package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/ioutil"
	"log"
	"net"
	"net/http"
	"strings"
	"time"

	"github.com/miekg/dns"
	"github.com/sparrc/go-ping"

	"git.nemunai.re/lectures/adlin/libadlin"
)

const (
	DEFAULT_RESOLVER = "2a01:e0a:2b:2250::1"
	year68           = 1 << 31 // For RFC1982 (Serial Arithmetic) calculations in 32 bits. Taken from miekg/dns
)

var (
	verbose           = false
	domainsHostingMap = map[string]string{}
)

// ICMP

func check_ping(ip string, cb func(pkt *ping.Packet)) (err error) {
	var pinger *ping.Pinger
	pinger, err = ping.NewPinger(ip)
	if err != nil {
		return
	}
	defer pinger.Stop()

	pinger.Timeout = time.Second * 5
	pinger.Count = 1
	pinger.OnRecv = cb
	pinger.SetPrivileged(true)
	pinger.Run()

	return
}

// PORT 53

func get_GLUE(domain string) (aaaa net.IP, err error) {
	client := dns.Client{Net: "tcp", Timeout: time.Second * 5}

	dnssrv := "[2a01:e0a:2b:2250::b]:53"
	if strings.HasSuffix(domain, adlin.DelegatedDomainSuffix) {
		dnssrv = "[2a01:e0a:2b:2250::b]:53"
	} else if v, ok := domainsHostingMap[domain]; ok {
		dnssrv = v
	} else {
		// Looking for root NS
		m := new(dns.Msg)
		m.SetQuestion(".", dns.TypeNS)
		m.RecursionDesired = false
		m.SetEdns0(4096, true)

		var r *dns.Msg
		r, _, err = client.Exchange(m, dnssrv)
		if err != nil {
			return
		}

		if r == nil {
			return nil, errors.New("response is nil during initial recursion")
		}
		if r.Rcode != dns.RcodeSuccess {
			return nil, errors.New("failed to get a valid answer during initial recursion")
		}

		for _, answer := range r.Answer {
			if t, ok := answer.(*dns.NS); ok {
				dnssrv = t.Ns + ":53"
			}
		}
		// Do casual recursion
		i := 0
	recursion:
		for i = 0; i < 10; i++ {
			m := new(dns.Msg)
			m.SetQuestion(domain, dns.TypeNS)
			m.RecursionDesired = false
			m.SetEdns0(4096, true)

			var r *dns.Msg
			r, _, err = client.Exchange(m, dnssrv)
			if err != nil {
				return
			}

			if r == nil {
				return nil, errors.New("response is nil during recursion")
			}
			if r.Rcode != dns.RcodeSuccess {
				return nil, errors.New("failed to get a valid answer during recursion")
			}

			for _, answer := range r.Ns {
				if t, ok := answer.(*dns.NS); ok {
					dnssrv = t.Ns + ":53"
					if t.Header().Name == domain {
						break recursion
					}
				}
			}
		}

		if i >= 10 {
			return nil, fmt.Errorf("too much name recursions")
		} else {
			domainsHostingMap[domain] = dnssrv
		}
	}

	m := new(dns.Msg)
	m.SetQuestion(domain, dns.TypeNS)
	m.RecursionDesired = false
	m.SetEdns0(4096, true)

	var r *dns.Msg
	r, _, err = client.Exchange(m, dnssrv)
	if err != nil {
		return
	}

	if r == nil {
		return nil, errors.New("response is nil")
	}
	if r.Rcode != dns.RcodeSuccess {
		return nil, errors.New("failed to get a valid answer")
	}

	for _, extra := range r.Extra {
		if t, ok := extra.(*dns.AAAA); ok {
			aaaa = t.AAAA
		}
	}

	return
}

func check_dns(domain, ip string) (aaaa net.IP, err error) {
	client := dns.Client{Timeout: time.Second * 5}

	m := new(dns.Msg)
	m.SetQuestion(domain, dns.TypeAAAA)

	var r *dns.Msg
	r, _, err = client.Exchange(m, fmt.Sprintf("[%s]:53", ip))
	if err != nil {
		return
	}

	if r == nil {
		err = errors.New("response is nil")
		return
	}
	if r.Rcode != dns.RcodeSuccess {
		err = errors.New("failed to get a valid answer")
		return
	}

	for _, answer := range r.Answer {
		if t, ok := answer.(*dns.AAAA); ok {
			aaaa = t.AAAA
		}
	}

	return
}

func check_dnssec(domain, ip string) (err error) {
	client := dns.Client{Net: "tcp", Timeout: time.Second * 10}

