class Gem::Commands::RebuildCommand

def arguments # :nodoc:
  "GEM_NAME      gem name on gem server\n" \
  "GEM_VERSION   gem version you are attempting to rebuild"
end

def build_gem(gem_name, source_date_epoch, output_file)
  gemspec = options[:gemspec_file] || find_gemspec("#{gem_name}.gemspec")
  if gemspec
    build_package(gemspec, source_date_epoch, output_file)
  else
    alert_error error_message(gem_name)
    terminate_interaction(1)
  end
end

def build_package(gemspec, source_date_epoch, output_file)
  with_source_date_epoch(source_date_epoch) do
    spec = Gem::Specification.load(gemspec)
    if spec
      Gem::Package.build(
        spec,
        options[:force],
        options[:strict],
        output_file
      )
    else
      alert_error "Error loading gemspec. Aborting."
      terminate_interaction 1
    end
  end
end

def compare(source_date_epoch, old_file, new_file)
  date = Time.at(source_date_epoch.to_i).strftime("%F %T %Z")
  old_hash = sha256(old_file)
  new_hash = sha256(new_file)
  say
  say "Built at: #{date} (#{source_date_epoch})"
  say "Original build saved to:   #{old_file}"
  say "Reproduced build saved to: #{new_file}"
  say "Working directory: #{options[:build_path] || Dir.pwd}"
  say
  say "Hash comparison:"
  say "  #{old_hash}\t#{old_file}"
  say "  #{new_hash}\t#{new_file}"
  say
  if old_hash == new_hash
    say "SUCCESS - original and rebuild hashes matched"
  else
    say "FAILURE - original and rebuild hashes did not match"
    say
    if options[:diff]
      if system("diffoscope", old_file, new_file).nil?
        alert_error "error: could not find `diffoscope` executable"
      end
    else
      say "Pass --diff for more details (requires diffoscope to be installed)."
    end
    terminate_interaction 1
  end
end

def description # :nodoc:
  <<-EOF
e rebuild command allows you to (attempt to) reproduce a build of a gem
om a ruby gemspec.
is command assumes the gemspec can be built with the `gem build` command.
 you use any of `gem build`, `rake build`, or`rake release` in the
ild/release process for a gem, it is a potential candidate.
u will need to match the RubyGems version used, since this is included in
e Gem metadata.
 the gem includes lockfiles (e.g. Gemfile.lock) and similar, it will
quire more effort to reproduce a build. For example, it might require
re precisely matched versions of Ruby and/or Bundler to be used.
  EOF
end

def download_gem(gem_name, gem_version, old_file)
  # This code was based loosely off the `gem fetch` command.
  version = "= #{gem_version}"
  dep = Gem::Dependency.new gem_name, version
  specs_and_sources, errors =
    Gem::SpecFetcher.fetcher.spec_for_dependency dep
  # There should never be more than one item in specs_and_sources,
  # since we search for an exact version.
  spec, source = specs_and_sources[0]
  if spec.nil?
    show_lookup_failure gem_name, version, errors, options[:domain]
    terminate_interaction 1
  end
  download_path = source.download spec
  FileUtils.move(download_path, old_file)
  say "Downloaded #{gem_name} version #{gem_version} as #{old_file}."
end

def error_message(gem_name)
  if gem_name
    "Couldn't find a gemspec file matching '#{gem_name}' in #{Dir.pwd}"
  else
    "Couldn't find a gemspec file in #{Dir.pwd}"
  end
end

def execute
  gem_name, gem_version = get_gem_name_and_version
  old_dir, new_dir = prep_dirs
  gem_filename = "#{gem_name}-#{gem_version}.gem"
  old_file = File.join(old_dir, gem_filename)
  new_file = File.join(new_dir, gem_filename)
  if options[:original_gem_file]
    FileUtils.copy_file(options[:original_gem_file], old_file)
  else
    download_gem(gem_name, gem_version, old_file)
  end
  rg_version = rubygems_version(old_file)
  unless rg_version == Gem::VERSION
    alert_error <<-EOF
u need to use the same RubyGems version #{gem_name} v#{gem_version} was built with.
gem_name} v#{gem_version} was built using RubyGems v#{rg_version}.
m files include the version of RubyGems used to build them.
is means in order to reproduce #{gem_filename}, you must also use RubyGems v#{rg_version}.
u're using RubyGems v#{Gem::VERSION}.
ease install RubyGems v#{rg_version} and try again.
    EOF
    terminate_interaction 1
  end
  source_date_epoch = get_timestamp(old_file).to_s
  if build_path = options[:build_path]
    Dir.chdir(build_path) { build_gem(gem_name, source_date_epoch, new_file) }
  else
    build_gem(gem_name, source_date_epoch, new_file)
  end
  compare(source_date_epoch, old_file, new_file)
end

def get_gem_name_and_version
  args = options[:args] || []
  if args.length == 2
    gem_name, gem_version = args
  elsif args.length > 2
    raise Gem::CommandLineError, "Too many arguments"
  else
    raise Gem::CommandLineError, "Expected GEM_NAME and GEM_VERSION arguments (gem rebuild GEM_NAME GEM_VERSION)"
  end
  [gem_name, gem_version]
end

def get_timestamp(file)
  mtime = nil
  File.open(file, Gem.binary_mode) do |f|
    Gem::Package::TarReader.new(f) do |tar|
      mtime = tar.seek("metadata.gz") {|tf| tf.header.mtime }
    end
  end
  mtime
end

def initialize
  super "rebuild", "Attempt to reproduce a build of a gem."
  add_option "--diff", "If the files don't match, compare them using diffoscope." do |_value, options|
    options[:diff] = true
  end
  add_option "--force", "Skip validation of the spec." do |_value, options|
    options[:force] = true
  end
  add_option "--strict", "Consider warnings as errors when validating the spec." do |_value, options|
    options[:strict] = true
  end
  add_option "--source GEM_SOURCE", "Specify the source to download the gem from." do |value, options|
    options[:source] = value
  end
  add_option "--original GEM_FILE", "Specify a local file to compare against (instead of downloading it)." do |value, options|
    options[:original_gem_file] = value
  end
  add_option "--gemspec GEMSPEC_FILE", "Specify the name of the gemspec file." do |value, options|
    options[:gemspec_file] = value
  end
  add_option "-C PATH", "Run as if gem build was started in <PATH> instead of the current working directory." do |value, options|
    options[:build_path] = value
  end
end

def prep_dirs
  rebuild_dir = Dir.mktmpdir("gem_rebuild")
  old_dir = File.join(rebuild_dir, "old")
  new_dir = File.join(rebuild_dir, "new")
  FileUtils.mkdir_p(old_dir)
  FileUtils.mkdir_p(new_dir)
  [old_dir, new_dir]
end

def rubygems_version(gem_file)
  Gem::Package.new(gem_file).spec.rubygems_version
end

def sha256(file)
  Digest::SHA256.hexdigest(Gem.read_binary(file))
end

def usage # :nodoc:
  "#{program_name} GEM_NAME GEM_VERSION"
end

def with_source_date_epoch(source_date_epoch)
  old_sde = ENV["SOURCE_DATE_EPOCH"]
  ENV["SOURCE_DATE_EPOCH"] = source_date_epoch.to_s
  yield
ensure
  ENV["SOURCE_DATE_EPOCH"] = old_sde
end