package util

// DedupeStrings returns a new slice holding each value of input once, in the
// order in which each value first appears. The input slice is not modified.
// A nil input returns nil.
func DedupeStrings(input []string) []string {
	if input == nil {
		return nil
	}

	seen := make(map[string]struct{}, len(input))
	out := make([]string, 0, len(input))

	for _, value := range input {
		if _, ok := seen[value]; ok {
			continue
		}
		seen[value] = struct{}{}
		out = append(out, value)
	}

	return out
}