index.js

const camelCase = require('camelcase')
const decamelize = require('decamelize')
const path = require('path')
const tokenizeArgString = require('./lib/tokenize-arg-string')
const util = require('util')

function parse (args, opts) {
  opts = Object.assign(Object.create(null), opts)
  // allow a string argument to be passed in rather
  // than an argv array.
  args = tokenizeArgString(args)

  // aliases might have transitive relationships, normalize this.
  const aliases = combineAliases(Object.assign(Object.create(null), opts.alias))
  const configuration = Object.assign({
    'short-option-groups': true,
    'camel-case-expansion': true,
    'dot-notation': true,
    'parse-numbers': true,
    'boolean-negation': true,
    'negation-prefix': 'no-',
    'duplicate-arguments-array': true,
    'flatten-duplicate-arrays': true,
    'populate--': false,
    'combine-arrays': false,
    'set-placeholder-key': false,
    'halt-at-non-option': false,
    'strip-aliased': false,
    'strip-dashed': false,
    'unknown-options-as-args': false,
    'nargs-eats-options': false
  }, opts.configuration)
  const defaults = Object.assign(Object.create(null), opts.default)
  const configObjects = opts.configObjects || []
  const envPrefix = opts.envPrefix
  const notFlagsOption = configuration['populate--']
  const notFlagsArgv = notFlagsOption ? '--' : '_'
  const newAliases = Object.create(null)
  const defaulted = Object.create(null)
  // allow a i18n handler to be passed in, default to a fake one (util.format).
  const __ = opts.__ || util.format
  const flags = {
    aliases: Object.create(null),
    arrays: Object.create(null),
    bools: Object.create(null),
    strings: Object.create(null),
    numbers: Object.create(null),
    counts: Object.create(null),
    normalize: Object.create(null),
    configs: Object.create(null),
    nargs: Object.create(null),
    coercions: Object.create(null),
    keys: []
  }
  const negative = /^-([0-9]+(\.[0-9]+)?|\.[0-9]+)$/
  const negatedBoolean = new RegExp('^--' + configuration['negation-prefix'] + '(.+)')

  ;[].concat(opts.array).filter(Boolean).forEach(function (opt) {
    const key = opt.key || opt

    // assign to flags[bools|strings|numbers]
    const assignment = Object.keys(opt).map(function (key) {
      return ({
        boolean: 'bools',
        string: 'strings',
        number: 'numbers'
      })[key]
    }).filter(Boolean).pop()

    // assign key to be coerced
    if (assignment) {
      flags[assignment][key] = true
    }

    flags.arrays[key] = true
    flags.keys.push(key)
  })

  ;[].concat(opts.boolean).filter(Boolean).forEach(function (key) {
    flags.bools[key] = true
    flags.keys.push(key)
  })

  ;[].concat(opts.string).filter(Boolean).forEach(function (key) {
    flags.strings[key] = true
    flags.keys.push(key)
  })

  ;[].concat(opts.number).filter(Boolean).forEach(function (key) {
    flags.numbers[key] = true
    flags.keys.push(key)
  })

  ;[].concat(opts.count).filter(Boolean).forEach(function (key) {
    flags.counts[key] = true
    flags.keys.push(key)
  })

  ;[].concat(opts.normalize).filter(Boolean).forEach(function (key) {
    flags.normalize[key] = true
    flags.keys.push(key)
  })

  Object.keys(opts.narg || {}).forEach(function (k) {
    flags.nargs[k] = opts.narg[k]
    flags.keys.push(k)
  })

  Object.keys(opts.coerce || {}).forEach(function (k) {
    flags.coercions[k] = opts.coerce[k]
    flags.keys.push(k)
  })

  if (Array.isArray(opts.config) || typeof opts.config === 'string') {
    ;[].concat(opts.config).filter(Boolean).forEach(function (key) {
      flags.configs[key] = true
    })
  } else {
    Object.keys(opts.config || {}).forEach(function (k) {
      flags.configs[k] = opts.config[k]
    })
  }

