rename.ts

import * as fs from 'fs/promises'
import * as path from 'path'

async function * readdirP (dir: string): AsyncGenerator<string> {
  for (const entry of await fs.readdir(dir, { withFileTypes: true })) {
    if (entry.isDirectory()) {
      for await (const sub of readdirP(path.join(dir, entry.name))) {
        yield sub
      }
    } else if (entry.isFile()) {
      yield path.join(dir, entry.name)
    }
  }
}

async function main (): Promise<void> {
  for await (const entry of readdirP(path.relative(process.cwd(), path.join(__dirname, '..', 'mjs')))) {
    const match = /^(.*)(\.(js|js\.map|d\.ts))$/.exec(entry)
    if (match == null) {
      continue
    }
    const file = match[1]
    const ext = match[2]
    if (ext === '.js') {
      let data = await fs.readFile(entry, 'utf-8')
      data = data.replace(/^((import|export)\s+.+from\s+')(.+)('\s*)/gm, (_, prefix: string, __, file: string, suffix: string) => {
        if (file.startsWith('./') && !file.endsWith('.mjs')) {
          file += '.mjs'
        }
        return `${prefix}${file}${suffix}`
      })
      data = data.replace(`//# sourceMappingURL=${path.basename(file)}.js.map`, `//# sourceMappingURL=${path.basename(file)}.mjs.map`)
      await fs.writeFile(entry, data)
      await fs.rename(entry, `${file}.mjs`)
    } else if (ext === '.js.map') {
      const data = JSON.parse(await fs.readFile(entry, 'utf-8'))
      data.file = `${file}.mjs`
      await fs.writeFile(entry, JSON.stringify(data))
      await fs.rename(entry, `${file}.mjs.map`)
    } else if (ext === '.d.ts') {
      await fs.rename(entry, `${file}.d.mts`)
    }
  }
}

main()
  .catch((e: Error) => {
    console.error(e)
    process.exit(1)
  })