text: var camelCase = require('camelcase')
  var decamelize = require('decamelize')
  var path = require('path')
  var tokenizeArgString = require('./lib/tokenize-arg-string')
  var util = require('util')
  
  function parse (args, opts) {
    if (!opts) opts = {}
    // allow a string argument to be passed in rather
    // than an argv array.
    args = tokenizeArgString(args)
  
    // aliases might have transitive relationships, normalize this.
    var aliases = combineAliases(opts.alias || {})
    var 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
    }, opts.configuration)
    var defaults = opts.default || {}
    var configObjects = opts.configObjects || []
    var envPrefix = opts.envPrefix
    var notFlagsOption = configuration['populate--']
    var notFlagsArgv = notFlagsOption ? '--' : '_'
    var newAliases = {}
    var defaulted = {}
    // allow a i18n handler to be passed in, default to a fake one (util.format).
    var __ = opts.__ || util.format
    var error = null
    var flags = {
      aliases: {},
      arrays: {},
      bools: {},
      strings: {},
      numbers: {},
      counts: {},
      normalize: {},
      configs: {},
      nargs: {},
      coercions: {},
      keys: []
    }
    var negative = /^-([0-9]+(\.[0-9]+)?|\.[0-9]+)$/
    var negatedBoolean = new RegExp('^--' + configuration['negation-prefix'] + '(.+)')
  
    ;[].concat(opts.array).filter(Boolean).forEach(function (opt) {
      var 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]
      })
    })
  
    checkConfiguration()
  
    var argv = { _: [] }
    var notFlags = []
  
    for (var i = 0; i < args.length; i++) {
      var arg = args[i]
      var broken
      var key
      var letters
      var m
      var next
      var 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]*)$/)
  
        // nargs format = '--f=monkey washing cat'
        if (checkAllAliases(m[1], flags.nargs)) {
          args.splice(i + 1, 0, m[2])
          i = eatNargs(i, m[1], args)
        // arrays format = '--f=a b c'
        } else if (checkAllAliases(m[1], flags.arrays)) {
          args.splice(i + 1, 0, m[2])
          i = eatArray(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]
  
        // nargs format = '--foo a b c'
        // should be truthy even if: flags.nargs[key] === 0
        if (checkAllAliases(key, flags.nargs) !== false) {
          i = eatNargs(i, key, args)
        // array format = '--foo a b c'
        } else if (checkAllAliases(key, flags.arrays)) {
          i = eatArray(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 (var 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]
  
            // nargs format = '-f=monkey washing cat'
            if (checkAllAliases(key, flags.nargs)) {
              args.splice(i + 1, 0, value)
              i = eatNargs(i, key, args)
            // array format = '-f=a b c'
            } else if (checkAllAliases(key, flags.arrays)) {
              args.splice(i + 1, 0, value)
              i = eatArray(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 !== '-') {
          // nargs format = '-f a b c'
          // should be truthy even if: flags.nargs[key] === 0
          if (checkAllAliases(key, flags.nargs) !== false) {
            i = eatNargs(i, key, args)
          // array format = '-f a b c'
          } else if (checkAllAliases(key, flags.arrays)) {
            i = eatArray(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) {
      var ii
      const toEat = checkAllAliases(key, flags.nargs)
  
      if (toEat === 0) {
        setArg(key, defaultValue(key))
        return i
      }
  
      // nargs will not consume flag arguments, e.g., -abc, --foo,
      // and terminates when one is observed.
      var available = 0
      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.hasOwnProperty(key)) {
          const defVal = defaults[key]
          argsToSet = Array.isArray(defVal) ? defVal : [defVal]
        }
      } else {
        for (var 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))
        }
      }
  
      setArg(key, argsToSet)
      return i
    }
  
    function setArg (key, val) {
      if (/-/.test(key) && configuration['camel-case-expansion']) {
        var alias = key.split('.').map(function (prop) {
          return camelCase(prop)
        }).join('.')
        addNewAlias(key, alias)
      }
  
      var value = processValue(key, val)
  
      var 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
          var 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)) {
        var keys = [key].concat(flags.aliases[key] || [])
        keys.forEach(function (key) {
          argv.__defineSetter__(key, function (v) {
            val = path.normalize(v)
          })
  
          argv.__defineGetter__(key, function () {
            return typeof val === 'string' ? path.normalize(val) : val
          })
        })
      }
    }
  
    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'
      }
  
      var 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) {
      var configLookup = {}
  
      // 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) {
        var configPath = argv[configKey] || configLookup[configKey]
        if (configPath) {
          try {
            var config = null
            var 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) {
        var value = config[key]
        var 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
  
      var 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
          var 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) {
      var coerce
      var applied = {}
      Object.keys(argv).forEach(function (key) {
        if (!applied.hasOwnProperty(key)) { // If we haven't already coerced this option via one of its aliases
          coerce = checkAllAliases(key, flags.coercions)
          if (typeof coerce === 'function') {
            try {
              var value = maybeCoerceNumber(key, coerce(argv[key]))
              ;([].concat(flags.aliases[key] || [], key)).forEach(ali => {
                applied[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) {
      var o = obj
  
      if (!configuration['dot-notation']) keys = [keys.join('.')]
  
      keys.slice(0, -1).forEach(function (key) {
        o = (o[key] || {})
      })
  
      var key = keys[keys.length - 1]
  
      if (typeof o !== 'object') return false
      else return key in o
    }
  
    function setKey (obj, keys, value) {
      var 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]
        }
      })
  
      var key = keys[keys.length - 1]
  
      var isTypeArray = checkAllAliases(keys.join('.'), flags.arrays)
      var isValueArray = Array.isArray(value)
      var 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))) {
        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']) {
              var 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']) {
              var 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) {
      var toCheck = [].concat(flags.aliases[key] || [], key)
      let setAlias = toCheck.find(key => flag.hasOwnProperty(key))
      return setAlias ? flag[setAlias] : false
    }
  
    function hasAnyFlag (key) {
      // XXX Switch to [].concat(...Object.values(flags)) once node.js 6 is dropped
      var toCheck = [].concat(...Object.keys(flags).map(k => flags[k]))
  
      return toCheck.some(function (flag) {
        return flag[key]
      })
    }
  
    function hasFlagsMatching (arg, ...patterns) {
      var toCheck = [].concat(...patterns)
      return toCheck.some(function (pattern) {
        var 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 }
      var hasAllFlags = true
      var letters = arg.slice(1).split('')
      var next
      for (var 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) {
      var def = {
        boolean: true,
        string: '',
        number: undefined,
        array: []
      }
  
      return def[type]
    }
  
    // given a flag, enforce a default type.
    function guessType (key) {
      var 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: argv,
      error: error,
      aliases: flags.aliases,
      newAliases: newAliases,
      defaulted: defaulted,
      configuration: configuration
    }
  }
  
  // if any aliases reference each other, we should
  // merge them together.
  function combineAliases (aliases) {
    var aliasArrays = []
    var change = true
    var combined = {}
  
    // 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 (var i = 0; i < aliasArrays.length; i++) {
        for (var ii = i + 1; ii < aliasArrays.length; ii++) {
          var 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) {
    var 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
  