Copy styles from one ASS subtitle file to another

transfer-ass-headers

#!/usr/bin/env node

// Copy styles from one ASS subtitle file to another by copying every section above [Events]

const fs = require('fs').promises

const sourcePath = process.argv[2]
const targetPath = process.argv[3]

async function main() {
  if (!await fs.stat(sourcePath) || !await fs.stat(targetPath)) {
    console.error(`Error: File not found "${sourcePath}" or "${targetPath}"`)
    return 1
  }

  const sourceText = (await fs.readFile(sourcePath)).toString()
  const targetText = (await fs.readFile(targetPath)).toString()

  const [ sourceHeaders, sourceEvents ] = sourceText.split(/^\[Events\] *$/m)
  const [ targetHeaders, targetEvents ] = targetText.split(/^\[Events\] *$/m)

  if (!sourceHeaders || !sourceEvents || !targetHeaders || !targetEvents) {
    console.error(`Files parsed incorrectly, aborting`)
    return 1
  }

  const finalText = sourceHeaders + '[Events]\n' + targetEvents

  const originalFilePath = targetPath.replace(/\.([^.]+)$/, '.orig.$1')
  await fs.rename(targetPath, originalFilePath)
  await fs.writeFile(targetPath, finalText)

  console.log(`Copied headers from "${sourcePath}" to "${targetPath}".`)
  console.log(`Original file renamed to "${originalFilePath}".`)

  return 0
}
main().then(code => process.exit(code))