market_screener/server/domains/screener/ScreenerEngine.ts

import {
  YahooFinanceClient,
  BenchmarkProvider,
  chunkArray,
  Stock,
  Etf,
  Bond,
  SIGNAL,
  SIGNAL_ORDER,
  SCORE_MODE,
  ASSET_TYPE,
} from '../../domains/shared';
import { DataMapper } from './transform/DataMapper';
import { RuleMerger } from './transform/RuleMerger';
import { StockScorer } from './scorers/StockScorer';
import { EtfScorer } from './scorers/EtfScorer';
import { BondScorer } from './scorers/BondScorer';
import type {
  Logger,
  MarketContext,
  Signal,
  AssetType,
  ScoreResult,
  ScreenerResult,
  ScreenerEngineOptions,
  ErrorResult,
  MappedData,
  StockData,
  EtfData,
  BondData,
} from '../../domains/shared';

export class ScreenerEngine {
  private static readonly BATCH_SIZE = 5;
  private static readonly BATCH_DELAY_MS = 1000;

  private logger: Logger;

  constructor(
    private readonly client: YahooFinanceClient,
    private readonly benchmarkProvider: BenchmarkProvider,
    { logger }: ScreenerEngineOptions = {},
  ) {
    // eslint-disable-next-line no-console
    this.logger = logger ?? {
      write: (msg: string) => process.stdout.write(msg),
      log: (...args: unknown[]) => console.log(...args),
      warn: (...args: unknown[]) => console.warn(...args),
    };
  }

  async screenTickers(tickers: string[]): Promise<ScreenerResult> {
    return this.screenInternal(tickers, false);
  }

  async screenWithProgress(tickers: string[]): Promise<ScreenerResult> {
    return this.screenInternal(tickers, true);
  }

  private async screenInternal(tickers: string[], showProgress: boolean): Promise<ScreenerResult> {
    const marketContext = await this.fetchMarketContext(showProgress);
    const results = this.initializeResults();
    const chunks = chunkArray(tickers, ScreenerEngine.BATCH_SIZE);
    let processed = 0;

    for (const chunk of chunks) {
      await this.processBatch(chunk, marketContext, results);
      processed += chunk.length;
      this.logProgress(showProgress, processed, tickers.length);
      await this.rateLimitDelay();
    }

    if (showProgress) {
      this.logger.write('\n');
    }

    return { ...results, marketContext };
  }

  private async fetchMarketContext(showProgress: boolean): Promise<MarketContext> {
    if (showProgress) {
      this.logger.write('⏳ Fetching market context...');
    }
    const context = await this.benchmarkProvider.getMarketContext();
    if (showProgress) {
      this.logger.write(' done\n');
    }
    return context;
  }

  private initializeResults(): Omit<ScreenerResult, 'marketContext'> {
    return { STOCK: [], ETF: [], BOND: [], ERROR: [] };
  }

  private async processBatch(
    tickers: string[],
    marketContext: MarketContext,
    results: Omit<ScreenerResult, 'marketContext'>,
  ): Promise<void> {
    const batch = await Promise.all(tickers.map((t) => this.fetch(t)));
    batch.forEach((data) => this.process(data, marketContext, results));
  }

  private logProgress(showProgress: boolean, processed: number, total: number): void {
    if (showProgress) {
      this.logger.write(`\r⏳ Screening tickers... ${processed}/${total}`);
    }
  }

  private async rateLimitDelay(): Promise<void> {
    await new Promise<void>((r) => setTimeout(r, ScreenerEngine.BATCH_DELAY_MS));
  }

  private async fetch(ticker: string): Promise<MappedData | ErrorResult> {
    try {
      const summary = await this.client.fetchSummary(ticker);
      if (!summary?.price) throw new Error('Empty response from Yahoo');
      return DataMapper.mapToStandardFormat(ticker, summary);
    } catch (err) {
      return { isError: true, ticker: ticker.toUpperCase(), message: (err as Error).message };
    }
  }

  private process(
    data: MappedData | ErrorResult,
    marketContext: MarketContext,
    results: Omit<ScreenerResult, 'marketContext'>,
  ): void {
    if ('isError' in data && data.isError) {
      const e = data as ErrorResult;
      results.ERROR.push({ ticker: e.ticker, message: e.message });
      return;
    }

    try {
      const asset = this.buildAsset(data as MappedData);
      const fundamental = this.score(asset, marketContext, SCORE_MODE.FUNDAMENTAL);
      const inflated = this.score(asset, marketContext, SCORE_MODE.INFLATED);

      (results[asset.type as AssetType] as unknown[]).push({
        asset,
        fundamental,
        inflated,
        signal: this.signal(fundamental.label, inflated.label),
      });
    } catch (err) {
      results.ERROR.push({
        ticker: ((data as { ticker?: string }).ticker || 'UNKNOWN').toUpperCase(),
        message: (err as Error).message,
      });
    }
  }

  // Typed scorer dispatch — instanceof narrows the asset so each scorer receives
  // its exact metrics type. No `as never` or unsafe casts required.
  private score(
    asset: Stock | Etf | Bond,
    marketContext: MarketContext,
    mode: string,
  ): ScoreResult {
    const rules = RuleMerger.getRulesForAsset(
      asset.type as AssetType,
      asset.metrics as { sector?: string },
      marketContext,
      mode,
    );
    if (asset instanceof Stock) return StockScorer.score(asset.metrics, rules);
    if (asset instanceof Etf) return EtfScorer.score(asset.metrics, rules);
    if (asset instanceof Bond) return BondScorer.score(asset.metrics, rules, marketContext);
    // TypeScript exhaustive check: all three branches are handled above.
    throw new Error('No scorer for unknown asset type');
  }

  private buildAsset(data: Record<string, unknown>): Stock | Etf | Bond {
    switch (((data.type as string) || ASSET_TYPE.STOCK).toUpperCase()) {
      case ASSET_TYPE.BOND:
        return new Bond(data as BondData);
      case ASSET_TYPE.ETF:
        return new Etf(data as EtfData);
      default:
        return new Stock(data as StockData);
    }
  }

  private signal(fundamentalLabel: string, inflatedLabel: string): Signal {
    const green = (l: string) => l.startsWith('🟢');
    const yellow = (l: string) => l.startsWith('🟡');
    if (green(fundamentalLabel)) return SIGNAL.STRONG_BUY;
    if (green(inflatedLabel) && yellow(fundamentalLabel)) return SIGNAL.MOMENTUM;
    if (green(inflatedLabel) && !green(fundamentalLabel)) return SIGNAL.SPECULATION;
    if (yellow(fundamentalLabel) || yellow(inflatedLabel)) return SIGNAL.NEUTRAL;
    return SIGNAL.AVOID;
  }

  signalOrder(signal: Signal): number {
    return SIGNAL_ORDER[signal] ?? 5;
  }

  getMarketContext(): Promise<MarketContext> {
    return this.benchmarkProvider.getMarketContext();
  }
}