optparse.rb

# frozen_string_literal: true
#
# optparse.rb - command-line option analysis with the OptionParser class.
#
# Author:: Nobu Nakada
# Documentation:: Nobu Nakada and Gavin Sinclair.
#
# See OptionParser for documentation.
#

#--
# == Developer Documentation (not for RDoc output)
#
# === Class tree
#
# - OptionParser:: front end
# - OptionParser::Switch:: each switches
# - OptionParser::List:: options list
# - OptionParser::ParseError:: errors on parsing
#   - OptionParser::AmbiguousOption
#   - OptionParser::NeedlessArgument
#   - OptionParser::MissingArgument
#   - OptionParser::InvalidOption
#   - OptionParser::InvalidArgument
#     - OptionParser::AmbiguousArgument
#
# === Object relationship diagram
#
#   +--------------+
#   | OptionParser |<>-----+
#   +--------------+       |                      +--------+
#                          |                    ,-| Switch |
#        on_head -------->+---------------+    /  +--------+
#        accept/reject -->| List          |<|>-
#                         |               |<|>-  +----------+
#        on ------------->+---------------+    `-| argument |
#                           :           :        |  class   |
#                         +---------------+      |==========|
#        on_tail -------->|               |      |pattern   |
#                         +---------------+      |----------|
#   OptionParser.accept ->| DefaultList   |      |converter |
#                reject   |(shared between|      +----------+
#                         | all instances)|
#                         +---------------+
#
#++
#
# == OptionParser
#
# === New to +OptionParser+?
#
# See the {Tutorial}[optparse/tutorial.rdoc].
#
# === Introduction
#
# OptionParser is a class for command-line option analysis.  It is much more
# advanced, yet also easier to use, than GetoptLong, and is a more Ruby-oriented
# solution.
#
# === Features
#
# 1. The argument specification and the code to handle it are written in the
#    same place.
# 2. It can output an option summary; you don't need to maintain this string
#    separately.
# 3. Optional and mandatory arguments are specified very gracefully.
# 4. Arguments can be automatically converted to a specified class.
# 5. Arguments can be restricted to a certain set.
#
# All of these features are demonstrated in the examples below.  See
# #make_switch for full documentation.
#
# === Minimal example
#
#   require 'optparse'
#
#   options = {}
#   OptionParser.new do |parser|
#     parser.banner = "Usage: example.rb [options]"
#
#     parser.on("-v", "--[no-]verbose", "Run verbosely") do |v|
#       options[:verbose] = v
#     end
#   end.parse!
#
#   p options
#   p ARGV
#
# === Generating Help
#
# OptionParser can be used to automatically generate help for the commands you
# write:
#
#   require 'optparse'
#
#   Options = Struct.new(:name)
#
#   class Parser
#     def self.parse(options)
#       args = Options.new("world")
#
#       opt_parser = OptionParser.new do |parser|
#         parser.banner = "Usage: example.rb [options]"
#
#         parser.on("-nNAME", "--name=NAME", "Name to say hello to") do |n|
#           args.name = n
#         end
#
#         parser.on("-h", "--help", "Prints this help") do
#           puts parser
#           exit
#         end
#       end
#
#       opt_parser.parse!(options)
#       return args
#     end
#   end
#   options = Parser.parse %w[--help]
#
#   #=>
#      # Usage: example.rb [options]
#      #     -n, --name=NAME                  Name to say hello to
#      #     -h, --help                       Prints this help
#
# === Required Arguments
#
# For options that require an argument, option specification strings may include an
# option name in all caps. If an option is used without the required argument,
# an exception will be raised.
#
#   require 'optparse'
#
#   options = {}
#   OptionParser.new do |parser|
#     parser.on("-r", "--require LIBRARY",
#               "Require the LIBRARY before executing your script") do |lib|
#       puts "You required #{lib}!"
#     end
#   end.parse!
#
# Used:
#
#   $ ruby optparse-test.rb -r
#   optparse-test.rb:9:in `<main>': missing argument: -r (OptionParser::MissingArgument)
#   $ ruby optparse-test.rb -r my-library
#   You required my-library!
#
# === Type Coercion
#
# OptionParser supports the ability to coerce command line arguments
# into objects for us.
#
# OptionParser comes with a few ready-to-use kinds of type
# coercion. They are:
#
# - Date  -- Anything accepted by +Date.parse+ (need to require +optparse/date+)
# - DateTime -- Anything accepted by +DateTime.parse+ (need to require +optparse/date+)
# - Time -- Anything accepted by +Time.httpdate+ or +Time.parse+ (need to require +optparse/time+)
# - URI  -- Anything accepted by +URI.parse+ (need to require +optparse/uri+)
# - Shellwords -- Anything accepted by +Shellwords.shellwords+ (need to require +optparse/shellwords+)
# - String -- Any non-empty string
# - Integer -- Any integer. Will convert octal. (e.g. 124, -3, 040)
# - Float -- Any float. (e.g. 10, 3.14, -100E+13)
# - Numeric -- Any integer, float, or rational (1, 3.4, 1/3)
# - DecimalInteger -- Like +Integer+, but no octal format.
# - OctalInteger -- Like +Integer+, but no decimal format.
# - DecimalNumeric -- Decimal integer or float.
# - TrueClass --  Accepts '+, yes, true, -, no, false' and
#   defaults as +true+
# - FalseClass -- Same as +TrueClass+, but defaults to +false+
# - Array -- Strings separated by ',' (e.g. 1,2,3)
# - Regexp -- Regular expressions. Also includes options.
#
# We can also add our own coercions, which we will cover below.
#
# ==== Using Built-in Conversions
#
# As an example, the built-in +Time+ conversion is used. The other built-in
# conversions behave in the same way.
# OptionParser will attempt to parse the argument
# as a +Time+. If it succeeds, that time will be passed to the
# handler block. Otherwise, an exception will be raised.
#
#   require 'optparse'
#   require 'optparse/time'
#   OptionParser.new do |parser|
#     parser.on("-t", "--time [TIME]", Time, "Begin execution at given time") do |time|
#       p time
#     end
#   end.parse!
#
# Used:
#
#   $ ruby optparse-test.rb  -t nonsense
#   ... invalid argument: -t nonsense (OptionParser::InvalidArgument)
#   $ ruby optparse-test.rb  -t 10-11-12
#   2010-11-12 00:00:00 -0500
#   $ ruby optparse-test.rb  -t 9:30
#   2014-08-13 09:30:00 -0400
#
# ==== Creating Custom Conversions
#
# The +accept+ method on OptionParser may be used to create converters.
# It specifies which conversion block to call whenever a class is specified.
# The example below uses it to fetch a +User+ object before the +on+ handler receives it.
#
#   require 'optparse'
#
#   User = Struct.new(:id, :name)
#
#   def find_user id
#     not_found = ->{ raise "No User Found for id #{id}" }
#     [ User.new(1, "Sam"),
#       User.new(2, "Gandalf") ].find(not_found) do |u|
#       u.id == id
#     end
#   end
#
#   op = OptionParser.new
#   op.accept(User) do |user_id|
#     find_user user_id.to_i
#   end
#
#   op.on("--user ID", User) do |user|
#     puts user
#   end
#
#   op.parse!
#
# Used:
#
#   $ ruby optparse-test.rb --user 1
#   #<struct User id=1, name="Sam">
#   $ ruby optparse-test.rb --user 2
#   #<struct User id=2, name="Gandalf">
#   $ ruby optparse-test.rb --user 3
#   optparse-test.rb:15:in `block in find_user': No User Found for id 3 (RuntimeError)
#
# === Store options to a Hash
#
# The +into+ option of +order+, +parse+ and so on methods stores command line options into a Hash.
#
#   require 'optparse'
#
#   options = {}
#   OptionParser.new do |parser|
#     parser.on('-a')
#     parser.on('-b NUM', Integer)
#     parser.on('-v', '--verbose')
#   end.parse!(into: options)
#
#   p options
#
# Used:
#
#   $ ruby optparse-test.rb -a
#   {:a=>true}
#   $ ruby optparse-test.rb -a -v
#   {:a=>true, :verbose=>true}
#   $ ruby optparse-test.rb -a -b 100
#   {:a=>true, :b=>100}
#
# === Complete example
#
# The following example is a complete Ruby program.  You can run it and see the
# effect of specifying various options.  This is probably the best way to learn
# the features of +optparse+.
#
#   require 'optparse'
#   require 'optparse/time'
#   require 'ostruct'
#   require 'pp'
#
#   class OptparseExample
#     Version = '1.0.0'
#
#     CODES = %w[iso-2022-jp shift_jis euc-jp utf8 binary]
#     CODE_ALIASES = { "jis" => "iso-2022-jp", "sjis" => "shift_jis" }
#
#     class ScriptOptions
#       attr_accessor :library, :inplace, :encoding, :transfer_type,
#                     :verbose, :extension, :delay, :time, :record_separator,
#                     :list
#
#       def initialize
#         self.library = []
#         self.inplace = false
#         self.encoding = "utf8"
#         self.transfer_type = :auto
#         self.verbose = false
#       end
#
#       def define_options(parser)
#         parser.banner = "Usage: example.rb [options]"
#         parser.separator ""
#         parser.separator "Specific options:"
#
#         # add additional options
#         perform_inplace_option(parser)
#         delay_execution_option(parser)
#         execute_at_time_option(parser)
#         specify_record_separator_option(parser)
#         list_example_option(parser)
#         specify_encoding_option(parser)
#         optional_option_argument_with_keyword_completion_option(parser)
#         boolean_verbose_option(parser)
#
#         parser.separator ""
#         parser.separator "Common options:"
#         # No argument, shows at tail.  This will print an options summary.
#         # Try it and see!
#         parser.on_tail("-h", "--help", "Show this message") do
#           puts parser
#           exit
#         end
#         # Another typical switch to print the version.
#         parser.on_tail("--version", "Show version") do
#           puts Version
#           exit
#         end
#       end
#
#       def perform_inplace_option(parser)
#         # Specifies an optional option argument
#         parser.on("-i", "--inplace [EXTENSION]",
#                   "Edit ARGV files in place",
#                   "(make backup if EXTENSION supplied)") do |ext|
#           self.inplace = true
#           self.extension = ext || ''
#           self.extension.sub!(/\A\.?(?=.)/, ".")  # Ensure extension begins with dot.
#         end
#       end
#
#       def delay_execution_option(parser)
#         # Cast 'delay' argument to a Float.
#         parser.on("--delay N", Float, "Delay N seconds before executing") do |n|
#           self.delay = n
#         end
#       end
#
#       def execute_at_time_option(parser)
#         # Cast 'time' argument to a Time object.
#         parser.on("-t", "--time [TIME]", Time, "Begin execution at given time") do |time|
#           self.time = time
#         end
#       end
#
#       def specify_record_separator_option(parser)
#         # Cast to octal integer.
#         parser.on("-F", "--irs [OCTAL]", OptionParser::OctalInteger,
#                   "Specify record separator (default \\0)") do |rs|
#           self.record_separator = rs
#         end
#       end
#
#       def list_example_option(parser)
#         # List of arguments.
#         parser.on("--list x,y,z", Array, "Example 'list' of arguments") do |list|
#           self.list = list
#         end
#       end
#
#       def specify_encoding_option(parser)
#         # Keyword completion.  We are specifying a specific set of arguments (CODES
#         # and CODE_ALIASES - notice the latter is a Hash), and the user may provide
#         # the shortest unambiguous text.
#         code_list = (CODE_ALIASES.keys + CODES).join(', ')
#         parser.on("--code CODE", CODES, CODE_ALIASES, "Select encoding",
#                   "(#{code_list})") do |encoding|
#           self.encoding = encoding
#         end
#       end
#
#       def optional_option_argument_with_keyword_completion_option(parser)
#         # Optional '--type' option argument with keyword completion.
#         parser.on("--type [TYPE]", [:text, :binary, :auto],
#                   "Select transfer type (text, binary, auto)") do |t|
#           self.transfer_type = t
#         end
#       end
#
#       def boolean_verbose_option(parser)
#         # Boolean switch.
#         parser.on("-v", "--[no-]verbose", "Run verbosely") do |v|
#           self.verbose = v
#         end
#       end
#     end
#
#     #
#     # Return a structure describing the options.
#     #
#     def parse(args)
#       # The options specified on the command line will be collected in
#       # *options*.
#
#       @options = ScriptOptions.new
#       @args = OptionParser.new do |parser|
#         @options.define_options(parser)
#         parser.parse!(args)
#       end
#       @options
#     end
#
#     attr_reader :parser, :options
#   end  # class OptparseExample
#
#   example = OptparseExample.new
#   options = example.parse(ARGV)
#   pp options # example.options
#   pp ARGV
#
# === Shell Completion
#
# For modern shells (e.g. bash, zsh, etc.), you can use shell
# completion for command line options.
#
# === Further documentation
#
# The above examples, along with the accompanying
# {Tutorial}[optparse/tutorial.rdoc],
# should be enough to learn how to use this class.
# If you have any questions, file a ticket at http://bugs.ruby-lang.org.
#
class OptionParser
  # The version string
  OptionParser::Version = "0.6.0"

