plan

type Changes struct {
	// Records that need to be created
	Create []*endpoint.Endpoint
	// Records that need to be updated (current data)
	UpdateOld []*endpoint.Endpoint
	// Records that need to be updated (desired data)
	UpdateNew []*endpoint.Endpoint
	// Records that need to be deleted
	Delete []*endpoint.Endpoint
}

type ConflictResolver interface {
	ResolveCreate(candidates []*endpoint.Endpoint) *endpoint.Endpoint
	ResolveUpdate(current *endpoint.Endpoint, candidates []*endpoint.Endpoint) *endpoint.Endpoint
}

type CreateOnlyPolicy struct{}

type PerResource struct{}

type Plan struct {
	// List of current records
	Current []*endpoint.Endpoint
	// List of desired records
	Desired []*endpoint.Endpoint
	// Policies under which the desired changes are calculated
	Policies []Policy
	// List of changes necessary to move towards desired state
	// Populated after calling Calculate()
	Changes *Changes
	// DomainFilter matches DNS names
	DomainFilter endpoint.DomainFilter
	// Property comparator compares custom properties of providers
	PropertyComparator PropertyComparator
}

type Policy interface {
	Apply(changes *Changes) *Changes
}

type PropertyComparator func(name string, previous string, current string) bool

type SyncPolicy struct{}

type UpsertOnlyPolicy struct{}