From ec2b46e7780a73026d822aef18bbf66525ae3c43 Mon Sep 17 00:00:00 2001
From: Shulhan <ms@kilabit.info>
Date: Mon, 29 Jan 2024 23:49:25 +0700
Subject: lib/totp: add method GenerateWithTime and GenerateNWithTime

The GenerateWithTime and GenerateNWithTime accept parameter
[time.Time] as the relative time for generated password.
---
 lib/totp/totp.go              | 22 +++++++++++--
 lib/totp/totp_example_test.go | 73 +++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 90 insertions(+), 5 deletions(-)

diff --git a/lib/totp/totp.go b/lib/totp/totp.go
index 953fb843..77e90a00 100644
--- a/lib/totp/totp.go
+++ b/lib/totp/totp.go
@@ -99,13 +99,31 @@ func (p *Protocol) Generate(secret []byte) (otp string, err error) {
 	return p.generateWithTimestamp(mac, now)
 }
 
-// GenerateN generate n number of passwords from (current time - N*timeStep)
-// until the curent time.
+// GenerateWithTime generate one time password using ts as time and secret.
+func (p *Protocol) GenerateWithTime(ts time.Time, secret []byte) (otp string, err error) {
+	var mac = hmac.New(p.fnHash, secret)
+	return p.generateWithTimestamp(mac, ts.Unix())
+}
+
+// GenerateN generate n number of passwords from (ts - 0*timeStep)
+// until (ts - N*timeStep).
 func (p *Protocol) GenerateN(secret []byte, n int) (listOTP []string, err error) {
 	var (
 		mac = hmac.New(p.fnHash, secret)
 		ts  = time.Now().Unix()
+	)
+	return p.generateN(mac, ts, n)
+}
 
+// GenerateNWithTime generate n number of passwords from (ts - 0*timeStep)
+// until (ts - N*timeStep).
+func (p *Protocol) GenerateNWithTime(ts time.Time, secret []byte, n int) (listOTP []string, err error) {
+	var mac = hmac.New(p.fnHash, secret)
+	return p.generateN(mac, ts.Unix(), n)
+}
+
+func (p *Protocol) generateN(mac hash.Hash, ts int64, n int) (listOTP []string, err error) {
+	var (
 		otp string
 		t   int64
 		x   int
diff --git a/lib/totp/totp_example_test.go b/lib/totp/totp_example_test.go
index 7958e6d0..2d8e12e3 100644
--- a/lib/totp/totp_example_test.go
+++ b/lib/totp/totp_example_test.go
@@ -2,20 +2,81 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package totp
+package totp_test
 
 import (
 	"encoding/hex"
 	"fmt"
 	"log"
+	"time"
+
+	"github.com/shuLhan/share/lib/totp"
 )
 
+func ExampleProtocol_GenerateNWithTime() {
+	var (
+		secretHex = `3132333435363738393031323334353637383930`
+
+		secret []byte
+		err    error
+	)
+
+	secret, err = hex.DecodeString(secretHex)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	var (
+		proto = totp.New(totp.CryptoHashSHA1, totp.DefCodeDigits, totp.DefTimeStep)
+		ts    = time.Date(2024, time.January, 29, 23, 37, 0, 0, time.UTC)
+
+		listOTP []string
+	)
+
+	listOTP, err = proto.GenerateNWithTime(ts, secret, 3)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println(listOTP)
+	// Output:
+	// [933840 870583 802638]
+}
+
+func ExampleProtocol_GenerateWithTime() {
+	var (
+		secretHex = `3132333435363738393031323334353637383930`
+
+		secret []byte
+		err    error
+	)
+
+	secret, err = hex.DecodeString(secretHex)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	var (
+		proto = totp.New(totp.CryptoHashSHA1, totp.DefCodeDigits, totp.DefTimeStep)
+		ts    = time.Date(2024, time.January, 29, 23, 37, 0, 0, time.UTC)
+
+		otp string
+	)
+
+	otp, err = proto.GenerateWithTime(ts, secret)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println(otp)
+	// Output:
+	// 933840
+}
+
 func ExampleProtocol_Verify() {
 	var (
 		secretHex = `3132333435363738393031323334353637383930`
-		proto     = New(CryptoHashSHA1, DefCodeDigits, DefTimeStep)
 
-		otp    string
 		err    error
 		secret []byte
 	)
@@ -25,6 +86,12 @@ func ExampleProtocol_Verify() {
 		log.Fatal(err)
 	}
 
+	var (
+		proto = totp.New(totp.CryptoHashSHA1, totp.DefCodeDigits, totp.DefTimeStep)
+
+		otp string
+	)
+
 	otp, _ = proto.Generate(secret)
 
 	if proto.Verify(secret, otp, 1) {
-- 
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