package redis_helper

import (
	"context"
	"crypto/rand"
	"encoding/base64"

	"github.com/go-redis/redis/v8"
)

type RedisPreempt struct {
	key                      string
	password                 string
	lockScript, unlockScript *redis.Script
	lastLockStatus           bool
}

// CreatePreempt used to create a redis preempt instance
func CreatePreempt(key string) *RedisPreempt {
	p := &RedisPreempt{
		key: key,
	}
	p.init()

	return p
}

// init redis preempt instance and some script
func (p *RedisPreempt) init() {
	byt := make([]byte, 18)
	_, _ = rand.Read(byt)
	p.password = base64.StdEncoding.EncodeToString(byt)
	p.lockScript = redis.NewScript(`
		if redis.call('get',KEYS[1]) == ARGV[1] then
			return redis.call('expire', KEYS[1], ARGV[2])
		else
			return redis.call('set', KEYS[1], ARGV[1], 'ex', ARGV[2], 'nx')
		end
	`)
	p.unlockScript = redis.NewScript(`
		if redis.call('get',KEYS[1]) == ARGV[1] then
			return redis.call('del', KEYS[1])
		else
			return 0
		end
	`)
}

// TryLock attempt to lock the master for ttlSecond
func (p *RedisPreempt) TryLock(ttlSecond int) (ok bool, err error) {
	ok, err = p.lockScript.Run(context.Background(), redisInstance, []string{p.key}, p.password, ttlSecond).Bool()
	p.lastLockStatus = ok
	return
}

// Unlock try to release the master permission
func (p *RedisPreempt) Unlock() (bool, error) {
	if p == nil {
		return false, nil
	}

	return p.unlockScript.Run(context.Background(), redisInstance, []string{p.key}, p.password).Bool()
}

// LastLockStatus get the last preempt status
func (p *RedisPreempt) LastLockStatus() bool {
	if p == nil {
		return false
	}

	return p.lastLockStatus
}