	// Get DNSKEY
	m := new(dns.Msg)
	m.SetEdns0(4096, true)
	m.SetQuestion(domain, dns.TypeDNSKEY)

	var r *dns.Msg
	r, _, err = client.Exchange(m, fmt.Sprintf("[%s]:53", ip))
	if err != nil {
		return
	}

	if r == nil {
		return errors.New("response is nil")
	}
	if r.Rcode != dns.RcodeSuccess {
		return errors.New("failed to get a valid answer when getting DNSKEY")
	}

	var rrs []dns.RR
	var dnskeys []*dns.DNSKEY
	var dnskeysig *dns.RRSIG
	for _, answer := range r.Answer {
		if t, ok := answer.(*dns.DNSKEY); ok {
			dnskeys = append(dnskeys, t)
			rrs = append(rrs, dns.RR(t))
		} else if t, ok := answer.(*dns.RRSIG); ok {
			dnskeysig = t
		}
	}

	if dnskeysig == nil {
		return fmt.Errorf("Unable to verify DNSKEY record signature: No RRSIG found for DNSKEY record.")
	}

	found := false
	for _, dnskey := range dnskeys {
		if err = dnskeysig.Verify(dnskey, rrs); err == nil {
			found = true
			break
		}
	}

	if !found {
		return fmt.Errorf("Unable to verify DNSKEY record signature: %w", err)
	}

	// Check AAAA validity
	m = new(dns.Msg)
	m.SetEdns0(4096, true)
	m.SetQuestion(domain, dns.TypeAAAA)

	r, _, err = client.Exchange(m, fmt.Sprintf("[%s]:53", ip))
	if err != nil {
		return
	}

	if r == nil {
		return errors.New("response is nil")
	}
	if r.Rcode != dns.RcodeSuccess {
		return errors.New("failed to get a valid answer when getting AAAA records")
	}

	rrs = []dns.RR{}
	var aaaas []*dns.AAAA
	var aaaasig *dns.RRSIG
	for _, answer := range r.Answer {
		if t, ok := answer.(*dns.AAAA); ok {
			aaaas = append(aaaas, t)
			rrs = append(rrs, t)
		} else if t, ok := answer.(*dns.RRSIG); ok {
			aaaasig = t
		}
	}

	if len(aaaas) == 0 {
		return errors.New("Something odd happen: no AAAA record found.")
	}

	if aaaasig == nil {
		return fmt.Errorf("Unable to verify AAAA record signature: No RRSIG found for AAAA record.")
	}

	found = false
	for _, dnskey := range dnskeys {
		if err = aaaasig.Verify(dnskey, rrs); err == nil {
			found = true

			if !aaaasig.ValidityPeriod(time.Now()) {
				utc := time.Now().UTC().Unix()

				modi := (int64(aaaasig.Inception) - utc) / year68
				ti := int64(aaaasig.Inception) + modi*year68

				mode := (int64(aaaasig.Expiration) - utc) / year68
				te := int64(aaaasig.Expiration) + mode*year68

				if ti > utc {
					return fmt.Errorf("Unable to verify AAAA record signature: signature not yet valid")
				} else if utc > te {
					return fmt.Errorf("Unable to verify AAAA record signature: signature expired")
				} else {
					return fmt.Errorf("Unable to verify AAAA record signature: signature expired or not yet valid")
				}
			}

			break
		}
	}

	if !found {
		return fmt.Errorf("Unable to verify AAAA record signature: %w", err)
	}

	// Check DS
	m = new(dns.Msg)
	m.SetQuestion(domain, dns.TypeDS)
	m.RecursionDesired = false
	m.SetEdns0(4096, true)

	r, _, err = client.Exchange(m, "[2a01:e0a:2b:2250::b]:53")
	if err != nil {
		return
	}

	if r == nil {
		return errors.New("response is nil")
	}
	if r.Rcode != dns.RcodeSuccess {
		return errors.New("failed to get a valid answer when getting DS records in parent server")
	}

	found = false
	for _, answer := range r.Answer {
		if t, ok := answer.(*dns.DS); ok {
			for _, dnskey := range dnskeys {
				expectedDS := dnskey.ToDS(dns.SHA256)
				if expectedDS.KeyTag == t.KeyTag && expectedDS.Algorithm == t.Algorithm && expectedDS.DigestType == t.DigestType && expectedDS.Digest == t.Digest {
					found = true
					err = nil
					break
				} else {
					err = fmt.Errorf("DS record found in parent zone differs from DNSKEY %v vs. %v.", expectedDS, t)
				}
			}
		}
	}

