'use strict'

const fs = require('graceful-fs')
const BB = require('bluebird')
const chmod = BB.promisify(fs.chmod)
const unlink = BB.promisify(fs.unlink)
let move
let pinflight

module.exports = moveFile
function moveFile (src, dest) {
  // This isn't quite an fs.rename -- the assumption is that
  // if `dest` already exists, and we get certain errors while
  // trying to move it, we should just not bother.
  //
  // In the case of cache corruption, users will receive an
  // EINTEGRITY error elsewhere, and can remove the offending
  // content their own way.
  //
  // Note that, as the name suggests, this strictly only supports file moves.
  return BB.fromNode(cb => {
    fs.link(src, dest, err => {
      if (err) {
        if (err.code === 'EEXIST' || err.code === 'EBUSY') {
          // file already exists, so whatever
        } else if (err.code === 'EPERM' && process.platform === 'win32') {
          // file handle stayed open even past graceful-fs limits
        } else {
          return cb(err)
        }
      }
      return cb()
    })
  }).then(() => {
    // content should never change for any reason, so make it read-only
    return BB.join(unlink(src), process.platform !== 'win32' && chmod(dest, '0444'))
  }).catch(() => {
    if (!pinflight) { pinflight = require('promise-inflight') }
    return pinflight('cacache-move-file:' + dest, () => {
      return BB.promisify(fs.stat)(dest).catch(err => {
        if (err.code !== 'ENOENT') {
          // Something else is wrong here. Bail bail bail
          throw err
        }
        // file doesn't already exist! let's try a rename -> copy fallback
        if (!move) { move = require('move-concurrently') }
        return move(src, dest, { BB, fs })
      })
    })
  })
}