// check to see if a bin is allowed to be overwritten
// either rejects or resolves to nothing.  return value not relevant.
const isWindows = require('./is-windows.js')
const binTarget = require('./bin-target.js')
const {resolve, dirname} = require('path')
const readCmdShim = require('read-cmd-shim')
const fs = require('fs')
const {promisify} = require('util')
const readlink = promisify(fs.readlink)

const checkBin = async ({bin, path, top, global, force}) => {
  // always ok to clobber when forced
  // always ok to clobber local bins, or when forced
  if (force || !global || !top)
    return

  // ok, need to make sure, then
  const target = resolve(binTarget({path, top}), bin)
  path = resolve(path)
  return isWindows ? checkShim({target, path}) : checkLink({target, path})
}

// only enoent is allowed.  anything else is a problem.
const handleReadLinkError = async ({er, target}) =>
  er.code === 'ENOENT' ? null
  : failEEXIST({target})

const checkLink = async ({target, path}) => {
  const current = await readlink(target)
    .catch(er => handleReadLinkError({er, target}))

  if (!current)
    return

  const resolved = resolve(dirname(target), current)

  if (resolved.toLowerCase().indexOf(path.toLowerCase()) !== 0)
    return failEEXIST({target})
}

const handleReadCmdShimError = ({er, target}) =>
  er.code === 'ENOENT' ? null
  : failEEXIST({target})

const failEEXIST = ({target}) =>
  Promise.reject(Object.assign(new Error('EEXIST: file already exists'), {
    path: target,
    code: 'EEXIST',
  }))

const checkShim = async ({target, path}) => {
  const shims = [
    target,
    target + '.cmd',
    target + '.ps1',
  ]
  await Promise.all(shims.map(async target => {
    const current = await readCmdShim(target)
      .catch(er => handleReadCmdShimError({er, target}))

    if (!current)
      return

    const resolved = resolve(dirname(target), current.replace(/\\/g, '/'))

    if (resolved.toLowerCase().indexOf(path.toLowerCase()) !== 0)
      return failEEXIST({target})
  }))
}

module.exports = checkBin
