feat: add random captcha

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

captcha/random.go

@@ -0,0 +1,13 @@
+package captcha
+
+import (
+	"math/rand"
+)
+
+func NewRandomCaptcha() Captcha {
+	availables := []func() Captcha{
+		NewBannerCaptcha,
+		NewMathCaptcha,
+	}
+	return availables[rand.Intn(len(availables))]() // nolint:gosec
+}

captcha/random_test.go

@@ -0,0 +1,30 @@
+package captcha_test
+
+import (
+	"fmt"
+	"math/rand"
+
+	"moul.io/captcha/captcha"
+)
+
+func ExampleNewRandomCaptcha() {
+	rand.Seed(42)
+
+	// first captcha
+	c := captcha.NewRandomCaptcha()
+	question, _ := c.Question()
+	fmt.Println(question)
+
+	// second captcha
+	c = captcha.NewRandomCaptcha()
+	question, _ = c.Question()
+	fmt.Println(question)
+
+	// Output:
+	// 3 + 4
+	//        _    _
+	//  _ __ | |_ | |_  _  _  ___
+	// | '_ \|  _||  _|| || |/ -_)
+	// | .__/ \__| \__| \_,_|\___|
+	// |_|
+}