justcaptcha/pkg/captcha/captcha.go

package captcha

import (
	"crypto/rand"
	"errors"
	"image"
	"math/big"
	"time"
)

const (
	maxAnswer = 999999
)

var errorNotFound = errors.New("captcha not found")

type Answer string

// ICaptcha interface that should be implemented by captcha.
type ICaptcha interface {
	// generateImage is used to create a captcha image.
	generateImage() *image.Image
	// GetImage() returns an image of captcha. Calls
	// generateImage() method if image doesn't exist.
	GetImage() *image.Image
	// GetAnswer returns a pregenerated answer.
	GetAnswer() Answer
	// Solve compares a stored answer with a passed one.
	// Sets field Solved to true if they are equal.
	Solve(answer Answer) bool
	// IsSolved returns field IsSolved.
	IsSolved() bool
	// Expiry returns a date after what captcha will expire.
	Expiry() time.Time
}

// Captcha is a base implementation of a CAPTCHA.
//
// All derivatives that embed this struct only need to
// implement GetImage() and generateImage() methods.
// And GetImage() could simply be copied.
//
// You need to do that because in Go there is no inheritance,
// and if you won't do that, calling a base GetImage
// method will call an empty base generateImage() method.
type Captcha struct {
	Image    image.Image
	Answer   Answer
	Solved   bool
	ExpireIn time.Time
}

func (c *Captcha) generateImage() *image.Image {
	return nil
}

func (c *Captcha) GetImage() *image.Image {
	if c.Image == nil {
		return c.generateImage()
	}

	return &c.Image
}

func (c *Captcha) Solve(answer Answer) bool {
	c.Solved = c.Answer == answer
	return c.Solved
}

func (c *Captcha) GetAnswer() Answer {
	if c.Answer == "" {
		c.Answer = generateAnswer()
	}
	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()))
}

func ExpiryDate(expiry time.Duration) time.Time {
	return time.Now().Add(expiry)
}