// apps/box-app-api/src/feature/ads/ad.service.ts
import { Injectable, Logger } from '@nestjs/common';
import { RedisService } from '@box/db/redis/redis.service';
import { MongoPrismaService } from '@box/db/prisma/mongo-prisma.service';
import { CacheKeys } from '@box/common/cache/cache-keys';
import { AdDto } from './dto/ad.dto';
import { AdListResponseDto, AdItemDto } from './dto';
import { AdType } from '@box/common/ads/ad-types';

interface AdPoolEntry {
  id: string;
  weight: number;
}

// This should match what mgnt-side rebuildSingleAdCache stores.
// We only care about a subset for now.
interface CachedAd {
  id: string;
  channelId?: string;
  adsModuleId?: string;
  advertiser?: string;
  title?: string;
  adsContent?: string | null;
  adsCoverImg?: string | null;
  adsUrl?: string | null;
  adType?: string | null;
  // startDt?: bigint;
  // expiryDt?: bigint;
  // seq?: number;
  // status?: number;
  // createAt?: bigint;
  // updateAt?: bigint;
}

export interface GetAdForPlacementParams {
  scene: string; // e.g. 'home' | 'detail' | 'player' | 'global'
  slot: string; // e.g. 'top' | 'carousel' | 'popup' | 'preroll' | ...
  adType: string; // e.g. 'BANNER' | 'CAROUSEL' | 'POPUP_IMAGE' | ...
  maxTries?: number; // optional, default 3
}

/**
 * Handles ad selection for app clients using prebuilt Redis pools.
 * Reads the ad pool for a given (scene, slot, adType), picks a candidate,
 * and maps the cached payload back into the public AdDto shape.
 */
@Injectable()
export class AdService {
  private readonly logger = new Logger(AdService.name);

  constructor(
    private readonly redis: RedisService,
    private readonly mongoPrisma: MongoPrismaService,
  ) {}

  /**
   * Core method for app-api:
   * Given a (scene, slot, adType), try to pick one ad from the prebuilt pool
   * and return its details as AdDto. Returns null if no suitable ad is found.
   */
  async getAdForPlacement(
    params: GetAdForPlacementParams,
  ): Promise<AdDto | null> {
    const { scene, slot, adType } = params;
    const maxTries = params.maxTries ?? 3;

    const poolKey = CacheKeys.appAdPoolByType(adType);
    const pool = await this.readPoolWithDiagnostics(poolKey, {
      scene,
      slot,
      adType,
    });

    if (!pool) {
      return null;
    }

    // Limit attempts so we don't loop too much if some ad entries are stale.
    const attempts = Math.min(maxTries, pool.length);

    // We'll try up to `attempts` random entries from the pool.
    const usedIndexes = new Set<number>();

    for (let i = 0; i < attempts; i++) {
      const idx = this.pickRandomIndex(pool.length, usedIndexes);
      if (idx === -1) break;

      usedIndexes.add(idx);

      const entry = pool[idx];
      const adKey = CacheKeys.appAdById(entry.id);

      const cachedAd =
        (await this.redis.getJson<CachedAd | null>(adKey)) ?? null;

      if (!cachedAd) {
        this.logger.debug(
          `getAdForPlacement: missing per-ad cache for adId=${entry.id}, key=${adKey}, poolKey=${poolKey}`,
        );
        continue;
      }

      const dto = this.mapCachedAdToDto(cachedAd, adType);
      return dto;
    }

    // All attempts failed to find a valid cached ad
    this.logger.debug(
      `getAdForPlacement: no usable ad found after ${attempts} attempt(s) for scene=${scene}, slot=${slot}, adType=${adType}, poolKey=${poolKey}`,
    );

    return null;
  }

  /**
   * Fetch and parse a pool entry list, while emitting useful diagnostics when
   * the pool is missing/empty or contains malformed JSON. Keeps API behavior
   * unchanged (returns null when the pool is not usable).
   */
  private async readPoolWithDiagnostics(
    poolKey: string,
    placement: Pick<GetAdForPlacementParams, 'scene' | 'slot' | 'adType'>,
  ): Promise<AdPoolEntry[] | null> {
    const raw = await this.redis.get(poolKey);

    if (raw === null) {
      this.logger.warn(
        `Ad pool cache miss for scene=${placement.scene}, slot=${placement.slot}, adType=${placement.adType}, key=${poolKey}. Cache may be cold; ensure cache-sync rebuilt pools.`,
      );
      return null;
    }

