Methods Solve, GetAnswer, IsSolved, and Expiry could be implemented once for a base Captcha struct. But GetImage and generateImage methods should be implemented by all structs that compose with base Captcha struct.

internal/captcha/captcha.go

@@ -34,6 +34,23 @@ type Captcha struct {
 	ExpireIn time.Time
 }
 
+func (c *Captcha) Solve(answer Answer) bool {
+	c.Solved = c.Answer == answer
+	return c.Solved
+}
+
+func (c *Captcha) GetAnswer() Answer {
+	return c.Answer
+}
+
+func (c *Captcha) IsSolved() bool {
+	return c.Solved
+}
+
+func (c *Captcha) Expiry() time.Time {
+	return c.ExpireIn
+}
+
 func GenerateAnswer() Answer {
 	ans, _ := rand.Int(rand.Reader, big.NewInt(maxAnswer))
 	return (Answer(ans.String()))

internal/captcha/dwelling_captcha.go

@@ -72,20 +72,3 @@ func (c *DwellingCaptcha) GetImage() *image.Image {
 
 	return &c.Image
 }
-
-func (c *DwellingCaptcha) Solve(answer Answer) bool {
-	c.Solved = c.Answer == answer
-	return c.Solved
-}
-
-func (c *DwellingCaptcha) GetAnswer() Answer {
-	return c.Answer
-}
-
-func (c *DwellingCaptcha) IsSolved() bool {
-	return c.Solved
-}
-
-func (c *DwellingCaptcha) Expiry() time.Time {
-	return c.ExpireIn
-}