package main

import (
	"crypto/sha256"
	"crypto/tls"
	"crypto/x509"
	"encoding/hex"
	"encoding/pem"
	"errors"
	"log"
	"net/http"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"sync"
	"time"
)

// CertInfo describes the certificate the web UI serves.
type CertInfo struct {
	Subject, Issuer string
	NotAfter        time.Time
	SelfSigned      bool
	Fingerprint     string // SHA-256, colon separated
}

func readCertInfo(path string) (CertInfo, bool) {
	data, err := os.ReadFile(path)
	if err != nil {
		return CertInfo{}, false
	}
	block, _ := pem.Decode(data)
	if block == nil {
		return CertInfo{}, false
	}
	c, err := x509.ParseCertificate(block.Bytes)
	if err != nil {
		return CertInfo{}, false
	}
	sum := sha256.Sum256(c.Raw)
	hexSum := strings.ToUpper(hex.EncodeToString(sum[:]))
	var pairs []string
	for i := 0; i < len(hexSum); i += 2 {
		pairs = append(pairs, hexSum[i:i+2])
	}
	return CertInfo{Subject: c.Subject.String(), Issuer: c.Issuer.String(), NotAfter: c.NotAfter,
		SelfSigned: c.Subject.String() == c.Issuer.String(), Fingerprint: strings.Join(pairs, ":")}, true
}

// certSource serves the certificate an ACME client keeps in dir while it is
// there and valid, and the self-signed one otherwise. Renewed files are picked
// up on the next connection.
type certSource struct {
	fallback tls.Certificate
	dir      string

	mu     sync.Mutex
	loaded tls.Certificate
	mod    time.Time
	ok     bool
}

func (c *certSource) get(*tls.ClientHelloInfo) (*tls.Certificate, error) {
	if c.dir == "" {
		return &c.fallback, nil
	}
	chain, key := filepath.Join(c.dir, "fullchain.pem"), filepath.Join(c.dir, "key.pem")
	a, errA := os.Stat(chain)
	b, errB := os.Stat(key)
	c.mu.Lock()
	defer c.mu.Unlock()
	if errA != nil || errB != nil {
		c.ok = false
		return &c.fallback, nil
	}
	mod := a.ModTime()
	if b.ModTime().After(mod) {
		mod = b.ModTime()
	}
	if !c.ok || !mod.Equal(c.mod) {
		cert, err := tls.LoadX509KeyPair(chain, key)
		c.mod = mod // do not retry a broken pair on every connection
		c.ok = err == nil
		if err != nil {
			log.Printf("certificate in %s: %v", c.dir, err)
		} else {
			c.loaded = cert
		}
	}
	if !c.ok {
		return &c.fallback, nil
	}
	return &c.loaded, nil
}

// ACMEForm is the certificate section of the settings (router.acme).
type ACMEForm struct {
	Enabled  bool
	Provider string // a connection of router.dnsProviders
	Domains  string // one per line or comma separated
	Email    string
	Staging  bool
	Agree    bool
}

func (s Settings) acme() ACMEForm {
	router, _ := s["router"].(map[string]any)
	c, _ := router["acme"].(map[string]any)
	flag := func(k string, def bool) bool {
		if v, ok := c[k].(bool); ok {
			return v
		}
		return def
	}
	return ACMEForm{Enabled: flag("enable", false), Provider: str(c, "provider"), Domains: strings.Join(stringList(c, "domains"), "\n"),
		Email: str(c, "email"), Staging: flag("staging", true), Agree: flag("acceptTerms", false)}
}

