filters.js

const { URL } = require("url");

const defaults = {
  mentionTypes: {
    likes: ["like-of"],
    reposts: ["repost-of"],
    comments: ["mention-of", "in-reply-to"],
  },
};

function stripOuterSlashes(str) {
  let start = 0;
  while (str[start++] === "/");
  let end = str.length;
  while (str[--end] === "/");
  return str.slice(start - 1, end + 1);
}

const filters = ({
  mentionTypes = defaults.mentionTypes,
  pageAliases = {},
}) => {
  const cleanedAliases = Object.keys(pageAliases).reduce((cleaned, key) => {
    cleaned[stripOuterSlashes(key.toLowerCase())] =
      typeof pageAliases[key] === "string"
        ? [stripOuterSlashes(pageAliases[key].toLowerCase())]
        : pageAliases[key].map((alias) =>
            stripOuterSlashes(alias.toLowerCase())
          );

    return cleaned;
  }, {});

  function filterWebmentions(webmentions, page) {
    const pageUrl = new URL(page, "https://lukeb.co.uk");
    const normalizedPagePath = stripOuterSlashes(
      pageUrl.pathname.toLowerCase()
    );

    const flattenedMentionTypes = Object.values(mentionTypes).flat();

    return webmentions
      .filter((mention) => {
        const target = new URL(mention["wm-target"]);
        const normalisedTargetPath = stripOuterSlashes(
          target.pathname.toLowerCase()
        );
        return (
          normalizedPagePath === normalisedTargetPath ||
          cleanedAliases[normalizedPagePath]?.includes(normalisedTargetPath)
        );
      })
      .filter(
        (entry) => !!entry.author && (!!entry.author.name || entry.author.url)
      )
      .filter((mention) =>
        flattenedMentionTypes.includes(mention["wm-property"])
      );
  }

  function count(webmentions, pageUrl) {
    const page =
      pageUrl ||
      this.page?.url ||
      this.ctx?.page?.url ||
      this.context?.environments?.page?.url;

    return filterWebmentions(webmentions, page).length;
  }

  function mentions(webmentions, pageUrl) {
    const page =
      pageUrl ||
      this.page?.url ||
      this.ctx?.page?.url ||
      this.context?.environments?.page?.url;

    const filteredWebmentions = filterWebmentions(webmentions, page);

    const returnedWebmentions = {
      total: filteredWebmentions.length,
    };

    Object.keys(mentionTypes).map((type) => {
      returnedWebmentions[type] = filteredWebmentions.filter((mention) =>
        mentionTypes[type].includes(mention["wm-property"])
      );
    });

    return returnedWebmentions;
  }

  return {
    count,
    mentions,
  };
};

filters.defaults = defaults;

module.exports = filters;