package route

import (
	"context"
	"errors"
	"net/netip"
	"strings"
	"time"

	"github.com/sagernet/sing-box/adapter"
	C "github.com/sagernet/sing-box/constant"
	"github.com/sagernet/sing-dns"
	"github.com/sagernet/sing/common/cache"
	E "github.com/sagernet/sing/common/exceptions"
	F "github.com/sagernet/sing/common/format"
	M "github.com/sagernet/sing/common/metadata"

	mDNS "github.com/miekg/dns"
)

type DNSReverseMapping struct {
	cache *cache.LruCache[netip.Addr, string]
}

func NewDNSReverseMapping() *DNSReverseMapping {
	return &DNSReverseMapping{
		cache: cache.New[netip.Addr, string](),
	}
}

func (m *DNSReverseMapping) Save(address netip.Addr, domain string, ttl int) {
	m.cache.StoreWithExpire(address, domain, time.Now().Add(time.Duration(ttl)*time.Second))
}

func (m *DNSReverseMapping) Query(address netip.Addr) (string, bool) {
	domain, loaded := m.cache.Load(address)
	return domain, loaded
}

func (r *Router) matchDNS(ctx context.Context, allowFakeIP bool, index int) (context.Context, dns.Transport, dns.DomainStrategy, adapter.DNSRule, int) {
	metadata := adapter.ContextFrom(ctx)
	if metadata == nil {
		panic("no context")
	}
	if index < len(r.dnsRules) {
		dnsRules := r.dnsRules
		if index != -1 {
			dnsRules = dnsRules[index+1:]
		}
		for ruleIndex, rule := range dnsRules {
			metadata.ResetRuleCache()
			if rule.Match(metadata) {
				detour := rule.Outbound()
				transport, loaded := r.transportMap[detour]
				if !loaded {
					r.dnsLogger.ErrorContext(ctx, "transport not found: ", detour)
					continue
				}
				if _, isFakeIP := transport.(adapter.FakeIPTransport); isFakeIP && !allowFakeIP {
					continue
				}
				displayRuleIndex := ruleIndex
				if index != -1 {
					displayRuleIndex += index + 1
				}
				r.dnsLogger.DebugContext(ctx, "match[", displayRuleIndex, "] ", rule.String(), " => ", detour)
				if rule.DisableCache() {
					ctx = dns.ContextWithDisableCache(ctx, true)
				}
				if rewriteTTL := rule.RewriteTTL(); rewriteTTL != nil {
					ctx = dns.ContextWithRewriteTTL(ctx, *rewriteTTL)
				}
				if clientSubnet := rule.ClientSubnet(); clientSubnet != nil {
					ctx = dns.ContextWithClientSubnet(ctx, *clientSubnet)
				}
				if domainStrategy, dsLoaded := r.transportDomainStrategy[transport]; dsLoaded {
					return ctx, transport, domainStrategy, rule, ruleIndex
				} else {
					return ctx, transport, r.defaultDomainStrategy, rule, ruleIndex
				}
			}
		}
	}
	if domainStrategy, dsLoaded := r.transportDomainStrategy[r.defaultTransport]; dsLoaded {
		return ctx, r.defaultTransport, domainStrategy, nil, -1
	} else {
		return ctx, r.defaultTransport, r.defaultDomainStrategy, nil, -1
	}
}

func (r *Router) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error) {
	if len(message.Question) > 0 {
		r.dnsLogger.DebugContext(ctx, "exchange ", formatQuestion(message.Question[0].String()))
	}
	var (
		response *mDNS.Msg
		cached   bool
		err      error
	)
	response, cached = r.dnsClient.ExchangeCache(ctx, message)
	if !cached {
		var metadata *adapter.InboundContext
		ctx, metadata = adapter.AppendContext(ctx)
		if len(message.Question) > 0 {
			metadata.QueryType = message.Question[0].Qtype
			switch metadata.QueryType {
			case mDNS.TypeA:
				metadata.IPVersion = 4
			case mDNS.TypeAAAA:
				metadata.IPVersion = 6
			}
			metadata.Domain = fqdnToDomain(message.Question[0].Name)
		}
		var (
			transport dns.Transport
			strategy  dns.DomainStrategy
			rule      adapter.DNSRule
			ruleIndex int
		)
		ruleIndex = -1
		for {
			var (
				dnsCtx       context.Context
				cancel       context.CancelFunc
				addressLimit bool
			)

