import { promisify } from 'util'
import { spawn, exec } from 'child_process'

const execPromise = promisify(exec)

export default function kill(pid, signal) {
  let pids = new Set([pid])
  let getSpawn = null
  let getPids = null

  switch (process.platform) {
    case 'win32':
      return execPromise('taskkill /pid ' + pid + ' /T /F').then(() => pids)
    case 'darwin':
      getSpawn = function(parentPid) {
        return spawn('pgrep', ['-P', parentPid])
      }
      getPids = function(data) {
        return data.match(/\d+/g).map(Number)
      }
      break
    default:
      getSpawn = function (parentPid) {
        return exec('ps -opid="" -oppid="" | grep ' + parentPid)
      }
      getPids = function(data, parentPid) {
        let output = data.trim().split('\n')
        return output.map(line => {
          let [child, parent] = line.trim().split(/ +/)

          if (Number(parent) === parentPid) {
            return Number(child)
          }

          return 0
        }).filter(x => x)
      }
      break
  }

  return buildTree(pids, getSpawn, getPids, pid)
    .then(function() {
      for (let pid of pids) {
        try {
          process.kill(pid, signal)
        } catch (err) {
          if (err.code !== 'ESRCH') throw err;
        }
      }
      return pids
    })
}

function buildTree(allPids, spawnGetChildren, spawnGetPids, parentPid) {
  allPids.add(parentPid)

  let ps = spawnGetChildren(parentPid)
  let data = ''
  let err = ''
  ps.stdout.on('data', function(buf) {
    data += buf.toString('ascii')
  })
  ps.stderr.on('data', function(buf) {
    err += buf.toString('ascii')
  })

  return new Promise(function(res, rej) {
    ps.on('close', function(code) {
      // Check if ps errored out
      if (code !== 0 && err.trim()) {
        return rej(new Error('Error running ps to kill processes:\n\t' + err))
      }

      // Check if we otherwise got an error code (usually means empty results)
      if (code !== 0 || !data.trim()) return res()

      let pids = spawnGetPids(data, parentPid)

      res(Promise.all(
        pids.filter(pid => pid && !allPids.has(pid))
          .map(buildTree.bind(this, allPids, spawnGetChildren, spawnGetPids))
      ))
    })
  })
}