import type { CrawledPage } from "./types";

export class Crawler {
  private maxPages: number;
  private timeoutMs: number;
  private visited: Set<string> = new Set();
  private pages: CrawledPage[] = [];
  private queue: string[] = [];

  constructor(options: { maxPages: number; timeoutMs: number }) {
    this.maxPages = options.maxPages;
    this.timeoutMs = options.timeoutMs;
  }

  async crawl(startUrl: string): Promise<CrawledPage[]> {
    this.visited.clear();
    this.pages = [];
    this.queue = [startUrl];

    while (this.queue.length > 0 && this.pages.length < this.maxPages) {
      const url = this.queue.shift()!;
      if (this.visited.has(url)) continue;
      this.visited.add(url);

      try {
        const page = await this.fetchPage(url);
        this.pages.push(page);
        for (const link of page.links) {
          if (!this.visited.has(link)) {
            this.queue.push(link);
          }
        }
      } catch {
        // Skip unreachable pages, continue crawl
      }
    }

    return this.pages;
  }

  private async fetchPage(url: string): Promise<CrawledPage> {
    const controller = new AbortController();
    const timeout = setTimeout(() => controller.abort(), this.timeoutMs);

    try {
      const res = await fetch(url, {
        signal: controller.signal,
        headers: { "User-Agent": "c0py/0.1" },
        redirect: "follow",
      });
      const body = await res.text();

      const links = this.extractLinks(body, url);

      return {
        url,
        path: new URL(url).pathname,
        title: this.extractTag(body, "title"),
        description: this.extractMetaDescription(body),
        statusCode: res.status,
        contentType: res.headers.get("content-type"),
        links,
      };
    } finally {
      clearTimeout(timeout);
    }
  }

  private extractLinks(html: string, baseUrl: string): string[] {
    const links: string[] = [];
    const re = /href\s*=\s*["']([^"']+)["']/gi;
    let m;
    while ((m = re.exec(html)) !== null) {
      try {
        const abs = new URL(m[1], baseUrl).href;
        if (!links.includes(abs)) links.push(abs);
      } catch {
        // Skip invalid URLs
      }
    }
    return links;
  }

  private extractTag(html: string, tag: string): string | null {
    const re = new RegExp(`<${tag}[^>]*>([\\s\\S]*?)<\\/${tag}>`, "i");
    const m = html.match(re);
    if (!m) return null;
    return m[1].replace(/<[^>]+>/g, "").trim().slice(0, 500) || null;
  }

  private extractMetaDescription(html: string): string | null {
    const re = /<meta[^>]*name=["']description["'][^>]*content=["']([^"']*)["']/i;
    const m = html.match(re);
    return m ? m[1].slice(0, 500) : null;
  }
}