    let parsed: unknown;
    try {
      parsed = JSON.parse(raw);
    } catch (err) {
      const message =
        err instanceof Error ? err.message : JSON.stringify(err ?? 'Unknown');
      this.logger.error(
        `Failed to parse ad pool JSON for key=${poolKey}: ${message}`,
      );
      return null;
    }

    if (!Array.isArray(parsed) || parsed.length === 0) {
      this.logger.warn(
        `Ad pool empty or invalid shape for scene=${placement.scene}, slot=${placement.slot}, adType=${placement.adType}, key=${poolKey}`,
      );
      return null;
    }

    return parsed as AdPoolEntry[];
  }

  /**
   * Pick a random index in [0, length-1] that is not in usedIndexes.
   * Returns -1 if all indexes are already used.
   */
  private pickRandomIndex(length: number, usedIndexes: Set<number>): number {
    if (usedIndexes.size >= length) return -1;

    // Simple approach: try a few times to find an unused index.
    // Since length is small in most pools, this is fine.
    for (let attempts = 0; attempts < 5; attempts++) {
      const idx = Math.floor(Math.random() * length);
      if (!usedIndexes.has(idx)) {
        return idx;
      }
    }

    // Fallback: linear scan for the first unused index
    for (let i = 0; i < length; i++) {
      if (!usedIndexes.has(i)) return i;
    }

    return -1;
  }

  /**
   * Map cached ad (as stored by mgnt-api) to the AdDto exposed to frontend.
   */
  private mapCachedAdToDto(cachedAd: CachedAd, fallbackAdType: string): AdDto {
    return {
      id: cachedAd.id,
      adType: cachedAd.adType ?? fallbackAdType,

      title: cachedAd.title ?? '',
      advertiser: cachedAd.advertiser ?? '',

      content: cachedAd.adsContent ?? undefined,
      coverImg: cachedAd.adsCoverImg ?? undefined,
      targetUrl: cachedAd.adsUrl ?? undefined,
    };
  }

  /**
   * Get paginated list of ads by type from Redis pool.
   * Reads the prebuilt ad pool from Redis, applies pagination, and fetches full ad details.
   *
   * Flow:
   * 1. Get total count from pool
   * 2. Compute start/stop indices for LRANGE
   * 3. Fetch poolEntries (AdPoolEntry array as JSON)
   * 4. Query MongoDB to fetch full ad details for the entries
   * 5. Reorder results to match Redis pool order
   * 6. Map to AdItemDto and return response
   */
  async listAdsByType(
    adType: string,
    page: number,
    size: number,
  ): Promise<AdListResponseDto> {
    const poolKey = CacheKeys.appAdPoolByType(adType);

    // Step 1: Get the entire pool from Redis
    // Note: The key should be a STRING (JSON), but might be a LIST from old implementation
    let poolEntries: AdPoolEntry[] = [];
    try {
      // First, try to get as JSON (STRING type)
      const jsonData = await this.redis.getJson<AdPoolEntry[]>(poolKey);
      if (jsonData && Array.isArray(jsonData)) {
        poolEntries = jsonData;
      } else {
        // If getJson failed or returned null, the key might not exist
        this.logger.warn(
          `Ad pool cache miss or invalid for adType=${adType}, key=${poolKey}`,
        );
      }
    } catch (err) {
      // If WRONGTYPE error, the key is stored as a different Redis type (likely from old code)
      // Delete the incompatible key so it can be rebuilt properly
      if (err instanceof Error && err.message?.includes('WRONGTYPE')) {
        this.logger.warn(
          `Ad pool key ${poolKey} has wrong type, deleting incompatible key`,
        );
        try {
          await this.redis.del(poolKey);
          this.logger.log(
            `Deleted incompatible ad pool key ${poolKey}. It will be rebuilt on next cache warmup.`,
          );
        } catch (delErr) {
          this.logger.error(
            `Failed to delete incompatible key ${poolKey}`,
            delErr instanceof Error ? delErr.stack : String(delErr),
          );
        }
      } else {
        this.logger.error(
          `Failed to read ad pool for adType=${adType}, key=${poolKey}`,
          err instanceof Error ? err.stack : String(err),
        );
      }
    }

    if (!Array.isArray(poolEntries) || poolEntries.length === 0) {
      this.logger.debug(
        `Ad pool empty or invalid for adType=${adType}, key=${poolKey}`,
      );
      return {
        page,
        size,
        total: 0,
        adType: adType as AdType,
        items: [],
      };
    }

    const total = poolEntries.length;

