package captcha

import (
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"errors"
	"image"
	"strconv"
	"time"
)

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

const DefaultExpiredScanInterval = 60 * time.Second

// ID is a CAPTCHA identifier.
type ID string

// NewID generates an ID as a sha256 hash of additionalData (usually IP-address),
// current time, answer and more, it adds a set of random bytes and encodes all
// of it with base64 in raw URL variant.
func NewID(additionalData string, answer Answer) ID {
	idHash := sha256.New()

	idHash.Write([]byte(additionalData))
	idHash.Write([]byte(strconv.FormatInt(time.Now().UnixMicro(), 16)))
	idHash.Write([]byte(answer))
	randData := make([]byte, 32)
	rand.Read(randData)
	idHash.Write(randData)

	return ID(base64.RawURLEncoding.EncodeToString(idHash.Sum(nil)))
}

// CaptchaDB interface with all necessary methods.
type CaptchaDB interface {
	New(data string, captcha Captcha) (Captcha, ID)
	GetExpiry() time.Duration
	SetExpiry(expiry time.Duration)
	Image(id ID, style string) (*image.Image, error)
	Solve(id ID, answer Answer) (bool, error)
	IsSolved(id ID) (bool, error)
	Remove(id ID) error
}