package captcha

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

const (
	maxIntAnswer = 999999
)

type Answer string

func NewIntAnswer() Answer {
	ans, _ := rand.Int(rand.Reader, big.NewInt(maxIntAnswer))
	return (Answer(ans.String()))
}

// Captcha interface that should be implemented by a CAPTCHA.
type Captcha interface {
	// Image generates and returns a pointer to an image of CAPTCHA.
	Image(style string) *image.Image
	// Answer returns a pregenerated answer.
	Answer() Answer
	// Solve compares a stored answer with a passed one.
	Solve(answer Answer) bool
	// IsSolved returns if a CAPTCHA is solved or not.
	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
// an Image() method.
type BaseCaptcha struct {
	answer   Answer
	solved   bool
	expireIn time.Time
}

func NewBaseCaptcha(expiry time.Duration) *BaseCaptcha {
	return &BaseCaptcha{
		expireIn: ExpiryDate(expiry),
	}
}

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

// Answer generates an integer answer for a CAPTCHA or just returns
// an existing one.
func (c *BaseCaptcha) Answer() Answer {
	if c.answer == "" {
		c.answer = NewIntAnswer()
	}
	return c.answer
}

// Solve sets solved field to true if given answer is right and returns a result
// of a check.
func (c *BaseCaptcha) Solve(answer Answer) bool {
	c.solved = c.answer == answer
	return c.solved
}

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

func (c *BaseCaptcha) Expiry() time.Time {
	return c.expireIn
}

// ExpiryDate returns a date when CAPTCHA expires. It adds a passed
// expiry duration to a current time.
func ExpiryDate(expiry time.Duration) time.Time {
	return time.Now().Add(expiry)
}