class Gem::Commands::UnpackCommand

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

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

def description
  <<-EOF
e unpack command allows you to examine the contents of a gem or modify
em to help diagnose a bug.
u can add the contents of the unpacked gem to the load path using the
BYLIB environment variable or -I:
$ gem unpack my_gem
Unpacked gem: '.../my_gem-1.0'
[edit my_gem-1.0/lib/my_gem.rb]
$ ruby -Imy_gem-1.0/lib -S other_program
u can repackage an unpacked gem using the build command.  See the build
mmand help for an example.
  EOF
end

def execute
  get_all_gem_names.each do |name|
    dependency = Gem::Dependency.new name, options[:version]
    path = get_path dependency
    unless path then
      alert_error "Gem '#{name}' not installed nor fetchable."
      next
    end
    if @options[:spec] then
      spec, metadata = get_metadata path
      if metadata.nil? then
        alert_error "--spec is unsupported on '#{name}' (old format gem)"
        next
      end
      spec_file = File.basename spec.spec_file
      open spec_file, 'w' do |io|
        io.write metadata
      end
    else
      basename = File.basename path, '.gem'
      target_dir = File.expand_path basename, options[:target]
      package = Gem::Package.new path
      package.extract_files target_dir
      say "Unpacked gem: '#{target_dir}'"
    end
  end
end

def find_in_cache(filename)
  Gem.path.each do |path|
    this_path = File.join(path, "cache", filename)
    return this_path if File.exist? this_path
  end
  return nil
end

def get_metadata path
  format = Gem::Package.new path
  spec = format.spec
  metadata = nil
  open path, Gem.binary_mode do |io|
    tar = Gem::Package::TarReader.new io
    tar.each_entry do |entry|
      case entry.full_name
      when 'metadata' then
        metadata = entry.read
      when 'metadata.gz' then
        metadata = Gem.gunzip entry.read
      end
    end
  end
  return spec, metadata
end

def get_path dependency
  return dependency.name if dependency.name =~ /\.gem$/i
  specs = dependency.matching_specs
  selected = specs.max_by { |s| s.version }
  return Gem::RemoteFetcher.fetcher.download_to_cache(dependency) unless
    selected
  return unless dependency.name =~ /^#{selected.name}$/i
  # We expect to find (basename).gem in the 'cache' directory.  Furthermore,
  # the name match must be exact (ignoring case).
  path = find_in_cache File.basename selected.cache_file
  return Gem::RemoteFetcher.fetcher.download_to_cache(dependency) unless path
  path
end

def initialize
  require 'fileutils'
  super 'unpack', 'Unpack an installed gem to the current directory',
        :version => Gem::Requirement.default,
        :target  => Dir.pwd
  add_option('--target=DIR',
             'target directory for unpacking') do |value, options|
    options[:target] = value
  end
  add_option('--spec', 'unpack the gem specification') do |value, options|
    options[:spec] = true
  end
  add_version_option
end

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