ringbuffer.go

package termfun

// stRingBuffer is directly borrowed from golang term

// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// stRingBuffer is a ring buffer of strings.
type stRingBuffer struct {
	// entries contains max elements.
	entries []string
	max     int
	// head contains the index of the element most recently added to the ring.
	head int
	// size contains the number of elements in the ring.
	size int
}

func (s *stRingBuffer) Add(a string) {
	if s.entries == nil {
		const defaultNumEntries = 100
		s.entries = make([]string, defaultNumEntries)
		s.max = defaultNumEntries
	}

	s.head = (s.head + 1) % s.max
	s.entries[s.head] = a
	if s.size < s.max {
		s.size++
	}
}

// NthPreviousEntry returns the value passed to the nth previous call to Add.
// If n is zero then the immediately prior value is returned, if one, then the
// next most recent, and so on. If such an element doesn't exist then ok is
// false.
func (s *stRingBuffer) NthPreviousEntry(n int) (value string, ok bool) {
	if n < 0 || n >= s.size {
		return "", false
	}
	index := s.head - n
	if index < 0 {
		index += s.max
	}
	return s.entries[index], true
}