@draftbox-co/gatsby-ghost-novela-theme/plugins/gatsby-plugin-ghost-manifest/src/gatsby-node.js

A Gatsby theme plugin for creating blogs from headless Ghost CMS.

const fs = require(`fs`);
const path = require(`path`);
const Promise = require(`bluebird`);
const sharp = require(`sharp`);
const { defaultIcons, doesIconExist } = require(`./common.js`);

sharp.simd(true);

function generateIcons(icons, srcIcon) {
  return Promise.map(icons, (icon) => {
    const size = parseInt(icon.sizes.substring(0, icon.sizes.lastIndexOf(`x`)));
    const imgPath = path.join(`public`, icon.src);

    return sharp(srcIcon)
      .resize(size)
      .toFile(imgPath)
      .then(() => {});
  });
}

exports.onPostBuild = async ({ graphql }, pluginOptions) => {
  let { icon, ...manifest } = pluginOptions;

  const { data } = await graphql(pluginOptions.query);
  const siteTitle = data.site.siteMetadata.siteTitle || "No Title";
  manifest = {
    ...manifest,
    name: siteTitle,
  };

  // Delete options we won't pass to the manifest.webmanifest.
  delete manifest.plugins;
  delete manifest.legacy;
  delete manifest.theme_color_in_head;
  delete manifest.query;

  // If icons are not manually defined, use the default icon set.
  if (!manifest.icons) {
    manifest.icons = defaultIcons;
  }

  // Determine destination path for icons.
  const iconPath = path.join(`public`, path.dirname(manifest.icons[0].src));

  //create destination directory if it doesn't exist
  if (!fs.existsSync(iconPath)) {
    fs.mkdirSync(iconPath);
  }

  fs.writeFileSync(
    path.join(`public`, `manifest.webmanifest`),
    JSON.stringify(manifest)
  );

  // Only auto-generate icons if a src icon is defined.
  if (icon !== undefined) {
    // Check if the icon exists
    if (!doesIconExist(icon)) {
      Promise.reject(
        `icon (${icon}) does not exist as defined in gatsby-config.js. Make sure the file exists relative to the root of the site.`
      );
    }
    generateIcons(manifest.icons, icon).then(() => {
      //images have been generated
      console.log(`done generating icons for manifest`);
      Promise.resolve();
    });
  } else {
    Promise.resolve();
  }
};