rogueserver/api/daily/common.go

/*
	Copyright (C) 2024  Pagefault Games

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU Affero General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU Affero General Public License for more details.

	You should have received a copy of the GNU Affero General Public License
	along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package daily

import (
	"crypto/md5"
	"crypto/rand"
	"encoding/base64"
	"encoding/binary"
	"fmt"
	"log"
	"os"
	"time"

	"github.com/pagefaultgames/rogueserver/db"
	"github.com/robfig/cron/v3"
)

const secondsPerDay = 60 * 60 * 24

var (
	scheduler = cron.New(cron.WithLocation(time.UTC))
	secret    []byte
)

func Init() error {
	var err error

	secret, err = os.ReadFile("secret.key")
	if err != nil {
		if !os.IsNotExist(err) {
			return fmt.Errorf("failed to read daily seed secret: %s", err)
		}

		newSecret := make([]byte, 32)
		_, err := rand.Read(newSecret)
		if err != nil {
			return fmt.Errorf("failed to generate daily seed secret: %s", err)
		}

		err = os.WriteFile("secret.key", newSecret, 0400)
		if err != nil {
			return fmt.Errorf("failed to write daily seed secret: %s", err)
		}

		secret = newSecret
	}

	seed, err := recordNewDaily()
	if err != nil {
		log.Print(err)
	}

	log.Printf("Daily Run Seed: %s", seed)

	_, err = scheduler.AddFunc("@daily", func() {
		time.Sleep(time.Second)

		seed, err = recordNewDaily()
		if err != nil {
			log.Printf("error while recording new daily: %s", err)
		} else {
			log.Printf("Daily Run Seed: %s", seed)
		}
	})
	if err != nil {
		return err
	}

	scheduler.Start()

	return nil
}

func Seed() string {
	return base64.StdEncoding.EncodeToString(deriveSeed(time.Now().UTC()))
}

func deriveSeed(seedTime time.Time) []byte {
	day := make([]byte, 8)
	binary.BigEndian.PutUint64(day, uint64(seedTime.Unix()/secondsPerDay))

	hashedSeed := md5.Sum(append(day, secret...))

	return hashedSeed[:]
}

func recordNewDaily() (string, error) {
	return db.TryAddDailyRun(Seed())
}