  # :stopdoc:
  NoArgument = [NO_ARGUMENT = :NONE, nil].freeze
  RequiredArgument = [REQUIRED_ARGUMENT = :REQUIRED, true].freeze
  OptionalArgument = [OPTIONAL_ARGUMENT = :OPTIONAL, false].freeze
  # :startdoc:

  #
  # Keyword completion module.  This allows partial arguments to be specified
  # and resolved against a list of acceptable values.
  #
  module Completion
    # :nodoc:

    def self.regexp(key, icase)
      Regexp.new('\A' + Regexp.quote(key).gsub(/\w+\b/, '\&\w*'), icase)
    end

    def self.candidate(key, icase = false, pat = nil, &block)
      pat ||= Completion.regexp(key, icase)
      candidates = []
      block.call do |k, *v|
        (if Regexp === k
           kn = ""
           k === key
         else
           kn = defined?(k.id2name) ? k.id2name : k
           pat === kn
         end) or next
        v << k if v.empty?
        candidates << [k, v, kn]
      end
      candidates
    end

    def candidate(key, icase = false, pat = nil, &_)
      Completion.candidate(key, icase, pat, &method(:each))
    end

    public
    def complete(key, icase = false, pat = nil)
      candidates = candidate(key, icase, pat, &method(:each)).sort_by {|k, v, kn| kn.size}
      if candidates.size == 1
        canon, sw, * = candidates[0]
      elsif candidates.size > 1
        canon, sw, cn = candidates.shift
        candidates.each do |k, v, kn|
          next if sw == v
          if String === cn and String === kn
            if cn.rindex(kn, 0)
              canon, sw, cn = k, v, kn
              next
            elsif kn.rindex(cn, 0)
              next
            end
          end
          throw :ambiguous, key
        end
      end
      if canon
        block_given? or return key, *sw
        yield(key, *sw)
      end
    end

    def convert(opt = nil, val = nil, *)
      val
    end
  end


  #
  # Map from option/keyword string to object with completion.
  #
  class OptionMap < Hash
    include Completion
  end


  #
  # Individual switch class.  Not important to the user.
  #
  # Defined within Switch are several Switch-derived classes: NoArgument,
  # RequiredArgument, etc.
  #
  class Switch
    # :nodoc:

    attr_reader :pattern, :conv, :short, :long, :arg, :desc, :block

    #
    # Guesses argument style from +arg+.  Returns corresponding
    # OptionParser::Switch class (OptionalArgument, etc.).
    #
    def self.guess(arg)
      case arg
      when ""
        t = self
      when /\A=?\[/
        t = Switch::OptionalArgument
      when /\A\s+\[/
        t = Switch::PlacedArgument
      else
        t = Switch::RequiredArgument
      end
      self >= t or incompatible_argument_styles(arg, t)
      t
    end

    def self.incompatible_argument_styles(arg, t)
      raise(ArgumentError, "#{arg}: incompatible argument styles\n  #{self}, #{t}",
            ParseError.filter_backtrace(caller(2)))
    end

    def self.pattern
      NilClass
    end

    def initialize(pattern = nil, conv = nil,
                   short = nil, long = nil, arg = nil,
                   desc = ([] if short or long), block = nil, &_block)
      raise if Array === pattern
      block ||= _block
      @pattern, @conv, @short, @long, @arg, @desc, @block =
        pattern, conv, short, long, arg, desc, block
    end

