const fs = require('fs'),
      fm = require('front-matter')

/** @type {import('next-sitemap').IConfig} */
module.exports = {
  siteUrl: process.env.SITE_URL || 'https://www.aaronjy.me',
  changefreq: 'weekly',
  generateRobotsTxt: true,
  autoLastmod: false,
  generateIndexSitemap: false,
  robotsTxtOptions: {
    policies: [
      {
        userAgent: '*',
        allow: '/'
      }
    ]
  },
  transform: async (config, path) => {
    const metadata = {
      loc: path
    };

    if (isHomepage(path)) {
      metadata.priority = 1;
    } else if (isBasePage(path)) {
      metadata.priority = 0.8;
    } else {
      if (isArticle(path)) {
        metadata.priority = 0.6;
        const attributes = getArticleAttibutes(`content${path}.md`);
        if (!attributes)
          return null;

        metadata.pubdate = attributes.pubdate ?? null;
        metadata.moddate = attributes.moddate ?? null;

        console.log("Calculated sitemap dates for article", path);
      }
    }

    return metadata;
  }
}

function isHomepage(path) {
  return path === "/";
}

function isBasePage(path) {
  return path.split("/").length === 2;
}

function isArticle(path) {
  return path.startsWith("/writing/");
}

function getArticleAttibutes(path) {
  const fileContents = fs.readFileSync(path, {
    encoding: 'utf-8'
  })

  // @ts-ignore
  const { attributes } = fm(fileContents);

  return {
    ...attributes,
    pubdate: attributes.pubdate?.toISOString() ?? null,
    moddate: attributes.moddate?.toISOString() ?? null
  };
}