			dnsCtx, transport, strategy, rule, ruleIndex = r.matchDNS(ctx, true, ruleIndex)
			dnsCtx, cancel = context.WithTimeout(dnsCtx, C.DNSTimeout)
			if rule != nil && rule.WithAddressLimit() && isAddressQuery(message) {
				addressLimit = true
				response, err = r.dnsClient.ExchangeWithResponseCheck(dnsCtx, transport, message, strategy, func(response *mDNS.Msg) bool {
					metadata.DestinationAddresses, _ = dns.MessageToAddresses(response)
					return rule.MatchAddressLimit(metadata)
				})
			} else {
				addressLimit = false
				response, err = r.dnsClient.Exchange(dnsCtx, transport, message, strategy)
			}
			cancel()
			if err != nil {
				if errors.Is(err, dns.ErrResponseRejected) {
					r.dnsLogger.DebugContext(ctx, E.Cause(err, "response rejected for ", formatQuestion(message.Question[0].String())))
				} else if len(message.Question) > 0 {
					r.dnsLogger.ErrorContext(ctx, E.Cause(err, "exchange failed for ", formatQuestion(message.Question[0].String())))
				} else {
					r.dnsLogger.ErrorContext(ctx, E.Cause(err, "exchange failed for <empty query>"))
				}
			}
			if !addressLimit || err == nil {
				break
			}
		}
	}
	if r.dnsReverseMapping != nil && len(message.Question) > 0 && response != nil && len(response.Answer) > 0 {
		for _, answer := range response.Answer {
			switch record := answer.(type) {
			case *mDNS.A:
				r.dnsReverseMapping.Save(M.AddrFromIP(record.A), fqdnToDomain(record.Hdr.Name), int(record.Hdr.Ttl))
			case *mDNS.AAAA:
				r.dnsReverseMapping.Save(M.AddrFromIP(record.AAAA), fqdnToDomain(record.Hdr.Name), int(record.Hdr.Ttl))
			}
		}
	}
	return response, err
}

func (r *Router) Lookup(ctx context.Context, domain string, strategy dns.DomainStrategy) ([]netip.Addr, error) {
	r.dnsLogger.DebugContext(ctx, "lookup domain ", domain)
	ctx, metadata := adapter.AppendContext(ctx)
	metadata.Domain = domain
	var (
		transport         dns.Transport
		transportStrategy dns.DomainStrategy
		rule              adapter.DNSRule
		ruleIndex         int
		resultAddrs       []netip.Addr
		err               error
	)
	ruleIndex = -1
	for {
		var (
			dnsCtx       context.Context
			cancel       context.CancelFunc
			addressLimit bool
		)
		metadata.ResetRuleCache()
		metadata.DestinationAddresses = nil
		dnsCtx, transport, transportStrategy, rule, ruleIndex = r.matchDNS(ctx, false, ruleIndex)
		if strategy == dns.DomainStrategyAsIS {
			strategy = transportStrategy
		}
		dnsCtx, cancel = context.WithTimeout(dnsCtx, C.DNSTimeout)
		if rule != nil && rule.WithAddressLimit() {
			addressLimit = true
			resultAddrs, err = r.dnsClient.LookupWithResponseCheck(dnsCtx, transport, domain, strategy, func(responseAddrs []netip.Addr) bool {
				metadata.DestinationAddresses = responseAddrs
				return rule.MatchAddressLimit(metadata)
			})
		} else {
			addressLimit = false
			resultAddrs, err = r.dnsClient.Lookup(dnsCtx, transport, domain, strategy)
		}
		cancel()
		if err != nil {
			if errors.Is(err, dns.ErrResponseRejected) {
				r.dnsLogger.DebugContext(ctx, "response rejected for ", domain)
			} else {
				r.dnsLogger.ErrorContext(ctx, E.Cause(err, "lookup failed for ", domain))
			}
		} else if len(resultAddrs) == 0 {
			r.dnsLogger.ErrorContext(ctx, "lookup failed for ", domain, ": empty result")
			err = dns.RCodeNameError
		}
		if !addressLimit || err == nil {
			break
		}
	}
	if len(resultAddrs) > 0 {
		r.dnsLogger.InfoContext(ctx, "lookup succeed for ", domain, ": ", strings.Join(F.MapToString(resultAddrs), " "))
	}
	return resultAddrs, err
}

func (r *Router) LookupDefault(ctx context.Context, domain string) ([]netip.Addr, error) {
	return r.Lookup(ctx, domain, dns.DomainStrategyAsIS)
}

func (r *Router) ClearDNSCache() {
	r.dnsClient.ClearCache()
	if r.platformInterface != nil {
		r.platformInterface.ClearDNSCache()
	}
}

func isAddressQuery(message *mDNS.Msg) bool {
	for _, question := range message.Question {
		if question.Qtype == mDNS.TypeA || question.Qtype == mDNS.TypeAAAA {
			return true
		}
	}
	return false
}

func fqdnToDomain(fqdn string) string {
	if mDNS.IsFqdn(fqdn) {
		return fqdn[:len(fqdn)-1]
	}
	return fqdn
}

func formatQuestion(string string) string {
	if strings.HasPrefix(string, ";") {
		string = string[1:]
	}
	string = strings.ReplaceAll(string, "\t", " ")
	for strings.Contains(string, "  ") {
		string = strings.ReplaceAll(string, "  ", " ")
	}
	return string
}