module Gem
 class << self

 ##
 # Returns full path of previous but one directory of dir in path
 # E.g. for '/usr/share/ruby', 'ruby', it returns '/usr'

 def previous_but_one_dir_to(path, dir)
 return unless path

 split_path = path.split(File::SEPARATOR)
 File.join(split_path.take_while { |one_dir| one_dir !~ /^#{dir}$/ }[0..-2])
 end
 private :previous_but_one_dir_to

 ##
 # Detects --install-dir option specified on command line.

 def opt_install_dir?
 @opt_install_dir ||= ARGV.include?('--install-dir') || ARGV.include?('-i')
 end
 private :opt_install_dir?

 ##
 # Detects --build-root option specified on command line.

 def opt_build_root?
 @opt_build_root ||= ARGV.include?('--build-root')
 end
 private :opt_build_root?

 ##
 # Tries to detect, if arguments and environment variables suggest that
 # 'gem install' is executed from rpmbuild.

 def rpmbuild?
 @rpmbuild ||= ENV['RPM_PACKAGE_NAME'] && (opt_install_dir? || opt_build_root?)
 end
 private :rpmbuild?

 ##
 # Default gems locations allowed on FHS system (/usr, /usr/share).
 # The locations are derived from directories specified during build
 # configuration.

 def default_locations
 @default_locations ||= {
 :system => previous_but_one_dir_to(RbConfig::CONFIG['vendordir'], RbConfig::CONFIG['RUBY_INSTALL_NAME']),
 :local => previous_but_one_dir_to(RbConfig::CONFIG['sitedir'], RbConfig::CONFIG['RUBY_INSTALL_NAME'])
 }
 end

 ##
 # For each location provides set of directories for binaries (:bin_dir)
 # platform independent (:gem_dir) and dependent (:ext_dir) files.

 def default_dirs
 @libdir ||= case RUBY_PLATFORM
 when 'java'
 RbConfig::CONFIG['datadir']
 else
 RbConfig::CONFIG['libdir']
 end

 @default_dirs ||= default_locations.inject(Hash.new) do |hash, location|
 destination, path = location

 hash[destination] = if path
 {
 :bin_dir => File.join(path, RbConfig::CONFIG['bindir'].split(File::SEPARATOR).last),
 :gem_dir => File.join(path, RbConfig::CONFIG['datadir'].split(File::SEPARATOR).last, 'gems'),
 :ext_dir => File.join(path, @libdir.split(File::SEPARATOR).last, 'gems')
 }
 else
 {
 :bin_dir => '',
 :gem_dir => '',
 :ext_dir => ''
 }
 end

 hash
 end
 end

 ##
 # Remove methods we are going to override. This avoids "method redefined;"
 # warnings otherwise issued by Ruby.

 remove_method :operating_system_defaults if method_defined? :operating_system_defaults
 remove_method :default_dir if method_defined? :default_dir
 remove_method :default_path if method_defined? :default_path
 remove_method :default_ext_dir_for if method_defined? :default_ext_dir_for

 ##
 # Regular user installs into user directory, root manages /usr/local.

 def operating_system_defaults
 unless opt_build_root?
 options = if Process.uid == 0
 "--install-dir=#{Gem.default_dirs[:local][:gem_dir]} --bindir #{Gem.default_dirs[:local][:bin_dir]}"
 else
 "--user-install --bindir #{File.join [Dir.home, 'bin']}"
 end

 {"gem" => options}
 else
 {}
 end
 end

 ##
 # RubyGems default overrides.

 def default_dir
 Gem.default_dirs[:system][:gem_dir]
 end

 def default_path
 path = default_dirs.collect {|location, paths| paths[:gem_dir]}
 path.unshift Gem.user_dir if File.exist? Gem.user_home
 path
 end

 def default_ext_dir_for base_dir
 dir = if rpmbuild?
 build_dir = base_dir.chomp Gem.default_dirs[:system][:gem_dir]
 if build_dir != base_dir
 File.join build_dir, Gem.default_dirs[:system][:ext_dir]
 end
 else
 dirs = Gem.default_dirs.detect {|location, paths| paths[:gem_dir] == base_dir}
 dirs && dirs.last[:ext_dir]
 end
 dir && File.join(dir, RbConfig::CONFIG['RUBY_INSTALL_NAME'])
 end

 # This method should be available since RubyGems 2.2 until RubyGems 3.0.
 # https://github.com/rubygems/rubygems/issues/749
 if method_defined? :install_extension_in_lib
 remove_method :install_extension_in_lib

 def install_extension_in_lib
 false
 end
 end
 end
end