package cursor

import "io"

// BufferedReaderAt uses a buffer to supplement an io.Reader
// with limited backward seeking.
type BufferedReaderAt struct{}

func NewBufferedReaderAt(r io.Reader, minBuffer uint64) *BufferedReaderAt

// ReadAt reads bytes from the underlying reader. If the offset is after
// the end of the buffer, ReadAt will first read and ignore bytes from the
// underlying reader until it reaches the offset. If the offset is
// before the start of the buffer, ReadAt will return an error.
//
// If your parser needs unlimited lookahead, you should probably
// just read the whole input into a slice and use BytesCursor.
func (b *BufferedReaderAt) ReadAt(dst []byte, offset int64) (int, error)

// RuneReader is an io.RuneReader backed by a Cursor, for compatibility
// with the regexp package.
type RuneReader struct {
	cursor Cursor[byte]
}

func NewRuneReader(c Cursor[byte]) *RuneReader {
	return &RuneReader{cursor: c}
}

func (r *RuneReader) Read(dst []byte) (int, error) {
	n, c, err := r.cursor.Read(dst)
	r.cursor = c
	return int(n), err
}

func (r *RuneReader) Cursor() Cursor[byte] {
	return r.cursor
}