/**
 * @ai-summary VIN decoding service with circuit breaker and fallback
 * @ai-context PostgreSQL first, vPIC API fallback, Redis caching
 */
import { Pool } from 'pg';
import CircuitBreaker from 'opossum';
import { VehicleDataRepository } from '../data/vehicle-data.repository';
import { VPICClient } from '../data/vpic-client';
import { PlatformCacheService } from './platform-cache.service';
import { VINDecodeResponse, VINDecodeResult } from '../models/responses';
import { logger } from '../../../core/logging/logger';

export class VINDecodeService {
  private repository: VehicleDataRepository;
  private vpicClient: VPICClient;
  private cache: PlatformCacheService;
  private circuitBreaker: CircuitBreaker;

  constructor(cache: PlatformCacheService) {
    this.cache = cache;
    this.repository = new VehicleDataRepository();
    this.vpicClient = new VPICClient();

    this.circuitBreaker = new CircuitBreaker(
      async (vin: string) => this.vpicClient.decodeVIN(vin),
      {
        timeout: 6000,
        errorThresholdPercentage: 50,
        resetTimeout: 30000,
        name: 'vpic-api'
      }
    );

    this.circuitBreaker.on('open', () => {
      logger.warn('Circuit breaker opened for vPIC API');
    });

    this.circuitBreaker.on('halfOpen', () => {
      logger.info('Circuit breaker half-open for vPIC API');
    });

    this.circuitBreaker.on('close', () => {
      logger.info('Circuit breaker closed for vPIC API');
    });
  }

  /**
   * Validate VIN format
   */
  validateVIN(vin: string): { valid: boolean; error?: string } {
    if (vin.length !== 17) {
      return { valid: false, error: 'VIN must be exactly 17 characters' };
    }

    const invalidChars = /[IOQ]/i;
    if (invalidChars.test(vin)) {
      return { valid: false, error: 'VIN contains invalid characters (cannot contain I, O, Q)' };
    }

    const validFormat = /^[A-HJ-NPR-Z0-9]{17}$/i;
    if (!validFormat.test(vin)) {
      return { valid: false, error: 'VIN contains invalid characters' };
    }

    return { valid: true };
  }

  /**
   * Decode VIN with multi-tier strategy:
   * 1. Check cache
   * 2. Try PostgreSQL function
   * 3. Fallback to vPIC API (with circuit breaker)
   */
  async decodeVIN(pool: Pool, vin: string): Promise<VINDecodeResponse> {
    const normalizedVIN = vin.toUpperCase().trim();

    const validation = this.validateVIN(normalizedVIN);
    if (!validation.valid) {
      return {
        vin: normalizedVIN,
        result: null,
        success: false,
        error: validation.error
      };
    }

    try {
      const cached = await this.cache.getVINDecode(normalizedVIN);
      if (cached) {
        logger.debug('VIN decode result retrieved from cache', { vin: normalizedVIN });
        return cached;
      }

      let result = await this.repository.decodeVIN(pool, normalizedVIN);
      
      if (result) {
        const response: VINDecodeResponse = {
          vin: normalizedVIN,
          result,
          success: true
        };
        await this.cache.setVINDecode(normalizedVIN, response, true);
        logger.info('VIN decoded successfully via PostgreSQL', { vin: normalizedVIN, make: result.make, model: result.model, year: result.year });
        return response;
      }

      logger.info('VIN not found in PostgreSQL, attempting vPIC fallback', { vin: normalizedVIN });

      try {
        result = await this.circuitBreaker.fire(normalizedVIN) as VINDecodeResult | null;
        
        if (result) {
          const response: VINDecodeResponse = {
            vin: normalizedVIN,
            result,
            success: true
          };
          await this.cache.setVINDecode(normalizedVIN, response, true);
          logger.info('VIN decoded successfully via vPIC fallback', { vin: normalizedVIN, make: result.make, model: result.model, year: result.year });
          return response;
        }
      } catch (circuitError) {
        logger.warn('vPIC API unavailable or circuit breaker open', { vin: normalizedVIN, error: circuitError });
      }

      const failureResponse: VINDecodeResponse = {
        vin: normalizedVIN,
        result: null,
        success: false,
        error: 'VIN not found in database and external API unavailable'
      };
      
      await this.cache.setVINDecode(normalizedVIN, failureResponse, false);
      return failureResponse;

    } catch (error) {
      logger.error('VIN decode error', { vin: normalizedVIN, error });
      return {
        vin: normalizedVIN,
        result: null,
        success: false,
        error: 'Internal server error during VIN decoding'
      };
    }
  }

  /**
   * Get circuit breaker status
   */
  getCircuitBreakerStatus(): { state: string; stats: any } {
    return {
      state: this.circuitBreaker.opened ? 'open' : this.circuitBreaker.halfOpen ? 'half-open' : 'closed',
      stats: this.circuitBreaker.stats
    };
  }
}