import { Injectable, Logger } from '@nestjs/common';
import { ConfigService } from '@nestjs/config';

const DEFAULT_SCRAPE_URL = 'https://ethio.forex/bank/CBET';

/** Matches USD buying/selling embedded in ethio.forex CBET page HTML (after entity unescape). */
const USD_RATE_REGEX =
  /currency_code":\[0,"USD"\],"currency_name":\[0,"US DOLLAR"\],"buying":\[0,([\d.]+)\],"selling":\[0,([\d.]+)\]/;

@Injectable()
export class CbeExchangeService {
  private readonly logger = new Logger(CbeExchangeService.name);
  private cachedRate: number | null = null;
  private cacheExpiresAt = 0;

  constructor(private readonly configService: ConfigService) {}

  /**
   * Returns the current CBE USD→ETB **selling** rate scraped from ethio.forex.
   * Cached for CBE_EXCHANGE_CACHE_TTL_MS; falls back to CBE_EXCHANGE_FALLBACK_RATE on failure.
   */
  async getUsdToEtbRate(): Promise<number> {
    const now = Date.now();

    if (this.cachedRate !== null && now < this.cacheExpiresAt) {
      return this.cachedRate;
    }

    const scrapeUrl = this.getScrapeUrl();
    const fallbackRate =
      this.configService.get<number>('app.cbeExchange.fallbackRate') ?? 130;
    const cacheTtlMs =
      this.configService.get<number>('app.cbeExchange.cacheTtlMs') ?? 3_600_000;

    try {
      const response = await fetch(scrapeUrl, {
        signal: AbortSignal.timeout(8_000),
        headers: { 'User-Agent': 'Mozilla/5.0' },
      });

      if (!response.ok) {
        throw new Error(`CBE scrape responded with status ${response.status}`);
      }

      const html = await response.text();
      const rates = this.parseScrapedRates(html);

      if (!rates) {
        throw new Error('USD rate not found in ethio.forex page HTML');
      }

      const rate = rates.selling;
      if (!Number.isFinite(rate) || rate <= 0) {
        throw new Error(`Invalid selling rate parsed: ${rate}`);
      }

      this.cachedRate = rate;
      this.cacheExpiresAt = now + cacheTtlMs;
      this.logger.log(
        `CBE USD→ETB rate refreshed from ethio.forex — buying=${rates.buying} selling=${rate}`,
      );
      return rate;
    } catch (err) {
      this.logger.error(
        `Failed to scrape CBE exchange rate — using fallback ${fallbackRate} ETB/USD. Error: ${(err as Error).message}`,
      );

      if (this.cachedRate !== null) {
        this.logger.warn(`Using previously cached CBE rate: ${this.cachedRate}`);
        return this.cachedRate;
      }

      return fallbackRate;
    }
  }

  private getScrapeUrl(): string {
    const configured =
      this.configService.get<string>('app.cbeExchange.scrapeUrl') ??
      this.configService.get<string>('app.cbeExchange.apiUrl');
    return configured?.trim() || DEFAULT_SCRAPE_URL;
  }

  private parseScrapedRates(
    html: string,
  ): { buying: number; selling: number } | null {
    const decoded = this.unescapeHtml(html);
    const match = USD_RATE_REGEX.exec(decoded);
    if (!match) return null;

    const buying = Number(match[1]);
    const selling = Number(match[2]);
    if (!Number.isFinite(buying) || !Number.isFinite(selling)) return null;

    return { buying, selling };
  }

  private unescapeHtml(html: string): string {
    return html
      .replace(/&quot;/g, '"')
      .replace(/&#34;/g, '"')
      .replace(/&amp;/g, '&')
      .replace(/&lt;/g, '<')
      .replace(/&gt;/g, '>');
  }
}