    #
    # Parses +arg+ and returns rest of +arg+ and matched portion to the
    # argument pattern. Yields when the pattern doesn't match substring.
    #
    def parse_arg(arg) # :nodoc:
      pattern or return nil, [arg]
      unless m = pattern.match(arg)
        yield(InvalidArgument, arg)
        return arg, []
      end
      if String === m
        m = [s = m]
      else
        m = m.to_a
        s = m[0]
        return nil, m unless String === s
      end
      raise InvalidArgument, arg unless arg.rindex(s, 0)
      return nil, m if s.length == arg.length
      yield(InvalidArgument, arg) # didn't match whole arg
      return arg[s.length..-1], m
    end
    private :parse_arg

    #
    # Parses argument, converts and returns +arg+, +block+ and result of
    # conversion. Yields at semi-error condition instead of raising an
    # exception.
    #
    def conv_arg(arg, val = []) # :nodoc:
      if conv
        val = conv.call(*val)
      else
        val = proc {|v| v}.call(*val)
      end
      return arg, block, val
    end
    private :conv_arg

    #
    # Produces the summary text. Each line of the summary is yielded to the
    # block (without newline).
    #
    # +sdone+::  Already summarized short style options keyed hash.
    # +ldone+::  Already summarized long style options keyed hash.
    # +width+::  Width of left side (option part). In other words, the right
    #            side (description part) starts after +width+ columns.
    # +max+::    Maximum width of left side -> the options are filled within
    #            +max+ columns.
    # +indent+:: Prefix string indents all summarized lines.
    #
    def summarize(sdone = {}, ldone = {}, width = 1, max = width - 1, indent = "")
      sopts, lopts = [], [], nil
      @short.each {|s| sdone.fetch(s) {sopts << s}; sdone[s] = true} if @short
      @long.each {|s| ldone.fetch(s) {lopts << s}; ldone[s] = true} if @long
      return if sopts.empty? and lopts.empty? # completely hidden

      left = [sopts.join(', ')]
      right = desc.dup

      while s = lopts.shift
        l = left[-1].length + s.length
        l += arg.length if left.size == 1 && arg
        l < max or sopts.empty? or left << +''
        left[-1] << (left[-1].empty? ? ' ' * 4 : ', ') << s
      end

      if arg
        left[0] << (left[1] ? arg.sub(/\A(\[?)=/, '\1') + ',' : arg)
      end
      mlen = left.collect {|ss| ss.length}.max.to_i
      while mlen > width and l = left.shift
        mlen = left.collect {|ss| ss.length}.max.to_i if l.length == mlen
        if l.length < width and (r = right[0]) and !r.empty?
          l = l.to_s.ljust(width) + ' ' + r
          right.shift
        end
        yield(indent + l)
      end

      while begin l = left.shift; r = right.shift; l or r end
        l = l.to_s.ljust(width) + ' ' + r if r and !r.empty?
        yield(indent + l)
      end

      self
    end

    def add_banner(to)  # :nodoc:
      unless @short or @long
        s = desc.join
        to << " [" + s + "]..." unless s.empty?
      end
      to
    end

    def match_nonswitch?(str)  # :nodoc:
      @pattern =~ str unless @short or @long
    end

    #
    # Main name of the switch.
    #
    def switch_name
      (long.first || short.first).sub(/\A-+(?:\[no-\])?/, '')
    end

    def compsys(sdone, ldone)   # :nodoc:
      sopts, lopts = [], []
      @short.each {|s| sdone.fetch(s) {sopts << s}; sdone[s] = true} if @short
      @long.each {|s| ldone.fetch(s) {lopts << s}; ldone[s] = true} if @long
      return if sopts.empty? and lopts.empty? # completely hidden

      (sopts+lopts).each do |opt|
        # "(-x -c -r)-l[left justify]"
        if /^--\[no-\](.+)$/ =~ opt
          o = $1
          yield("--#{o}", desc.join(""))
          yield("--no-#{o}", desc.join(""))
        else
          yield("#{opt}", desc.join(""))
        end
      end
    end

    def pretty_print_contents(q) # :nodoc:
      if @block
        q.text ":" + @block.source_location.join(":") + ":"
        first = false
      else
        first = true
      end
      [@short, @long].each do |list|
        list.each do |opt|
          if first
            q.text ":"
            first = false
          end
          q.breakable
          q.text opt
        end
      end
    end

    def pretty_print(q)         # :nodoc:
      q.object_group(self) {pretty_print_contents(q)}
    end

    def omitted_argument(val)   # :nodoc:
      val.pop if val.size == 3 and val.last.nil?
      val
    end

    #
    # Switch that takes no arguments.
    #
    class NoArgument < self

      #
      # Raises an exception if any arguments given.
      #
      def parse(arg, argv)
        yield(NeedlessArgument, arg) if arg
        conv_arg(arg)
      end

      def self.incompatible_argument_styles(*) # :nodoc:
      end

      def self.pattern          # :nodoc:
        Object
      end

      def pretty_head           # :nodoc:
        "NoArgument"
      end
    end

    #
    # Switch that takes an argument.
    #
    class RequiredArgument < self

      #
      # Raises an exception if argument is not present.
      #
      def parse(arg, argv, &_)
        unless arg
          raise MissingArgument if argv.empty?
          arg = argv.shift
        end
        conv_arg(*parse_arg(arg, &method(:raise)))
      end

      def pretty_head           # :nodoc:
        "Required"
      end
    end

    #
    # Switch that can omit argument.
    #
    class OptionalArgument < self

      #
      # Parses argument if given, or uses default value.
      #
      def parse(arg, argv, &error)
        if arg
          conv_arg(*parse_arg(arg, &error))
        else
          omitted_argument conv_arg(arg)
        end
      end

      def pretty_head           # :nodoc:
        "Optional"
      end
    end

    #
    # Switch that takes an argument, which does not begin with '-' or is '-'.
    #
    class PlacedArgument < self

      #
      # Returns nil if argument is not present or begins with '-' and is not '-'.
      #
      def parse(arg, argv, &error)
        if !(val = arg) and (argv.empty? or /\A-./ =~ (val = argv[0]))
          return nil, block
        end
        opt = (val = parse_arg(val, &error))[1]
        val = conv_arg(*val)
        if opt and !arg
          argv.shift
        else
          omitted_argument val
          val[0] = nil
        end
        val
      end

      def pretty_head           # :nodoc:
        "Placed"
      end
    end
  end

  #
  # Simple option list providing mapping from short and/or long option
  # string to OptionParser::Switch and mapping from acceptable argument to
  # matching pattern and converter pair. Also provides summary feature.
  #
  class List
    # :nodoc:

    # Map from acceptable argument types to pattern and converter pairs.
    attr_reader :atype

    # Map from short style option switches to actual switch objects.
    attr_reader :short

    # Map from long style option switches to actual switch objects.
    attr_reader :long

    # List of all switches and summary string.
    attr_reader :list

    #
    # Just initializes all instance variables.
    #
    def initialize
      @atype = {}
      @short = OptionMap.new
      @long = OptionMap.new
      @list = []
    end

    def pretty_print(q)         # :nodoc:
      q.group(1, "(", ")") do
        @list.each do |sw|
          next unless Switch === sw
          q.group(1, "(" + sw.pretty_head, ")") do
            sw.pretty_print_contents(q)
          end
        end
      end
    end

    #
    # See OptionParser.accept.
    #
    def accept(t, pat = /.*/m, &block)
      if pat
        pat.respond_to?(:match) or
          raise TypeError, "has no 'match'", ParseError.filter_backtrace(caller(2))
      else
        pat = t if t.respond_to?(:match)
      end
      unless block
        block = pat.method(:convert).to_proc if pat.respond_to?(:convert)
      end
      @atype[t] = [pat, block]
    end

    #
    # See OptionParser.reject.
    #
    def reject(t)
      @atype.delete(t)
    end

    #
    # Adds +sw+ according to +sopts+, +lopts+ and +nlopts+.
    #
    # +sw+::     OptionParser::Switch instance to be added.
    # +sopts+::  Short style option list.
    # +lopts+::  Long style option list.
    # +nlopts+:: Negated long style options list.
    #
    def update(sw, sopts, lopts, nsw = nil, nlopts = nil) # :nodoc:
      sopts.each {|o| @short[o] = sw} if sopts
      lopts.each {|o| @long[o] = sw} if lopts
      nlopts.each {|o| @long[o] = nsw} if nsw and nlopts
      used = @short.invert.update(@long.invert)
      @list.delete_if {|o| Switch === o and !used[o]}
    end
    private :update