	if !found {
		if err == nil {
			return fmt.Errorf("Unable to find a valid DS record in parent zone.")
		} else {
			return err
		}
	}

	return
}

// PORT 80

func check_http(ip, dn string) (err error) {
	client := &http.Client{
		CheckRedirect: func(req *http.Request, via []*http.Request) error {
			return http.ErrUseLastResponse
		},
	}

	req, errr := http.NewRequest("GET", fmt.Sprintf("http://[%s]/", ip), nil)
	if errr != nil {
		return errr
	}

	if dn != "" {
		req.Header.Add("Host", strings.TrimSuffix(dn, "."))
	}

	var resp *http.Response
	resp, err = client.Do(req)
	if err != nil {
		return
	}
	defer resp.Body.Close()

	if dn != "" && resp.StatusCode >= 400 {
		return fmt.Errorf("Bad status, got: %d (%s)", resp.StatusCode, resp.Status)
	}

	_, err = ioutil.ReadAll(resp.Body)
	return
}

// PORT 443

func check_https(domain, ip string) (err error) {
	var resp *http.Response
	resp, err = http.Get(fmt.Sprintf("https://%s/", strings.TrimSuffix(domain, ".")))
	if err != nil {
		return
	}
	defer resp.Body.Close()

	if resp.StatusCode >= 300 && resp.StatusCode < 400 {
		loc := resp.Header.Get("Location")
		if loc != "" && strings.HasSuffix(dns.Fqdn(loc), domain) {
			if dns.Fqdn(loc) == domain {
				return fmt.Errorf("Redirection loop %s redirect to %s", domain, loc)
			} else if err = check_https(dns.Fqdn(loc), ip); err != nil {
				return fmt.Errorf("Error after following redirection to %s: %w", loc, err)
			} else {
				return
			}
		}
	}

	if resp.StatusCode >= 300 {
		return fmt.Errorf("Bad status, got: %d (%s)", resp.StatusCode, resp.Status)
	}

	_, err = ioutil.ReadAll(resp.Body)
	return
}

// MATRIX

type matrix_result struct {
	WellKnownResult struct {
		Server string `json:"m.server"`
		Result string `json:"result"`
	}
	DNSResult struct {
		SRVError *struct {
			Message string
		}
	}
	ConnectionReports map[string]struct {
		Errors []string
	}
	ConnectionErrors map[string]struct {
		Message string
	}
	Version struct {
		Name    string `json:"name"`
		Version string `json:"version"`
	}
	FederationOK bool `json:"FederationOK"`
}

func check_matrix(domain string) (version string, err error) {
	var resp *http.Response
	resp, err = http.Get(fmt.Sprintf("https://federation-tester.adlin.nemunai.re/api/report?server_name=%s", strings.TrimSuffix(domain, ".")))
	if err != nil {
		return
	}
	defer resp.Body.Close()

	if resp.StatusCode >= 300 {
		return "", fmt.Errorf("Sorry, the federation tester is broken. Check on https://federationtester.matrix.org/#%s", strings.TrimSuffix(domain, "."))
	}

	var federationTest matrix_result
	if err = json.NewDecoder(resp.Body).Decode(&federationTest); err != nil {
		log.Printf("Error in check_matrix, when decoding json: %w", err.Error())
		return "", fmt.Errorf("Sorry, the federation tester is broken. Check on https://federationtester.matrix.org/#%s", strings.TrimSuffix(domain, "."))
	} else if federationTest.FederationOK {
		version = federationTest.Version.Name + " " + federationTest.Version.Version
		return version, nil
	} else if federationTest.DNSResult.SRVError != nil && federationTest.WellKnownResult.Result != "" {
		return "", fmt.Errorf("%s OR %s", federationTest.DNSResult.SRVError.Message, federationTest.WellKnownResult.Result)
	} else if len(federationTest.ConnectionErrors) > 0 {
		var msg strings.Builder
		for srv, cerr := range federationTest.ConnectionErrors {
			if msg.Len() > 0 {
				msg.WriteString("; ")
			}
			msg.WriteString(srv)
			msg.WriteString(": ")
			msg.WriteString(cerr.Message)
		}
		return "", fmt.Errorf("Connection errors: %s", msg.String())
	} else if federationTest.WellKnownResult.Server != strings.TrimSuffix(domain, ".") {
		return "", fmt.Errorf("Bad homeserver_name: got %s, expected %s.", federationTest.WellKnownResult.Server, strings.TrimSuffix(domain, "."))
	} else {
		return "", fmt.Errorf("An unimplemented error occurs. Please report to nemunaire. But know that federation seems to be broken. Check https://federationtester.matrix.org/#%s", strings.TrimSuffix(domain, "."))
	}
}

