/**
 * Link classifier — assigns priority and category to discovered URLs.
 *
 * Categories:
 * - 'nav'       : site navigation (homepage, top-level pages) — highest priority
 * - 'auth'      : login/register/password flows — high priority
 * - 'app'       : authenticated app screens — high priority
 * - 'content'   : blog/docs/articles — medium priority
 * - 'api'       : REST/GraphQL API endpoints — detected, not crawled as screens
 * - 'resource'  : static assets (JS/CSS/img/fonts) — skip
 * - 'external'  : different domain — skip unless cross-domain crawl enabled
 * - 'low-value' : pagination, sort, filter query strings — deprioritize
 */

export type LinkCategory = 'nav' | 'auth' | 'app' | 'content' | 'api' | 'resource' | 'external' | 'low-value';

export interface ClassifiedLink {
  url: string;
  category: LinkCategory;
  priority: number; // 0-100, higher = crawl sooner
  reason: string;
}

const RESOURCE_EXT = /\.(js|css|png|jpg|jpeg|gif|svg|ico|woff|woff2|ttf|eot|mp4|mp3|pdf|zip|gz|tar|exe|dmg|apk)(\?|$)/i;
const API_PATTERN = /\/(api|graphql|gql|rest|v\d+)\//i;
const AUTH_PATTERN = /\/(login|signin|sign-in|register|signup|sign-up|auth|oauth|sso|password|forgot|reset|logout|signout)\b/i;
const LOW_VALUE_PATTERN = /[?&](page|p|offset|sort|order|filter|q|search|tag|category|color|size|brand)=/i;
const PAGINATION_PATTERN = /\/page\/\d+|\/p\/\d+|\bpage=\d+/i;

export function classifyLink(url: string, baseUrl: string): ClassifiedLink {
  let parsed: URL;
  let baseHost: string;
  try {
    parsed = new URL(url);
    baseHost = new URL(baseUrl).hostname;
  } catch {
    return { url, category: 'low-value', priority: 0, reason: 'invalid URL' };
  }

  const path = parsed.pathname + parsed.search;
  const isExternal = parsed.hostname !== baseHost;

  if (isExternal) return { url, category: 'external', priority: 0, reason: 'different domain' };
  if (RESOURCE_EXT.test(path)) return { url, category: 'resource', priority: 0, reason: 'static asset extension' };
  if (API_PATTERN.test(path)) return { url, category: 'api', priority: 10, reason: 'API path pattern' };
  if (AUTH_PATTERN.test(path)) return { url, category: 'auth', priority: 90, reason: 'auth flow pattern' };
  if (PAGINATION_PATTERN.test(path)) return { url, category: 'low-value', priority: 15, reason: 'pagination' };
  if (LOW_VALUE_PATTERN.test(path)) return { url, category: 'low-value', priority: 20, reason: 'filter/sort query param' };

  const segments = parsed.pathname.split('/').filter(Boolean);
  if (segments.length === 0) return { url, category: 'nav', priority: 100, reason: 'homepage' };
  if (segments.length === 1) return { url, category: 'nav', priority: 80, reason: 'top-level nav' };
  if (segments.length <= 3) return { url, category: 'app', priority: 60, reason: 'app screen' };

  return { url, category: 'content', priority: 40, reason: 'deep content page' };
}

export function classifyLinks(urls: string[], baseUrl: string): ClassifiedLink[] {
  return urls.map(u => classifyLink(u, baseUrl))
    .sort((a, b) => b.priority - a.priority);
}

export function filterCrawlable(classified: ClassifiedLink[]): ClassifiedLink[] {
  return classified.filter(l => l.category !== 'resource' && l.category !== 'external' && l.category !== 'api');
}