class Gem::CommandManager

def self.instance
  @command_manager ||= new
end

def self.reset
  @command_manager = nil
end

def [](command_name)
  command_name = command_name.intern
  return nil if @commands[command_name].nil?
  @commands[command_name] ||= load_and_instantiate(command_name)
end

def command_names
  @commands.keys.collect {|key| key.to_s}.sort
end

def find_command(cmd_name)
  possibilities = find_command_possibilities cmd_name
  if possibilities.size > 1 then
    raise Gem::CommandLineError,
          "Ambiguous command #{cmd_name} " \
          "matches [#{possibilities.join(', ')}]"
  elsif possibilities.empty? then
    raise Gem::CommandLineError, "Unknown command #{cmd_name}"
  end
  self[possibilities.first]
end

def find_command_possibilities(cmd_name)
  len = cmd_name.length
  found = command_names.select { |name| cmd_name == name[0, len] }
  exact = found.find { |name| name == cmd_name }
  exact ? [exact] : found
end

def initialize
  require 'timeout'
  @commands = {}
  register_command :build
  register_command :cert
  register_command :check
  register_command :cleanup
  register_command :contents
  register_command :dependency
  register_command :environment
  register_command :fetch
  register_command :generate_index
  register_command :help
  register_command :install
  register_command :list
  register_command :lock
  register_command :mirror
  register_command :outdated
  register_command :owner
  register_command :pristine
  register_command :push
  register_command :query
  register_command :rdoc
  register_command :search
  register_command :server
  register_command :sources
  register_command :specification
  register_command :stale
  register_command :uninstall
  register_command :unpack
  register_command :update
  register_command :which
  register_command :yank
end

def instance
  self
end

def load_and_instantiate(command_name)
  command_name = command_name.to_s
  const_name = command_name.capitalize.gsub(/_(.)/) { $1.upcase } << "Command"
  load_error = nil
  begin
    begin
      require "rubygems/commands/#{command_name}_command"
    rescue LoadError => e
      load_error = e
    end
    Gem::Commands.const_get(const_name).new
  rescue Exception => e
    e = load_error if load_error
    alert_error "Loading command: #{command_name} (#{e.class})\n\t#{e}"
    ui.backtrace e
  end
end

def process_args(args, build_args=nil)
  args = args.to_str.split(/\s+/) if args.respond_to?(:to_str)
  if args.empty? then
    say Gem::Command::HELP
    terminate_interaction 1
  end
  case args.first
  when '-h', '--help' then
    say Gem::Command::HELP
    terminate_interaction 0
  when '-v', '--version' then
    say Gem::VERSION
    terminate_interaction 0
  when /^-/ then
    alert_error "Invalid option: #{args.first}.  See 'gem --help'."
    terminate_interaction 1
  else
    cmd_name = args.shift.downcase
    cmd = find_command cmd_name
    cmd.invoke_with_build_args args, build_args
  end
end

def register_command(command, obj=false)
  @commands[command] = obj
end

def run(args, build_args=nil)
  process_args(args, build_args)
rescue StandardError, Timeout::Error => ex
  alert_error "While executing gem ... (#{ex.class})\n    #{ex.to_s}"
  ui.backtrace ex
  if Gem.configuration.really_verbose and \
       ex.kind_of?(Gem::Exception) and ex.source_exception
    e = ex.source_exception
    ui.errs.puts "Because of: (#{e.class})\n    #{e.to_s}"
    ui.backtrace e
  end
  terminate_interaction(1)
rescue Interrupt
  alert_error "Interrupted"
  terminate_interaction(1)
end

def unregister_command(command)
  @commands.delete command
end