package logic

import (
	"context"
	"crypto/rand"
	"encoding/binary"
	"fmt"

	"spark-server/internal/module/user/entity"
	"spark-server/internal/pkg/errs"
)

const (
	codeTTLSeconds      = 300
	codeCooldownSeconds = 60
)

// EmailCodeTTLSeconds is the OTP lifetime returned to clients.
const EmailCodeTTLSeconds = codeTTLSeconds

// CodeStore is the email OTP cache (Redis).
type CodeStore interface {
	Put(ctx context.Context, email, code string, ttlSeconds int) error
	Get(ctx context.Context, email string) (string, error)
	Del(ctx context.Context, email string) error
	SetCooldown(ctx context.Context, email string, ttlSeconds int) (bool, error)
}

func (s *Service) SendEmailCode(ctx context.Context, email string) error {
	if s == nil || s.codes == nil {
		return errs.ErrAvailable
	}
	email = entity.NormalizeEmail(email)
	if email == "" {
		return errs.ErrInvalidArgument
	}
	if entity.IsTestEmail(email) {
		return nil
	}
	ok, err := s.codes.SetCooldown(ctx, email, codeCooldownSeconds)
	if err != nil {
		return err
	}
	if !ok {
		return errs.ErrRateLimited
	}
	code, err := randomDigits(6)
	if err != nil {
		return errs.ErrInner.WithError("email-code", err)
	}
	return s.codes.Put(ctx, email, code, codeTTLSeconds)
}

func randomDigits(n int) (string, error) {
	if n <= 0 {
		return "", fmt.Errorf("digits")
	}
	var buf [8]byte
	out := make([]byte, n)
	for i := 0; i < n; i++ {
		if _, err := rand.Read(buf[:4]); err != nil {
			return "", err
		}
		out[i] = '0' + byte(binary.BigEndian.Uint32(buf[:4])%10)
	}
	return string(out), nil
}