package domain

import (
	"errors"
	"math"
)

var (
	ErrInvalidRevision  = errors.New("command revision must be nonzero")
	ErrRevisionOverflow = errors.New("command revision overflow")
	ErrStaleRevision    = errors.New("stale command revision")
	ErrFutureRevision   = errors.New("unexpected future command revision")
)

type CommandRevision uint64

const InitialCommandRevision CommandRevision = 1

type RevisionRelation uint8

const (
	RevisionInvalid RevisionRelation = iota
	RevisionStale
	RevisionCurrent
	RevisionFuture
)

func CompareRevision(current, incoming CommandRevision) RevisionRelation {
	if current == 0 || incoming == 0 {
		return RevisionInvalid
	}
	if incoming < current {
		return RevisionStale
	}
	if incoming > current {
		return RevisionFuture
	}
	return RevisionCurrent
}

func ValidateCurrentRevision(current, incoming CommandRevision) error {
	switch CompareRevision(current, incoming) {
	case RevisionCurrent:
		return nil
	case RevisionStale:
		return ErrStaleRevision
	case RevisionFuture:
		return ErrFutureRevision
	default:
		return ErrInvalidRevision
	}
}

// NextRevision durably orders a new cancel or signal intent.
func NextRevision(current CommandRevision) (CommandRevision, error) {
	if current == 0 {
		return 0, ErrInvalidRevision
	}
	if current == math.MaxUint64 {
		return 0, ErrRevisionOverflow
	}
	return current + 1, nil
}