// Source: https://github.com/bortzmeyer/check-soa/blob/master/check-soa.go
// 2-Clause BSD License:  Copyright (c) 2012, Stephane Bortzmeyer All rights reserved.
// A simple program to have rapidly an idea of the health of a DNS
// zone. It queries each name server of the zone for the SOA record and
// displays the value of the serial number for each server.
//
// Stephane Bortzmeyer <bortzmeyer@nic.fr>
// Heavily modified for RSMon

package cdns

import (
	"errors"
	"fmt"
	"net"
	"strings"
	"time"

	"github.com/miekg/dns"
	"github.com/weppos/publicsuffix-go/publicsuffix"

	"rocketgit.ru/rsmon/worker/app/models"
)

const (
	stateOK   = "OK"
	stateERR  = "ERR"
	stateWARN = "WARN"
)

var localhost net.IP

func init() {
	localhost = net.ParseIP("127.0.0.1")
}

// Perform checks if domain is resolvable via it's DNS servers
func Perform(c *models.Check) *Result {
	result := &Result{}
	result.State = "FAIL"
	host := c.Monitor.Host

	if host == "" {
		result.State = "FAIL"
		result.Error = errors.New("empty host name")
		return result
	}

	start := time.Now()
	// log.Println("run dns:", host)
	if host == "localhost" || strings.HasPrefix(host, "localhost:") {
		result.Warnings = append(result.Warnings, "DNS check not possible for localhost, please disable")
		return result
	}
	addr := net.ParseIP(host)
	if addr != nil {
		result.Warnings = append(result.Warnings, "DNS check not possible for ip address, please disable")
		return result
	}

	zname, err := publicsuffix.Domain(host)
	if err != nil {
		result.Warnings = append(result.Warnings, "Failed to get public suffix: "+err.Error())
		zname = host
	}
	// if zname != host {
	// result.Infos = append(result.Infos, "not top level domain, running NS check for "+zname)
	// }

	zone := dns.Fqdn(zname)
	nsChan := make(chan DNSreply)
	// log.Println(zone)
	go localQuery(nsChan, zone, dns.TypeNS)
	nsResult := <-nsChan
	if nsResult.r == nil {
		// All recursive resolvers were unreachable, so this worker could not
		// establish whether the domain is healthy. Do not open an outage event.
		result.State = "FAIL"
		result.Error = fmt.Errorf("cannot retrieve the list of name servers for %s: %s", zone, nsResult.err)
		return result
	}
	if nsResult.r.Rcode == dns.RcodeNameError {
		result.State = stateERR
		result.Error = fmt.Errorf("no such domain %s", zone)
		return result
	}
	// spew.Dump(nsResult)

	nslist := make(map[string]nameServer, 0)
	for i := range nsResult.r.Answer {
		ans := nsResult.r.Answer[i]
		if ns, ok := ans.(*dns.NS); ok {
			name := ns.Ns
			nslist[name] = nameServer{name: name, ips: make([]string, MaxAddresses)}
		}
	}

	// spew.Dump(nslist)

	numNS, numNSaddr, success, results := masterTask(zone, nslist)
	if success {
		result.State = stateOK
	} else {
		result.State = stateERR
	}

	if numNS == 0 {
		result.State = stateERR
		result.Error = fmt.Errorf("no NS records for zone \"%s\"", zone)
		return result
	}
	if numNSaddr == 0 {
		result.State = stateERR
		result.Error = fmt.Errorf("no IP addresses for name servers of %s", zone)
		return result
	}

	gallOK := true
	ganyOK := false
	failedNS := []string{}

	lzone := dns.Fqdn(host)

	for _, rzt := range results { //nolint:gocritic // range copy is acceptable here
		// spew.Dump(rzt)

		allOK := true
		anyOK := false
		ns := NSServer{Name: rzt.name}
		for i := 0; i < len(rzt.ips); i++ {
			ip := NSIP{
				ResponseTime: rzt.rtts[i],
				IP:           rzt.ips[i],
			}
			if rzt.success[i] {
				anyOK = true
				ganyOK = true
				ip.State = stateOK
				ip.Serial = rzt.serial[i]
			} else {
				allOK = false
				gallOK = false
				ip.State = stateERR
				ip.Error = errors.New(rzt.errMsg[i])
				failedNS = append(failedNS, rzt.name)
				// spew.Dump(rzt)
			}
			ns.NSIPs = append(ns.NSIPs, ip)

			if result.State == stateOK {
				// spew.Dump(ns)
				// log.Println("fetching records for", lzone, "from", ns.NSIPs[0].IP)
				ns.Response, err = FetchARecords(lzone, ns.NSIPs[0].IP)
				if err != nil {
					ns.State = stateERR
					ns.Error = err
					gallOK = false
					failedNS = append(failedNS, rzt.name+"/"+ns.NSIPs[0].IP)
					// log.Println("failed:", err)
				}
			}
		}

		if len(rzt.ips) == 0 {
			ns.State = stateERR
			ns.Error = errors.New(rzt.globalErrMsg)
			failedNS = append(failedNS, rzt.name+"/no ip for dns server")
			gallOK = false
		} else {
			if allOK {
				ns.State = stateOK
			} else {
				if anyOK {
					ns.State = "WARN"
					// log.Println("failed NS")
					// spew.Dump(ns)
					if ns.Error == nil {
						ns.Error = errors.New("some servers failed")
					}
				} else {
					ns.State = stateERR
					if ns.Error == nil {
						ns.Error = errors.New("all servers failed")
					}
				}
			}
		}

		result.NSServers = append(result.NSServers, ns)
	}

	if gallOK {
		result.State = stateOK
	} else {
		if ganyOK {
			result.State = stateWARN
			result.Warnings = append(result.Warnings, "some servers failed: "+strings.Join(failedNS, ","))
		} else {
			result.State = stateERR
			if result.Error == nil {
				result.Error = errors.New("all servers failed")
			}
		}
	}

	for _, ni := range result.NSServers {
		// log.Println(ni.Name)
		for _, r := range ni.Response {
			ip := r.Value.Inet
			if ip.Equal(localhost) {
				result.State = stateERR
				err := "resolves to localhost/127.0.0.1"
				if result.Error == nil {
					result.Error = errors.New(err)
				} else if result.Error.Error() != err {
					result.Warnings = append(result.Warnings, err)
				}
			}
			// log.Println(r.Name, r.Kind, r.Value)
		}
	}

	_, maxt := result.Times()
	if maxt > 2*time.Second {
		if result.State == stateOK {
			result.State = stateWARN
		}
		result.Warnings = append(result.Warnings, "slow")
	}

	result.Duration = time.Since(start)

	// spew.Dump(result)

	return result
}