import Dot from 'dot';
import { encodeXML } from 'entities';
import { readFile, writeFile } from 'fs/promises';
import { join } from 'path';
import { debuglog } from 'util';

const internals = {
  debuglog: debuglog('blog'),

  kFeedName: 'feed.xml',

  extractTitle(postText) {

    return postText.trim()
      .split('\n')[0]
      .replace('#', '')
      .replace(/&/g, '&')
      .trim();
  }
};

/**
 * Generates an RSS feed XML file
 *
 * @name RSSGenerator
 * @param {string} source the source directory
 * @param {string} target the target directory
 * @param {Array.<Blog.tPost>} posts the list of posts
 */
export default async function RSSGenerator(source, target, posts) {

  internals.debuglog('Generating RSS');
  const feedTarget = join(target, internals.kFeedName);
  const feedLocation = join(source, internals.kFeedName);

  internals.debuglog(`Reading ${feedLocation}`);
  const feedTemplate = await readFile(feedLocation, { encoding: 'utf8' });

  internals.debuglog('Writing RSS');
  posts = posts.map((post) => ({
    ...post,
    createdOn: (new Date(post.createdOn)).toUTCString(),
    title: internals.extractTitle(post.raw),
    html: encodeXML(post.html)
  }));
  const feedXml = Dot.template(feedTemplate, {
    ...Dot.templateSettings,
    strip: false
  })({ posts });
  await writeFile(feedTarget, feedXml);
}