    #
    # Inserts +switch+ at the head of the list, and associates short, long
    # and negated long options. Arguments are:
    #
    # +switch+::      OptionParser::Switch instance to be inserted.
    # +short_opts+::  List of short style options.
    # +long_opts+::   List of long style options.
    # +nolong_opts+:: List of long style options with "no-" prefix.
    #
    #   prepend(switch, short_opts, long_opts, nolong_opts)
    #
    def prepend(*args)
      update(*args)
      @list.unshift(args[0])
    end

    #
    # Appends +switch+ at the tail of the list, and associates short, long
    # and negated long options. Arguments are:
    #
    # +switch+::      OptionParser::Switch instance to be inserted.
    # +short_opts+::  List of short style options.
    # +long_opts+::   List of long style options.
    # +nolong_opts+:: List of long style options with "no-" prefix.
    #
    #   append(switch, short_opts, long_opts, nolong_opts)
    #
    def append(*args)
      update(*args)
      @list.push(args[0])
    end

    #
    # Searches +key+ in +id+ list. The result is returned or yielded if a
    # block is given. If it isn't found, nil is returned.
    #
    def search(id, key)
      if list = __send__(id)
        val = list.fetch(key) {return nil}
        block_given? ? yield(val) : val
      end
    end

    #
    # Searches list +id+ for +opt+ and the optional patterns for completion
    # +pat+. If +icase+ is true, the search is case insensitive. The result
    # is returned or yielded if a block is given. If it isn't found, nil is
    # returned.
    #
    def complete(id, opt, icase = false, *pat, &block)
      __send__(id).complete(opt, icase, *pat, &block)
    end

    def get_candidates(id)
      yield __send__(id).keys
    end

    #
    # Iterates over each option, passing the option to the +block+.
    #
    def each_option(&block)
      list.each(&block)
    end

    #
    # Creates the summary table, passing each line to the +block+ (without
    # newline). The arguments +args+ are passed along to the summarize
    # method which is called on every option.
    #
    def summarize(*args, &block)
      sum = []
      list.reverse_each do |opt|
        if opt.respond_to?(:summarize) # perhaps OptionParser::Switch
          s = []
          opt.summarize(*args) {|l| s << l}
          sum.concat(s.reverse)
        elsif !opt or opt.empty?
          sum << ""
        elsif opt.respond_to?(:each_line)
          sum.concat([*opt.each_line].reverse)
        else
          sum.concat([*opt.each].reverse)
        end
      end
      sum.reverse_each(&block)
    end

    def add_banner(to)  # :nodoc:
      list.each do |opt|
        if opt.respond_to?(:add_banner)
          opt.add_banner(to)
        end
      end
      to
    end

    def compsys(*args, &block)  # :nodoc:
      list.each do |opt|
        if opt.respond_to?(:compsys)
          opt.compsys(*args, &block)
        end
      end
    end
  end

  #
  # Hash with completion search feature. See OptionParser::Completion.
  #
  class CompletingHash < Hash
    include Completion

    #
    # Completion for hash key.
    #
    def match(key)
      *values = fetch(key) {
        raise AmbiguousArgument, catch(:ambiguous) {return complete(key)}
      }
      return key, *values
    end
  end

  # :stopdoc:

  #
  # Enumeration of acceptable argument styles. Possible values are:
  #
  # NO_ARGUMENT::       The switch takes no arguments. (:NONE)
  # REQUIRED_ARGUMENT:: The switch requires an argument. (:REQUIRED)
  # OPTIONAL_ARGUMENT:: The switch requires an optional argument. (:OPTIONAL)
  #
  # Use like --switch=argument (long style) or -Xargument (short style). For
  # short style, only portion matched to argument pattern is treated as
  # argument.
  #
  ArgumentStyle = {}
  NoArgument.each {|el| ArgumentStyle[el] = Switch::NoArgument}
  RequiredArgument.each {|el| ArgumentStyle[el] = Switch::RequiredArgument}
  OptionalArgument.each {|el| ArgumentStyle[el] = Switch::OptionalArgument}
  ArgumentStyle.freeze

  #
  # Switches common used such as '--', and also provides default
  # argument classes
  #
  DefaultList = List.new
  DefaultList.short['-'] = Switch::NoArgument.new {}
  DefaultList.long[''] = Switch::NoArgument.new {throw :terminate}


  COMPSYS_HEADER = <<'XXX'      # :nodoc:

typeset -A opt_args
local context state line

_arguments -s -S \
XXX

  def compsys(to, name = File.basename($0)) # :nodoc:
    to << "#compdef #{name}\n"
    to << COMPSYS_HEADER
    visit(:compsys, {}, {}) {|o, d|
      to << %Q[  "#{o}[#{d.gsub(/[\\\"\[\]]/, '\\\\\&')}]" \\\n]
    }
    to << "  '*:file:_files' && return 0\n"
  end

  def help_exit
    if STDOUT.tty? && (pager = ENV.values_at(*%w[RUBY_PAGER PAGER]).find {|e| e && !e.empty?})
      less = ENV["LESS"]
      args = [{"LESS" => "#{!less || less.empty? ? '-' : less}Fe"}, pager, "w"]
      print = proc do |f|
        f.puts help
      rescue Errno::EPIPE
        # pager terminated
      end
      if Process.respond_to?(:fork) and false
        IO.popen("-") {|f| f ? Process.exec(*args, in: f) : print.call(STDOUT)}
        # unreachable
      end
      IO.popen(*args, &print)
    else
      puts help
    end
    exit
  end

  #
  # Default options for ARGV, which never appear in option summary.
  #
  Officious = {}

  #
  # --help
  # Shows option summary.
  #
  Officious['help'] = proc do |parser|
    Switch::NoArgument.new do |arg|
      parser.help_exit
    end
  end

  #
  # --*-completion-bash=WORD
  # Shows candidates for command line completion.
  #
  Officious['*-completion-bash'] = proc do |parser|
    Switch::RequiredArgument.new do |arg|
      puts parser.candidate(arg)
      exit
    end
  end

  #
  # --*-completion-zsh[=NAME:FILE]
  # Creates zsh completion file.
  #
  Officious['*-completion-zsh'] = proc do |parser|
    Switch::OptionalArgument.new do |arg|
      parser.compsys(STDOUT, arg)
      exit
    end
  end

  #
  # --version
  # Shows version string if Version is defined.
  #
  Officious['version'] = proc do |parser|
    Switch::OptionalArgument.new do |pkg|
      if pkg
        begin
          require_relative 'optparse/version'
        rescue LoadError
        else
          show_version(*pkg.split(/,/)) or
            abort("#{parser.program_name}: no version found in package #{pkg}")
          exit
        end
      end
      v = parser.ver or abort("#{parser.program_name}: version unknown")
      puts v
      exit
    end
  end

  # :startdoc:

  #
  # Class methods
  #

  #
  # Initializes a new instance and evaluates the optional block in context
  # of the instance. Arguments +args+ are passed to #new, see there for
  # description of parameters.
  #
  # This method is *deprecated*, its behavior corresponds to the older #new
  # method.
  #
  def self.with(*args, &block)
    opts = new(*args)
    opts.instance_eval(&block)
    opts
  end

  #
  # Returns an incremented value of +default+ according to +arg+.
  #
  def self.inc(arg, default = nil)
    case arg
    when Integer
      arg.nonzero?
    when nil
      default.to_i + 1
    end
  end

  #
  # See self.inc
  #
  def inc(*args)
    self.class.inc(*args)
  end

  #
  # Initializes the instance and yields itself if called with a block.
  #
  # +banner+:: Banner message.
  # +width+::  Summary width.
  # +indent+:: Summary indent.
  #
  def initialize(banner = nil, width = 32, indent = ' ' * 4)
    @stack = [DefaultList, List.new, List.new]
    @program_name = nil
    @banner = banner
    @summary_width = width
    @summary_indent = indent
    @default_argv = ARGV
    @require_exact = false
    @raise_unknown = true
    add_officious
    yield self if block_given?
  end

  def add_officious  # :nodoc:
    list = base()
    Officious.each do |opt, block|
      list.long[opt] ||= block.call(self)
    end
  end

  #
  # Terminates option parsing. Optional parameter +arg+ is a string pushed
  # back to be the first non-option argument.
  #
  def terminate(arg = nil)
    self.class.terminate(arg)
  end
  #
  # See #terminate.
  #
  def self.terminate(arg = nil)
    throw :terminate, arg
  end