  // create a lookup table that takes into account all
  // combinations of aliases: {f: ['foo'], foo: ['f']}
  extendAliases(opts.key, aliases, opts.default, flags.arrays)

  // apply default values to all aliases.
  Object.keys(defaults).forEach(function (key) {
    (flags.aliases[key] || []).forEach(function (alias) {
      defaults[alias] = defaults[key]
    })
  })

  let error = null
  checkConfiguration()

  let notFlags = []

  const argv = Object.assign(Object.create(null), { _: [] })
  // TODO(bcoe): for the first pass at removing object prototype  we didn't
  // remove all prototypes from objects returned by this API, we might want
  // to gradually move towards doing so.
  const argvReturn = {}

  for (let i = 0; i < args.length; i++) {
    const arg = args[i]
    let broken
    let key
    let letters
    let m
    let next
    let value

    // any unknown option (except for end-of-options, "--")
    if (arg !== '--' && isUnknownOptionAsArg(arg)) {
      argv._.push(arg)
    // -- separated by =
    } else if (arg.match(/^--.+=/) || (
      !configuration['short-option-groups'] && arg.match(/^-.+=/)
    )) {
      // Using [\s\S] instead of . because js doesn't support the
      // 'dotall' regex modifier. See:
      // http://stackoverflow.com/a/1068308/13216
      m = arg.match(/^--?([^=]+)=([\s\S]*)$/)

      // arrays format = '--f=a b c'
      if (checkAllAliases(m[1], flags.arrays)) {
        args.splice(i + 1, 0, m[2])
        i = eatArray(i, m[1], args)
      } else if (checkAllAliases(m[1], flags.nargs)) {
        // nargs format = '--f=monkey washing cat'
        args.splice(i + 1, 0, m[2])
        i = eatNargs(i, m[1], args)
      } else {
        setArg(m[1], m[2])
      }
    } else if (arg.match(negatedBoolean) && configuration['boolean-negation']) {
      key = arg.match(negatedBoolean)[1]
      setArg(key, checkAllAliases(key, flags.arrays) ? [false] : false)

    // -- separated by space.
    } else if (arg.match(/^--.+/) || (
      !configuration['short-option-groups'] && arg.match(/^-[^-]+/)
    )) {
      key = arg.match(/^--?(.+)/)[1]

      if (checkAllAliases(key, flags.arrays)) {
        // array format = '--foo a b c'
        i = eatArray(i, key, args)
      } else if (checkAllAliases(key, flags.nargs) !== false) {
        // nargs format = '--foo a b c'
        // should be truthy even if: flags.nargs[key] === 0
        i = eatNargs(i, key, args)
      } else {
        next = args[i + 1]

        if (next !== undefined && (!next.match(/^-/) ||
          next.match(negative)) &&
          !checkAllAliases(key, flags.bools) &&
          !checkAllAliases(key, flags.counts)) {
          setArg(key, next)
          i++
        } else if (/^(true|false)$/.test(next)) {
          setArg(key, next)
          i++
        } else {
          setArg(key, defaultValue(key))
        }
      }

    // dot-notation flag separated by '='.
    } else if (arg.match(/^-.\..+=/)) {
      m = arg.match(/^-([^=]+)=([\s\S]*)$/)
      setArg(m[1], m[2])

    // dot-notation flag separated by space.
    } else if (arg.match(/^-.\..+/) && !arg.match(negative)) {
      next = args[i + 1]
      key = arg.match(/^-(.\..+)/)[1]

      if (next !== undefined && !next.match(/^-/) &&
        !checkAllAliases(key, flags.bools) &&
        !checkAllAliases(key, flags.counts)) {
        setArg(key, next)
        i++
      } else {
        setArg(key, defaultValue(key))
      }
    } else if (arg.match(/^-[^-]+/) && !arg.match(negative)) {
      letters = arg.slice(1, -1).split('')
      broken = false

      for (let j = 0; j < letters.length; j++) {
        next = arg.slice(j + 2)

        if (letters[j + 1] && letters[j + 1] === '=') {
          value = arg.slice(j + 3)
          key = letters[j]

          if (checkAllAliases(key, flags.arrays)) {
            // array format = '-f=a b c'
            args.splice(i + 1, 0, value)
            i = eatArray(i, key, args)
          } else if (checkAllAliases(key, flags.nargs)) {
            // nargs format = '-f=monkey washing cat'
            args.splice(i + 1, 0, value)
            i = eatNargs(i, key, args)
          } else {
            setArg(key, value)
          }

          broken = true
          break
        }

        if (next === '-') {
          setArg(letters[j], next)
          continue
        }

