feat: add books APIs

pkg/validator/validator.go

@@ -0,0 +1,77 @@
+package validator
+
+import (
+	"fmt"
+	"net/mail"
+	"strings"
+	"unicode/utf8"
+)
+
+// Errors collects validation errors for a request.
+type Errors struct {
+	Fields map[string]string `json:"fields"`
+}
+
+// New creates a new Errors instance.
+func New() *Errors {
+	return &Errors{Fields: make(map[string]string)}
+}
+
+// Add records a validation error for a field.
+func (e *Errors) Add(field, message string) {
+	e.Fields[field] = message
+}
+
+// Valid returns true if there are no validation errors.
+func (e *Errors) Valid() bool {
+	return len(e.Fields) == 0
+}
+
+// Error implements the error interface.
+func (e *Errors) Error() string {
+	parts := make([]string, 0, len(e.Fields))
+	for field, msg := range e.Fields {
+		parts = append(parts, fmt.Sprintf("%s: %s", field, msg))
+	}
+	return strings.Join(parts, "; ")
+}
+
+// --- Common validators ---
+
+// Required checks that a string is not empty.
+func Required(v *Errors, field, value string) {
+	if strings.TrimSpace(value) == "" {
+		v.Add(field, "is required")
+	}
+}
+
+// MaxLength checks that a string doesn't exceed a maximum length.
+func MaxLength(v *Errors, field, value string, max int) {
+	if utf8.RuneCountInString(value) > max {
+		v.Add(field, fmt.Sprintf("must be at most %d characters", max))
+	}
+}
+
+// MinLength checks that a string meets a minimum length.
+func MinLength(v *Errors, field, value string, min int) {
+	if utf8.RuneCountInString(value) < min {
+		v.Add(field, fmt.Sprintf("must be at least %d characters", min))
+	}
+}
+
+// Email checks that a string is a valid email address.
+func Email(v *Errors, field, value string) {
+	if _, err := mail.ParseAddress(value); err != nil {
+		v.Add(field, "must be a valid email address")
+	}
+}
+
+// In checks that a string is one of the allowed values.
+func In(v *Errors, field, value string, allowed ...string) {
+	for _, a := range allowed {
+		if value == a {
+			return
+		}
+	}
+	v.Add(field, fmt.Sprintf("must be one of: %s", strings.Join(allowed, ", ")))
+}