package inventory

import "github.com/shcizo/package-updater/internal/protocol"

// Diff compares two snapshots. upserts holds services that are new or
// changed in next; removes holds the keys of services missing from next.
func Diff(prev, next []protocol.Service) (upserts []protocol.Service, removes []string) {
	old := make(map[string]protocol.Service, len(prev))
	for _, s := range prev {
		old[s.Key()] = s
	}
	seen := make(map[string]struct{}, len(next))
	for _, s := range next {
		seen[s.Key()] = struct{}{}
		if o, ok := old[s.Key()]; !ok || o != s {
			upserts = append(upserts, s)
		}
	}
	for _, s := range prev {
		if _, ok := seen[s.Key()]; !ok {
			removes = append(removes, s.Key())
		}
	}
	return upserts, removes
}