        // current letter is an alphabetic character and next value is a number
        if (/[A-Za-z]/.test(letters[j]) &&
          /^-?\d+(\.\d*)?(e-?\d+)?$/.test(next)) {
          setArg(letters[j], next)
          broken = true
          break
        }

        if (letters[j + 1] && letters[j + 1].match(/\W/)) {
          setArg(letters[j], next)
          broken = true
          break
        } else {
          setArg(letters[j], defaultValue(letters[j]))
        }
      }

      key = arg.slice(-1)[0]

      if (!broken && key !== '-') {
        if (checkAllAliases(key, flags.arrays)) {
          // array format = '-f a b c'
          i = eatArray(i, key, args)
        } else if (checkAllAliases(key, flags.nargs) !== false) {
          // nargs format = '-f a b c'
          // should be truthy even if: flags.nargs[key] === 0
          i = eatNargs(i, key, args)
        } else {
          next = args[i + 1]

          if (next !== undefined && (!/^(-|--)[^-]/.test(next) ||
            next.match(negative)) &&
            !checkAllAliases(key, flags.bools) &&
            !checkAllAliases(key, flags.counts)) {
            setArg(key, next)
            i++
          } else if (/^(true|false)$/.test(next)) {
            setArg(key, next)
            i++
          } else {
            setArg(key, defaultValue(key))
          }
        }
      }
    } else if (arg === '--') {
      notFlags = args.slice(i + 1)
      break
    } else if (configuration['halt-at-non-option']) {
      notFlags = args.slice(i)
      break
    } else {
      argv._.push(maybeCoerceNumber('_', arg))
    }
  }

  // order of precedence:
  // 1. command line arg
  // 2. value from env var
  // 3. value from config file
  // 4. value from config objects
  // 5. configured default value
  applyEnvVars(argv, true) // special case: check env vars that point to config file
  applyEnvVars(argv, false)
  setConfig(argv)
  setConfigObjects()
  applyDefaultsAndAliases(argv, flags.aliases, defaults, true)
  applyCoercions(argv)
  if (configuration['set-placeholder-key']) setPlaceholderKeys(argv)

  // for any counts either not in args or without an explicit default, set to 0
  Object.keys(flags.counts).forEach(function (key) {
    if (!hasKey(argv, key.split('.'))) setArg(key, 0)
  })

  // '--' defaults to undefined.
  if (notFlagsOption && notFlags.length) argv[notFlagsArgv] = []
  notFlags.forEach(function (key) {
    argv[notFlagsArgv].push(key)
  })

  if (configuration['camel-case-expansion'] && configuration['strip-dashed']) {
    Object.keys(argv).filter(key => key !== '--' && key.includes('-')).forEach(key => {
      delete argv[key]
    })
  }

  if (configuration['strip-aliased']) {
    // XXX Switch to [].concat(...Object.values(aliases)) once node.js 6 is dropped
    ;[].concat(...Object.keys(aliases).map(k => aliases[k])).forEach(alias => {
      if (configuration['camel-case-expansion']) {
        delete argv[alias.split('.').map(prop => camelCase(prop)).join('.')]
      }

      delete argv[alias]
    })
  }

  // how many arguments should we consume, based
  // on the nargs option?
  function eatNargs (i, key, args) {
    let ii
    const toEat = checkAllAliases(key, flags.nargs)

