package captcha

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

const (
	maxAnswer = 999999
)

type Answer string

// Captcha interface that should be implemented by captcha.
type Captcha interface {
	// Image generates and returns an image of captcha.
	Image(style string) 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
}

// BaseCaptcha 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 BaseCaptcha struct {
	Answer   Answer
	Solved   bool
	ExpireIn time.Time
}

func (c *BaseCaptcha) Image(style string) *image.Image {
	return nil
}

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

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

func (c *BaseCaptcha) IsSolved() bool {
	return c.Solved
}

func (c *BaseCaptcha) 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)
}