feat: generate uuid V7 base on provided time

uuid_test.go

@@ -884,6 +884,32 @@ func TestVersion7FromReader(t *testing.T) {
 	}
 }
 
+func TestVersion7FromReaderWithTime(t *testing.T) {
+	myString := "8059ddhdle77cb52"
+	// other tests affects `lastV7time`, so we need to reset it
+	lastV7time = 0
+	timeFunc := func() time.Time {
+		return time.Date(1992, time.November, 5, 8, 8, 8, 8, time.UTC)
+	}
+
+	id, err := NewV7FromReaderWithTime(bytes.NewReader([]byte(myString)), timeFunc)
+	if err != nil {
+		t.Fatal("failed generating UUID from a reader with time")
+	}
+	if id.String() != "00a7dc05-8640-7000-ac65-373763623532" {
+		t.Errorf("expected deterministic result 00a7dc05-8640-7000-ac65-373763623532 got %s", id.String())
+	}
+
+	id, err = NewV7FromReaderWithTime(bytes.NewReader([]byte(myString)), timeFunc)
+	if err != nil {
+		t.Fatal("failed generating UUID from a reader with time")
+	}
+
+	if id.String() != "00a7dc05-8640-7001-ac65-373763623532" {
+		t.Errorf("expected deterministic result on sequential call 00a7dc05-8640-7001-ac65-373763623532 got %s", id.String())
+	}
+}
+
 func TestVersion7Monotonicity(t *testing.T) {
 	length := 10000
 	u1 := Must(NewV7()).String()

version7.go

@@ -6,6 +6,7 @@ package uuid
 
 import (
 	"io"
+	"time"
 )
 
 // UUID version 7 features a time-ordered value field derived from the widely
@@ -25,7 +26,7 @@ func NewV7() (UUID, error) {
 	if err != nil {
 		return uuid, err
 	}
-	makeV7(uuid[:])
+	makeV7(uuid[:], timeNow)
 	return uuid, nil
 }
 
@@ -38,14 +39,27 @@ func NewV7FromReader(r io.Reader) (UUID, error) {
 		return uuid, err
 	}
 
-	makeV7(uuid[:])
+	makeV7(uuid[:], timeNow)
+	return uuid, nil
+}
+
+// NewV7FromReaderWithTime returns a Version 7 UUID based on the provided time function.
+// it uses NewRandomFromReader fill random bits and the provided time function to get the time.
+// On error, NewV7FromReader returns Nil and an error.
+func NewV7FromReaderWithTime(r io.Reader, timeFunc func() time.Time) (UUID, error) {
+	uuid, err := NewRandomFromReader(r)
+	if err != nil {
+		return uuid, err
+	}
+
+	makeV7(uuid[:], timeFunc)
 	return uuid, nil
 }
 
 // makeV7 fill 48 bits time (uuid[0] - uuid[5]), set version b0111 (uuid[6])
 // uuid[8] already has the right version number (Variant is 10)
 // see function NewV7 and NewV7FromReader
-func makeV7(uuid []byte) {
+func makeV7(uuid []byte, timeFunc func() time.Time) {
 	/*
 		 0                   1                   2                   3
 		 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
@@ -61,7 +75,7 @@ func makeV7(uuid []byte) {
 	*/
 	_ = uuid[15] // bounds check
 
-	t, s := getV7Time()
+	t, s := getV7Time(timeFunc)
 
 	uuid[0] = byte(t >> 40)
 	uuid[1] = byte(t >> 32)
@@ -85,11 +99,11 @@ const nanoPerMilli = 1000000
 // getV7Time returns the time in milliseconds and nanoseconds / 256.
 // The returned (milli << 12 + seq) is guaranteed to be greater than
 // (milli << 12 + seq) returned by any previous call to getV7Time.
-func getV7Time() (milli, seq int64) {
+func getV7Time(timeFunc func() time.Time) (milli, seq int64) {
 	timeMu.Lock()
 	defer timeMu.Unlock()
 
-	nano := timeNow().UnixNano()
+	nano := timeFunc().UnixNano()
 	milli = nano / nanoPerMilli
 	// Sequence number is between 0 and 3906 (nanoPerMilli>>8)
 	seq = (nano - milli*nanoPerMilli) >> 8