package utils

import "sync"

// SequenceNumberGenerator can be used to generate increasing numbers.
type SequenceNumberGenerator interface {

	// Next returns the next number
	Next() uint64

	// Revert can be used to decrease the number (e.g. in case of an error)
	Revert()
}

// DefaultSequenceNumberGenerator is a mutex protected implementation of SequenceNumberGenerator
type DefaultSequenceNumberGenerator struct {
	sequenceNumber     uint64
	sequenceNumberLock sync.Mutex
}

// NewDefaultSequenceNumberGenerator returns an instance of DefaultSequenceNumberGenerator as pointer
// of SequenceNumberGenerator.
func NewDefaultSequenceNumberGenerator() *SequenceNumberGenerator {
	var generator SequenceNumberGenerator = &DefaultSequenceNumberGenerator{
		sequenceNumber:     0,
		sequenceNumberLock: sync.Mutex{},
	}
	return &generator
}

// Next implements SequenceNumberGenerator.Next
func (g *DefaultSequenceNumberGenerator) Next() uint64 {
	g.sequenceNumberLock.Lock()
	defer g.sequenceNumberLock.Unlock()
	next := g.sequenceNumber
	g.sequenceNumber += 1
	return next
}

// Revert implements SequenceNumberGenerator.Revert
func (g *DefaultSequenceNumberGenerator) Revert() {
	g.sequenceNumberLock.Lock()
	defer g.sequenceNumberLock.Unlock()
	g.sequenceNumber -= 1
}