import { Injectable, Logger } from '@nestjs/common';
import { RedisService } from '@box/db/redis/redis.service';

/**
 * Tag metadata interface for parsing from cache.
 * Matches the structure stored in box:app:tag:list:{categoryId} keys.
 *
 * This represents Tag entities, NOT Category entities.
 * Tags do not have a subtitle field (that's in Category).
 * NOTE: Tags no longer have channelId (removed from schema).
 */
export interface TagMetadata {
  id: string;
  name: string;
  seq: number;
  status: number;
  createAt: string; // ISO string or numeric string
  updateAt: string; // ISO string or numeric string
  categoryId: string;
}

export interface VideoPayload {
  id: string;
  title: string;
  coverImg: string;
  coverImgNew: string;
  videoTime: number;
  country: string;
  firstTag: string;
  secondTags: string[];
  preFileName: string;
  desc: string;
  size: string;
  updatedAt: string;
  filename: string;
  fieldNameFs: string;
  ext: string;
}

export interface RawVideoPayloadRow {
  id: string;
  title: string;
  coverImg: string;
  coverImgNew: string;
  videoTime: number;
  country: string;
  firstTag: string;
  secondTags: string[];
  preFileName: string;
  desc: string;
  size: bigint;
  updatedAt: Date;
  filename: string;
  fieldNameFs: string;
  ext: string;
}

export function toVideoPayload(row: RawVideoPayloadRow): VideoPayload {
  return {
    id: row.id,
    title: row.title ?? '',
    coverImg: row.coverImg ?? '',
    coverImgNew: row.coverImgNew ?? '',
    videoTime: row.videoTime ?? 0,
    country: row.country ?? '',
    firstTag: row.firstTag ?? '',
    secondTags: Array.isArray(row.secondTags) ? row.secondTags : [],
    preFileName: row.preFileName ?? '',
    desc: row.desc ?? '',
    size: row.size?.toString() ?? '0',
    updatedAt: row.updatedAt?.toISOString() ?? new Date().toISOString(),
    filename: row.filename ?? '',
    fieldNameFs: row.fieldNameFs ?? '',
    ext: row.ext ?? '',
  };
}

export function parseVideoPayload(value: string | null): VideoPayload | null {
  if (!value) return null;
  try {
    return JSON.parse(value) as VideoPayload;
  } catch {
    return null;
  }
}

/**
 * VideoCacheHelper provides type-safe, centralized Redis operations for video cache keys.
 *
 * KEY TYPE EXPECTATIONS:
 * - Video ID lists (category, tag, pool): Redis LIST containing video IDs (24-char hex strings)
 * - Tag metadata lists: Redis LIST containing Tag JSON objects
 * - Video details: Redis STRING containing Video JSON object
 *
 * This helper ensures:
 * 1. Consistent Redis command usage (LIST commands for lists, not GET/SET)
 * 2. Type safety for video IDs vs metadata
 * 3. Centralized error handling and logging
 * 4. TTL management
 *
 * @example
 * // Save video IDs to a category list
 * await helper.saveVideoIdList('box:app:video:category:list:123', ['vid1', 'vid2'], 3600);
 *
 * // Read video IDs with pagination
 * const videoIds = await helper.getVideoIdList('box:app:video:category:list:123', 0, 19);
 *
 * // Read tag metadata
 * const tags = await helper.getTagListForCategory('box:app:tag:list:123');
 */
@Injectable()
export class VideoCacheHelper {
  private readonly logger = new Logger(VideoCacheHelper.name);

  constructor(private readonly redis: RedisService) {}

  /**
   * Save a list of video IDs to a Redis LIST key.
   *
   * REDIS OPERATIONS:
   * 1. DEL key (remove existing data)
   * 2. RPUSH key videoId1 videoId2 ... (push all IDs)
   * 3. EXPIRE key ttlSeconds (set TTL if provided)
   *
   * KEY TYPE: LIST
   * VALUE TYPE: Video IDs (24-character hex strings, MongoDB ObjectId format)
   *
   * @param key - Redis key (e.g., 'box:app:video:category:list:{categoryId}')
   * @param videoIds - Array of video IDs to store
   * @param ttlSeconds - Optional TTL in seconds (no expiration if omitted)
   *
   * @throws Error if Redis operations fail
   *
   * @example
   * await helper.saveVideoIdList(
   *   'box:app:video:category:list:abc123',
   *   ['507f1f77bcf86cd799439011', '507f1f77bcf86cd799439012'],
   *   3600
   * );
   */
  async saveVideoIdList(
    key: string,
    videoIds: string[],
    ttlSeconds?: number,
  ): Promise<void> {
    try {
      if (!videoIds || videoIds.length === 0) {
        await this.redis.del(key);
        this.logger.debug(`[SaveVideoIdList] Cleared empty key: ${key}`);
        return;
      }

