package main

import (
	"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"
)

var verbose = false

// 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}

	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, "[2a01:e0a:2b:2250::b]:53")
	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")
	}
	if r.Rcode != dns.RcodeSuccess {
		err = errors.New("failed to get a valid answer")
	}

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

	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
}

// 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
	}
	log.Println("Checking students...")

	for _, 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
				}

				dnsIP := stdIP
				// 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)
				}

				// Check DNS
				if addr, err := check_dns(std.MyDelegatedDomain(), dnsIP); err == nil {
					if verbose {
						log.Printf("%s just unlocked DNS challenge\n", std.Login)
					}
					if _, err := std.UnlockChallenge(100*(tunnel_version-1)+3, ""); err != nil {
						log.Printf("Unable to register challenge for %s: %s\n", std.Login, err.Error())
					}

					// Check HTTP with DNS
					if addr == nil {
						log.Printf("%s and HTTP (with DNS ip=%s): skipped due to empty response\n", std.Login, addr.String())
					} 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 addr == nil {
						log.Printf("%s and HTTPS (with DNS ip=%s): skipped due to empty response\n", std.Login, addr.String())
					} 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)
						}
					}
				} 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(100*(tunnel_version-1)+0, ""); err != nil {
						log.Printf("Unable to register challenge for %s: %s\n", std.Login, err.Error())
					}
				} else {
					std.RegisterChallengeError(100*(tunnel_version-1)+0, 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
			})
		}
	}
}