module RDoc::Encoding

def self.read_file filename, encoding, force_transcode = false
  content = open filename, "rb" do |f| f.read end
  content.gsub!("\r\n", "\n") if RUBY_PLATFORM =~ /mswin|mingw/
  utf8 = content.sub!(/\A\xef\xbb\xbf/, '')
  RDoc::Encoding.set_encoding content
  if Object.const_defined? :Encoding then
    begin
      encoding ||= Encoding.default_external
      orig_encoding = content.encoding
      if not orig_encoding.ascii_compatible? then
        content.encode! encoding
      elsif utf8 then
        content.force_encoding Encoding::UTF_8
        content.encode! encoding
      else
        # assume the content is in our output encoding
        content.force_encoding encoding
      end
      unless content.valid_encoding? then
        # revert and try to transcode
        content.force_encoding orig_encoding
        content.encode! encoding
      end
      unless content.valid_encoding? then
        warn "unable to convert #{filename} to #{encoding}, skipping"
        content = nil
      end
    rescue Encoding::InvalidByteSequenceError,
           Encoding::UndefinedConversionError => e
      if force_transcode then
        content.force_encoding orig_encoding
        content.encode!(encoding,
                        :invalid => :replace, :undef => :replace,
                        :replace => '?')
        return content
      else
        warn "unable to convert #{e.message} for #{filename}, skipping"
        return nil
      end
    end
  end
  content
rescue ArgumentError => e
  raise unless e.message =~ /unknown encoding name - (.*)/
  warn "unknown encoding name \"#{$1}\" for #{filename}, skipping"
  nil
rescue Errno::EISDIR, Errno::ENOENT
  nil
end

def self.set_encoding string
  string =~ /\A(?:#!.*\n)?(.*\n)/
  first_line = $1
  name = case first_line
         when /^<\?xml[^?]*encoding=(["'])(.*?)\1/ then $2
         when /\b(?:en)?coding[=:]\s*([^\s;]+)/i   then $1
         else                                           return
         end
  string.sub! first_line, ''
  return unless Object.const_defined? :Encoding
  enc = Encoding.find name
  string.force_encoding enc if enc
end