func (s Settings) applyACME(f ACMEForm) error {
	errs := FormErrors{}
	f.Provider, f.Email = strings.TrimSpace(f.Provider), strings.TrimSpace(f.Email)
	var domains []any
	for _, d := range splitList(f.Domains) {
		if !ddnsHostRe.MatchString(d) || !strings.Contains(d, ".") {
			errs["domains"] = d + " is not a host name"
			break
		}
		domains = append(domains, strings.ToLower(d))
	}
	if f.Provider != "" {
		p, ok := s.dnsProviderMap()[f.Provider].(map[string]any)
		switch {
		case !ok:
			errs["provider"] = "choose one of the DNS providers"
		case !slices.Contains(acmeTypes, str(p, "type")):
			errs["provider"] = "lego has no DNS provider " + str(p, "type") + "; it is for dynamic DNS"
		case acmeTokens[str(p, "type")] != "" && str(p, "secretFile") == "":
			errs["provider"] = "this account has no token (add it on the DNS providers page)"
		case acmeTokens[str(p, "type")] == "" && str(p, "environmentFile") == "":
			errs["provider"] = "this account has no certificate variables (add them on the DNS providers page)"
		}
	}
	if f.Email != "" && !strings.Contains(f.Email, "@") {
		errs["email"] = "an e-mail address"
	}
	if f.Enabled {
		if f.Provider == "" {
			errs["provider"] = "choose a DNS provider (add one on the DNS providers page)"
		}
		if len(domains) == 0 {
			errs["domains"] = "name at least one host"
		}
		if f.Email == "" {
			errs["email"] = "an address Let's Encrypt can write to about expiry"
		}
		if !f.Agree {
			errs["agree"] = "accept the Let's Encrypt subscriber agreement"
		}
	}
	if len(errs) > 0 {
		return errs
	}
	c := obj(obj(s, "router"), "acme")
	c["enable"], c["staging"], c["acceptTerms"] = f.Enabled, f.Staging, f.Agree
	set := func(k, v string) {
		if v == "" {
			delete(c, k)
		} else {
			c[k] = v
		}
	}
	set("provider", f.Provider)
	set("email", f.Email)
	if len(domains) > 0 {
		c["domains"] = domains
	} else {
		delete(c, "domains")
	}
	return nil
}

type certificateData struct {
	Cert      CertInfo
	Has       bool
	Serving   string // "acme" or "self-signed"
	Form      ACMEForm
	Errors    FormErrors
	Providers []DNSProvider
	Status    string // the order's last result
	Failed    bool   // the last order did not succeed: the log is shown open
	Log       string
}

// servedCert is what the web UI hands out: the ACME certificate if it is there.
func (a *app) servedCert() (CertInfo, bool, string) {
	if a.sys.ACMEDir != "" {
		if c, ok := readCertInfo(filepath.Join(a.sys.ACMEDir, "fullchain.pem")); ok {
			return c, true, "acme"
		}
	}
	c, ok := readCertInfo(filepath.Join(a.sys.StateDir, "webui", "cert.pem"))
	return c, ok, "self-signed"
}

func (a *app) certificateData(s Settings, f ACMEForm, errs FormErrors) certificateData {
	var providers []DNSProvider
	for _, p := range a.dnsProviders(s) {
		if p.ACME {
			providers = append(providers, p)
		}
	}
	d := certificateData{Form: f, Errors: errs, Providers: providers}
	d.Cert, d.Has, d.Serving = a.servedCert()
	if first := splitList(f.Domains); len(first) > 0 && s.acme().Enabled {
		unit := "acme-order-renew-" + strings.ToLower(first[0]) + ".service"
		if st := unitProperty(unit, "ActiveState"); st != "" {
			res := unitProperty(unit, "Result")
			d.Status = st + ", result " + res
			d.Failed = res != "success" || st == "failed"
			d.Log, _ = command("journalctl", "--no-pager", "-o", "cat", "-n", "15", "-u", unit)
		}
	}
	return d
}

func (a *app) certificatePage(w http.ResponseWriter, r *http.Request, sess session) {
	p := page{Title: "Certificate", CSRF: sess.csrf, LoggedIn: true}
	s, err := loadSettings(a.sys.settingsPath())
	if err != nil {
		p.Error = err.Error()
		a.render(w, "certificate", p)
		return
	}
	p.Data = a.certificateData(s, s.acme(), nil)
	a.render(w, "certificate", p)
}

func (a *app) certificateSave(w http.ResponseWriter, r *http.Request, sess session) {
	p := page{Title: "Certificate", CSRF: sess.csrf, LoggedIn: true}
	s, err := loadSettings(a.sys.settingsPath())
	if err != nil {
		p.Error = err.Error()
		a.render(w, "certificate", p)
		return
	}
	v := r.PostFormValue
	f := ACMEForm{Enabled: v("enabled") == "on", Provider: v("provider"), Domains: v("domains"), Email: v("email"),
		Staging: v("staging") == "on", Agree: v("agree") == "on"}
	if err := s.applyACME(f); err != nil {
		var fe FormErrors
		errors.As(err, &fe)
		p.Error = "Please correct the marked fields."
		p.Data = a.certificateData(s, f, fe)
		w.WriteHeader(http.StatusUnprocessableEntity)
		a.render(w, "certificate", p)
		return
	}
	if err := s.save(a.sys.settingsPath()); err != nil {
		p.Error = "Saving: " + err.Error()
		a.render(w, "certificate", p)
		return
	}
	back(w, r, "Saved. Apply to order the certificate; this page shows how it went.")
}