  @stack = [DefaultList]
  #
  # Returns the global top option list.
  #
  # Do not use directly.
  #
  def self.top() DefaultList end

  #
  # Directs to accept specified class +t+. The argument string is passed to
  # the block in which it should be converted to the desired class.
  #
  # +t+::   Argument class specifier, any object including Class.
  # +pat+:: Pattern for argument, defaults to +t+ if it responds to match.
  #
  #   accept(t, pat, &block)
  #
  def accept(*args, &blk) top.accept(*args, &blk) end
  #
  # See #accept.
  #
  def self.accept(*args, &blk) top.accept(*args, &blk) end

  #
  # Directs to reject specified class argument.
  #
  # +type+:: Argument class specifier, any object including Class.
  #
  #   reject(type)
  #
  def reject(*args, &blk) top.reject(*args, &blk) end
  #
  # See #reject.
  #
  def self.reject(*args, &blk) top.reject(*args, &blk) end

  #
  # Instance methods
  #

  # Heading banner preceding summary.
  attr_writer :banner

  # Program name to be emitted in error message and default banner,
  # defaults to $0.
  attr_writer :program_name

  # Width for option list portion of summary. Must be Numeric.
  attr_accessor :summary_width

  # Indentation for summary. Must be String (or have + String method).
  attr_accessor :summary_indent

  # Strings to be parsed in default.
  attr_accessor :default_argv

  # Whether to require that options match exactly (disallows providing
  # abbreviated long option as short option).
  attr_accessor :require_exact

  # Whether to raise at unknown option.
  attr_accessor :raise_unknown

  #
  # Heading banner preceding summary.
  #
  def banner
    unless @banner
      @banner = +"Usage: #{program_name} [options]"
      visit(:add_banner, @banner)
    end
    @banner
  end

  #
  # Program name to be emitted in error message and default banner, defaults
  # to $0.
  #
  def program_name
    @program_name || File.basename($0, '.*')
  end

  # for experimental cascading :-)
  alias set_banner banner=
  alias set_program_name program_name=
  alias set_summary_width summary_width=
  alias set_summary_indent summary_indent=

  # Version
  attr_writer :version
  # Release code
  attr_writer :release

  #
  # Version
  #
  def version
    (defined?(@version) && @version) || (defined?(::Version) && ::Version)
  end

  #
  # Release code
  #
  def release
    (defined?(@release) && @release) || (defined?(::Release) && ::Release) || (defined?(::RELEASE) && ::RELEASE)
  end

  #
  # Returns version string from program_name, version and release.
  #
  def ver
    if v = version
      str = +"#{program_name} #{[v].join('.')}"
      str << " (#{v})" if v = release
      str
    end
  end

  #
  # Shows warning message with the program name
  #
  # +mesg+:: Message, defaulted to +$!+.
  #
  # See Kernel#warn.
  #
  def warn(mesg = $!)
    super("#{program_name}: #{mesg}")
  end

  #
  # Shows message with the program name then aborts.
  #
  # +mesg+:: Message, defaulted to +$!+.
  #
  # See Kernel#abort.
  #
  def abort(mesg = $!)
    super("#{program_name}: #{mesg}")
  end

  #
  # Subject of #on / #on_head, #accept / #reject
  #
  def top
    @stack[-1]
  end

  #
  # Subject of #on_tail.
  #
  def base
    @stack[1]
  end

  #
  # Pushes a new List.
  #
  # If a block is given, yields +self+ and returns the result of the
  # block, otherwise returns +self+.
  #
  def new
    @stack.push(List.new)
    if block_given?
      yield self
    else
      self
    end
  end

  #
  # Removes the last List.
  #
  def remove
    @stack.pop
  end

  #
  # Puts option summary into +to+ and returns +to+. Yields each line if
  # a block is given.
  #
  # +to+:: Output destination, which must have method <<. Defaults to [].
  # +width+:: Width of left side, defaults to @summary_width.
  # +max+:: Maximum length allowed for left side, defaults to +width+ - 1.
  # +indent+:: Indentation, defaults to @summary_indent.
  #
  def summarize(to = [], width = @summary_width, max = width - 1, indent = @summary_indent, &blk)
    nl = "\n"
    blk ||= proc {|l| to << (l.index(nl, -1) ? l : l + nl)}
    visit(:summarize, {}, {}, width, max, indent, &blk)
    to
  end

  #
  # Returns option summary string.
  #
  def help; summarize("#{banner}".sub(/\n?\z/, "\n")) end
  alias to_s help

  def pretty_print(q)           # :nodoc:
    q.object_group(self) do
      first = true
      if @stack.size > 2
        @stack.each_with_index do |s, i|
          next if i < 2
          next if s.list.empty?
          if first
            first = false
            q.text ":"
          end
          q.breakable
          s.pretty_print(q)
        end
      end
    end
  end

  def inspect                   # :nodoc:
    require 'pp'
    pretty_print_inspect
  end

  #
  # Returns option summary list.
  #
  def to_a; summarize("#{banner}".split(/^/)) end

  #
  # Checks if an argument is given twice, in which case an ArgumentError is
  # raised. Called from OptionParser#switch only.
  #
  # +obj+:: New argument.
  # +prv+:: Previously specified argument.
  # +msg+:: Exception message.
  #
  def notwice(obj, prv, msg) # :nodoc:
    unless !prv or prv == obj
      raise(ArgumentError, "argument #{msg} given twice: #{obj}",
            ParseError.filter_backtrace(caller(2)))
    end
    obj
  end
  private :notwice

  SPLAT_PROC = proc {|*a| a.length <= 1 ? a.first : a} # :nodoc:

  # :call-seq:
  #   make_switch(params, block = nil)
  #
  # :include: ../doc/optparse/creates_option.rdoc
  #
  def make_switch(opts, block = nil)
    short, long, nolong, style, pattern, conv, not_pattern, not_conv, not_style = [], [], []
    ldesc, sdesc, desc, arg = [], [], []
    default_style = Switch::NoArgument
    default_pattern = nil
    klass = nil
    q, a = nil
    has_arg = false

    opts.each do |o|
      # argument class
      next if search(:atype, o) do |pat, c|
        klass = notwice(o, klass, 'type')
        if not_style and not_style != Switch::NoArgument
          not_pattern, not_conv = pat, c
        else
          default_pattern, conv = pat, c
        end
      end

      # directly specified pattern(any object possible to match)
      if (!(String === o || Symbol === o)) and o.respond_to?(:match)
        pattern = notwice(o, pattern, 'pattern')
        if pattern.respond_to?(:convert)
          conv = pattern.method(:convert).to_proc
        else
          conv = SPLAT_PROC
        end
        next
      end

      # anything others
      case o
      when Proc, Method
        block = notwice(o, block, 'block')
      when Array, Hash
        case pattern
        when CompletingHash
        when nil
          pattern = CompletingHash.new
          conv = pattern.method(:convert).to_proc if pattern.respond_to?(:convert)
        else
          raise ArgumentError, "argument pattern given twice"
        end
        o.each {|pat, *v| pattern[pat] = v.fetch(0) {pat}}
      when Module
        raise ArgumentError, "unsupported argument type: #{o}", ParseError.filter_backtrace(caller(4))
      when *ArgumentStyle.keys
        style = notwice(ArgumentStyle[o], style, 'style')
      when /^--no-([^\[\]=\s]*)(.+)?/
        q, a = $1, $2
        o = notwice(a ? Object : TrueClass, klass, 'type')
        not_pattern, not_conv = search(:atype, o) unless not_style
        not_style = (not_style || default_style).guess(arg = a) if a
        default_style = Switch::NoArgument
        default_pattern, conv = search(:atype, FalseClass) unless default_pattern
        ldesc << "--no-#{q}"
        (q = q.downcase).tr!('_', '-')
        long << "no-#{q}"
        nolong << q
      when /^--\[no-\]([^\[\]=\s]*)(.+)?/
        q, a = $1, $2
        o = notwice(a ? Object : TrueClass, klass, 'type')
        if a
          default_style = default_style.guess(arg = a)
          default_pattern, conv = search(:atype, o) unless default_pattern
        end
        ldesc << "--[no-]#{q}"
        (o = q.downcase).tr!('_', '-')
        long << o
        not_pattern, not_conv = search(:atype, FalseClass) unless not_style
        not_style = Switch::NoArgument
        nolong << "no-#{o}"
      when /^--([^\[\]=\s]*)(.+)?/
        q, a = $1, $2
        if a
          o = notwice(NilClass, klass, 'type')
          default_style = default_style.guess(arg = a)
          default_pattern, conv = search(:atype, o) unless default_pattern
        end
        ldesc << "--#{q}"
        (o = q.downcase).tr!('_', '-')
        long << o
      when /^-(\[\^?\]?(?:[^\\\]]|\\.)*\])(.+)?/
        q, a = $1, $2
        o = notwice(Object, klass, 'type')
        if a
          default_style = default_style.guess(arg = a)
          default_pattern, conv = search(:atype, o) unless default_pattern
        else
          has_arg = true
        end
        sdesc << "-#{q}"
        short << Regexp.new(q)
      when /^-(.)(.+)?/
        q, a = $1, $2
        if a
          o = notwice(NilClass, klass, 'type')
          default_style = default_style.guess(arg = a)
          default_pattern, conv = search(:atype, o) unless default_pattern
        end
        sdesc << "-#{q}"
        short << q
      when /^=/
        style = notwice(default_style.guess(arg = o), style, 'style')
        default_pattern, conv = search(:atype, Object) unless default_pattern
      else
        desc.push(o) if o && !o.empty?
      end
    end

