package dns

import (
	"context"
	"sort"
	"strconv"

	"github.com/xtls/xray-core/common/errors"
	"github.com/xtls/xray-core/common/net"
	"github.com/xtls/xray-core/common/strmatcher"
	"github.com/xtls/xray-core/features/dns"
)

// StaticHosts represents static domain-ip mapping in DNS server.
type StaticHosts struct {
	ips      [][]net.Address
	matchers *strmatcher.MatcherGroup
}

// NewStaticHosts creates a new StaticHosts instance.
func NewStaticHosts(hosts []*Config_HostMapping) (*StaticHosts, error) {
	g := new(strmatcher.MatcherGroup)
	sh := &StaticHosts{
		ips:      make([][]net.Address, len(hosts)+16),
		matchers: g,
	}

	for _, mapping := range hosts {
		matcher, err := toStrMatcher(mapping.Type, mapping.Domain)
		if err != nil {
			return nil, errors.New("failed to create domain matcher").Base(err)
		}
		id := g.Add(matcher)
		ips := make([]net.Address, 0, len(mapping.Ip)+1)
		switch {
		case len(mapping.ProxiedDomain) > 0:
			if mapping.ProxiedDomain[0] == '#' {
				rcode, err := strconv.Atoi(mapping.ProxiedDomain[1:])
				if err != nil {
					return nil, err
				}
				ips = append(ips, dns.RCodeError(rcode))
			} else {
				ips = append(ips, net.DomainAddress(mapping.ProxiedDomain))
			}
		case len(mapping.Ip) > 0:
			for _, ip := range mapping.Ip {
				addr := net.IPAddress(ip)
				if addr == nil {
					return nil, errors.New("invalid IP address in static hosts: ", ip).AtWarning()
				}
				ips = append(ips, addr)
			}
		}

		sh.ips[id] = ips
	}

	return sh, nil
}

func filterIP(ips []net.Address, option dns.IPOption) []net.Address {
	filtered := make([]net.Address, 0, len(ips))
	for _, ip := range ips {
		if (ip.Family().IsIPv4() && option.IPv4Enable) || (ip.Family().IsIPv6() && option.IPv6Enable) {
			filtered = append(filtered, ip)
		}
	}
	return filtered
}

func (h *StaticHosts) lookupInternal(domain string) []net.Address {
	MatchSlice := h.matchers.Match(domain)
	sort.Slice(MatchSlice, func(i, j int) bool {
		return MatchSlice[i] < MatchSlice[j]
	})
	if len(MatchSlice) == 0 {
		return nil
	}
	return h.ips[MatchSlice[0]]
}

func (h *StaticHosts) lookup(domain string, option dns.IPOption, maxDepth int) ([]net.Address, error) {
	switch addrs := h.lookupInternal(domain); {
	case len(addrs) == 0: // Not recorded in static hosts, return nil
		return addrs, nil
	case len(addrs) == 1:
		if err, ok := addrs[0].(dns.RCodeError); ok {
			return nil, err
		}
		if addrs[0].Family().IsDomain() { // Try to unwrap domain
			errors.LogDebug(context.Background(), "found replaced domain: ", domain, " -> ", addrs[0].Domain(), ". Try to unwrap it")
			if maxDepth > 0 {
				unwrapped, err := h.lookup(addrs[0].Domain(), option, maxDepth-1)
				if err != nil {
					return nil, err
				}
				if unwrapped != nil {
					return unwrapped, nil
				}
			}
			return addrs, nil
		}
		fallthrough
	default: // IP record found, return a non-nil IP array
		return filterIP(addrs, option), nil
	}
}

// Lookup returns IP addresses or proxied domain for the given domain, if exists in this StaticHosts.
func (h *StaticHosts) Lookup(domain string, option dns.IPOption) ([]net.Address, error) {
	return h.lookup(domain, option, 5)
}