module RDoc::Encoding

def self.read_file filename, encoding, force_transcode = false
  content = File.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/, '')
  enc = RDoc::Encoding.detect_encoding content
  content = RDoc::Encoding.change_encoding content, enc if enc
  begin
    encoding ||= Encoding.default_external
    orig_encoding = content.encoding
    if not orig_encoding.ascii_compatible? then
      content = content.encode encoding
    elsif utf8 then
      content = RDoc::Encoding.change_encoding content, Encoding::UTF_8
      content = content.encode encoding
    else
      # assume the content is in our output encoding
      content = RDoc::Encoding.change_encoding content, encoding
    end
    unless content.valid_encoding? then
      # revert and try to transcode
      content = RDoc::Encoding.change_encoding content, orig_encoding
      content = 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 = RDoc::Encoding.change_encoding content, orig_encoding
      content = content.encode(encoding,
                               :invalid => :replace,
                               :undef => :replace,
                               :replace => '?')
      return content
    else
      warn "unable to convert #{e.message} for #{filename}, skipping"
      return nil
    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