    default_pattern, conv = search(:atype, default_style.pattern) unless default_pattern
    if !(short.empty? and long.empty?)
      if has_arg and default_style == Switch::NoArgument
        default_style = Switch::RequiredArgument
      end
      s = (style || default_style).new(pattern || default_pattern,
                                       conv, sdesc, ldesc, arg, desc, block)
    elsif !block
      if style or pattern
        raise ArgumentError, "no switch given", ParseError.filter_backtrace(caller)
      end
      s = desc
    else
      short << pattern
      s = (style || default_style).new(pattern,
                                       conv, nil, nil, arg, desc, block)
    end
    return s, short, long,
      (not_style.new(not_pattern, not_conv, sdesc, ldesc, nil, desc, block) if not_style),
      nolong
  end

  # ----
  # Option definition phase methods
  #
  # These methods are used to define options, or to construct an
  # OptionParser instance in other words.

  # :call-seq:
  #   define(*params, &block)
  #
  # :include: ../doc/optparse/creates_option.rdoc
  #
  def define(*opts, &block)
    top.append(*(sw = make_switch(opts, block)))
    sw[0]
  end

  # :call-seq:
  #   on(*params, &block)
  #
  # :include: ../doc/optparse/creates_option.rdoc
  #
  def on(*opts, &block)
    define(*opts, &block)
    self
  end
  alias def_option define

  # :call-seq:
  #   define_head(*params, &block)
  #
  # :include: ../doc/optparse/creates_option.rdoc
  #
  def define_head(*opts, &block)
    top.prepend(*(sw = make_switch(opts, block)))
    sw[0]
  end

  # :call-seq:
  #   on_head(*params, &block)
  #
  # :include: ../doc/optparse/creates_option.rdoc
  #
  # The new option is added at the head of the summary.
  #
  def on_head(*opts, &block)
    define_head(*opts, &block)
    self
  end
  alias def_head_option define_head

  # :call-seq:
  #   define_tail(*params, &block)
  #
  # :include: ../doc/optparse/creates_option.rdoc
  #
  def define_tail(*opts, &block)
    base.append(*(sw = make_switch(opts, block)))
    sw[0]
  end

  #
  # :call-seq:
  #   on_tail(*params, &block)
  #
  # :include: ../doc/optparse/creates_option.rdoc
  #
  # The new option is added at the tail of the summary.
  #
  def on_tail(*opts, &block)
    define_tail(*opts, &block)
    self
  end
  alias def_tail_option define_tail

  #
  # Add separator in summary.
  #
  def separator(string)
    top.append(string, nil, nil)
  end

  # ----
  # Arguments parse phase methods
  #
  # These methods parse +argv+, convert, and store the results by
  # calling handlers.  As these methods do not modify +self+, +self+
  # can be frozen.

  #
  # Parses command line arguments +argv+ in order. When a block is given,
  # each non-option argument is yielded. When optional +into+ keyword
  # argument is provided, the parsed option values are stored there via
  # <code>[]=</code> method (so it can be Hash, or OpenStruct, or other
  # similar object).
  #
  # Returns the rest of +argv+ left unparsed.
  #
  def order(*argv, **keywords, &nonopt)
    argv = argv[0].dup if argv.size == 1 and Array === argv[0]
    order!(argv, **keywords, &nonopt)
  end

  #
  # Same as #order, but removes switches destructively.
  # Non-option arguments remain in +argv+.
  #
  def order!(argv = default_argv, into: nil, **keywords, &nonopt)
    setter = ->(name, val) {into[name.to_sym] = val} if into
    parse_in_order(argv, setter, **keywords, &nonopt)
  end

  def parse_in_order(argv = default_argv, setter = nil, exact: require_exact, **, &nonopt)  # :nodoc:
    opt, arg, val, rest = nil
    nonopt ||= proc {|a| throw :terminate, a}
    argv.unshift(arg) if arg = catch(:terminate) {
      while arg = argv.shift
        case arg
        # long option
        when /\A--([^=]*)(?:=(.*))?/m
          opt, rest = $1, $2
          opt.tr!('_', '-')
          begin
            if exact
              sw, = search(:long, opt)
            else
              sw, = complete(:long, opt, true)
            end
          rescue ParseError
            throw :terminate, arg unless raise_unknown
            raise $!.set_option(arg, true)
          else
            unless sw
              throw :terminate, arg unless raise_unknown
              raise InvalidOption, arg
            end
          end
          begin
            opt, cb, val = sw.parse(rest, argv) {|*exc| raise(*exc)}
            val = callback!(cb, 1, val) if cb
            callback!(setter, 2, sw.switch_name, val) if setter
          rescue ParseError
            raise $!.set_option(arg, rest)
          end

        # short option
        when /\A-(.)((=).*|.+)?/m
          eq, rest, opt = $3, $2, $1
          has_arg, val = eq, rest
          begin
            sw, = search(:short, opt)
            unless sw
              begin
                sw, = complete(:short, opt)
                # short option matched.
                val = arg.delete_prefix('-')
                has_arg = true
              rescue InvalidOption
                raise if exact
                # if no short options match, try completion with long
                # options.
                sw, = complete(:long, opt)
                eq ||= !rest
              end
            end
          rescue ParseError
            throw :terminate, arg unless raise_unknown
            raise $!.set_option(arg, true)
          end
          begin
            opt, cb, val = sw.parse(val, argv) {|*exc| raise(*exc) if eq}
          rescue ParseError
            raise $!.set_option(arg, arg.length > 2)
          else
            raise InvalidOption, arg if has_arg and !eq and arg == "-#{opt}"
          end
          begin
            argv.unshift(opt) if opt and (!rest or (opt = opt.sub(/\A-*/, '-')) != '-')
            val = callback!(cb, 1, val) if cb
            callback!(setter, 2, sw.switch_name, val) if setter
          rescue ParseError
            raise $!.set_option(arg, arg.length > 2)
          end

        # non-option argument
        else
          catch(:prune) do
            visit(:each_option) do |sw0|
              sw = sw0
              sw.block.call(arg) if Switch === sw and sw.match_nonswitch?(arg)
            end
            nonopt.call(arg)
          end
        end
      end

      nil
    }

    visit(:search, :short, nil) {|sw| sw.block.call(*argv) if !sw.pattern}

    argv
  end
  private :parse_in_order

  # Calls callback with _val_.
  def callback!(cb, max_arity, *args) # :nodoc:
    args.compact!

    if (size = args.size) < max_arity and cb.to_proc.lambda?
      (arity = cb.arity) < 0 and arity = (1-arity)
      arity = max_arity if arity > max_arity
      args[arity - 1] = nil if arity > size
    end
    cb.call(*args)
  end
  private :callback!