    if (toEat === 0) {
      setArg(key, defaultValue(key))
      return i
    }

    let available = 0
    if (configuration['nargs-eats-options']) {
      // classic behavior, yargs eats positional and dash arguments.
      if (args.length - (i + 1) < toEat) error = Error(__('Not enough arguments following: %s', key))
      available = toEat
    } else {
      // nargs will not consume flag arguments, e.g., -abc, --foo,
      // and terminates when one is observed.
      for (ii = i + 1; ii < args.length; ii++) {
        if (!args[ii].match(/^-[^0-9]/) || args[ii].match(negative) || isUnknownOptionAsArg(args[ii])) available++
        else break
      }
      if (available < toEat) error = Error(__('Not enough arguments following: %s', key))
    }

    const consumed = Math.min(available, toEat)
    for (ii = i + 1; ii < (consumed + i + 1); ii++) {
      setArg(key, args[ii])
    }

    return (i + consumed)
  }

  // if an option is an array, eat all non-hyphenated arguments
  // following it... YUM!
  // e.g., --foo apple banana cat becomes ["apple", "banana", "cat"]
  function eatArray (i, key, args) {
    let argsToSet = []
    let next = args[i + 1]

    if (checkAllAliases(key, flags.bools) && !(/^(true|false)$/.test(next))) {
      argsToSet.push(true)
    } else if (isUndefined(next) || (/^-/.test(next) && !negative.test(next) && !isUnknownOptionAsArg(next))) {
      // for keys without value ==> argsToSet remains an empty []
      // set user default value, if available
      if (defaults[key] !== undefined) {
        const defVal = defaults[key]
        argsToSet = Array.isArray(defVal) ? defVal : [defVal]
      }
    } else {
      for (let ii = i + 1; ii < args.length; ii++) {
        next = args[ii]
        if (/^-/.test(next) && !negative.test(next) && !isUnknownOptionAsArg(next)) break
        i = ii
        argsToSet.push(processValue(key, next))
      }
    }

    // If both array and nargs are configured, create an error if less than
    // nargs positionals were found:
    const toEat = checkAllAliases(key, flags.nargs)
    if (toEat && argsToSet.length < toEat) {
      error = Error(__('Not enough arguments following: %s', key))
    }

    setArg(key, argsToSet)
    return i
  }

  function setArg (key, val) {
    if (/-/.test(key) && configuration['camel-case-expansion']) {
      const alias = key.split('.').map(function (prop) {
        return camelCase(prop)
      }).join('.')
      addNewAlias(key, alias)
    }

    const value = processValue(key, val)
    const splitKey = key.split('.')
    setKey(argv, splitKey, value)

    // handle populating aliases of the full key
    if (flags.aliases[key]) {
      flags.aliases[key].forEach(function (x) {
        x = x.split('.')
        setKey(argv, x, value)
      })
    }

    // handle populating aliases of the first element of the dot-notation key
    if (splitKey.length > 1 && configuration['dot-notation']) {
      ;(flags.aliases[splitKey[0]] || []).forEach(function (x) {
        x = x.split('.')

        // expand alias with nested objects in key
        const a = [].concat(splitKey)
        a.shift() // nuke the old key.
        x = x.concat(a)

        setKey(argv, x, value)
      })
    }

    // Set normalize getter and setter when key is in 'normalize' but isn't an array
    if (checkAllAliases(key, flags.normalize) && !checkAllAliases(key, flags.arrays)) {
      const keys = [key].concat(flags.aliases[key] || [])
      keys.forEach(function (key) {
        Object.defineProperty(argvReturn, key, {
          get () {
            return val
          },
          set (value) {
            val = typeof value === 'string' ? path.normalize(value) : value
          }
        })
      })
    }
  }

  function addNewAlias (key, alias) {
    if (!(flags.aliases[key] && flags.aliases[key].length)) {
      flags.aliases[key] = [alias]
      newAliases[alias] = true
    }
    if (!(flags.aliases[alias] && flags.aliases[alias].length)) {
      addNewAlias(alias, key)
    }
  }

  function processValue (key, val) {
    // strings may be quoted, clean this up as we assign values.
    if (typeof val === 'string' &&
      (val[0] === "'" || val[0] === '"') &&
      val[val.length - 1] === val[0]
    ) {
      val = val.substring(1, val.length - 1)
    }

