refactored for maintainability

internal/validation/stringfield.go

@@ -0,0 +1,106 @@
+package validation
+
+import (
+	"fmt"
+	"slices"
+	"strings"
+	"unicode"
+)
+
+type StringField struct {
+	Field
+	Value string
+}
+
+func newStringField(key string, g Getter) *StringField {
+	return &StringField{
+		Value: g.Get(key),
+		Field: newField(key, g),
+	}
+}
+
+// Required enforces a non empty string
+func (s *StringField) Required() *StringField {
+	if s.Value == "" {
+		s.getter.AddCheck(newFailedCheck(
+			"Field not provided",
+			fmt.Sprintf("%s is required", s.Key),
+		))
+	}
+	return s
+}
+
+// Optional will skip all validations if value is empty
+func (s *StringField) Optional() *StringField {
+	if s.Value == "" {
+		s.optional = true
+	}
+	return s
+}
+
+// MaxLength enforces a maximum string length
+func (s *StringField) MaxLength(length int) *StringField {
+	if len(s.Value) > length && !s.optional {
+		s.getter.AddCheck(newFailedCheck(
+			"Input too long",
+			fmt.Sprintf("%s is too long, max %v chars", s.Key, length),
+		))
+	}
+	return s
+}
+
+// MinLength enforces a minimum string length
+func (s *StringField) MinLength(length int) *StringField {
+	if len(s.Value) < length && !s.optional {
+		s.getter.AddCheck(newFailedCheck(
+			"Input too short",
+			fmt.Sprintf("%s is too short, min %v chars", s.Key, length),
+		))
+	}
+	return s
+}
+
+// AlphaNumeric enforces the string contains only letters and numbers
+func (s *StringField) AlphaNumeric() *StringField {
+	if s.optional {
+		return s
+	}
+	for _, r := range s.Value {
+		if !unicode.IsLetter(r) && !unicode.IsDigit(r) {
+			s.getter.AddCheck(newFailedCheck(
+				"Invalid characters",
+				fmt.Sprintf("%s must contain only letters and numbers.", s.Key),
+			))
+			return s
+		}
+	}
+	return s
+}
+
+func (s *StringField) AllowedValues(allowed []string) *StringField {
+	if !slices.Contains(allowed, s.Value) && !s.optional {
+		s.getter.AddCheck(newFailedCheck(
+			"Value not allowed",
+			fmt.Sprintf("%s must be one of: %s", s.Key, strings.Join(allowed, ",")),
+		))
+	}
+	return s
+}
+
+// ToUpper transforms the string to uppercase
+func (s *StringField) ToUpper() *StringField {
+	s.Value = strings.ToUpper(s.Value)
+	return s
+}
+
+// ToLower transforms the string to lowercase
+func (s *StringField) ToLower() *StringField {
+	s.Value = strings.ToLower(s.Value)
+	return s
+}
+
+// TrimSpace removes leading and trailing whitespace
+func (s *StringField) TrimSpace() *StringField {
+	s.Value = strings.TrimSpace(s.Value)
+	return s
+}