update

utils/hasher/hasher.go

@@ -0,0 +1,74 @@
+package hasher
+
+import (
+	"hash/maphash"
+	"strconv"
+	"sync"
+
+	"github.com/navidrome/navidrome/utils/random"
+)
+
+var instance = NewHasher()
+
+func Reseed(id string) {
+	instance.Reseed(id)
+}
+
+func SetSeed(id string, seed string) {
+	instance.SetSeed(id, seed)
+}
+
+func CurrentSeed(id string) string {
+	instance.mutex.RLock()
+	defer instance.mutex.RUnlock()
+	return instance.seeds[id]
+}
+
+func HashFunc() func(id, str string) uint64 {
+	return instance.HashFunc()
+}
+
+type Hasher struct {
+	seeds    map[string]string
+	mutex    sync.RWMutex
+	hashSeed maphash.Seed
+}
+
+func NewHasher() *Hasher {
+	h := new(Hasher)
+	h.seeds = make(map[string]string)
+	h.hashSeed = maphash.MakeSeed()
+	return h
+}
+
+// SetSeed sets a seed for the given id
+func (h *Hasher) SetSeed(id string, seed string) {
+	h.mutex.Lock()
+	defer h.mutex.Unlock()
+	h.seeds[id] = seed
+}
+
+// Reseed generates a new random seed for the given id
+func (h *Hasher) Reseed(id string) {
+	_ = h.reseed(id)
+}
+
+func (h *Hasher) reseed(id string) string {
+	seed := strconv.FormatUint(random.Uint64(), 36)
+	h.SetSeed(id, seed)
+	return seed
+}
+
+// HashFunc returns a function that hashes a string using the seed for the given id
+func (h *Hasher) HashFunc() func(id, str string) uint64 {
+	return func(id, str string) uint64 {
+		h.mutex.RLock()
+		seed, ok := h.seeds[id]
+		h.mutex.RUnlock()
+		if !ok {
+			seed = h.reseed(id)
+		}
+
+		return maphash.Bytes(h.hashSeed, []byte(seed+str))
+	}
+}