package rules

import (
	"errors"
	"time"

	"github.com/v2ray/v2ray-core/app/router"
	"github.com/v2ray/v2ray-core/common/collect"
	v2net "github.com/v2ray/v2ray-core/common/net"
)

var (
	InvalidRule      = errors.New("Invalid Rule")
	NoRuleApplicable = errors.New("No rule applicable")
)

type cacheEntry struct {
	tag        string
	err        error
	validUntil time.Time
}

func newCacheEntry(tag string, err error) *cacheEntry {
	this := &cacheEntry{
		tag: tag,
		err: err,
	}
	this.Extend()
	return this
}

func (this *cacheEntry) IsValid() bool {
	return this.validUntil.Before(time.Now())
}

func (this *cacheEntry) Extend() {
	this.validUntil = time.Now().Add(time.Hour)
}

type Router struct {
	rules []*Rule
	cache *collect.ValidityMap
}

func NewRouter() *Router {
	return &Router{
		rules: make([]*Rule, 0, 16),
		cache: collect.NewValidityMap(3600),
	}
}

func (this *Router) AddRule(rule *Rule) *Router {
	this.rules = append(this.rules, rule)
	return this
}

func (this *Router) takeDetourWithoutCache(dest v2net.Destination) (string, error) {
	for _, rule := range this.rules {
		if rule.Apply(dest) {
			return rule.Tag, nil
		}
	}
	return "", NoRuleApplicable
}

func (this *Router) TakeDetour(dest v2net.Destination) (string, error) {
	rawEntry := this.cache.Get(dest)
	if rawEntry == nil {
		tag, err := this.takeDetourWithoutCache(dest)
		this.cache.Set(dest, newCacheEntry(tag, err))
		return tag, err
	}
	entry := rawEntry.(*cacheEntry)
	return entry.tag, entry.err
}

type RouterFactory struct {
}

func (this *RouterFactory) Create(rawConfig interface{}) (router.Router, error) {
	config := rawConfig.(*RouterRuleConfig)
	rules := config.Rules()
	router := NewRouter()
	for _, rule := range rules {
		if rule == nil {
			return nil, InvalidRule
		}
		router.AddRule(rule)
	}
	return router, nil
}

func init() {
	router.RegisterRouter("rules", &RouterFactory{})
}