package reader

// DISCLAIMER
// ----------
// Some of the content of this file is inspired or copied from
// the golang standard library

import (
	"bufio"
	"fmt"
	"io"
)

// Maximum line length
var maxLineLength = 4096

// ChunkReader struct
type ChunkReader struct {
	reader  *bufio.Reader // the reader
	isEnded bool          // If we are done (2 consecutive CRLF)
}

// NewReader creates a new reader
func NewReader(r io.Reader) *ChunkReader {

	br, ok := r.(*bufio.Reader)
	if !ok {
		br = bufio.NewReader(r)
	}

	return &ChunkReader{reader: br}

}

// Read reads a chunk, err is io.EOF when done
func (r *ChunkReader) Read() ([]byte, error) {

	// 1. If already ended
	if r.isEnded {
		return nil, io.EOF
	}

	// 2. Read line
	var line []byte
	line, err := r.reader.ReadSlice('\n')

	// 3. manage errors
	if err == io.EOF {
		err = io.ErrUnexpectedEOF
	}

	if err != nil {
		return nil, err
	}

	if len(line) > maxLineLength {
		return nil, fmt.Errorf("HTTP line %d exceeded buffer size %d", len(line), maxLineLength)
	}

	// 4. Trim
	line = removeTrailingSpace(line)

	// 5. Manage ending line
	if len(line) == 0 {
		r.isEnded = true
		return line, io.EOF
	}

	return line, nil

}

func removeTrailingSpace(b []byte) []byte {
	for len(b) > 0 && isASCIISpace(b[len(b)-1]) {
		b = b[:len(b)-1]
	}
	return b
}

func isASCIISpace(b byte) bool {
	return b == ' ' || b == '\t' || b == '\r' || b == '\n'
}