,
  }))
}

async function getFollowingReelsFeed({
  userId,
  page,
  limit,
  postFilter,
  mapPostsWithUsers,
}) {
  const follows = await UserFollowModel.find({ followerId: userId })
    .select('followingId')
    .lean()
  const followingIds = follows.map((f) => f.followingId)

  if (!followingIds.length) {
    const suggestedUsers = await getSuggestedFollowUsers(userId)
    return {
      posts: [],
      totalPages: 0,
      totalItems: 0,
      feedMeta: { emptyFollowing: true, suggestedUsers },
    }
  }

  const suggestedUsers = await getSuggestedFollowUsers(userId)

  let posts = await PostModel.find({
    ...postFilter,
    status: postStatusFilter(),
    user_id: { $in: followingIds },
  })
    .sort({ createdAt: -1 })
    .lean()

  const userIds = [...new Set(posts.map((p) => String(p.user_id)))]
  const users = await UserModel.find({ _id: { $in: userIds } })
    .select(
      '_id user_name first_name last_name expertise sub_expertise province city user_level show_location profile_image is_verified user_score rate blocked_users'
    )
    .lean()

  posts = await mapPostsWithUsers(posts, users, { id: userId })

  const totalItems = posts.length
  const pageNum = parseInt(page, 10) || 1
  const limitNum = parseInt(limit, 10) || 10
  const startIndex = (pageNum - 1) * limitNum
  const paginatedPosts = posts.slice(startIndex, startIndex + limitNum)

  return {
    posts: paginatedPosts,
    totalPages: Math.ceil(totalItems / limitNum) || 1,
    totalItems,
    feedMeta: { emptyFollowing: false, suggestedUsers },
  }
}

async function getSavedReelsFeed({
  userId,
  page,
  limit,
  postFilter,
  mapPostsWithUsers,
}) {
  const pageNum = Math.max(1, parseInt(page, 10) || 1)
  const limitNum = Math.min(30, Math.max(1, parseInt(limit, 10) || 10))
  const skip = (pageNum - 1) * limitNum

  const totalItems = await PostBookmarkModel.countDocuments({ userId })
  const bookmarks = await PostBookmarkModel.find({ userId })
    .sort({ createdAt: -1 })
    .skip(skip)
    .limit(limitNum)
    .lean()

  const postIds = bookmarks.map((b) => b.postId)
  if (!postIds.length) {
    return {
      posts: [],
      totalPages: Math.ceil(totalItems / limitNum) || 0,
      totalItems,
      feedMeta: { emptySaved: true },
    }
  }

  let posts = await PostModel.find({
    _id: { $in: postIds },
    status: postStatusFilter(),
    ...postFilter,
  }).lean()

  const orderMap = new Map(postIds.map((id, idx) => [String(id), idx]))
  posts.sort(
    (a, b) =>
      (orderMap.get(String(a._id)) ?? 0) - (orderMap.get(String(b._id)) ?? 0)
  )

  const userIds = [...new Set(posts.map((p) => p.user_id))]
  const users = await UserModel.find({ _id: { $in: userIds } })
    .select(
      '_id user_name first_name last_name expertise sub_expertise province city user_level show_location profile_image is_verified user_score rate blocked_users'
    )
    .lean()

  posts = await mapPostsWithUsers(posts, users, { id: userId })

  return {
    posts,
    totalPages: Math.ceil(totalItems / limitNum) || 1,
    totalItems,
    feedMeta: { emptySaved: totalItems === 0 },
  }
}

async function getNearMeReelsFeed({
  lat,
  lng,
  page,
  limit,
  postFilter,
  mapPostsWithUsers,
  decodedToken,
}) {
  const parsedLat = parseFloat(lat)
  const parsedLng = parseFloat(lng)
  if (!Number.isFinite(parsedLat) || !Number.isFinite(parsedLng)) {
    return {
      posts: [],
      totalPages: 0,
      totalItems: 0,
      feedMeta: { needsLocation: true },
    }
  }

  let posts = await PostModel.find({
    ...postFilter,
    status: postStatusFilter(),
    lat: { $nin: [null, ''] },
    lng: { $nin: [null, ''] },
  })
    .sort({ createdAt: -1 })
    .lean()

  posts = filterPostsByDistance(
    posts,
    parsedLat,
    parsedLng,
    NEAR_ME_RADIUS_METERS
  )

  if (!posts.length) {
    return {
      posts: [],
      totalPages: 0,
      totalItems: 0,
      feedMeta: { emptyNearMe: true },
    }
  }

  const userIds = [...new Set(posts.map((p) => p.user_id))]
  const users = await UserModel.find({ _id: { $in: userIds } })
    .select(
      '_id user_name first_name last_name expertise sub_expertise province city user_level show_location profile_image is_verified user_score rate lat lng blocked_users'
    )
    .lean()

  posts = await mapPostsWithUsers(posts, users, decodedToken)

  const totalItems = posts.length
  const pageNum = parseInt(page, 10) || 1
  const limitNum = parseInt(limit, 10) || 10
  const startIndex = (pageNum - 1) * limitNum
  const paginatedPosts = posts.slice(startIndex, startIndex + limitNum)

  return {
    posts: paginatedPosts,
    totalPages: Math.ceil(totalItems / limitNum) || 1,
    totalItems,
    feedMeta: { emptyNearMe: totalItems === 0 },
  }
}

module.exports = {
  getSuggestedFollowUsers,
  getFollowingReelsFeed,
  getSavedReelsFeed,
  getNearMeReelsFeed,
}