import { Injectable, ServiceUnavailableException } from '@nestjs/common';
import { load } from 'cheerio';
import { LRUCache } from 'lru-cache';

const REGISTRY_CACHE_TTL_MS = 21_600_000;
const REQUEST_TIMEOUT_MS = 10_000;
const COLUMN_COUNT = 6;
const ISIN_COLUMN = 3;
const DATE_COLUMN = 5;

const registryUrl = 'https://ratings.ru/ratings/issues/';
export type NcrRating = {
  agency: 'NCR';
  date: string;
  observedAt: string;
  sourceUrl: string;
  status: 'active' | 'withdrawn';
  value: null | string;
};

@Injectable()
export class NcrRatingsClient {
  // Public registry contains no user data. Share one download across all issues.
  private readonly cache = new LRUCache<
    string,
    Promise<Map<string, NcrRating>>
  >({ max: 1, ttl: REGISTRY_CACHE_TTL_MS });

  async rating(isin: string): Promise<NcrRating | null> {
    const key = isin.trim().toUpperCase();
    if (!/^[A-Z]{2}[A-Z0-9]{9}\d$/.test(key)) return null;
    let pending = this.cache.get('registry');
    if (!pending) {
      pending = this.registry().catch(() => {
        // Bound outage traffic too; never present a failed download as no rating.
        if (this.cache.get('registry') === pending) {
          this.cache.set('registry', pending, { ttl: 60_000 });
        }
        throw new ServiceUnavailableException({ code: 'NCR_UNAVAILABLE' });
      });
      this.cache.set('registry', pending);
    }
    return (await pending).get(key) ?? null;
  }

  private async registry(): Promise<Map<string, NcrRating>> {
    const response = await fetch(registryUrl, {
      signal: AbortSignal.timeout(REQUEST_TIMEOUT_MS),
    });
    if (!response.ok) throw new Error('NCR unavailable');
    const $ = load(await response.text());
    const table = $('#issues-table');
    const headings = table
      .find('thead th')
      .map((_, cell) => $(cell).text().trim())
      .get();
    if (
      table.length !== 1 ||
      headings.length !== COLUMN_COUNT ||
      headings[2] !== 'Рейтинг' ||
      // eslint-disable-next-line security/detect-object-injection -- Column indexes are local numeric constants.
      headings[ISIN_COLUMN] !== 'ISIN' ||
      // eslint-disable-next-line security/detect-object-injection -- Column indexes are local numeric constants.
      headings[DATE_COLUMN] !== 'Дата'
    ) {
      throw new Error('NCR registry changed');
    }
    const observedAt = new Date().toISOString();
    const result = new Map<string, NcrRating>();
    table.find('tbody tr').each((_, row) => {
      const cells = $(row).find('td');
      if (cells.length !== COLUMN_COUNT) throw new Error('NCR row changed');
      const isin = cells.eq(ISIN_COLUMN).text().trim().toUpperCase();
      // Unassigned issues cannot safely be matched to a held instrument.
      if (!/^[A-Z]{2}[A-Z0-9]{9}\d$/.test(isin)) return;
      const raw = cells.eq(2).text().replace(/\s+/g, ' ').trim();
      const withdrawn = raw.toLowerCase() === 'рейтинг отозван';
      if (
        !withdrawn &&
        !/^(?:AAA|A{1,2}[+-]?|B{1,3}[+-]?|CCC[+-]?|C{1,2}|D)\.ru$/.test(
          raw,
        )
      ) {
        throw new Error('NCR rating changed');
      }
      const dateParts = /^(\d{2})\.(\d{2})\.(\d{4})$/.exec(
        cells.eq(DATE_COLUMN).text().trim(),
      );
      const href = cells.eq(ISIN_COLUMN).find('a').attr('href');
      if (!dateParts || !href || !/^\/ratings\/issues\/\d+\/$/.test(href)) {
        throw new Error('NCR identity missing');
      }
      const date = `${dateParts[3]}-${dateParts[2]}-${dateParts[1]}`;
      if (
        !Number.isFinite(Date.parse(date)) ||
        new Date(date).toISOString().slice(0, 10) !== date
      ) {
        throw new Error('NCR date invalid');
      }
      const rating: NcrRating = {
        agency: 'NCR',
        value: withdrawn ? null : raw,
        status: withdrawn ? 'withdrawn' : 'active',
        date,
        sourceUrl: `https://ratings.ru${href}`,
        observedAt,
      };
      const previous = result.get(isin);
      if (
        previous &&
        previous.date === date &&
        (previous.value !== rating.value || previous.status !== rating.status)
      ) {
        throw new Error('NCR rating ambiguous');
      }
      if (!previous || previous.date < date) result.set(isin, rating);
    });
    if (!result.size) throw new Error('NCR registry empty');
    return result;
  }
}