package dns

import (
	"context"
	"strconv"
	"strings"

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

// StaticHosts represents static domain-ip mapping in DNS server.
type StaticHosts struct {
	responses [][]net.Address
	matcher   geodata.DomainMatcher
}

// NewStaticHosts creates a new StaticHosts instance.
func NewStaticHosts(hosts []*Config_HostMapping) (*StaticHosts, error) {
	reps := make([][]net.Address, 0, len(hosts))
	rules := make([]*geodata.DomainRule, 0, len(hosts))

	for _, mapping := range hosts {
		rep := make([]net.Address, 0, len(mapping.Ip))
		switch {
		case len(mapping.ProxiedDomain) > 0:
			if mapping.ProxiedDomain[0] == '#' {
				rcode, err := strconv.Atoi(mapping.ProxiedDomain[1:])
				if err != nil {
					return nil, err
				}
				rep = append(rep, dns.RCodeError(rcode))
			} else {
				rep = append(rep, net.DomainAddress(mapping.ProxiedDomain))
			}
		case len(mapping.Ip) > 0:
			for _, ip := range mapping.Ip {
				addr := net.IPAddress(ip)
				if addr == nil {
					errors.LogError(context.Background(), "invalid IP address in static hosts: ", ip, ", ignore this ip for rule: ", mapping.Domain)
					continue
				}
				rep = append(rep, addr)
			}
		}
		reps = append(reps, rep)
		rules = append(rules, mapping.Domain)
	}

	if len(rules) == 0 {
		return &StaticHosts{}, nil
	}

	matcher, err := geodata.DomainReg.BuildDomainMatcher(rules)
	if err != nil {
		return nil, err
	}
	return &StaticHosts{
		responses: reps,
		matcher:   matcher,
	}, 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, error) {
	ips := make([]net.Address, 0)
	found := false
	for _, idx := range h.matcher.Match(domain) {
		for _, rep := range h.responses[idx] {
			if err, ok := rep.(dns.RCodeError); ok {
				if uint16(err) == 0 {
					return nil, dns.ErrEmptyResponse
				}
				return nil, err
			}
		}
		ips = append(ips, h.responses[idx]...)
		found = true
	}
	if !found {
		return nil, nil
	}
	return ips, nil
}

func (h *StaticHosts) lookup(domain string, option dns.IPOption, maxDepth int) ([]net.Address, error) {
	domain = strings.ToLower(domain)
	switch addrs, err := h.lookupInternal(domain); {
	case err != nil:
		return nil, err
	case addrs == nil: // Not recorded in static hosts, return nil
		return nil, nil
	case len(addrs) == 0: // Domain recorded, but no valid IP returned
		return addrs, nil
	case len(addrs) == 1 && 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
	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) {
	if h.matcher == nil {
		return nil, nil
	}
	return h.lookup(domain, option, 5)
}