  #
  # Parses command line arguments +argv+ in permutation mode and returns
  # list of non-option arguments. When optional +into+ keyword
  # argument is provided, the parsed option values are stored there via
  # <code>[]=</code> method (so it can be Hash, or OpenStruct, or other
  # similar object).
  #
  def permute(*argv, **keywords)
    argv = argv[0].dup if argv.size == 1 and Array === argv[0]
    permute!(argv, **keywords)
  end

  #
  # Same as #permute, but removes switches destructively.
  # Non-option arguments remain in +argv+.
  #
  def permute!(argv = default_argv, **keywords)
    nonopts = []
    order!(argv, **keywords, &nonopts.method(:<<))
    argv[0, 0] = nonopts
    argv
  end

  #
  # Parses command line arguments +argv+ in order when environment variable
  # POSIXLY_CORRECT is set, and in permutation mode otherwise.
  # When optional +into+ keyword argument is provided, the parsed option
  # values are stored there via <code>[]=</code> method (so it can be Hash,
  # or OpenStruct, or other similar object).
  #
  def parse(*argv, **keywords)
    argv = argv[0].dup if argv.size == 1 and Array === argv[0]
    parse!(argv, **keywords)
  end

  #
  # Same as #parse, but removes switches destructively.
  # Non-option arguments remain in +argv+.
  #
  def parse!(argv = default_argv, **keywords)
    if ENV.include?('POSIXLY_CORRECT')
      order!(argv, **keywords)
    else
      permute!(argv, **keywords)
    end
  end

  #
  # Wrapper method for getopts.rb.
  #
  #   params = ARGV.getopts("ab:", "foo", "bar:", "zot:Z;zot option")
  #   # params["a"] = true   # -a
  #   # params["b"] = "1"    # -b1
  #   # params["foo"] = "1"  # --foo
  #   # params["bar"] = "x"  # --bar x
  #   # params["zot"] = "z"  # --zot Z
  #
  # Option +symbolize_names+ (boolean) specifies whether returned Hash keys should be Symbols; defaults to +false+ (use Strings).
  #
  #   params = ARGV.getopts("ab:", "foo", "bar:", "zot:Z;zot option", symbolize_names: true)
  #   # params[:a] = true   # -a
  #   # params[:b] = "1"    # -b1
  #   # params[:foo] = "1"  # --foo
  #   # params[:bar] = "x"  # --bar x
  #   # params[:zot] = "z"  # --zot Z
  #
  def getopts(*args, symbolize_names: false, **keywords)
    argv = Array === args.first ? args.shift : default_argv
    single_options, *long_options = *args

    result = {}

    single_options.scan(/(.)(:)?/) do |opt, val|
      if val
        result[opt] = nil
        define("-#{opt} VAL")
      else
        result[opt] = false
        define("-#{opt}")
      end
    end if single_options

    long_options.each do |arg|
      arg, desc = arg.split(';', 2)
      opt, val = arg.split(':', 2)
      if val
        result[opt] = val.empty? ? nil : val
        define("--#{opt}=#{result[opt] || "VAL"}", *[desc].compact)
      else
        result[opt] = false
        define("--#{opt}", *[desc].compact)
      end
    end

    parse_in_order(argv, result.method(:[]=), **keywords)
    symbolize_names ? result.transform_keys(&:to_sym) : result
  end

  #
  # See #getopts.
  #
  def self.getopts(*args, symbolize_names: false)
    new.getopts(*args, symbolize_names: symbolize_names)
  end

  #
  # Traverses @stack, sending each element method +id+ with +args+ and
  # +block+.
  #
  def visit(id, *args, &block) # :nodoc:
    @stack.reverse_each do |el|
      el.__send__(id, *args, &block)
    end
    nil
  end
  private :visit

  #
  # Searches +key+ in @stack for +id+ hash and returns or yields the result.
  #
  def search(id, key) # :nodoc:
    block_given = block_given?
    visit(:search, id, key) do |k|
      return block_given ? yield(k) : k
    end
  end
  private :search

  #
  # Completes shortened long style option switch and returns pair of
  # canonical switch and switch descriptor OptionParser::Switch.
  #
  # +typ+::   Searching table.
  # +opt+::   Searching key.
  # +icase+:: Search case insensitive if true.
  # +pat+::   Optional pattern for completion.
  #
  def complete(typ, opt, icase = false, *pat) # :nodoc:
    if pat.empty?
      search(typ, opt) {|sw| return [sw, opt]} # exact match or...
    end
    ambiguous = catch(:ambiguous) {
      visit(:complete, typ, opt, icase, *pat) {|o, *sw| return sw}
    }
    exc = ambiguous ? AmbiguousOption : InvalidOption
    raise exc.new(opt, additional: self.method(:additional_message).curry[typ])
  end
  private :complete

  #
  # Returns additional info.
  #
  def additional_message(typ, opt)
    return unless typ and opt and defined?(DidYouMean::SpellChecker)
    all_candidates = []
    visit(:get_candidates, typ) do |candidates|
      all_candidates.concat(candidates)
    end
    all_candidates.select! {|cand| cand.is_a?(String) }
    checker = DidYouMean::SpellChecker.new(dictionary: all_candidates)
    DidYouMean.formatter.message_for(all_candidates & checker.correct(opt))
  end

  #
  # Return candidates for +word+.
  #
  def candidate(word)
    list = []
    case word
    when '-'
      long = short = true
    when /\A--/
      word, arg = word.split(/=/, 2)
      argpat = Completion.regexp(arg, false) if arg and !arg.empty?
      long = true
    when /\A-/
      short = true
    end
    pat = Completion.regexp(word, long)
    visit(:each_option) do |opt|
      next unless Switch === opt
      opts = (long ? opt.long : []) + (short ? opt.short : [])
      opts = Completion.candidate(word, true, pat, &opts.method(:each)).map(&:first) if pat
      if /\A=/ =~ opt.arg
        opts.map! {|sw| sw + "="}
        if arg and CompletingHash === opt.pattern
          if opts = opt.pattern.candidate(arg, false, argpat)
            opts.map!(&:last)
          end
        end
      end
      list.concat(opts)
    end
    list
  end

  #
  # Loads options from file names as +filename+. Does nothing when the file
  # is not present. Returns whether successfully loaded.
  #
  # +filename+ defaults to basename of the program without suffix in a
  # directory ~/.options, then the basename with '.options' suffix
  # under XDG and Haiku standard places.
  #
  # The optional +into+ keyword argument works exactly like that accepted in
  # method #parse.
  #
  def load(filename = nil, **keywords)
    unless filename
      basename = File.basename($0, '.*')
      return true if load(File.expand_path(basename, '~/.options'), **keywords) rescue nil
      basename << ".options"
      return [
        # XDG
        ENV['XDG_CONFIG_HOME'],
        '~/.config',
        *ENV['XDG_CONFIG_DIRS']&.split(File::PATH_SEPARATOR),

        # Haiku
        '~/config/settings',
      ].any? {|dir|
        next if !dir or dir.empty?
        load(File.expand_path(basename, dir), **keywords) rescue nil
      }
    end
    begin
      parse(*File.readlines(filename, chomp: true), **keywords)
      true
    rescue Errno::ENOENT, Errno::ENOTDIR
      false
    end
  end

  #
  # Parses environment variable +env+ or its uppercase with splitting like a
  # shell.
  #
  # +env+ defaults to the basename of the program.
  #
  def environment(env = File.basename($0, '.*'), **keywords)
    env = ENV[env] || ENV[env.upcase] or return
    require 'shellwords'
    parse(*Shellwords.shellwords(env), **keywords)
  end

  #
  # Acceptable argument classes
  #

  #
  # Any string and no conversion. This is fall-back.
  #
  accept(Object) {|s,|s or s.nil?}

  accept(NilClass) {|s,|s}

  #
  # Any non-empty string, and no conversion.
  #
  accept(String, /.+/m) {|s,*|s}

  #
  # Ruby/C-like integer, octal for 0-7 sequence, binary for 0b, hexadecimal
  # for 0x, and decimal for others; with optional sign prefix. Converts to
  # Integer.
  #
  decimal = '\d+(?:_\d+)*'
  binary = 'b[01]+(?:_[01]+)*'
  hex = 'x[\da-f]+(?:_[\da-f]+)*'
  octal = "0(?:[0-7]+(?:_[0-7]+)*|#{binary}|#{hex})?"
  integer = "#{octal}|#{decimal}"

  accept(Integer, %r"\A[-+]?(?:#{integer})\z"io) {|s,|
    begin
      Integer(s)
    rescue ArgumentError
      raise OptionParser::InvalidArgument, s
    end if s
  }

  #
  # Float number format, and converts to Float.
  #
  float = "(?:#{decimal}(?=(.)?)(?:\\.(?:#{decimal})?)?|\\.#{decimal})(?:E[-+]?#{decimal})?"
  floatpat = %r"\A[-+]?#{float}\z"io
  accept(Float, floatpat) {|s,| s.to_f if s}