    // handle parsing boolean arguments --foo=true --bar false.
    if (checkAllAliases(key, flags.bools) || checkAllAliases(key, flags.counts)) {
      if (typeof val === 'string') val = val === 'true'
    }

    let value = Array.isArray(val)
      ? val.map(function (v) { return maybeCoerceNumber(key, v) })
      : maybeCoerceNumber(key, val)

    // increment a count given as arg (either no value or value parsed as boolean)
    if (checkAllAliases(key, flags.counts) && (isUndefined(value) || typeof value === 'boolean')) {
      value = increment
    }

    // Set normalized value when key is in 'normalize' and in 'arrays'
    if (checkAllAliases(key, flags.normalize) && checkAllAliases(key, flags.arrays)) {
      if (Array.isArray(val)) value = val.map(path.normalize)
      else value = path.normalize(val)
    }
    return value
  }

  function maybeCoerceNumber (key, value) {
    if (!checkAllAliases(key, flags.strings) && !checkAllAliases(key, flags.bools) && !Array.isArray(value)) {
      const shouldCoerceNumber = isNumber(value) && configuration['parse-numbers'] && (
        Number.isSafeInteger(Math.floor(value))
      )
      if (shouldCoerceNumber || (!isUndefined(value) && checkAllAliases(key, flags.numbers))) value = Number(value)
    }
    return value
  }

  // set args from config.json file, this should be
  // applied last so that defaults can be applied.
  function setConfig (argv) {
    const configLookup = Object.create(null)

    // expand defaults/aliases, in-case any happen to reference
    // the config.json file.
    applyDefaultsAndAliases(configLookup, flags.aliases, defaults)

    Object.keys(flags.configs).forEach(function (configKey) {
      const configPath = argv[configKey] || configLookup[configKey]
      if (configPath) {
        try {
          let config = null
          const resolvedConfigPath = path.resolve(process.cwd(), configPath)

          if (typeof flags.configs[configKey] === 'function') {
            try {
              config = flags.configs[configKey](resolvedConfigPath)
            } catch (e) {
              config = e
            }
            if (config instanceof Error) {
              error = config
              return
            }
          } else {
            config = require(resolvedConfigPath)
          }

          setConfigObject(config)
        } catch (ex) {
          if (argv[configKey]) error = Error(__('Invalid JSON config file: %s', configPath))
        }
      }
    })
  }

  // set args from config object.
  // it recursively checks nested objects.
  function setConfigObject (config, prev) {
    Object.keys(config).forEach(function (key) {
      const value = config[key]
      const fullKey = prev ? prev + '.' + key : key

      // if the value is an inner object and we have dot-notation
      // enabled, treat inner objects in config the same as
      // heavily nested dot notations (foo.bar.apple).
      if (typeof value === 'object' && value !== null && !Array.isArray(value) && configuration['dot-notation']) {
        // if the value is an object but not an array, check nested object
        setConfigObject(value, fullKey)
      } else {
        // setting arguments via CLI takes precedence over
        // values within the config file.
        if (!hasKey(argv, fullKey.split('.')) || (checkAllAliases(fullKey, flags.arrays) && configuration['combine-arrays'])) {
          setArg(fullKey, value)
        }
      }
    })
  }

  // set all config objects passed in opts
  function setConfigObjects () {
    if (typeof configObjects === 'undefined') return
    configObjects.forEach(function (configObject) {
      setConfigObject(configObject)
    })
  }

  function applyEnvVars (argv, configOnly) {
    if (typeof envPrefix === 'undefined') return

    const prefix = typeof envPrefix === 'string' ? envPrefix : ''
    Object.keys(process.env).forEach(function (envVar) {
      if (prefix === '' || envVar.lastIndexOf(prefix, 0) === 0) {
        // get array of nested keys and convert them to camel case
        const keys = envVar.split('__').map(function (key, i) {
          if (i === 0) {
            key = key.substring(prefix.length)
          }
          return camelCase(key)
        })

        if (((configOnly && flags.configs[keys.join('.')]) || !configOnly) && !hasKey(argv, keys)) {
          setArg(keys.join('.'), process.env[envVar])
        }
      }
    })
  }

