refactor: migrate utils in backend

backend/utils.go

@@ -0,0 +1,93 @@
+package main
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"math/rand"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/google/uuid"
+)
+
+var (
+	usernamePattern = regexp.MustCompile(`^[0-9A-Za-z]+$`)
+	passwordPattern = regexp.MustCompile(`^[!-~]+$`)
+)
+
+// IsValidUsername reports whether s is a valid username.
+func IsValidUsername(s string) bool {
+	return usernamePattern.MatchString(s)
+}
+
+// IsValidPassword reports whether s is a valid password.
+func IsValidPassword(s string) bool {
+	return passwordPattern.MatchString(s)
+}
+
+// ComputePasswordHash returns the lowercased SHA-256 hex digest of password.
+func ComputePasswordHash(password string) string {
+	sum := sha256.Sum256([]byte(password))
+	return hex.EncodeToString(sum[:])
+}
+
+// GenerateUUID returns a new UUID string, preferring version 1 (mirroring
+// python's uuid.uuid1()), falling back to a random version-4 UUID on error.
+func GenerateUUID() string {
+	u, err := uuid.NewUUID()
+	if err != nil {
+		u = uuid.New()
+	}
+	return u.String()
+}
+
+// GenerateToken returns a SHA-256 hex digest of the username concatenated with
+// a fresh UUID.
+func GenerateToken(username string) string {
+	sum := sha256.Sum256([]byte(username + GenerateUUID()))
+	return hex.EncodeToString(sum[:])
+}
+
+// GenerateSalt returns a random salt in the inclusive range [0, 6172748].
+func GenerateSalt() int {
+	return rand.Intn(6172749)
+}
+
+// ComputePasswordHashWithSalt returns the lowercased SHA-256 hex digest of
+// passwordHashed concatenated with the decimal string form of salt.
+func ComputePasswordHashWithSalt(passwordHashed string, salt int) string {
+	sum := sha256.Sum256([]byte(passwordHashed + strconv.Itoa(salt)))
+	return hex.EncodeToString(sum[:])
+}
+
+// GetCurrentTimestamp returns the current UNIX timestamp in seconds.
+func GetCurrentTimestamp() int {
+	return int(time.Now().Unix())
+}
+
+// GetTokenExpireOn returns the timestamp 2 days from now, used as the token
+// expiry.
+func GetTokenExpireOn() int {
+	return GetCurrentTimestamp() + 60*60*24*2
+}
+
+// Str2Bool reports whether s, compared case-insensitively, equals "true".
+func Str2Bool(s string) bool {
+	return strings.ToLower(s) == "true"
+}
+
+// GCD returns the greatest common divisor of a and b via the Euclidean
+// algorithm.
+func GCD(a, b int) int {
+	for b != 0 {
+		a, b = b, a%b
+	}
+	return a
+}
+
+// LCM returns the least common multiple of a and b.
+func LCM(a, b int) int {
+	return (a * b) / GCD(a, b)
+}