package term

// Ring is a fixed-size byte ring buffer holding the most recent output.
type Ring struct {
	buf   []byte
	start int
	n     int
}

func NewRing(size int) *Ring { return &Ring{buf: make([]byte, size)} }

func (r *Ring) Write(p []byte) {
	size := len(r.buf)
	if len(p) >= size {
		copy(r.buf, p[len(p)-size:])
		r.start, r.n = 0, size
		return
	}
	end := (r.start + r.n) % size
	first := copy(r.buf[end:], p)
	copy(r.buf, p[first:])
	if r.n+len(p) > size {
		r.start = (end + len(p)) % size
		r.n = size
	} else {
		r.n += len(p)
	}
}

func (r *Ring) Bytes() []byte {
	out := make([]byte, r.n)
	first := copy(out, r.buf[r.start:])
	if first < r.n {
		copy(out[first:], r.buf[:r.n-first])
	}
	return out
}