      // Delete existing key first
      await this.redis.del(key);

      // Push all video IDs to the list
      await this.redis.rpush(key, ...videoIds);

      // Set TTL if provided
      if (ttlSeconds && ttlSeconds > 0) {
        await this.redis.expire(key, ttlSeconds);
      }

      this.logger.debug(
        `[SaveVideoIdList] Saved key=${key} count=${videoIds.length} ttl=${ttlSeconds ? ttlSeconds + 's' : 'none'}`,
      );
    } catch (err) {
      this.logger.error(
        `[SaveVideoIdList] Failed for key=${key}: ${err instanceof Error ? err.message : String(err)}`,
        err instanceof Error ? err.stack : undefined,
      );
      throw err;
    }
  }

  /**
   * Get a range of video IDs from a Redis LIST key.
   *
   * REDIS OPERATION: LRANGE key start stop
   * KEY TYPE: LIST
   * VALUE TYPE: Video IDs (24-character hex strings)
   *
   * @param key - Redis key (e.g., 'box:app:video:category:list:{categoryId}')
   * @param start - Start index (0-based, default 0)
   * @param stop - Stop index (-1 for all, default -1)
   * @returns Array of video IDs
   *
   * @example
   * // Get all video IDs
   * const allIds = await helper.getVideoIdList('box:app:video:category:list:abc123');
   *
   * // Get first 20 video IDs (pagination)
   * const pageIds = await helper.getVideoIdList('box:app:video:category:list:abc123', 0, 19);
   */
  async getVideoIdList(key: string, start = 0, stop = -1): Promise<string[]> {
    try {
      const videoIds = await this.readListRangeWithLegacy(
        key,
        start,
        stop,
        async (legacyData) => {
          await this.saveVideoIdList(key, legacyData);
        },
      );
      return videoIds;
    } catch (err) {
      this.logger.error(
        `Failed to get video ID list from ${key}`,
        err instanceof Error ? err.stack : String(err),
      );
      return [];
    }
  }

  /**
   * Get the length of a video ID list.
   *
   * REDIS OPERATION: LLEN key
   * KEY TYPE: LIST
   *
   * @param key - Redis key
   * @returns Number of items in the list
   *
   * @example
   * const count = await helper.getVideoIdListLength('box:app:video:category:list:abc123');
   */
  async getVideoIdListLength(key: string): Promise<number> {
    try {
      const length = await this.redis.llen(key);
      if (length > 0) {
        return length;
      }
      const legacyList = await this.readListRangeWithLegacy(
        key,
        0,
        -1,
        async (legacyData) => {
          await this.saveVideoIdList(key, legacyData);
        },
      );
      return legacyList.length;
    } catch (err) {
      this.logger.error(
        `Failed to get list length for ${key}`,
        err instanceof Error ? err.stack : String(err),
      );
      return 0;
    }
  }

  /**
   * Save tag metadata list to Redis.
   *
   * REDIS OPERATIONS:
   * 1. DEL key
   * 2. RPUSH key (JSON.stringify(tag1)) (JSON.stringify(tag2)) ...
   * 3. EXPIRE key ttlSeconds (if provided)
   *
   * KEY TYPE: LIST
   * VALUE TYPE: Tag JSON objects (stringified)
   *
   * @param key - Redis key (e.g., 'box:app:tag:list:{categoryId}')
   * @param tags - Array of tag metadata objects
   * @param ttlSeconds - Optional TTL in seconds
   *
   * @example
   * await helper.saveTagList('box:app:tag:list:abc123', [
   *   { id: '1', name: 'Action', seq: 1, ... },
   *   { id: '2', name: 'Drama', seq: 2, ... }
   * ], 3600);
   */
  async saveTagList(
    key: string,
    tags: TagMetadata[],
    ttlSeconds?: number,
  ): Promise<void> {
    try {
      if (!tags || tags.length === 0) {
        await this.redis.del(key);
        this.logger.debug(`[SaveTagList] Cleared empty key: ${key}`);
        return;
      }

      // Delete existing key
      await this.redis.del(key);

      // Push all tags as JSON strings
      const tagJsonStrings = tags.map((tag) => JSON.stringify(tag));
      await this.redis.rpush(key, ...tagJsonStrings);

