laic-backend/service/captcha_service.go

package service

import (
	"bytes"
	"crypto/rand"
	"image"
	"image/color"
	"image/png"
	"math/big"
	"strings"
	"time"

	"github.com/google/uuid"

	"laic-backend/cache"
	"laic-backend/common"
)

const captchaCookie = "laic_captcha"

var captchaChars = []byte("23456789ABCDEFGHJKLMNPQRSTUVWXYZ")

var captchaGlyphs = map[byte][7]string{
	'2': {"11110", "00001", "00010", "00100", "01000", "10000", "11111"},
	'3': {"11110", "00001", "00110", "00001", "00001", "00001", "11110"},
	'4': {"00010", "00110", "01010", "10010", "11111", "00010", "00010"},
	'5': {"11111", "10000", "11110", "00001", "00001", "10001", "01110"},
	'6': {"00110", "01000", "10000", "11110", "10001", "10001", "01110"},
	'7': {"11111", "00001", "00010", "00100", "01000", "01000", "01000"},
	'8': {"01110", "10001", "10001", "01110", "10001", "10001", "01110"},
	'9': {"01110", "10001", "10001", "01111", "00001", "00010", "11100"},
	'A': {"01110", "10001", "10001", "11111", "10001", "10001", "10001"},
	'B': {"11110", "10001", "10001", "11110", "10001", "10001", "11110"},
	'C': {"01111", "10000", "10000", "10000", "10000", "10000", "01111"},
	'D': {"11110", "10001", "10001", "10001", "10001", "10001", "11110"},
	'E': {"11111", "10000", "10000", "11110", "10000", "10000", "11111"},
	'F': {"11111", "10000", "10000", "11110", "10000", "10000", "10000"},
	'G': {"01111", "10000", "10000", "10111", "10001", "10001", "01111"},
	'H': {"10001", "10001", "10001", "11111", "10001", "10001", "10001"},
	'J': {"00001", "00001", "00001", "00001", "10001", "10001", "01110"},
	'K': {"10001", "10010", "10100", "11000", "10100", "10010", "10001"},
	'M': {"10001", "11011", "10101", "10101", "10001", "10001", "10001"},
	'N': {"10001", "11001", "10101", "10011", "10001", "10001", "10001"},
	'P': {"11110", "10001", "10001", "11110", "10000", "10000", "10000"},
	'Q': {"01110", "10001", "10001", "10001", "10101", "10010", "01101"},
	'R': {"11110", "10001", "10001", "11110", "10100", "10010", "10001"},
	'S': {"01111", "10000", "10000", "01110", "00001", "00001", "11110"},
	'T': {"11111", "00100", "00100", "00100", "00100", "00100", "00100"},
	'U': {"10001", "10001", "10001", "10001", "10001", "10001", "01110"},
	'V': {"10001", "10001", "10001", "10001", "10001", "01010", "00100"},
	'W': {"10001", "10001", "10001", "10101", "10101", "11011", "10001"},
	'X': {"10001", "10001", "01010", "00100", "01010", "10001", "10001"},
	'Y': {"10001", "10001", "01010", "00100", "00100", "00100", "00100"},
	'Z': {"11111", "00001", "00010", "00100", "01000", "10000", "11111"},
}

func NewCaptcha() (string, []byte, error) {
	id := uuid.NewString()
	answer := make([]byte, 4)
	for i := range answer {
		n, err := rand.Int(rand.Reader, big.NewInt(int64(len(captchaChars))))
		if err != nil {
			return "", nil, err
		}
		answer[i] = captchaChars[n.Int64()]
	}
	if err := common.SetValueWithExpired(cache.CaptchaKeyOf(id), string(answer), 5*60); err != nil {
		return "", nil, err
	}
	img := image.NewRGBA(image.Rect(0, 0, 160, 48))
	for y := 0; y < 48; y++ {
		for x := 0; x < 160; x++ {
			img.Set(x, y, color.RGBA{R: 242, G: 247, B: 250, A: 255})
		}
	}
	for i := 0; i < 7; i++ {
		x := 9 + i*23
		for y := 5; y < 43; y++ {
			img.Set(x, y, color.RGBA{R: 130, G: 180, B: 205, A: 180})
		}
	}
	for i, ch := range answer {
		drawGlyph(img, ch, 15+i*35, 12, color.RGBA{R: 31, G: 91, B: 130, A: 255})
	}
	var out bytes.Buffer
	if err := png.Encode(&out, img); err != nil {
		return "", nil, err
	}
	return id, out.Bytes(), nil
}

func drawGlyph(img *image.RGBA, ch byte, left, top int, fill color.Color) {
	glyph, ok := captchaGlyphs[ch]
	if !ok {
		return
	}
	for y, row := range glyph {
		for x, bit := range row {
			if bit == '1' {
				for dy := 0; dy < 3; dy++ {
					for dx := 0; dx < 3; dx++ {
						img.Set(left+x*3+dx, top+y*3+dy, fill)
					}
				}
			}
		}
	}
}

func CheckCaptcha(id, answer string) bool {
	stored, err := common.GetString(cache.CaptchaKeyOf(id))
	if err != nil || stored == "" || !strings.EqualFold(strings.TrimSpace(stored), strings.TrimSpace(answer)) {
		return false
	}
	_ = common.Delete(cache.CaptchaKeyOf(id))
	return true
}

func CaptchaCookieName() string { return captchaCookie }
func CaptchaTTL() time.Duration { return 5 * time.Minute }