class Fluent::Plugin::TailInput::TailWatcher::FIFO

def <<(chunk)
  # Although "chunk" is most likely transient besides String#force_encoding itself
  # won't affect the actual content of it, it is also probable that "chunk" is
  # a reused buffer and changing its encoding causes some problems on the caller side.
  #
  # Actually, the caller here is specific and "chunk" comes from IO#partial with
  # the second argument, which the function always returns as a return value.
  #
  # Feeding a string that has its encoding attribute set to any double-byte or
  # quad-byte encoding to IO#readpartial as the second arguments results in an
  # assertion failure on Ruby < 2.4.0 for unknown reasons.
  orig_encoding = chunk.encoding
  chunk.force_encoding(from_encoding)
  @buffer << chunk
  # Thus the encoding needs to be reverted back here
  chunk.force_encoding(orig_encoding)
end

def bytesize
  @buffer.bytesize
end

def convert(s)
  if @need_enc
    s.encode!(@encoding, @from_encoding)
  else
    s
  end
rescue
  s.encode!(@encoding, @from_encoding, :invalid => :replace, :undef => :replace)
end

def initialize(from_encoding, encoding)
  @from_encoding = from_encoding
  @encoding = encoding
  @need_enc = from_encoding != encoding
  @buffer = ''.force_encoding(from_encoding)
  @eol = "\n".encode(from_encoding).freeze
end

def next_line
  idx = @buffer.index(@eol)
  convert(@buffer.slice!(0, idx + 1)) unless idx.nil?
end