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utils/postEngagement.js

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+const PostBookmarkModel = require('../models/PostBookmarkModel')
+const PostSendModel = require('../models/PostSendModel')
+const PostShareModel = require('../models/PostShareModel')
+const UserFollowModel = require('../models/UserFollowModel')
+const ExploreInteractionModel = require('../models/ExploreInteractionModel')
+const UserModel = require('../models/UserModel')
+const StoryModel = require('../models/StoryModel')
+
+async function attachPostEngagementFields(posts, viewerId) {
+  if (!posts?.length) return posts
+
+  const postIds = posts.map((p) => p._id)
+  const authorIds = [...new Set(posts.map((p) => String(p.user_id)))]
+
+  const [bookmarkAgg, sendAgg, shareAgg, viewAgg, authorDocs, userBookmarks, userFollows, activeStories] = await Promise.all([
+    PostBookmarkModel.aggregate([
+      { $match: { postId: { $in: postIds } } },
+      { $group: { _id: '$postId', count: { $sum: 1 } } },
+    ]),
+    PostSendModel.aggregate([
+      { $match: { postId: { $in: postIds } } },
+      { $group: { _id: '$postId', count: { $sum: 1 } } },
+    ]),
+    PostShareModel.aggregate([
+      { $match: { postId: { $in: postIds } } },
+      { $group: { _id: '$postId', count: { $sum: 1 } } },
+    ]),
+    ExploreInteractionModel.aggregate([
+      {
+        $match: {
+          targetType: 'post',
+          targetId: { $in: postIds },
+          action: 'view',
+        },
+      },
+      { $group: { _id: '$targetId', count: { $sum: 1 } } },
+    ]),
+    UserModel.find({ _id: { $in: authorIds } })
+      .select('_id allow_save_posts')
+      .lean(),
+    viewerId
+      ? PostBookmarkModel.find({ userId: viewerId, postId: { $in: postIds } })
+          .select('postId')
+          .lean()
+      : [],
+    viewerId
+      ? UserFollowModel.find({
+          followerId: viewerId,
+          followingId: { $in: authorIds },
+        })
+          .select('followingId')
+          .lean()
+      : [],
+    StoryModel.find({ user_id: { $in: authorIds }, expires_at: { $gt: new Date() } })
+      .select('user_id viewers')
+      .lean(),
+  ])
+
+  const savesMap = Object.fromEntries(
+    bookmarkAgg.map((b) => [String(b._id), b.count])
+  )
+  const sendsMap = Object.fromEntries(
+    sendAgg.map((s) => [String(s._id), s.count])
+  )
+  const sharesMap = Object.fromEntries(
+    shareAgg.map((s) => [String(s._id), s.count])
+  )
+  const viewsMap = Object.fromEntries(
+    viewAgg.map((v) => [String(v._id), v.count])
+  )
+  const allowSaveMap = Object.fromEntries(
+    authorDocs.map((u) => [String(u._id), u.allow_save_posts !== false])
+  )
+  const savedSet = new Set(userBookmarks.map((b) => String(b.postId)))
+  const followSet = new Set(userFollows.map((f) => String(f.followingId)))
+
+  const storiesByAuthor = {}
+  activeStories.forEach((s) => {
+    const key = String(s.user_id)
+    if (!storiesByAuthor[key]) storiesByAuthor[key] = []
+    storiesByAuthor[key].push(s)
+  })
+  const hasStorySet = new Set(Object.keys(storiesByAuthor))
+  const unviewedStorySet = new Set(
+    Object.keys(storiesByAuthor).filter((authorId) =>
+      storiesByAuthor[authorId].some(
+        (s) => !s.viewers?.some((v) => String(v.user_id) === String(viewerId))
+      )
+    )
+  )
+
+  return posts.map((post) => ({
+    ...post,
+    savesCount: savesMap[String(post._id)] || 0,
+    sendsCount: sendsMap[String(post._id)] || 0,
+    sharesCount: sharesMap[String(post._id)] || 0,
+    viewsCount: viewsMap[String(post._id)] || 0,
+    author_allow_save: allowSaveMap[String(post.user_id)] !== false,
+    is_saved: savedSet.has(String(post._id)),
+    is_following: followSet.has(String(post.user_id)),
+    has_story: hasStorySet.has(String(post.user_id)),
+    has_unviewed_story: viewerId ? unviewedStorySet.has(String(post.user_id)) : hasStorySet.has(String(post.user_id)),
+  }))
+}
+
+async function attachSinglePostEngagement(post, viewerId) {
+  const [enriched] = await attachPostEngagementFields([post], viewerId)
+  return enriched
+}
+
+module.exports = {
+  attachPostEngagementFields,
+  attachSinglePostEngagement,
+}