package server

import (
	"crypto/tls"
	"errors"
	"strings"
	"sync"

	"git.polynom.me/rio/internal/certificates"
	"git.polynom.me/rio/internal/context"
	"git.polynom.me/rio/internal/dns"
	"git.polynom.me/rio/internal/repo"

	"github.com/go-acme/lego/v4/lego"

	log "github.com/sirupsen/logrus"
)

var (
	// To access requestingDomains, first acquire the lock.
	domainsLock = sync.Mutex{}

	// Domain -> _. Check if domain is a key here to see if we're already requesting
	// or renewing a certificate for that domain.
	workingDomains = make(map[string]bool)
)

func lockIfUnlockedDomain(domain string) bool {
	domainsLock.Lock()
	defer domainsLock.Unlock()

	_, found := workingDomains[domain]
	if !found {
		workingDomains[domain] = true
	}

	return found
}

func unlockDomain(domain string) {
	domainsLock.Lock()
	defer domainsLock.Unlock()

	delete(workingDomains, domain)
}

func buildDomainList(domain, pagesDomain string) []string {
	if domain == pagesDomain || strings.HasSuffix(domain, pagesDomain) {
		return []string{
			pagesDomain,
			"*." + pagesDomain,
		}
	}

	return []string{domain}
}

func getDomainKey(domain, pagesDomain string) string {
	if domain == pagesDomain || strings.HasSuffix(domain, pagesDomain) {
		return "*." + pagesDomain
	}

	return domain
}

func getUsername(sni, pagesDomain string) (string, error) {
	if !strings.HasSuffix(sni, pagesDomain) {
		log.Debugf("'%s' is not a subdomain of '%s'", sni, pagesDomain)

		// Note: We do not check err here because err != nil
		// always implies that cname == "", which does not have
		// pagesDomain as a suffix.
		query, err := dns.LookupCNAME(sni)
		if !strings.HasSuffix(query, pagesDomain) {
			log.Warnf("Got ServerName for Domain %s that we're not responsible for. CNAME '%s', err: %v", sni, query, err)
			return "", errors.New("CNAME does not resolve to subdomain of pages domain")
		}

		return dns.ExtractUsername(pagesDomain, query), nil
	}

	return dns.ExtractUsername(pagesDomain, sni), nil
}

func MakeTlsConfig(pagesDomain, cachePath string, cache *certificates.CertificatesCache, acmeClient *lego.Client, ctx *context.GlobalContext) *tls.Config {
	return &tls.Config{
		GetCertificate: func(info *tls.ClientHelloInfo) (*tls.Certificate, error) {
			// Validate that we should even care about this domain
			isPagesDomain := info.ServerName == pagesDomain
			username, err := getUsername(info.ServerName, pagesDomain)
			if err != nil {
				log.Warnf("Failed to get username for %s: %v", info.ServerName, err)
				return cache.FallbackCertificate.TlsCertificate, nil
			}

			// Find the correct certificate
			domainKey := getDomainKey(info.ServerName, pagesDomain)
			cert, found := cache.Certificates[domainKey]
			if found {
				if cert.IsValid() {
					return cert.TlsCertificate, nil
				} else {
					if !isPagesDomain && !repo.CanRequestCertificate(username, ctx) {
						log.Warnf(
							"Cannot renew certificate for %s because CanRequestCertificate(%s) returned false",
							info.ServerName,
							username,
						)
						return cert.TlsCertificate, nil
					}

					// If we're already working on the domain,
					// return the old certificate
					if lockIfUnlockedDomain(domainKey) {
						return cert.TlsCertificate, nil
					}
					defer unlockDomain(domainKey)

					// Renew the certificate
					log.Infof("Certificate for %s expired, renewing", info.ServerName)
					newCert, err := certificates.RenewCertificate(&cert, acmeClient)
					if err != nil {
						log.Errorf("Failed to renew certificate for %s: %v", info.ServerName, err)
						return cert.TlsCertificate, nil
					}

					log.Info("Successfully renewed certificate!")
					cache.AddCert(newCert, cachePath)
					return newCert.TlsCertificate, nil
				}
			} else {
				if !isPagesDomain && !repo.CanRequestCertificate(username, ctx) {
					log.Warnf(
						"Cannot request certificate for %s because CanRequestCertificate(%s) returned false",
						info.ServerName,
						username,
					)
					return cache.FallbackCertificate.TlsCertificate, nil
				}

				// Don't request if we're already requesting.
				key := getDomainKey(info.ServerName, pagesDomain)
				if lockIfUnlockedDomain(domainKey) {
					return cache.FallbackCertificate.TlsCertificate, nil
				}
				defer unlockDomain(key)

				// Request new certificate
				log.Infof("Obtaining new certificate for %s...", info.ServerName)
				cert, err := certificates.ObtainNewCertificate(
					buildDomainList(info.ServerName, pagesDomain),
					domainKey,
					acmeClient,
				)
				if err != nil {
					log.Errorf(
						"Failed to get certificate for %s: %v",
						info.ServerName,
						err,
					)
					return cache.FallbackCertificate.TlsCertificate, nil
				}

				// Add to cache and flush
				log.Info("Successfully obtained new certificate!")
				cache.AddCert(cert, cachePath)
				return cert.TlsCertificate, nil
			}
		},
		NextProtos: []string{
			"http/0.9",
			"http/1.0",
			"http/1.1",
			"h2",
			"h2c",
		},
		MinVersion: tls.VersionTLS12,
		CipherSuites: []uint16{
			tls.TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256,
			tls.TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384,
			tls.TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305,
			tls.TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305,
		},
	}
}