      // Set TTL if provided
      if (ttlSeconds && ttlSeconds > 0) {
        await this.redis.expire(key, ttlSeconds);
      }

      this.logger.debug(
        `[SaveTagList] Saved key=${key} count=${tags.length} ttl=${ttlSeconds ? ttlSeconds + 's' : 'none'}`,
      );
    } catch (err) {
      this.logger.error(
        `[SaveTagList] Failed for key=${key}: ${err instanceof Error ? err.message : String(err)}`,
        err instanceof Error ? err.stack : undefined,
      );
      throw err;
    }
  }

  /**
   * Get tag metadata list for a category.
   *
   * REDIS OPERATION: LRANGE key 0 -1
   * KEY TYPE: LIST
   * VALUE TYPE: Tag JSON objects (stringified)
   *
   * Parses each JSON string into a TagMetadata object.
   * Skips items that fail to parse (logs warning).
   *
   * @param key - Redis key (e.g., 'box:app:tag:list:{categoryId}')
   * @returns Array of parsed tag metadata objects
   *
   * @example
   * const tags = await helper.getTagListForCategory('box:app:tag:list:abc123');
   * // Returns: [{ id: '1', name: 'Action', ... }, { id: '2', name: 'Drama', ... }]
   */
  async getTagListForCategory(key: string): Promise<TagMetadata[]> {
    try {
      const items = await this.readListRangeWithLegacy(
        key,
        0,
        -1,
        async (legacyData) => {
      const tags = this.parseTagMetadataStrings(legacyData, key);
      if (tags.length > 0) {
        await this.saveTagList(key, tags);
      }
        },
      );

      return this.parseTagMetadataStrings(items, key);
    } catch (err) {
      this.logger.error(
        `[GetTagList] Failed for key=${key}: ${err instanceof Error ? err.message : String(err)}`,
        err instanceof Error ? err.stack : undefined,
      );
      return [];
    }
  }

  /**
   * Check if a key exists in Redis.
   *
   * REDIS OPERATION: EXISTS key
   *
   * @param key - Redis key to check
   * @returns true if key exists, false otherwise
   *
   * @example
   * const exists = await helper.keyExists('box:app:video:category:list:abc123');
   */
  async keyExists(key: string): Promise<boolean> {
    try {
      const result = await this.redis.exists(key);
      return result > 0;
    } catch (err) {
      this.logger.error(
        `Failed to check existence of ${key}`,
        err instanceof Error ? err.stack : String(err),
      );
      return false;
    }
  }

  /**
   * Delete a key from Redis.
   *
   * REDIS OPERATION: DEL key
   *
   * @param key - Redis key to delete
   * @returns Number of keys deleted (0 or 1)
   *
   * @example
   * await helper.deleteKey('box:app:video:category:list:abc123');
   */
  async deleteKey(key: string): Promise<number> {
    try {
      return await this.redis.del(key);
    } catch (err) {
      this.logger.error(
        `Failed to delete key ${key}`,
        err instanceof Error ? err.stack : String(err),
      );
      return 0;
    }
  }

  private legacyPrefixedKey(key: string): string {
    return `box:${key}`;
  }

  private async readListRangeWithLegacy(
    key: string,
    start: number,
    stop: number,
    migrate: (legacyData: string[]) => Promise<void>,
  ): Promise<string[]> {
    const result = await this.redis.lrange(key, start, stop);
    if (result.length > 0) {
      return result;
    }

    const legacyKey = this.legacyPrefixedKey(key);
    const legacyData = await this.redis.lrange(legacyKey, start, stop);

    if (!legacyData.length) {
      return [];
    }

    this.logger.warn(
      `[VideoCacheHelper] Legacy key triggered: ${legacyKey}, rehydrating ${key}`,
    );

    await migrate(legacyData);
    return legacyData;
  }

  private parseTagMetadataStrings(raw: string[], key: string): TagMetadata[] {
    const tags: TagMetadata[] = [];
    let malformedCount = 0;

    for (const item of raw) {
      try {
        const parsed = JSON.parse(item) as TagMetadata;
        tags.push(parsed);
      } catch {
        malformedCount++;
      }
    }

    if (malformedCount > 0) {
      this.logger.warn(
        `[GetTagList] key=${key}: parsed ${tags.length} tags, skipped ${malformedCount} malformed items`,
      );
    } else {
      this.logger.debug(
        `[GetTagList] key=${key}: parsed ${tags.length} tags`,
      );
    }

    return tags;
  }
}