  function applyCoercions (argv) {
    let coerce
    const applied = new Set()
    Object.keys(argv).forEach(function (key) {
      if (!applied.has(key)) { // If we haven't already coerced this option via one of its aliases
        coerce = checkAllAliases(key, flags.coercions)
        if (typeof coerce === 'function') {
          try {
            const value = maybeCoerceNumber(key, coerce(argv[key]))
            ;([].concat(flags.aliases[key] || [], key)).forEach(ali => {
              applied.add(ali)
              argv[ali] = value
            })
          } catch (err) {
            error = err
          }
        }
      }
    })
  }

  function setPlaceholderKeys (argv) {
    flags.keys.forEach((key) => {
      // don't set placeholder keys for dot notation options 'foo.bar'.
      if (~key.indexOf('.')) return
      if (typeof argv[key] === 'undefined') argv[key] = undefined
    })
    return argv
  }

  function applyDefaultsAndAliases (obj, aliases, defaults, canLog = false) {
    Object.keys(defaults).forEach(function (key) {
      if (!hasKey(obj, key.split('.'))) {
        setKey(obj, key.split('.'), defaults[key])
        if (canLog) defaulted[key] = true

        ;(aliases[key] || []).forEach(function (x) {
          if (hasKey(obj, x.split('.'))) return
          setKey(obj, x.split('.'), defaults[key])
        })
      }
    })
  }

  function hasKey (obj, keys) {
    let o = obj

    if (!configuration['dot-notation']) keys = [keys.join('.')]

    keys.slice(0, -1).forEach(function (key) {
      o = (o[key] || {})
    })

    const key = keys[keys.length - 1]

    if (typeof o !== 'object') return false
    else return key in o
  }

  function setKey (obj, keys, value) {
    let o = obj

    if (!configuration['dot-notation']) keys = [keys.join('.')]

    keys.slice(0, -1).forEach(function (key, index) {
      if (typeof o === 'object' && o[key] === undefined) {
        o[key] = {}
      }

      if (typeof o[key] !== 'object' || Array.isArray(o[key])) {
        // ensure that o[key] is an array, and that the last item is an empty object.
        if (Array.isArray(o[key])) {
          o[key].push({})
        } else {
          o[key] = [o[key], {}]
        }

        // we want to update the empty object at the end of the o[key] array, so set o to that object
        o = o[key][o[key].length - 1]
      } else {
        o = o[key]
      }
    })

    const key = keys[keys.length - 1]
    const isTypeArray = checkAllAliases(keys.join('.'), flags.arrays)
    const isValueArray = Array.isArray(value)
    let duplicate = configuration['duplicate-arguments-array']

    // nargs has higher priority than duplicate
    if (!duplicate && checkAllAliases(key, flags.nargs)) {
      duplicate = true
      if ((!isUndefined(o[key]) && flags.nargs[key] === 1) || (Array.isArray(o[key]) && o[key].length === flags.nargs[key])) {
        o[key] = undefined
      }
    }

    if (value === increment) {
      o[key] = increment(o[key])
    } else if (Array.isArray(o[key])) {
      if (duplicate && isTypeArray && isValueArray) {
        o[key] = configuration['flatten-duplicate-arrays'] ? o[key].concat(value) : (Array.isArray(o[key][0]) ? o[key] : [o[key]]).concat([value])
      } else if (!duplicate && Boolean(isTypeArray) === Boolean(isValueArray)) {
        o[key] = value
      } else {
        o[key] = o[key].concat([value])
      }
    } else if (o[key] === undefined && isTypeArray) {
      o[key] = isValueArray ? value : [value]
    } else if (duplicate && !(
      o[key] === undefined ||
        checkAllAliases(key, flags.counts) ||
        checkAllAliases(key, flags.bools)
    )) {
      o[key] = [o[key], value]
    } else {
      o[key] = value
    }
  }

