back_end_oudelaa/src/modules/feed/feed.service.ts

import { Injectable, NotFoundException } from '@nestjs/common';
import { Types } from 'mongoose';
import { decodeOffsetCursor, encodeOffsetCursor } from '../../common/utils/cursor.util';
import { PostType } from '../../common/enums/post-type.enum';
import { PostVisibility } from '../../common/enums/post-visibility.enum';
import { UsersRepository } from '../users/users.repository';
import { UserDocument } from '../users/schemas/user.schema';
import { FeedQueryDto } from './dto/feed-query.dto';
import { FeedRepository } from './feed.repository';

@Injectable()
export class FeedService {
  constructor(
    private readonly feedRepository: FeedRepository,
    private readonly usersRepository: UsersRepository,
  ) {}

  async getMyFeed(currentUserId: string, query: FeedQueryDto) {
    const currentUser = await this.usersRepository.findById(currentUserId);
    if (!currentUser) {
      throw new NotFoundException('Current user not found');
    }

    const limit = query.limit ?? 20;
    const cursorOffset = decodeOffsetCursor(query.cursor);
    const page = query.page ?? 1;
    const followingOnly = query.followingOnly ?? false;
    const radiusKm = query.radiusKm ?? 30;

    const followingIds = await this.feedRepository.findFollowingIds(currentUserId);
    const visibleAuthorIds = followingOnly ? [currentUserId, ...followingIds] : null;

    const filter: Record<string, unknown> = {
      $or: [
        { visibility: PostVisibility.PUBLIC },
        { authorId: new Types.ObjectId(currentUserId) },
      ],
    };

    if (visibleAuthorIds) {
      filter.authorId = { $in: visibleAuthorIds.map((id) => new Types.ObjectId(id)) };
    }

    const candidates = await this.feedRepository.findCandidatePosts(filter, Math.max(limit * 12, 300));

    const scored = candidates
      .filter((post) => {
        if (!query.preferredPostType) {
          return true;
        }
        return post.postType === query.preferredPostType;
      })
      .map((post) => ({
        post,
        score: this.scorePost({
          currentUser,
          currentUserId,
          followingIds,
          post,
          preferredPostType: query.preferredPostType,
          radiusKm,
        }),
      }))
      .sort(
        (a, b) =>
          b.score - a.score ||
          new Date((b.post as any).createdAt ?? 0).getTime() - new Date((a.post as any).createdAt ?? 0).getTime(),
      );

    const total = scored.length;
    const skip = cursorOffset ?? (page - 1) * limit;
    const items = scored.slice(skip, skip + limit).map((entry) => ({
      ...entry.post.toObject(),
      feedScore: Number(entry.score.toFixed(3)),
    }));
    const nextOffset = skip + items.length;
    const nextCursor = nextOffset < total ? encodeOffsetCursor(nextOffset) : null;

    return {
      items,
      page,
      limit,
      total,
      totalPages: Math.ceil(total / limit) || 1,
      nextCursor,
    };
  }

  async getTrending(query: FeedQueryDto) {
    const limit = query.limit ?? 20;
    const cursorOffset = decodeOffsetCursor(query.cursor);
    const page = query.page ?? 1;
    const skip = cursorOffset ?? (page - 1) * limit;

    const [items, total] = await Promise.all([
      this.feedRepository.findTrendingPublicPosts(skip, limit),
      this.feedRepository.count({ visibility: PostVisibility.PUBLIC }),
    ]);
    const nextOffset = skip + items.length;
    const nextCursor = nextOffset < total ? encodeOffsetCursor(nextOffset) : null;

    return {
      items,
      page,
      limit,
      total,
      totalPages: Math.ceil(total / limit) || 1,
      nextCursor,
    };
  }

  private scorePost(input: {
    currentUser: UserDocument;
    currentUserId: string;
    followingIds: string[];
    post: any;
    preferredPostType?: PostType;
    radiusKm: number;
  }): number {
    const { currentUser, currentUserId, followingIds, post, preferredPostType, radiusKm } = input;
    const author: any = post.authorId;
    const authorId = typeof author === 'string' ? author : author?._id?.toString?.() ?? '';
    const isOwnPost = authorId === currentUserId;
    const isFollowing = followingIds.includes(authorId);

    const ageMs = Date.now() - new Date(post.createdAt).getTime();
    const ageHours = ageMs / (1000 * 60 * 60);
    const freshness = Math.max(0, 36 - ageHours);

    const engagement = post.likesCount * 3 + post.commentsCount * 4 + post.savesCount * 5;
    const hashtagMatches = this.intersectionCount(
      this.buildPreferenceTokens(currentUser),
      (post.hashtags ?? []).map((x: string) => x.toLowerCase()),
    );

    const distanceKm = this.computeDistanceKm(
      currentUser.latitude,
      currentUser.longitude,
      author?.latitude ?? null,
      author?.longitude ?? null,
    );
    const nearbyBoost =
      typeof distanceKm === 'number' && distanceKm <= radiusKm ? Math.max(0, 25 - distanceKm / 2) : 0;

    let score = 0;
    score += engagement;
    score += freshness;
    score += isOwnPost ? 10 : 0;
    score += isFollowing ? 40 : 0;
    score += post.postType === preferredPostType ? 18 : 0;
    score += hashtagMatches * 9;
    score += nearbyBoost;
    score += author?.isVerified ? 8 : 0;
    score += Math.min(20, Math.floor((author?.followersCount ?? 0) / 200));

    return score;
  }

  private buildPreferenceTokens(user: UserDocument): string[] {
    const tokens = [
      ...(user.musicGenres ?? []),
      ...(user.favoriteInstruments ?? []),
      ...(user.favoriteMaqamat ?? []),
      ...(user.musicRoles ?? []),
    ]
      .map((item) => item.trim().toLowerCase())
      .filter(Boolean);

    return Array.from(new Set(tokens));
  }

  private intersectionCount(a: string[], b: string[]): number {
    if (!a.length || !b.length) {
      return 0;
    }

    const right = new Set(b);
    let count = 0;
    for (const item of a) {
      if (right.has(item)) {
        count += 1;
      }
    }
    return count;
  }

  private computeDistanceKm(
    lat1: number | null | undefined,
    lon1: number | null | undefined,
    lat2: number | null | undefined,
    lon2: number | null | undefined,
  ): number | null {
    if (
      typeof lat1 !== 'number' ||
      typeof lon1 !== 'number' ||
      typeof lat2 !== 'number' ||
      typeof lon2 !== 'number'
    ) {
      return null;
    }

    const toRad = (deg: number) => (deg * Math.PI) / 180;
    const earthKm = 6371;
    const dLat = toRad(lat2 - lat1);
    const dLon = toRad(lon2 - lon1);
    const a =
      Math.sin(dLat / 2) ** 2 +
      Math.cos(toRad(lat1)) * Math.cos(toRad(lat2)) * Math.sin(dLon / 2) ** 2;
    const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
    return earthKm * c;
  }
}