package letsencrypt

import (
	"encoding/json"
	"io/ioutil"
	"log"
	"time"

	"github.com/mholt/caddy/server"
	"github.com/xenolf/lego/acme"
)

// keepCertificatesRenewed is a permanently-blocking function
// that loops indefinitely and, on a regular schedule, checks
// certificates for expiration and initiates a renewal of certs
// that are expiring soon.
func keepCertificatesRenewed(configs []server.Config) {
	ticker := time.Tick(renewInterval)
	for range ticker {
		if err := processCertificateRenewal(configs); err != nil {
			log.Printf("[ERROR] cert renewal: %v", err)
		}
	}
}

// checkCertificateRenewal loops through all configured
// sites and looks for certificates to renew. Nothing is mutated
// through this function. The changes happen directly on disk.
func processCertificateRenewal(configs []server.Config) error {
	log.Print("[INFO] Processing certificate renewals...")

	for _, cfg := range configs {
		// Check if this entry is TLS enabled and managed by LE
		if !cfg.TLS.Enabled || !existingCertAndKey(cfg.Host) {
			continue
		}

		// Read the certificate and get the NotAfter time.
		certBytes, err := ioutil.ReadFile(storage.SiteCertFile(cfg.Host))
		if err != nil {
			return err
		}
		expTime, err := acme.GetPEMCertExpiration(certBytes)
		if err != nil {
			return err
		}

		// The time returned from the certificate is always in UTC.
		// So calculate the time left with local time as UTC.
		// Directly convert it to days for the following checks.
		daysLeft := int(expTime.Sub(time.Now().UTC()).Hours() / 24)

		// Renew on two or less days remaining.
		if daysLeft <= 2 {
			log.Printf("[WARN] There are %d days left on the certificate of %s. Trying to renew now.", daysLeft, cfg.Host)
			client, err := newClient(getEmail(cfg))
			if err != nil {
				return err
			}

			// Read metadata
			metaBytes, err := ioutil.ReadFile(storage.SiteMetaFile(cfg.Host))
			if err != nil {
				return err
			}

			privBytes, err := ioutil.ReadFile(storage.SiteKeyFile(cfg.Host))
			if err != nil {
				return err
			}

			var certMeta acme.CertificateResource
			err = json.Unmarshal(metaBytes, &certMeta)
			certMeta.Certificate = certBytes
			certMeta.PrivateKey = privBytes

			// Renew certificate.
			// TODO: revokeOld should be an option in the caddyfile
			newCertMeta, err := client.RenewCertificate(certMeta, true)
			if err != nil {
				return err
			}

			saveCertsAndKeys([]acme.CertificateResource{newCertMeta})
		}

		// Warn on 14 days remaining
		if daysLeft <= 14 {
			log.Printf("[WARN] There are %d days left on the certificate of %s. Will renew on two days left.\n", daysLeft, cfg.Host)
		}
	}

	return nil
}