// Main

func minTunnelVersion(std *adlin.Student, suffixip int) (int, error) {
	tunnels, err := std.GetTunnelTokens()
	if err != nil {
		return 0, err
	}

	var minversion int = 2147483647
	for _, tunnel := range tunnels {
		if tunnel.Version == 0 {
			continue
		}

		if tunnel.Dump != nil && tunnel.Version < minversion && suffixip == tunnel.SuffixIP {
			minversion = tunnel.Version
		}
	}

	return minversion, nil
}

func studentsChecker() {
	students, err := adlin.GetStudents()
	if err != nil {
		log.Println("Unable to check students:", err)
		return
	}
	check_matrix_for := (time.Now().Second()/30)*5 + time.Now().Minute()%5

	log.Printf("Checking students... (std_matrix%%10=%d)\n", check_matrix_for)

	for istd, s := range students {
		time.Sleep(250 * time.Millisecond)
		// Check ping
		std := s
		tuns, err := std.GetActivesTunnels()
		if err != nil {
			continue
		}

		for _, tun := range tuns {
			stdIP := tun.GetStudentIP()
			go check_ping(stdIP, func(pkt *ping.Packet) {
				tunnel_version, err := minTunnelVersion(std, tun.SuffixIP)
				if verbose {
					log.Printf("%s PONG (on %x); version=%d (%v)\n", std.Login, tun.SuffixIP, tunnel_version, err)
				}
				std.OnPong(true)

				if tunnel_version == 2147483647 || tunnel_version == 0 {
					log.Printf("%s unknown tunnel version: %d skipping tests (%v)", std.Login, tunnel_version, err)
					return
				}

				// PingResolver
				if tunnel_version == 3 {
					tmp := strings.Split(stdIP, ":")
					tmp[len(tmp)-1] = "2"
					stdResolverIP := strings.Join(tmp, ":")
					go check_ping(stdResolverIP, func(_ *ping.Packet) {
						if verbose {
							log.Printf("%s resolver PONG", std.Login)
						}
						if _, err := std.UnlockChallenge(CheckMap[tunnel_version][PingResolver], ""); err != nil {
							log.Printf("Unable to register challenge for %s: %s\n", std.Login, err.Error())
						}
					})
				}

				dnsIP := stdIP
				var glueErr error
				// Is GLUE defined?
				if glueIP, err := get_GLUE(std.MyDelegatedDomain()); glueIP != nil {
					dnsIP = glueIP.String()

					if verbose {
						log.Printf("%s has defined GLUE: %s\n", std.Login, dnsIP)
					}
				} else if err != nil {
					log.Printf("%s and GLUE: %s\n", std.Login, err)
					glueErr = err
				}

				// Check DNS
				if addr, err := check_dns(std.MyDelegatedDomain(), dnsIP); err == nil {
					if addr == nil {
						dnsAt := " at " + dnsIP
						if glueErr != nil {
							dnsAt = " + there is a problem with the GLUE record: " + glueErr.Error()
						}
						if errreg := std.RegisterChallengeError(100*(tunnel_version-1)+3, fmt.Errorf("%s: empty response from the server%s", std.MyDelegatedDomain(), dnsAt)); errreg != nil {
							log.Printf("Unable to register challenge error for %s: %s\n", std.Login, errreg)
						}
					} else {
						if verbose {
							log.Printf("%s just unlocked DNS challenge\n", std.Login)
						}
						if _, err := std.UnlockChallenge(100*(tunnel_version-1)+3, addr.String()); err != nil {
							log.Printf("Unable to register challenge for %s: %s\n", std.Login, err.Error())
						}

						// Check HTTP with DNS
						if glueErr != nil {
							std.RegisterChallengeError(100*(tunnel_version-1)+4, fmt.Errorf("Unable to perform the test due to GLUE problem: %w", glueErr))
						} else if err := check_http(addr.String(), std.MyDelegatedDomain()); err == nil {
							if verbose {
								log.Printf("%s just unlocked HTTP challenge\n", std.Login)
							}
							if _, err := std.UnlockChallenge(100*(tunnel_version-1)+4, ""); err != nil {
								log.Printf("Unable to register challenge for %s: %s\n", std.Login, err.Error())
							}
						} else {
							std.RegisterChallengeError(100*(tunnel_version-1)+4, err)
							if verbose {
								log.Printf("%s and HTTP (with DNS ip=%s): %s\n", std.Login, addr.String(), err)
							}
						}