    // Step 2: Compute pagination indices
    const start = (page - 1) * size;
    const stop = start + size - 1;

    // Check if page is out of range
    if (start >= total) {
      this.logger.debug(
        `Page out of range: page=${page}, size=${size}, total=${total}`,
      );
      return {
        page,
        size,
        total,
        adType: adType as AdType,
        items: [],
      };
    }

    // Step 3: Slice the pool entries for this page
    const pagedEntries = poolEntries.slice(start, stop + 1);
    const adIds = pagedEntries.map((entry) => entry.id);

    // Step 4: Query MongoDB for full ad details
    let ads: Awaited<ReturnType<typeof this.mongoPrisma.ads.findMany>>;
    try {
      const now = BigInt(Date.now());
      ads = await this.mongoPrisma.ads.findMany({
        where: {
          id: { in: adIds },
          status: 1,
          startDt: { lte: now },
          OR: [{ expiryDt: BigInt(0) }, { expiryDt: { gte: now } }],
        },
      });
    } catch (err) {
      this.logger.error(
        `Failed to query ads from MongoDB for adIds=${adIds.join(',')}`,
        err instanceof Error ? err.stack : String(err),
      );
      return {
        page,
        size,
        total,
        adType: adType as AdType,
        items: [],
      };
    }

    // Step 5: Create a map of ads by ID for fast lookup
    const adMap = new Map(ads.map((ad) => [ad.id, ad]));

    // Step 6: Reorder results to match the pool order and map to AdItemDto
    const items: AdItemDto[] = [];
    for (const entry of pagedEntries) {
      const ad = adMap.get(entry.id);
      if (!ad) {
        this.logger.debug(
          `Ad not found in MongoDB for adId=${entry.id} from pool`,
        );
        continue;
      }

      items.push({
        id: ad.id,
        advertiser: ad.advertiser ?? '',
        title: ad.title ?? '',
        adsContent: ad.adsContent ?? null,
        adsCoverImg: ad.adsCoverImg ?? null,
        adsUrl: ad.adsUrl ?? null,
        startDt: ad.startDt.toString(),
        expiryDt: ad.expiryDt.toString(),
        seq: ad.seq ?? 0,
      });
    }

    return {
      page,
      size,
      total,
      adType: adType as AdType,
      items,
    };
  }

  /**
   * Get an ad by ID and validate it's enabled and within date range.
   * Returns the ad with its relationships (channel, adsModule) loaded.
   * Returns null if ad is not found, disabled, or outside date range.
   */
  async getAdByIdValidated(adsId: string): Promise<{
    id: string;
    channelId: string;
    adsModuleId: string;
    adType: string;
    adsUrl: string | null;
    advertiser: string;
    title: string;
  } | null> {
    const now = BigInt(Date.now());

    try {
      const ad = await this.mongoPrisma.ads.findUnique({
        where: { id: adsId },
        include: {
          channel: { select: { id: true } },
          adsModule: { select: { id: true, adType: true } },
        },
      });

      if (!ad) {
        this.logger.debug(`Ad not found: adsId=${adsId}`);
        return null;
      }

      // Validate status (1 = enabled)
      if (ad.status !== 1) {
        this.logger.debug(`Ad is disabled: adsId=${adsId}`);
        return null;
      }

      // Validate date range
      if (ad.startDt > now) {
        this.logger.debug(`Ad not started yet: adsId=${adsId}`);
        return null;
      }

      // If expiryDt is 0, it means no expiry; otherwise check if expired
      if (ad.expiryDt !== BigInt(0) && ad.expiryDt < now) {
        this.logger.debug(`Ad expired: adsId=${adsId}`);
        return null;
      }

      return {
        id: ad.id,
        channelId: ad.channelId,
        adsModuleId: ad.adsModuleId,
        adType: ad.adsModule.adType,
        adsUrl: ad.adsUrl,
        advertiser: ad.advertiser,
        title: ad.title,
      };
    } catch (err) {
      this.logger.error(
        `Error fetching ad by ID: adsId=${adsId}`,
        err instanceof Error ? err.stack : String(err),
      );
      return null;
    }
  }
}