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