"use strict"
module.exports = require('./loader')(global, loadImplementation);

/**
 * Node.js version of loadImplementation.
 *
 * Requires the given implementation and returns the registration
 * containing {Promise, implementation}
 *
 * If implementation is undefined or global.Promise, loads it
 * Otherwise uses require
 */
function loadImplementation(implementation){
  var impl = null

  if(shouldPreferGlobalPromise(implementation)){
    // if no implementation or env specified use global.Promise
    impl = {
      Promise: global.Promise,
      implementation: 'global.Promise'
    }
  } else if(implementation){
    // if implementation specified, require it
    var lib = require(implementation)
    impl = {
      Promise: lib.Promise || lib,
      implementation: implementation
    }
  } else {
    // try to auto detect implementation. This is non-deterministic
    // and should prefer other branches, but this is our last chance
    // to load something without throwing error
    impl = tryAutoDetect()
  }

  if(impl === null){
    throw new Error('Cannot find any-promise implementation nor'+
      ' global.Promise. You must install polyfill or call'+
      ' require("any-promise/register") with your preferred'+
      ' implementation, e.g. require("any-promise/register/bluebird")'+
      ' on application load prior to any require("any-promise").')
  }

  return impl
}

/**
 * Determines if the global.Promise should be preferred if an implementation
 * has not been registered.
 */
function shouldPreferGlobalPromise(implementation){
  if(implementation){
    return implementation === 'global.Promise'
  } else if(typeof global.Promise !== 'undefined'){
    // Load global promise if implementation not specified
    // Versions < 0.11 did not have global Promise
    // Do not use for version < 0.12 as version 0.11 contained buggy versions
    var version = (/v(\d+)\.(\d+)\.(\d+)/).exec(process.version)
    return !(version && +version[1] == 0 && +version[2] < 12)
  }

  // do not have global.Promise or another implementation was specified
  return false
}

/**
 * Look for common libs as last resort there is no guarantee that
 * this will return a desired implementation or even be deterministic.
 * The priority is also nearly arbitrary. We are only doing this
 * for older versions of Node.js <0.12 that do not have a reasonable
 * global.Promise implementation and we the user has not registered
 * the preference. This preserves the behavior of any-promise <= 0.1
 * and may be deprecated or removed in the future
 */
function tryAutoDetect(){
  var libs = [
      "es6-promise",
      "promise",
      "native-promise-only",
      "bluebird",
      "rsvp",
      "when",
      "q",
      "pinkie",
      "lie",
      "vow"]
  var i = 0, len = libs.length
  for(; i < len; i++){
    try {
      return loadImplementation(libs[i])
    } catch(e){}
  }
  return null
}