require 'fileutils'
require 'rubygems/command'
require 'rubygems/installer'
require 'rubygems/version_option'

class Gem::Commands::UnpackCommand < Gem::Command

  include Gem::VersionOption

  def initialize
    super 'unpack', 'Unpack an installed gem to the current directory',
          :version => Gem::Requirement.default
    add_version_option
  end

  def arguments # :nodoc:
    "GEMNAME       name of gem to unpack"
  end

  def defaults_str # :nodoc:
    "--version '#{Gem::Requirement.default}'"
  end

  def usage # :nodoc:
    "#{program_name} GEMNAME"
  end

  #--
  # TODO: allow, e.g., 'gem unpack rake-0.3.1'.  Find a general solution for
  # this, so that it works for uninstall as well.  (And check other commands
  # at the same time.)
  def execute
    gemname = get_one_gem_name
    path = get_path(gemname, options[:version])
    if path
      target_dir = File.basename(path).sub(/\.gem$/, '')
      FileUtils.mkdir_p target_dir
      Gem::Installer.new(path).unpack(File.expand_path(target_dir))
      say "Unpacked gem: '#{target_dir}'"
    else
      alert_error "Gem '#{gemname}' not installed."
    end
  end

  # Return the full path to the cached gem file matching the given
  # name and version requirement.  Returns 'nil' if no match.
  #
  # Example:
  #
  #   get_path('rake', '> 0.4')   # -> '/usr/lib/ruby/gems/1.8/cache/rake-0.4.2.gem'
  #   get_path('rake', '< 0.1')   # -> nil
  #   get_path('rak')             # -> nil (exact name required)
  #--
  # TODO: This should be refactored so that it's a general service. I don't
  # think any of our existing classes are the right place though.  Just maybe
  # 'Cache'?
  #
  # TODO: It just uses Gem.dir for now.  What's an easy way to get the list of
  # source directories?
  def get_path(gemname, version_req)
    return gemname if gemname =~ /\.gem$/i
    specs = Gem::SourceIndex.from_installed_gems.search(/\A#{gemname}\z/, version_req)
    selected = specs.sort_by { |s| s.version }.last
    return nil if selected.nil?
    # We expect to find (basename).gem in the 'cache' directory.
    # Furthermore, the name match must be exact (ignoring case).
    if gemname =~ /^#{selected.name}$/i
      filename = selected.full_name + '.gem'
      return File.join(Gem.dir, 'cache', filename)
    else
      return nil
    end
  end

end