package blacktip

import (
	"context"
	"crypto/tls"
	"errors"
	"path/filepath"
	"strings"
	"time"

	"git.veillax.com/Veillax/reef/model"
	"golang.org/x/crypto/acme"
	"golang.org/x/crypto/acme/autocert"
)

// Certificates for https ports come from Let's Encrypt via autocert, using the
// TLS-ALPN-01 challenge on the same port 443 listener, so nothing extra has to
// be opened. A wildcard hostname such as *.example.com gets a separate
// certificate for each subdomain on its first visit.

type acmeState struct {
	mgr     *autocert.Manager
	email   string
	staging bool
	tried   map[string]time.Time
	certs   map[string]string
}

// configureACME builds the manager. Caller holds b.mu.
func (b *Blacktip) configureACME(email string, staging bool) {
	a := &b.acme
	if a.tried == nil {
		a.tried, a.certs = map[string]time.Time{}, map[string]string{}
	}
	if a.mgr != nil && a.email == email && a.staging == staging {
		return
	}
	m := &autocert.Manager{
		Prompt:     autocert.AcceptTOS,
		Cache:      autocert.DirCache(filepath.Join(b.cfg.DataDir, "certs")),
		HostPolicy: b.hostPolicy,
		Email:      email,
	}
	if staging {
		m.Client = &acme.Client{DirectoryURL: "https://acme-staging-v02.api.letsencrypt.org/directory"}
	}
	a.mgr, a.email, a.staging = m, email, staging
	a.tried = map[string]time.Time{}
}

// hostPolicy only lets us request certificates for hostnames we actually serve over https.
func (b *Blacktip) hostPolicy(_ context.Context, host string) error {
	b.mu.Lock()
	defer b.mu.Unlock()
	for _, ms := range b.maps {
		if ms.m.Proto == model.ProtoHTTPS && model.HostMatches(ms.m.Hostname, strings.ToLower(host)) {
			return nil
		}
	}
	return errors.New("not a hostname served here")
}

func (b *Blacktip) getCert(hello *tls.ClientHelloInfo) (*tls.Certificate, error) {
	if b.cfg.GetCertificate != nil {
		return b.cfg.GetCertificate(hello)
	}
	b.mu.Lock()
	mgr := b.acme.mgr
	b.mu.Unlock()
	if mgr == nil {
		return nil, errors.New("certificates are not configured yet")
	}
	return mgr.GetCertificate(hello)
}

// warmCerts requests certificates ahead of the first visitor so problems show up in the UI.
// Caller holds b.mu.
func (b *Blacktip) warmCerts(ms []model.Mapping) {
	for _, m := range ms {
		if m.Proto != model.ProtoHTTPS || strings.HasPrefix(m.Hostname, "*") {
			continue
		}
		host := m.Hostname
		if b.cfg.GetCertificate != nil {
			b.acme.certs[host] = "custom certificate"
			continue
		}
		wait := 12 * time.Hour
		if strings.HasPrefix(b.acme.certs[host], "error") {
			wait = 3 * time.Minute
		}
		if t, ok := b.acme.tried[host]; ok && time.Since(t) < wait {
			continue
		}
		b.acme.tried[host] = time.Now()
		b.acme.certs[host] = "requesting…"
		mgr := b.acme.mgr
		go func() {
			ctx, cancel := context.WithTimeout(b.ctx, 2*time.Minute)
			defer cancel()
			done := make(chan error, 1)
			go func() {
				_, err := mgr.GetCertificate(&tls.ClientHelloInfo{ServerName: host})
				done <- err
			}()
			var err error
			select {
			case err = <-done:
			case <-ctx.Done():
				err = ctx.Err()
			}
			b.mu.Lock()
			if err != nil {
				b.acme.certs[host] = "error: " + err.Error()
			} else {
				b.acme.certs[host] = "valid"
			}
			b.mu.Unlock()
			go b.report()
		}()
	}
}

// certStatus describes the certificate for m. Caller holds b.mu.
func (b *Blacktip) certStatus(m model.Mapping) string {
	if m.Proto != model.ProtoHTTPS {
		return ""
	}
	if strings.HasPrefix(m.Hostname, "*") {
		if b.tr != nil {
			if b.cfg.Traefik.NoACME {
				return "self-signed (Traefik default certificate)"
			}
			if b.cfg.Traefik.ACMEDNS == "" {
				return "error: wildcard certificates need -acme-dns <provider>"
			}
			return "wildcard certificate via DNS challenge"
		}
		return "issued per subdomain on first visit"
	}
	if s := b.acme.certs[m.Hostname]; s != "" {
		return s
	}
	return "pending"
}

// acmeFailing reports whether any certificate request failed. Caller holds b.mu.
func (b *Blacktip) acmeFailing() bool {
	for _, s := range b.acme.certs {
		if strings.HasPrefix(s, "error") {
			return true
		}
	}
	return false
}