package router

import (
	"errors"

	"v2ray.com/core/app"
	"v2ray.com/core/app/dns"
	"v2ray.com/core/common/log"
	v2net "v2ray.com/core/common/net"
)

const (
	APP_ID = app.ID(3)
)

var (
	ErrInvalidRule      = errors.New("Invalid Rule")
	ErrNoRuleApplicable = errors.New("No rule applicable")
)

type Router struct {
	domainStrategy Config_DomainStrategy
	rules          []Rule
	cache          *RoutingTable
	dnsServer      dns.Server
}

func NewRouter(config *Config, space app.Space) *Router {
	r := &Router{
		domainStrategy: config.DomainStrategy,
		cache:          NewRoutingTable(),
		rules:          make([]Rule, len(config.Rule)),
	}

	space.InitializeApplication(func() error {
		for idx, rule := range config.Rule {
			r.rules[idx].Tag = rule.Tag
			cond, err := rule.BuildCondition()
			if err != nil {
				return err
			}
			r.rules[idx].Condition = cond
		}

		if !space.HasApp(dns.APP_ID) {
			log.Error("DNS: Router is not found in the space.")
			return app.ErrMissingApplication
		}
		r.dnsServer = space.GetApp(dns.APP_ID).(dns.Server)
		return nil
	})
	return r
}

func (this *Router) Release() {

}

// Private: Visible for testing.
func (this *Router) ResolveIP(dest v2net.Destination) []v2net.Destination {
	ips := this.dnsServer.Get(dest.Address.Domain())
	if len(ips) == 0 {
		return nil
	}
	dests := make([]v2net.Destination, len(ips))
	for idx, ip := range ips {
		if dest.Network == v2net.Network_TCP {
			dests[idx] = v2net.TCPDestination(v2net.IPAddress(ip), dest.Port)
		} else {
			dests[idx] = v2net.UDPDestination(v2net.IPAddress(ip), dest.Port)
		}
	}
	return dests
}

func (this *Router) takeDetourWithoutCache(dest v2net.Destination) (string, error) {
	for _, rule := range this.rules {
		if rule.Apply(dest) {
			return rule.Tag, nil
		}
	}
	if this.domainStrategy == Config_IpIfNonMatch && dest.Address.Family().IsDomain() {
		log.Info("Router: Looking up IP for ", dest)
		ipDests := this.ResolveIP(dest)
		if ipDests != nil {
			for _, ipDest := range ipDests {
				log.Info("Router: Trying IP ", ipDest)
				for _, rule := range this.rules {
					if rule.Apply(ipDest) {
						return rule.Tag, nil
					}
				}
			}
		}
	}

	return "", ErrNoRuleApplicable
}

func (this *Router) TakeDetour(dest v2net.Destination) (string, error) {
	destStr := dest.String()
	found, tag, err := this.cache.Get(destStr)
	if !found {
		tag, err := this.takeDetourWithoutCache(dest)
		this.cache.Set(destStr, tag, err)
		return tag, err
	}
	return tag, err
}