feat: add math captcha

Signed-off-by: Manfred Touron <94029+moul@users.noreply.github.com>

captcha/math.go

@@ -0,0 +1,39 @@
+package captcha
+
+import (
+	"fmt"
+	"math/rand"
+	"strconv"
+	"strings"
+)
+
+type mathCaptcha struct {
+	equation string
+	result   int
+}
+
+func NewMathCaptcha() Captcha {
+	a := rand.Intn(5) + 1 // nolint:gosec,gomnd
+	b := rand.Intn(5) + 1 // nolint:gosec,gomnd
+	equation := fmt.Sprintf("%d + %d", a, b)
+	result := a + b
+	return mathCaptcha{equation, result}
+}
+
+func (c mathCaptcha) Question() (string, error) {
+	return c.equation, nil
+}
+
+func (c mathCaptcha) Validate(input string) (bool, error) {
+	input = strings.TrimSpace(input)
+	if input == "" {
+		return false, nil
+	}
+	nb, err := strconv.Atoi(input)
+	if err != nil {
+		return false, fmt.Errorf("invalid input: %w", err)
+	}
+	return nb == c.result, nil
+}
+
+var _ Captcha = (*mathCaptcha)(nil)

captcha/math_test.go

@@ -0,0 +1,38 @@
+package captcha_test
+
+import (
+	"fmt"
+	"math/rand"
+
+	"moul.io/captcha/captcha"
+)
+
+func ExampleNewMathCaptcha() {
+	rand.Seed(42)
+	captcha := captcha.NewMathCaptcha()
+	question, _ := captcha.Question()
+	fmt.Println(question)
+
+	valid, _ := captcha.Validate("42")
+	fmt.Println(valid)
+
+	valid, _ = captcha.Validate("lorem ipsum")
+	fmt.Println(valid)
+
+	valid, _ = captcha.Validate("1 + 3")
+	fmt.Println(valid)
+
+	valid, _ = captcha.Validate("4")
+	fmt.Println(valid)
+
+	valid, _ = captcha.Validate("\n 4\t \n\n \t")
+	fmt.Println(valid)
+
+	// Output:
+	// 1 + 3
+	// false
+	// false
+	// false
+	// true
+	// true
+}