Rollup plugin to rename imports in an ES modules

rollup-plugin-web-dependencies.js

import fs from 'fs'

/**
 * @example
 * // In rollup.config.js
 * export default {
 *   // ...
 *   plugins: [
 *     webDependencies({
 *       // Use pika cdn by default
 *       'preact': '^8.5.2',
 *       // Use custom location
 *       'redux': 'https://cdn.pika.dev/redux/^4.0.4'
 *     })
 *   ]
 * }
 * 
 * // In package.json
 * {
 *   "webDependencies": {
 *     "preact": "^8.5.2",
 *     "redux": "https://cdn.pika.dev/redux/^4.0.4"
 *   }
 * }
 */
export default function webDependencies(webDepencencies = {}) {
  return {
    name: 'web-dependencies',
    transform(code) {
      this.externals.forEach(({ pattern, source }) => code.replace(
        pattern,
        `$1'${source}'$2`
      )
    },

    async options(opts) {
      opts = { external: [], ...opts }

      const pkg = await new Promise((resolve) => {
        fs.readFile('package.json', (error, content) => resolve(error
          ? {}
          : JSON.parse(content.toString())
        ))
      })

      this.externals = Object
        .entries({ ...pkg.webDependencies, ...webDependencies })
        .map((name, source) => {
          opts.external.push(name)

          return {
            pattern: new RegExp(`^(\s*import\s+.?)(?:'${name}'|"${name}")(\s*;?\s*)$`, 'mg'),
            source: /^https?:\/\//.test(source)
              ? source
              : `https://cdn.pika.dev/${name}/${source}`
          }
        }

      return opts
    }
  }
}