						// Check HTTPs with DNS
						if glueErr != nil {
							std.RegisterChallengeError(100*(tunnel_version-1)+5, fmt.Errorf("Unable to perform the test due to GLUE problem: %w", glueErr))
						} else if err := check_https(std.MyDelegatedDomain(), addr.String()); err == nil {
							if verbose {
								log.Printf("%s just unlocked HTTPS challenge\n", std.Login)
							}
							if _, err := std.UnlockChallenge(100*(tunnel_version-1)+5, ""); err != nil {
								log.Printf("Unable to register challenge for %s: %s\n", std.Login, err.Error())
							}
						} else {
							std.RegisterChallengeError(100*(tunnel_version-1)+5, err)
							if verbose {
								log.Printf("%s and HTTPS (with DNS ip=%s): %s\n", std.Login, addr.String(), err)
							}
						}

						// Check Matrix (only if GLUE Ok and defer contraint)
						if glueErr == nil && istd%10 == check_matrix_for {
							if v, err := check_matrix(std.MyDelegatedDomain()); err == nil {
								if verbose {
									log.Printf("%s just unlocked Matrix challenge\n", std.Login)
								}
								if _, err := std.UnlockChallenge(100*(tunnel_version-1)+6, v); err != nil {
									log.Printf("Unable to register challenge for %s: %s\n", std.Login, err.Error())
								}
							} else {
								std.RegisterChallengeError(100*(tunnel_version-1)+6, err)
								if verbose {
									log.Printf("%s and Matrix: %s\n", std.Login, err)
								}
							}
						}

						// Check DNSSEC (only if GLUE Ok)
						if glueErr == nil {
							if err := check_dnssec(std.MyDelegatedDomain(), dnsIP); err == nil {
								if verbose {
									log.Printf("%s just unlocked DNSSEC challenge\n", std.Login)
								}
								if _, err := std.UnlockChallenge(100*(tunnel_version-1)+7, ""); err != nil {
									log.Printf("Unable to register challenge for %s: %s\n", std.Login, err.Error())
								}
							} else {
								std.RegisterChallengeError(100*(tunnel_version-1)+7, err)
								if verbose {
									log.Printf("%s and DNSSEC: %s\n", std.Login, err)
								}
							}
						}
					}
				} else {
					if errreg := std.RegisterChallengeError(100*(tunnel_version-1)+3, err); errreg != nil {
						log.Printf("Unable to register challenge error for %s: %s\n", std.Login, errreg)
					}
					if verbose {
						log.Printf("%s and DNS: %s\n", std.Login, err)
					}
				}

				// Check HTTP without DNS
				if err := check_http(stdIP, ""); err == nil {
					if verbose {
						log.Printf("%s just unlocked HTTP IP (without DNS) challenge\n", std.Login)
					}
					if _, err := std.UnlockChallenge(CheckMap[tunnel_version][HTTPonIP], ""); err != nil {
						log.Printf("Unable to register challenge for %s: %s\n", std.Login, err.Error())
					}
				} else {
					std.RegisterChallengeError(CheckMap[tunnel_version][HTTPonIP], err)
					if verbose {
						log.Printf("%s and HTTP IP (without DNS): %s\n", std.Login, err)
					}
				}

				// Check DNS for association
				if addr, err := check_dns(std.MyAssociatedDomain(), DEFAULT_RESOLVER); err == nil {
					// Check HTTP on delegated domain
					if err := check_http(addr.String(), std.MyAssociatedDomain()); err == nil {
						if verbose {
							log.Printf("%s just unlocked HTTP (without DNS) challenge\n", std.Login)
						}
						if _, err := std.UnlockChallenge(100*(tunnel_version-1)+1, ""); err != nil {
							log.Printf("Unable to register challenge for %s: %s\n", std.Login, err.Error())
						}
					} else {
						std.RegisterChallengeError(100*(tunnel_version-1)+1, err)
						if verbose {
							log.Printf("%s and HTTP (without DNS): %s\n", std.Login, err)
						}
					}

					// Check HTTPs without DNS
					if err := check_https(std.MyAssociatedDomain(), stdIP); err == nil {
						if verbose {
							log.Printf("%s just unlocked HTTPS challenge\n", std.Login)
						}
						if _, err := std.UnlockChallenge(100*(tunnel_version-1)+2, ""); err != nil {
							log.Printf("Unable to register challenge for %s: %s\n", std.Login, err.Error())
						}
					} else {
						std.RegisterChallengeError(100*(tunnel_version-1)+2, err)
						if verbose {
							log.Printf("%s and HTTPS (without DNS): %s\n", std.Login, err)
						}
					}
				}

				return
			})
		}
	}
}