  // extend the aliases list with inferred aliases.
  function extendAliases (...args) {
    args.forEach(function (obj) {
      Object.keys(obj || {}).forEach(function (key) {
        // short-circuit if we've already added a key
        // to the aliases array, for example it might
        // exist in both 'opts.default' and 'opts.key'.
        if (flags.aliases[key]) return

        flags.aliases[key] = [].concat(aliases[key] || [])
        // For "--option-name", also set argv.optionName
        flags.aliases[key].concat(key).forEach(function (x) {
          if (/-/.test(x) && configuration['camel-case-expansion']) {
            const c = camelCase(x)
            if (c !== key && flags.aliases[key].indexOf(c) === -1) {
              flags.aliases[key].push(c)
              newAliases[c] = true
            }
          }
        })
        // For "--optionName", also set argv['option-name']
        flags.aliases[key].concat(key).forEach(function (x) {
          if (x.length > 1 && /[A-Z]/.test(x) && configuration['camel-case-expansion']) {
            const c = decamelize(x, '-')
            if (c !== key && flags.aliases[key].indexOf(c) === -1) {
              flags.aliases[key].push(c)
              newAliases[c] = true
            }
          }
        })
        flags.aliases[key].forEach(function (x) {
          flags.aliases[x] = [key].concat(flags.aliases[key].filter(function (y) {
            return x !== y
          }))
        })
      })
    })
  }

  // return the 1st set flag for any of a key's aliases (or false if no flag set)
  function checkAllAliases (key, flag) {
    const toCheck = [].concat(flags.aliases[key] || [], key)
    const keys = Object.keys(flag)
    const setAlias = toCheck.find(key => keys.includes(key))
    return setAlias ? flag[setAlias] : false
  }

  function hasAnyFlag (key) {
    const toCheck = [].concat(Object.keys(flags).map(k => flags[k]))
    return toCheck.some(function (flag) {
      return Array.isArray(flag) ? flag.includes(key) : flag[key]
    })
  }

  function hasFlagsMatching (arg, ...patterns) {
    const toCheck = [].concat(...patterns)
    return toCheck.some(function (pattern) {
      const match = arg.match(pattern)
      return match && hasAnyFlag(match[1])
    })
  }

  // based on a simplified version of the short flag group parsing logic
  function hasAllShortFlags (arg) {
    // if this is a negative number, or doesn't start with a single hyphen, it's not a short flag group
    if (arg.match(negative) || !arg.match(/^-[^-]+/)) { return false }
    let hasAllFlags = true
    let next
    const letters = arg.slice(1).split('')
    for (let j = 0; j < letters.length; j++) {
      next = arg.slice(j + 2)

      if (!hasAnyFlag(letters[j])) {
        hasAllFlags = false
        break
      }

      if ((letters[j + 1] && letters[j + 1] === '=') ||
        next === '-' ||
        (/[A-Za-z]/.test(letters[j]) && /^-?\d+(\.\d*)?(e-?\d+)?$/.test(next)) ||
        (letters[j + 1] && letters[j + 1].match(/\W/))) {
        break
      }
    }
    return hasAllFlags
  }

  function isUnknownOptionAsArg (arg) {
    return configuration['unknown-options-as-args'] && isUnknownOption(arg)
  }

  function isUnknownOption (arg) {
    // ignore negative numbers
    if (arg.match(negative)) { return false }
    // if this is a short option group and all of them are configured, it isn't unknown
    if (hasAllShortFlags(arg)) { return false }
    // e.g. '--count=2'
    const flagWithEquals = /^-+([^=]+?)=[\s\S]*$/
    // e.g. '-a' or '--arg'
    const normalFlag = /^-+([^=]+?)$/
    // e.g. '-a-'
    const flagEndingInHyphen = /^-+([^=]+?)-$/
    // e.g. '-abc123'
    const flagEndingInDigits = /^-+([^=]+?\d+)$/
    // e.g. '-a/usr/local'
    const flagEndingInNonWordCharacters = /^-+([^=]+?)\W+.*$/
    // check the different types of flag styles, including negatedBoolean, a pattern defined near the start of the parse method
    return !hasFlagsMatching(arg, flagWithEquals, negatedBoolean, normalFlag, flagEndingInHyphen, flagEndingInDigits, flagEndingInNonWordCharacters)
  }

