package dns

import (
	"context"
	go_errors "errors"
	"sync"
	"time"

	"github.com/xtls/xray-core/common"
	"github.com/xtls/xray-core/common/errors"
	"github.com/xtls/xray-core/common/net"
	"github.com/xtls/xray-core/common/signal/pubsub"
	"github.com/xtls/xray-core/common/task"
	dns_feature "github.com/xtls/xray-core/features/dns"
	"golang.org/x/net/dns/dnsmessage"
)

type CacheController struct {
	sync.RWMutex
	ips             map[string]*record
	pub             *pubsub.Service
	cacheCleanup    *task.Periodic
	name            string
	disableCache    bool
	serveStale      bool
	serveExpiredTTL int32
}

func NewCacheController(name string, disableCache bool, serveStale bool, serveExpiredTTL uint32) *CacheController {
	c := &CacheController{
		name:            name,
		disableCache:    disableCache,
		serveStale:      serveStale,
		serveExpiredTTL: -int32(serveExpiredTTL),
		ips:             make(map[string]*record),
		pub:             pubsub.NewService(),
	}

	c.cacheCleanup = &task.Periodic{
		Interval: time.Minute,
		Execute:  c.CacheCleanup,
	}
	return c
}

// CacheCleanup clears expired items from cache
func (c *CacheController) CacheCleanup() error {
	now := time.Now()
	if c.serveStale && c.serveExpiredTTL != 0 {
		now = now.Add(time.Duration(c.serveExpiredTTL) * time.Second)
	}

	c.Lock()
	defer c.Unlock()

	if len(c.ips) == 0 {
		return errors.New("nothing to do. stopping...")
	}

	for domain, record := range c.ips {
		if record.A != nil && record.A.Expire.Before(now) {
			record.A = nil
		}
		if record.AAAA != nil && record.AAAA.Expire.Before(now) {
			record.AAAA = nil
		}

		if record.A == nil && record.AAAA == nil {
			errors.LogDebug(context.Background(), c.name, "cache cleanup ", domain)
			delete(c.ips, domain)
		} else {
			c.ips[domain] = record
		}
	}

	if len(c.ips) == 0 {
		c.ips = make(map[string]*record)
	}

	return nil
}

func (c *CacheController) updateIP(req *dnsRequest, ipRec *IPRecord) {
	elapsed := time.Since(req.start)

	c.Lock()
	rec, found := c.ips[req.domain]
	if !found {
		rec = &record{}
	}

	switch req.reqType {
	case dnsmessage.TypeA:
		rec.A = ipRec
	case dnsmessage.TypeAAAA:
		rec.AAAA = ipRec
	}

	errors.LogInfo(context.Background(), c.name, " got answer: ", req.domain, " ", req.reqType, " -> ", ipRec.IP, " ", elapsed)
	c.ips[req.domain] = rec

	switch req.reqType {
	case dnsmessage.TypeA:
		c.pub.Publish(req.domain+"4", nil)
	case dnsmessage.TypeAAAA:
		c.pub.Publish(req.domain+"6", nil)
	}

	c.Unlock()
	if !c.serveStale || c.serveExpiredTTL != 0 {
		common.Must(c.cacheCleanup.Start())
	}
}

func (c *CacheController) findIPsForDomain(domain string, option dns_feature.IPOption) ([]net.IP, int32, bool, bool, error) {
	c.RLock()
	record, found := c.ips[domain]
	c.RUnlock()

	if !found {
		return nil, 0, true, true, errRecordNotFound
	}

	var errs []error
	var allIPs []net.IP
	var rTTL int32 = dns_feature.DefaultTTL

	mergeReq := option.IPv4Enable && option.IPv6Enable

	isARecordExpired := true
	if option.IPv4Enable {
		ips, ttl, err := record.A.getIPs()
		if ttl > 0 {
			isARecordExpired = false
		}
		if !mergeReq {
			return ips, ttl, isARecordExpired, true, err
		}
		if ttl < rTTL {
			rTTL = ttl
		}
		if len(ips) > 0 {
			allIPs = append(allIPs, ips...)
		}
		errs = append(errs, err)

	}

	isAAAARecordExpired := true
	if option.IPv6Enable {
		ips, ttl, err := record.AAAA.getIPs()
		if ttl > 0 {
			isAAAARecordExpired = false
		}
		if !mergeReq {
			return ips, ttl, true, isAAAARecordExpired, err
		}
		if ttl < rTTL {
			rTTL = ttl
		}
		if len(ips) > 0 {
			allIPs = append(allIPs, ips...)
		}
		errs = append(errs, err)

	}

	if go_errors.Is(errs[0], errRecordNotFound) || go_errors.Is(errs[1], errRecordNotFound) {
		return nil, 0, isARecordExpired, isAAAARecordExpired, errRecordNotFound
	}

	if len(allIPs) > 0 {
		return allIPs, rTTL, isARecordExpired, isAAAARecordExpired, nil
	}
	if go_errors.Is(errs[0], errs[1]) {
		return nil, rTTL, isARecordExpired, isAAAARecordExpired, errs[0]
	}
	return nil, rTTL, isARecordExpired, isAAAARecordExpired, errors.Combine(errs...)
}

func (c *CacheController) registerSubscribers(domain string, option dns_feature.IPOption) (sub4 *pubsub.Subscriber, sub6 *pubsub.Subscriber) {
	// ipv4 and ipv6 belong to different subscription groups
	if option.IPv4Enable {
		sub4 = c.pub.Subscribe(domain + "4")
	}
	if option.IPv6Enable {
		sub6 = c.pub.Subscribe(domain + "6")
	}
	return
}

func closeSubscribers(sub4 *pubsub.Subscriber, sub6 *pubsub.Subscriber) {
	if sub4 != nil {
		sub4.Close()
	}
	if sub6 != nil {
		sub6.Close()
	}
}