package alert

import (
	"sort"
	"strings"
)

type LabelSet map[string]string

var (
	// cache the signature of an empty label set.
	emptyLabelSignature = hashNew()
)

func (ls LabelSet) Fingerprint() uint64 {
	return labelSetToFingerprint(ls)
}

// labelSetToFingerprint works exactly as LabelsToSignature but takes a LabelSet as
// parameter (rather than a label map) and returns a Fingerprint.
func labelSetToFingerprint(ls LabelSet) uint64 {
	if len(ls) == 0 {
		return uint64(emptyLabelSignature)
	}

	labelNames := make(LabelNames, 0, len(ls))
	for labelName := range ls {
		labelNames = append(labelNames, labelName)
	}
	sort.Sort(labelNames)

	sum := hashNew()
	for _, labelName := range labelNames {
		sum = hashAdd(sum, string(labelName))
		sum = hashAddByte(sum, SeparatorByte)
		sum = hashAdd(sum, string(ls[labelName]))
		sum = hashAddByte(sum, SeparatorByte)
	}
	return uint64(sum)
}

const (
	offset64           = 14695981039346656037
	prime64            = 1099511628211
	SeparatorByte byte = 255
)

// hashNew initializies a new fnv64a hash value.
func hashNew() uint64 {
	return offset64
}

// hashAdd adds a string to a fnv64a hash value, returning the updated hash.
func hashAdd(h uint64, s string) uint64 {
	for i := 0; i < len(s); i++ {
		h ^= uint64(s[i])
		h *= prime64
	}
	return h
}

// hashAddByte adds a byte to a fnv64a hash value, returning the updated hash.
func hashAddByte(h uint64, b byte) uint64 {
	h ^= uint64(b)
	h *= prime64
	return h
}

// LabelNames is a sortable LabelName slice. In implements sort.Interface.
type LabelNames []string

func (l LabelNames) Len() int {
	return len(l)
}

func (l LabelNames) Less(i, j int) bool {
	return l[i] < l[j]
}

func (l LabelNames) Swap(i, j int) {
	l[i], l[j] = l[j], l[i]
}

func (l LabelNames) String() string {
	labelStrings := make([]string, 0, len(l))
	for _, label := range l {
		labelStrings = append(labelStrings, string(label))
	}
	return strings.Join(labelStrings, ", ")
}