class HTTPX::Transcoder::Chunker::Decoder

def each
  loop do
    case @state
    when :length
      index = @buffer.index(CRLF)
      return unless index && index.positive?
      # Read hex-length
      hexlen = @buffer.byteslice(0, index)
      @buffer = @buffer.byteslice(index..-1) || "".b
      hexlen[/\h/] || raise(Error, "wrong chunk size line: #{hexlen}")
      @chunk_length = hexlen.hex
      # check if is last chunk
      @finished = @chunk_length.zero?
      nextstate(:crlf)
    when :crlf
      crlf_size = @finished && !@trailers ? 4 : 2
      # consume CRLF
      return if @buffer.bytesize < crlf_size
      raise Error, "wrong chunked encoding format" unless @buffer.start_with?(CRLF * (crlf_size / 2))
      @buffer = @buffer.byteslice(crlf_size..-1)
      if @chunk_length.nil?
        nextstate(:length)
      else
        return if @finished
        nextstate(:data)
      end
    when :data
      chunk = @buffer.byteslice(0, @chunk_length)
      @buffer = @buffer.byteslice(@chunk_length..-1) || "".b
      @chunk_buffer << chunk
      @chunk_length -= chunk.bytesize
      if @chunk_length.zero?
        yield @chunk_buffer unless @chunk_buffer.empty?
        @chunk_buffer.clear
        @chunk_length = nil
        nextstate(:crlf)
      end
    end
    break if @buffer.empty?
  end
end

def finished?
  @finished
end

def initialize(buffer, trailers = false)
  @buffer = buffer
  @chunk_length = nil
  @chunk_buffer = "".b
  @finished = false
  @state = :length
  @trailers = trailers
end

def nextstate(state)
  @state = state
end

def to_s
  @buffer
end