usage: $ ./git-remove.js <anchor> <amount>

git-remove.js

#!/usr/bin/env node
const execa = require('execa')
const fs = require('fs')
const tmp = require('tmp')

// Main
{
  const [anchor, amount = 1] = process.argv.slice(-2).map(Number)

  gitRebaseInteractive(anchor, function (operations, amount) {
    operations = operations
      // Replace comments
      .replace(/#.*/g, '')
      // Each line would be a cell
      .split('\n')
      // Get rid of empty lines
      .filter(Boolean)

    // Commits we would like to drop
    const dropOperations = operations
      .slice(0, amount)
      .map(operation => operation.replace('pick', 'drop'))

    // Commits we would like to pick
    const pickOperations = operations.slice(amount)

    // Composing final rebase file
    return []
      .concat(dropOperations)
      .concat(pickOperations)
      .join('\n')

  }, [amount])

  console.log(`Removed ${amount} commits starting ${anchor}`)
}

// Runs a git-rebase-interactive in a non interactive manner by providing a script
// which will handle things automatically
function gitRebaseInteractive(head, fn, args) {
  execa.sync('git', ['rebase', '-i', head], {
    env: {
      GIT_SEQUENCE_EDITOR: gitEdit(fn, args)
    }
  })
}

// Evaluates a script in a new process which should edit a git file.
// The input of the provided function should be the contents of the file and the output
// should be the new contents of the file
function gitEdit(fn, args) {
  args = args.map(arg => `'${arg}'`).join(', ')

  const body = fn.toString()
    .replace(/\\/g, '\\\\')
    .replace(/`/g, '\\`')

  const scriptFile = tmp.fileSync({ unsafeCleanup: true })

  fs.writeFileSync(scriptFile.name, `
    const fs = require('fs')

    const file = process.argv[process.argv.length - 1]
    let content = fs.readFileSync(file).toString()
    content = new Function(\`return (${body}).apply(this, arguments)\`)(content, ${args})
    fs.writeFileSync(file, content)
    fs.unlinkSync('${scriptFile.name}')
  `)

  return `node ${scriptFile.name}`
}