import { z } from 'zod';
import type { Article } from '../shared/protocol.ts';

const pageSchema = z.object({
  pageid: z.number().int().positive().max(Number.MAX_SAFE_INTEGER), ns: z.literal(0),
  title: z.string().trim().min(1).max(200), extract: z.string().max(4096).optional(),
  lastrevid: z.number().int().positive().max(Number.MAX_SAFE_INTEGER),
  thumbnail: z.object({ source: z.string().url().max(1500) }).optional(),
  categories: z.array(z.object({ title: z.string().min(1).max(300) })).max(50).optional(),
});
const responseSchema = z.object({ query: z.object({ pages: z.array(z.unknown()).max(10) }) });
const MAX_RESPONSE_BYTES = 512 * 1024;
const MAX_ATTEMPTS = 3;
const imageOrigins = new Set(['https://upload.wikimedia.org', 'https://thumb.wikimedia.org']);

function category(title: string, categories: string[]): string {
  const text = `${title} ${categories.join(' ')}`.toLowerCase();
  if (/astronom|planet|space|galax|moon|star\b/.test(text)) return 'Space';
  if (/animal|plant|species|ocean|biolog|mollusc/.test(text)) return 'Nature';
  if (/births|deaths|people|scientist/.test(text)) return 'People';
  if (/physic|chem|math|science|technolog/.test(text)) return 'Science';
  if (/histor|ancient|archaeolog|empire/.test(text)) return 'History';
  return 'Culture';
}
async function readJson(response: Response): Promise<unknown> {
  const length = response.headers.get('content-length');
  if (!response.ok || response.redirected ||
      !/^application\/json(?:\s*;|\s*$)/i.test(response.headers.get('content-type') ?? '') ||
      (length !== null && (!/^\d+$/.test(length) || Number(length) > MAX_RESPONSE_BYTES)) || !response.body) {
    await response.body?.cancel();
    throw new Error('Invalid Wikipedia API response');
  }
  const reader = response.body.getReader();
  const chunks: Uint8Array[] = [];
  let size = 0;
  try {
    for (;;) {
      const { done, value } = await reader.read();
      if (done) break;
      size += value.byteLength;
      if (size > MAX_RESPONSE_BYTES) throw new Error('Wikipedia response too large');
      chunks.push(value);
    }
    return JSON.parse(new TextDecoder('utf-8', { fatal: true }).decode(Buffer.concat(chunks)));
  } finally {
    await reader.cancel();
    reader.releaseLock();
  }
}

function pictureUrl(value: string | undefined): string | undefined {
  if (!value) return undefined;
  try {
    const url = new URL(value);
    return url.protocol === 'https:' && imageOrigins.has(url.origin) && !url.username && !url.password && !url.hash
      ? url.toString() : undefined;
  } catch { return undefined; }
}

export class WikipediaArticleSource {
  private readonly fetcher: typeof globalThis.fetch;
  private active = 0;

  constructor(fetcher: typeof globalThis.fetch = globalThis.fetch) { this.fetcher = fetcher; }

  async random(): Promise<Article> {
    if (this.active >= 4) throw new Error('Wikipedia article service is busy');
    this.active++;
    try {
      for (let attempt = 0; attempt < MAX_ATTEMPTS; attempt++) {
        try {
          const url = new URL('https://en.wikipedia.org/w/api.php');
          url.search = new URLSearchParams({ action: 'query', format: 'json', formatversion: '2',
            generator: 'random', grnnamespace: '0', grnlimit: '10', prop: 'extracts|pageimages|info|categories',
            exintro: '1', explaintext: '1', exchars: '900', piprop: 'thumbnail', pithumbsize: '800', cllimit: '20' }).toString();
          const response = await this.fetcher(url, { signal: AbortSignal.timeout(3500), redirect: 'error',
            headers: { 'User-Agent': 'Wikideck/0.1 (experimental Wikipedia article cards)', Accept: 'application/json' } });
          const data = responseSchema.parse(await readJson(response));
          for (const rawPage of data.query.pages) {
            const parsedPage = pageSchema.safeParse(rawPage);
            if (!parsedPage.success) continue;
            const page = parsedPage.data;
            const image = pictureUrl(page.thumbnail?.source);
            const extract = page.extract?.trim();
            if (!image || !extract || extract.length < 40) continue;
            return { pageId: page.pageid, title: page.title, extract: extract.slice(0, 900), image,
              url: `https://en.wikipedia.org/?curid=${page.pageid}`, revisionId: page.lastrevid,
              source: 'live', category: category(page.title, page.categories?.map(c => c.title) ?? []) };
          }
        } catch { /* Try another random API response, but keep the number of attempts bounded. */ }
      }
      throw new Error('Wikipedia did not return an article with a picture after three attempts');
    } finally {
      this.active--;
    }
  }
}

export const wikipediaArticles = new WikipediaArticleSource();