package updateip

import (
	"strings"
	"unicode/utf8"
)

// CompressLabel returns the smallest possible subdomain label for the provided record against the domain.
func CompressLabel(domainName, recordName string) string {
	domainName = UnFqdn(domainName)
	recordName = UnFqdn(recordName)
	if strings.EqualFold(domainName, recordName) {
		return "@"
	} else if i := indexFold(recordName, "."+domainName); i > -1 {
		return recordName[:i]
	}
	return recordName
}

// ExapandLabel gives the full DNS label for the (abbreviated) record.
func ExapandLabel(domainName, recordName string) string {
	if strings.EqualFold(domainName, recordName) {
		return recordName
	} else if IsFqdn(recordName) {
		return recordName
	} else if recordName == "@" {
		return domainName
	} else if i := strings.LastIndex(recordName, ".@"); i > -1 {
		return recordName[:i] + "." + domainName
	}
	return recordName + "." + domainName
}

// indexFold returns the index of the first instance of substr in s (case insensitive), or -1 if substr is not present in s.
func indexFold(s, substr string) int {
	ns := len(s)
	nb := len(substr)
	if ns < nb {
		return -1
	}
	if nb == 0 {
		return 0
	}
	if ns == nb {
		if strings.EqualFold(s, substr) {
			return 0
		}
		return -1
	}

	l := ns - nb
	for i := 0; i <= l; {
		src := s[i : i+nb]
		if strings.EqualFold(src, substr) {
			return i
		}
		_, z := utf8.DecodeRuneInString(src)
		i += z
	}
	return -1
}

// hasSuffixFold Tests if the string s ends with the specified suffix (case insensitive).
func hasSuffixFold(s, suffix string) bool {
	return len(s) >= len(suffix) && strings.EqualFold(s[len(s)-len(suffix):], suffix)
}