improved random string generation

main.go

@@ -1,8 +1,6 @@
 package main
 
 import (
-	"backend/args_parser"
-	"backend/config"
 	"backend/logger"
 	"backend/src/handlers"
 	"backend/src/middleware"
@@ -10,6 +8,8 @@ import (
 	"backend/src/repo"
 	"backend/src/services"
 	"backend/src/utils"
+	"backend/utils/args_parser"
+	"backend/utils/config"
 	"crypto/rsa"
 	"crypto/x509"
 	"database/sql"

src/services/shortlink_service.go

@@ -2,10 +2,8 @@ package services
 
 import (
 	"backend/src/repo"
+	"backend/src/utils"
 	"fmt"
-	"math/rand"
-	"strings"
-	"time"
 )
 
 type ShortlinkService interface {
@@ -20,33 +18,18 @@ type NewShortlinkServiceParams struct {
 
 func NewShortlinkSevice(params NewShortlinkServiceParams) ShortlinkService {
 	return &shortlinkService{
+		randomUtil: *utils.NewRand(),
 		cache:      params.Cache,
 	}
 }
 
 type shortlinkService struct {
+	randomUtil utils.RandomUtil
 	cache      repo.Cache[string, string]
 }
 
-func (s *shortlinkService) randomStr() string {
-	src := rand.NewSource(time.Now().UnixMicro())
-	randGen := rand.New(src)
-
-	builder := strings.Builder{}
-	for i := 0; i < 9; i++ {
-		offset := 0x41
-		if randGen.Int()%2 == 1 {
-			offset = 0x61
-		}
-
-		byte := offset + (randGen.Int() % 26)
-		builder.WriteRune(rune(byte))
-	}
-	return builder.String()
-}
-
 func (s *shortlinkService) CreateLink(in string) (string, error) {
-	str := s.randomStr()
+	str := s.randomUtil.RandomID(10, utils.CharsetAll)
 	s.cache.Set(str, in, 7*24*60*60)
 	return str, nil
 }

src/utils/random.go

@@ -0,0 +1,70 @@
+package utils
+
+import (
+	"math/rand"
+	"strings"
+	"time"
+)
+
+type Charset int
+
+const (
+	CharsetAll Charset = iota
+	CharsetLettersLower
+	CharsetLettersUpper
+	CharsetLetters
+	CharsetNumeric
+)
+
+type charsetPart struct {
+	Offset int
+	Size   int
+}
+
+var charsets = map[Charset][]charsetPart{}
+
+func NewRand() *RandomUtil {
+	charsetLettersLower := charsetPart{ //CharsetLettersLower
+		Offset: 0x41,
+		Size:   26,
+	}
+
+	charsetLettersUpper := charsetPart{ //CharsetLettersUpper
+		Offset: 0x61,
+		Size:   26,
+	}
+
+	charsetNumeric := charsetPart{ //CharsetLettersNumeric
+		Offset: 0x30,
+		Size:   10,
+	}
+
+	charsets = map[Charset][]charsetPart{
+		CharsetNumeric:      {charsetNumeric},
+		CharsetLettersLower: {charsetLettersLower},
+		CharsetLettersUpper: {charsetLettersUpper},
+		CharsetLetters:      {charsetLettersLower, charsetLettersUpper},
+		CharsetAll:          {charsetLettersLower, charsetLettersUpper, charsetNumeric},
+	}
+
+	return &RandomUtil{}
+}
+
+type RandomUtil struct{}
+
+func (r *RandomUtil) RandomID(outputLenght int, charset Charset) string {
+	src := rand.NewSource(time.Now().UnixMicro())
+	randGen := rand.New(src)
+
+	charsetData := charsets[charset]
+
+	builder := strings.Builder{}
+	for i := 0; i < outputLenght; i++ {
+		charsetIdx := randGen.Int() % len(charsetData)
+		charsetPart := charsetData[charsetIdx]
+
+		byte := charsetPart.Offset + (randGen.Int() % charsetPart.Size)
+		builder.WriteRune(rune(byte))
+	}
+	return builder.String()
+}