  // make a best effor to pick a default value
  // for an option based on name and type.
  function defaultValue (key) {
    if (!checkAllAliases(key, flags.bools) &&
        !checkAllAliases(key, flags.counts) &&
        `${key}` in defaults) {
      return defaults[key]
    } else {
      return defaultForType(guessType(key))
    }
  }

  // return a default value, given the type of a flag.,
  // e.g., key of type 'string' will default to '', rather than 'true'.
  function defaultForType (type) {
    const def = {
      boolean: true,
      string: '',
      number: undefined,
      array: []
    }

    return def[type]
  }

  // given a flag, enforce a default type.
  function guessType (key) {
    let type = 'boolean'
    if (checkAllAliases(key, flags.strings)) type = 'string'
    else if (checkAllAliases(key, flags.numbers)) type = 'number'
    else if (checkAllAliases(key, flags.bools)) type = 'boolean'
    else if (checkAllAliases(key, flags.arrays)) type = 'array'
    return type
  }

  function isNumber (x) {
    if (x === null || x === undefined) return false
    // if loaded from config, may already be a number.
    if (typeof x === 'number') return true
    // hexadecimal.
    if (/^0x[0-9a-f]+$/i.test(x)) return true
    // don't treat 0123 as a number; as it drops the leading '0'.
    if (x.length > 1 && x[0] === '0') return false
    return /^[-]?(?:\d+(?:\.\d*)?|\.\d+)(e[-+]?\d+)?$/.test(x)
  }

  function isUndefined (num) {
    return num === undefined
  }

  // check user configuration settings for inconsistencies
  function checkConfiguration () {
    // count keys should not be set as array/narg
    Object.keys(flags.counts).find(key => {
      if (checkAllAliases(key, flags.arrays)) {
        error = Error(__('Invalid configuration: %s, opts.count excludes opts.array.', key))
        return true
      } else if (checkAllAliases(key, flags.nargs)) {
        error = Error(__('Invalid configuration: %s, opts.count excludes opts.narg.', key))
        return true
      }
    })
  }

  return {
    argv: Object.assign(argvReturn, argv),
    error: error,
    aliases: Object.assign({}, flags.aliases),
    newAliases: Object.assign({}, newAliases),
    defaulted: Object.assign({}, defaulted),
    configuration: configuration
  }
}

// if any aliases reference each other, we should
// merge them together.
function combineAliases (aliases) {
  const aliasArrays = []
  const combined = Object.create(null)
  let change = true

  // turn alias lookup hash {key: ['alias1', 'alias2']} into
  // a simple array ['key', 'alias1', 'alias2']
  Object.keys(aliases).forEach(function (key) {
    aliasArrays.push(
      [].concat(aliases[key], key)
    )
  })

  // combine arrays until zero changes are
  // made in an iteration.
  while (change) {
    change = false
    for (let i = 0; i < aliasArrays.length; i++) {
      for (let ii = i + 1; ii < aliasArrays.length; ii++) {
        const intersect = aliasArrays[i].filter(function (v) {
          return aliasArrays[ii].indexOf(v) !== -1
        })

        if (intersect.length) {
          aliasArrays[i] = aliasArrays[i].concat(aliasArrays[ii])
          aliasArrays.splice(ii, 1)
          change = true
          break
        }
      }
    }
  }

  // map arrays back to the hash-lookup (de-dupe while
  // we're at it).
  aliasArrays.forEach(function (aliasArray) {
    aliasArray = aliasArray.filter(function (v, i, self) {
      return self.indexOf(v) === i
    })
    combined[aliasArray.pop()] = aliasArray
  })

  return combined
}

// this function should only be called when a count is given as an arg
// it is NOT called to set a default value
// thus we can start the count at 1 instead of 0
function increment (orig) {
  return orig !== undefined ? orig + 1 : 1
}

function Parser (args, opts) {
  const result = parse(args.slice(), opts)
  return result.argv
}

// parse arguments and return detailed
// meta information, aliases, etc.
Parser.detailed = function (args, opts) {
  return parse(args.slice(), opts)
}

module.exports = Parser