// markdown-it plugin for:
// 1. adding target="_blank" to external links
// 2. normalize internal links to end with `.html`

import type MarkdownIt from 'markdown-it';
import type { MarkdownParsedData } from '../markdown';
import { URL } from 'url';

const indexRE = /(^|.*\/)index.md(#?.*)$/i;

export const linkPlugin = (md: MarkdownIt, externalAttrs: Record<string, string>) => {
  md.renderer.rules.link_open = (tokens, idx, options, _env, self) => {
    const token = tokens[idx];
    const hrefIndex = token.attrIndex('href');
    if (hrefIndex >= 0) {
      const hrefAttr = token.attrs![hrefIndex];
      const url = hrefAttr[1];
      const isExternal = /^https?:/.test(url);
      if (isExternal) {
        Object.entries(externalAttrs).forEach(([key, val]) => {
          token.attrSet(key, val);
        });
      } else if (
        // internal anchor links
        !url.startsWith('#') &&
        // mail links
        !url.startsWith('mailto:')
      ) {
        normalizeHref(hrefAttr);
      }
    }
    return self.renderToken(tokens, idx, options);
  };

  function normalizeHref(hrefAttr: [string, string]) {
    let url = hrefAttr[1];

    const indexMatch = url.match(indexRE);
    if (indexMatch) {
      const [, path, hash] = indexMatch;
      url = path + hash;
    } else {
      let cleanUrl = url.replace(/\#.*$/, '').replace(/\?.*$/, '');
      // .md -> .html
      if (cleanUrl.endsWith('.md')) {
        cleanUrl = cleanUrl.replace(/\.md$/, '.html');
      }
      // ./foo -> ./foo.html
      if (!cleanUrl.endsWith('.html') && !cleanUrl.endsWith('/')) {
        cleanUrl += '.html';
      }
      const parsed = new URL(url, 'http://a.com');
      url = cleanUrl + parsed.search + parsed.hash;
    }

    // ensure leading . for relative paths
    if (!url.startsWith('/') && !/^\.\//.test(url)) {
      url = './' + url;
    }

    // export it for existence check
    const data = (md as any).__data as MarkdownParsedData;
    const links = data.links || (data.links = []);
    links.push(url.replace(/\.html$/, ''));

    // markdown-it encodes the uri
    hrefAttr[1] = decodeURI(url);
  }
};