  #
  # Generic numeric format, converts to Integer for integer format, Float
  # for float format, and Rational for rational format.
  #
  real = "[-+]?(?:#{octal}|#{float})"
  accept(Numeric, /\A(#{real})(?:\/(#{real}))?\z/io) {|s, d, f, n,|
    if n
      Rational(d, n)
    elsif f
      Float(s)
    else
      Integer(s)
    end
  }

  #
  # Decimal integer format, to be converted to Integer.
  #
  DecimalInteger = /\A[-+]?#{decimal}\z/io
  accept(DecimalInteger, DecimalInteger) {|s,|
    begin
      Integer(s, 10)
    rescue ArgumentError
      raise OptionParser::InvalidArgument, s
    end if s
  }

  #
  # Ruby/C like octal/hexadecimal/binary integer format, to be converted to
  # Integer.
  #
  OctalInteger = /\A[-+]?(?:[0-7]+(?:_[0-7]+)*|0(?:#{binary}|#{hex}))\z/io
  accept(OctalInteger, OctalInteger) {|s,|
    begin
      Integer(s, 8)
    rescue ArgumentError
      raise OptionParser::InvalidArgument, s
    end if s
  }

  #
  # Decimal integer/float number format, to be converted to Integer for
  # integer format, Float for float format.
  #
  DecimalNumeric = floatpat     # decimal integer is allowed as float also.
  accept(DecimalNumeric, floatpat) {|s, f|
    begin
      if f
        Float(s)
      else
        Integer(s)
      end
    rescue ArgumentError
      raise OptionParser::InvalidArgument, s
    end if s
  }

  #
  # Boolean switch, which means whether it is present or not, whether it is
  # absent or not with prefix no-, or it takes an argument
  # yes/no/true/false/+/-.
  #
  yesno = CompletingHash.new
  %w[- no false].each {|el| yesno[el] = false}
  %w[+ yes true].each {|el| yesno[el] = true}
  yesno['nil'] = false          # should be nil?
  accept(TrueClass, yesno) {|arg, val| val == nil or val}
  #
  # Similar to TrueClass, but defaults to false.
  #
  accept(FalseClass, yesno) {|arg, val| val != nil and val}

  #
  # List of strings separated by ",".
  #
  accept(Array) do |s, |
    if s
      s = s.split(',').collect {|ss| ss unless ss.empty?}
    end
    s
  end

  #
  # Regular expression with options.
  #
  accept(Regexp, %r"\A/((?:\\.|[^\\])*)/([[:alpha:]]+)?\z|.*") do |all, s, o|
    f = 0
    if o
      f |= Regexp::IGNORECASE if /i/ =~ o
      f |= Regexp::MULTILINE if /m/ =~ o
      f |= Regexp::EXTENDED if /x/ =~ o
      case o = o.delete("imx")
      when ""
      when "u"
        s = s.encode(Encoding::UTF_8)
      when "e"
        s = s.encode(Encoding::EUC_JP)
      when "s"
        s = s.encode(Encoding::SJIS)
      when "n"
        f |= Regexp::NOENCODING
      else
        raise OptionParser::InvalidArgument, "unknown regexp option - #{o}"
      end
    else
      s ||= all
    end
    Regexp.new(s, f)
  end

  #
  # Exceptions
  #

  #
  # Base class of exceptions from OptionParser.
  #
  class ParseError < RuntimeError
    # Reason which caused the error.
    Reason = 'parse error'

    # :nodoc:
    def initialize(*args, additional: nil)
      @additional = additional
      @arg0, = args
      @args = args
      @reason = nil
    end

    attr_reader :args
    attr_writer :reason
    attr_accessor :additional

    #
    # Pushes back erred argument(s) to +argv+.
    #
    def recover(argv)
      argv[0, 0] = @args
      argv
    end

    def self.filter_backtrace(array)
      unless $DEBUG
        array.delete_if(&%r"\A#{Regexp.quote(__FILE__)}:"o.method(:=~))
      end
      array
    end

    def set_backtrace(array)
      super(self.class.filter_backtrace(array))
    end

    def set_option(opt, eq)
      if eq
        @args[0] = opt
      else
        @args.unshift(opt)
      end
      self
    end

    #
    # Returns error reason. Override this for I18N.
    #
    def reason
      @reason || self.class::Reason
    end

    def inspect
      "#<#{self.class}: #{args.join(' ')}>"
    end

    #
    # Default stringizing method to emit standard error message.
    #
    def message
      "#{reason}: #{args.join(' ')}#{additional[@arg0] if additional}"
    end

    alias to_s message
  end

  #
  # Raises when ambiguously completable string is encountered.
  #
  class AmbiguousOption < ParseError
    const_set(:Reason, 'ambiguous option')
  end

  #
  # Raises when there is an argument for a switch which takes no argument.
  #
  class NeedlessArgument < ParseError
    const_set(:Reason, 'needless argument')
  end

  #
  # Raises when a switch with mandatory argument has no argument.
  #
  class MissingArgument < ParseError
    const_set(:Reason, 'missing argument')
  end

  #
  # Raises when switch is undefined.
  #
  class InvalidOption < ParseError
    const_set(:Reason, 'invalid option')
  end

  #
  # Raises when the given argument does not match required format.
  #
  class InvalidArgument < ParseError
    const_set(:Reason, 'invalid argument')
  end

  #
  # Raises when the given argument word can't be completed uniquely.
  #
  class AmbiguousArgument < InvalidArgument
    const_set(:Reason, 'ambiguous argument')
  end

  #
  # Miscellaneous
  #

  #
  # Extends command line arguments array (ARGV) to parse itself.
  #
  module Arguable

    #
    # Sets OptionParser object, when +opt+ is +false+ or +nil+, methods
    # OptionParser::Arguable#options and OptionParser::Arguable#options= are
    # undefined. Thus, there is no ways to access the OptionParser object
    # via the receiver object.
    #
    def options=(opt)
      unless @optparse = opt
        class << self
          undef_method(:options)
          undef_method(:options=)
        end
      end
    end

    #
    # Actual OptionParser object, automatically created if nonexistent.
    #
    # If called with a block, yields the OptionParser object and returns the
    # result of the block. If an OptionParser::ParseError exception occurs
    # in the block, it is rescued, a error message printed to STDERR and
    # +nil+ returned.
    #
    def options
      @optparse ||= OptionParser.new
      @optparse.default_argv = self
      block_given? or return @optparse
      begin
        yield @optparse
      rescue ParseError
        @optparse.warn $!
        nil
      end
    end

    #
    # Parses +self+ destructively in order and returns +self+ containing the
    # rest arguments left unparsed.
    #
    def order!(**keywords, &blk) options.order!(self, **keywords, &blk) end

    #
    # Parses +self+ destructively in permutation mode and returns +self+
    # containing the rest arguments left unparsed.
    #
    def permute!(**keywords) options.permute!(self, **keywords) end

    #
    # Parses +self+ destructively and returns +self+ containing the
    # rest arguments left unparsed.
    #
    def parse!(**keywords) options.parse!(self, **keywords) end

    #
    # Substitution of getopts is possible as follows. Also see
    # OptionParser#getopts.
    #
    #   def getopts(*args)
    #     ($OPT = ARGV.getopts(*args)).each do |opt, val|
    #       eval "$OPT_#{opt.gsub(/[^A-Za-z0-9_]/, '_')} = val"
    #     end
    #   rescue OptionParser::ParseError
    #   end
    #
    def getopts(*args, symbolize_names: false, **keywords)
      options.getopts(self, *args, symbolize_names: symbolize_names, **keywords)
    end

    #
    # Initializes instance variable.
    #
    def self.extend_object(obj)
      super
      obj.instance_eval {@optparse = nil}
    end

    def initialize(*args)       # :nodoc:
      super
      @optparse = nil
    end
  end

  #
  # Acceptable argument classes. Now contains DecimalInteger, OctalInteger
  # and DecimalNumeric. See Acceptable argument classes (in source code).
  #
  module Acceptables
    const_set(:DecimalInteger, OptionParser::DecimalInteger)
    const_set(:OctalInteger, OptionParser::OctalInteger)
    const_set(:DecimalNumeric, OptionParser::DecimalNumeric)
  end
end

# ARGV is arguable by OptionParser
ARGV.extend(OptionParser::Arguable)

# An alias for OptionParser.
OptParse = OptionParser  # :nodoc: