// box-app-api/src/feature/recommendation/recommendation.service.ts
import { Injectable, Logger } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';
import { RedisService } from '@box/db/redis/redis.service';
import { PrismaMongoService } from '../../prisma/prisma-mongo.service';
import { VideoRecommendationDto } from './dto/video-recommendation.dto';
import { AdRecommendationDto } from './dto/ad-recommendation.dto';
import {
  EnrichedVideoRecommendationDto,
  EnrichedAdRecommendationDto,
} from './dto/enriched-recommendation.dto';

interface VideoCandidate {
  videoId: string;
  score: number;
  source: string;
}

interface AdCandidate {
  adId: string;
  score: number;
  source: string;
}

export interface AdRecommendationContext {
  // channelId: string;
  adsModuleId: string;
  limit?: number;
}

@Injectable()
export class RecommendationService {
  private readonly logger = new Logger(RecommendationService.name);

  // Channel boost factor (multiplier for same-channel videos)
  private readonly channelBoost: number;

  // Minimum candidates before falling back to global
  private readonly minCandidatesBeforeFallback: number;

  constructor(
    private readonly redis: RedisService,
    private readonly prisma: PrismaMongoService,
    private readonly configService: ConfigService,
  ) {
    this.channelBoost = parseFloat(
      this.configService.get<string>('RECOMMENDATION_CHANNEL_BOOST') ?? '1.1',
    );
    this.minCandidatesBeforeFallback = parseInt(
      this.configService.get<string>(
        'RECOMMENDATION_MIN_CANDIDATES_BEFORE_FALLBACK',
      ) ?? '5',
      10,
    );

    this.logger.log(
      `📊 Recommendation config: channelBoost=${this.channelBoost}, minCandidatesBeforeFallback=${this.minCandidatesBeforeFallback}`,
    );
  }

  /**
   * Get similar videos based on tags and Redis scores.
   * Algorithm:
   * 1. Fetch current video's tags and channelId
   * 2. Query Redis sorted sets for each tag (video:tag:<tagId>:score)
   * 3. Merge and deduplicate candidates
   * 4. Apply channel boost if same channelId
   * 5. Fall back to global set if not enough candidates
   * 6. Sort by boosted score descending and return top N
   */
  async getSimilarVideos(
    currentVideoId: string,
    limit: number = 10,
  ): Promise<VideoRecommendationDto[]> {
    this.logger.debug(
      `Getting similar videos for videoId=${currentVideoId}, limit=${limit}`,
    );

    try {
      // 1. Fetch current video metadata
      const currentVideo = await this.prisma.videoMedia.findUnique({
        where: { id: currentVideoId },
        select: { tagIds: true, categoryIds: true },
      });

      if (!currentVideo) {
        this.logger.warn(`Video not found: ${currentVideoId}`);
        return [];
      }

      const { tagIds } = currentVideo;
      // Use first category ID from categoryIds array
      const categoryId =
        Array.isArray(currentVideo.categoryIds) &&
        currentVideo.categoryIds.length > 0
          ? currentVideo.categoryIds[0]
          : '';

      this.logger.debug(
        `Video has ${tagIds?.length ?? 0} tags, categoryId=${categoryId}`,
      );

      // 2. Collect candidates from tag-based sorted sets
      const candidates = new Map<string, VideoCandidate>();

      if (tagIds && tagIds.length > 0) {
        await this.fetchCandidatesFromTags(tagIds, candidates);
      }

      // 3. Remove current video from candidates
      candidates.delete(currentVideoId);

      this.logger.debug(
        `Found ${candidates.size} tag-based candidates (after removing current video)`,
      );

      // 4. Fall back to global set if not enough candidates
      if (candidates.size < this.minCandidatesBeforeFallback) {
        await this.fetchCandidatesFromGlobal(
          limit * 2, // Fetch more to ensure enough after filtering
          candidates,
          currentVideoId,
        );
      }

      // 5. Apply channel boost if available
      if (categoryId) {
        await this.applyChannelBoost(candidates, categoryId);
      }

      // 6. Sort by boosted score and take top N
      const sortedCandidates = Array.from(candidates.values())
        .sort((a, b) => b.score - a.score)
        .slice(0, limit);

      this.logger.debug(
        `Returning ${sortedCandidates.length} recommendations for videoId=${currentVideoId}`,
      );

      return sortedCandidates.map((candidate) => ({
        videoId: candidate.videoId,
        score: candidate.score,
        source: candidate.source,
      }));
    } catch (error: any) {
      this.logger.error(
        `Failed to get similar videos for ${currentVideoId}: ${error?.message ?? error}`,
        error?.stack,
      );
      return [];
    }
  }

  /**
   * Fetch candidates from tag-based Redis sorted sets.
   */
  private async fetchCandidatesFromTags(
    tagIds: string[],
    candidates: Map<string, VideoCandidate>,
  ): Promise<void> {
    const client = (this.redis as any).ensureClient();

    for (const tagId of tagIds) {
      try {
        const key = `video:tag:${tagId}:score`;
        // Fetch top 20 per tag (adjustable)
        const results = await client.zrevrange(key, 0, 19, 'WITHSCORES');

        // Parse results: [member1, score1, member2, score2, ...]
        for (let i = 0; i < results.length; i += 2) {
          const videoId = results[i];
          const score = parseFloat(results[i + 1]);

          // Keep highest score if video appears in multiple tags
          const existing = candidates.get(videoId);
          if (!existing || score > existing.score) {
            candidates.set(videoId, {
              videoId,
              score,
              source: 'tag-based',
            });
          }
        }

        this.logger.debug(
          `Fetched ${results.length / 2} candidates from tag ${tagId}`,
        );
      } catch (error: any) {
        this.logger.warn(
          `Failed to fetch candidates from tag ${tagId}: ${error?.message ?? error}`,
        );
        // Continue with other tags
      }
    }
  }

  /**
   * Fetch candidates from global Redis sorted set as fallback.
   */
  private async fetchCandidatesFromGlobal(
    count: number,
    candidates: Map<string, VideoCandidate>,
    excludeVideoId: string,
  ): Promise<void> {
    try {
      const client = (this.redis as any).ensureClient();
      const results = await client.zrevrange(
        'video:global:score',
        0,
        count - 1,
        'WITHSCORES',
      );

      let added = 0;
      for (let i = 0; i < results.length; i += 2) {
        const videoId = results[i];
        const score = parseFloat(results[i + 1]);

        // Skip excluded video and videos already in candidates
        if (videoId === excludeVideoId || candidates.has(videoId)) {
          continue;
        }

        candidates.set(videoId, {
          videoId,
          score,
          source: 'global',
        });
        added++;
      }

      this.logger.debug(
        `Added ${added} candidates from global set (fetched ${results.length / 2} total)`,
      );
    } catch (error: any) {
      this.logger.error(
        `Failed to fetch global candidates: ${error?.message ?? error}`,
        error?.stack,
      );
    }
  }

  /**
   * Apply channel boost to videos from the same channel.
   */
  private async applyChannelBoost(
    candidates: Map<string, VideoCandidate>,
    channelId: string,
  ): Promise<void> {
    if (this.channelBoost === 1.0) {
      return; // No boost configured
    }

    try {
      const videoIds = Array.from(candidates.keys());
      if (videoIds.length === 0) {
        return;
      }

      // Batch fetch categoryIds for all candidates
      const videos = await this.prisma.videoMedia.findMany({
        where: { id: { in: videoIds } },
        select: { id: true, categoryIds: true },
      });

      let boostedCount = 0;
      for (const video of videos) {
        // Check if this video belongs to the current category
        if (
          Array.isArray(video.categoryIds) &&
          video.categoryIds.includes(channelId)
        ) {
          const candidate = candidates.get(video.id);
          if (candidate) {
            candidate.score *= this.channelBoost;
            candidate.source = 'channel-boost';
            boostedCount++;
          }
        }
      }

      this.logger.debug(
        `Applied channel boost to ${boostedCount} videos from channel ${channelId}`,
      );
    } catch (error: any) {
      this.logger.warn(
        `Failed to apply channel boost: ${error?.message ?? error}`,
      );
      // Continue without boost
    }
  }

  /**
   * Get similar ads with strict channel and module filtering.
   * Algorithm:
   * 1. Fetch eligible ads from Mongo (same adsModuleId, active, valid dates)
   * 2. Get scores from Redis ads:global:score for eligible ads
   * 3. Sort by score descending and return top N
   * 4. Exclude current adId
   */
  async getSimilarAds(
    currentAdId: string,
    context: AdRecommendationContext,
  ): Promise<AdRecommendationDto[]> {
    const { adsModuleId, limit = 5 } = context;

    this.logger.debug(
      `Getting similar ads for adId=${currentAdId}, adsModuleId=${adsModuleId}, limit=${limit}`,
    );

    try {
      // 1. Get current timestamp for date filtering
      const now = BigInt(Date.now());

      // 2. Fetch eligible ads from Mongo with strict filters
      const eligibleAds = await this.prisma.ads.findMany({
        where: {
          adsModuleId,
          status: 1, // Active only
          startDt: { lte: now }, // Started
          expiryDt: { gte: now }, // Not expired
          id: { not: currentAdId }, // Exclude current ad
        },
        select: { id: true },
        take: limit * 3, // Fetch more to ensure enough after scoring
      });

      if (eligibleAds.length === 0) {
        this.logger.warn(
          `No eligible ads found for adsModuleId=${adsModuleId}`,
        );
        return [];
      }

      this.logger.debug(
        `Found ${eligibleAds.length} eligible ads after filtering`,
      );

      // 3. Fetch scores from Redis for eligible ads
      const candidates: AdCandidate[] = [];
      const client = (this.redis as any).ensureClient();

      for (const ad of eligibleAds) {
        try {
          const score = await client.zscore('ads:global:score', ad.id);
          if (score !== null) {
            candidates.push({
              adId: ad.id,
              score: parseFloat(score),
              source: 'filtered',
            });
          } else {
            // No score in Redis, assign default low score
            candidates.push({
              adId: ad.id,
              score: 0,
              source: 'filtered',
            });
          }
        } catch (error: any) {
          this.logger.warn(
            `Failed to fetch score for ad ${ad.id}: ${error?.message ?? error}`,
          );
          // Assign default score
          candidates.push({
            adId: ad.id,
            score: 0,
            source: 'filtered',
          });
        }
      }

      // 4. Sort by score descending and take top N
      const sortedCandidates = candidates
        .sort((a, b) => b.score - a.score)
        .slice(0, limit);

      this.logger.debug(
        `Returning ${sortedCandidates.length} ad recommendations for adId=${currentAdId}`,
      );

      return sortedCandidates.map((candidate) => ({
        adId: candidate.adId,
        score: candidate.score,
        source: candidate.source,
      }));
    } catch (error: any) {
      this.logger.error(
        `Failed to get similar ads: ${error?.message ?? error}`,
        error?.stack,
      );
      return [];
    }
  }

  /**
   * Legacy simple ad recommendation (kept for backward compatibility).
   * Use getSimilarAds with context for production.
   */
  async getSimilarAdsSimple(
    currentAdId: string,
    limit: number = 10,
  ): Promise<VideoRecommendationDto[]> {
    this.logger.debug(
      `Getting similar ads (simple) for adId=${currentAdId}, limit=${limit}`,
    );

    try {
      const client = (this.redis as any).ensureClient();
      const results = await client.zrevrange(
        'ads:global:score',
        0,
        limit * 2 - 1,
        'WITHSCORES',
      );

      const ads: VideoRecommendationDto[] = [];
      for (let i = 0; i < results.length; i += 2) {
        const adId = results[i];
        const score = parseFloat(results[i + 1]);

        // Skip current ad
        if (adId === currentAdId) {
          continue;
        }

        ads.push({
          videoId: adId, // Using videoId field for adId
          score,
          source: 'global',
        });

        if (ads.length >= limit) {
          break;
        }
      }

      this.logger.debug(`Returning ${ads.length} ad recommendations`);
      return ads;
    } catch (error: any) {
      this.logger.error(
        `Failed to get similar ads: ${error?.message ?? error}`,
        error?.stack,
      );
      return [];
    }
  }

  /**
   * Get enriched video recommendations with metadata for 'You may also like' feature.
   * Public endpoint that returns full video details.
   */
  async getEnrichedVideoRecommendations(
    currentVideoId: string,
    limit: number = 6,
  ): Promise<EnrichedVideoRecommendationDto[]> {
    this.logger.debug(
      `Getting enriched video recommendations for videoId=${currentVideoId}, limit=${limit}`,
    );

    try {
      // 1. Get basic recommendations from existing logic
      const recommendations = await this.getSimilarVideos(
        currentVideoId,
        limit,
      );

      if (recommendations.length === 0) {
        return [];
      }

      // 2. Fetch full video metadata for enrichment
      const videoIds = recommendations.map((r) => r.videoId);
      const videos = await this.prisma.videoMedia.findMany({
        where: {
          id: { in: videoIds },
          status: 'Completed',
          // listStatus: 1, // Only on-shelf videos
        },
        select: {
          id: true,
          title: true,
          coverImgNew: true,
          coverImg: true,
          videoTime: true,
          listStatus: true,
        },
      });

      // 3. Create lookup map for fast access
      const videoMap = new Map(videos.map((v) => [v.id, v]));

      // 4. Enrich recommendations with metadata
      const enriched: EnrichedVideoRecommendationDto[] = [];
      for (const rec of recommendations) {
        const video = videoMap.get(rec.videoId);
        if (video) {
          enriched.push({
            videoId: video.id,
            title: video.title,
            coverImg: video.coverImgNew || video.coverImg,
            score: rec.score,
            videoTime: video.videoTime,
            listStatus: video.listStatus,
          });
        }
      }

      this.logger.debug(
        `Returning ${enriched.length} enriched video recommendations`,
      );
      return enriched;
    } catch (error: any) {
      this.logger.error(
        `Failed to get enriched video recommendations: ${error?.message ?? error}`,
        error?.stack,
      );
      return [];
    }
  }

  /**
   * Get enriched ad recommendations with metadata for 'You may also like' feature.
   * Public endpoint that returns full ad details with channel/module filtering.
   */
  async getEnrichedAdRecommendations(
    currentAdId: string,
    context: AdRecommendationContext,
  ): Promise<EnrichedAdRecommendationDto[]> {
    const { adsModuleId, limit = 3 } = context;

    this.logger.debug(
      `Getting enriched ad recommendations for adId=${currentAdId}, adsModuleId=${adsModuleId}, limit=${limit}`,
    );

    try {
      // 1. Get basic recommendations from existing logic
      const recommendations = await this.getSimilarAds(currentAdId, {
        adsModuleId,
        limit,
      });

      if (recommendations.length === 0) {
        return [];
      }

      // 2. Fetch full ad metadata for enrichment
      const adIds = recommendations.map((r) => r.adId);
      const ads = await this.prisma.ads.findMany({
        where: {
          id: { in: adIds },
          status: 1, // Only active ads
        },
        select: {
          id: true,
          title: true,
          adsCoverImg: true,
          adsUrl: true,
          advertiser: true,
        },
      });

      // 3. Create lookup map for fast access
      const adMap = new Map(ads.map((a) => [a.id, a]));

      // 4. Enrich recommendations with metadata
      const enriched: EnrichedAdRecommendationDto[] = [];
      for (const rec of recommendations) {
        const ad = adMap.get(rec.adId);
        if (ad) {
          enriched.push({
            adId: ad.id,
            title: ad.title,
            adsCoverImg: ad.adsCoverImg || '',
            score: rec.score,
            adsUrl: ad.adsUrl || undefined,
            advertiser: ad.advertiser,
          });
        }
      }

      this.logger.debug(
        `Returning ${enriched.length} enriched ad recommendations`,
      );
      return enriched;
    } catch (error: any) {
      this.logger.error(
        `Failed to get enriched ad recommendations: ${error?.message ?? error}`,
        error?.stack,
      );
      return [];
    }
  }
}