package main

import (
	"bufio"
	"bytes"
	"flag"
	"fmt"
	"io/ioutil"
	"net/http"
	"os"
	"path/filepath"
	"regexp"
	"time"

	"github.com/golang/glog"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"

	"golang.org/x/crypto/ssh"
)

var (
	addr            = flag.String("addr", "localhost:9999", "HTTP listen address for prometheus /metrics")
	host            = flag.String("host", "localhost:22", "host:port log into and scrape")
	refreshInterval = flag.Duration("refresh", 5*time.Minute, "refresh interval time")
	user            = flag.String("user", os.Getenv("USER"), "ssh user")
)

const snapshotListCmd = "/sbin/zfs list -t snapshot -H -o name -s name"

// Example: @auto-20171001.1400-2w
var (
	snapshotPattern = regexp.MustCompile(`^([^@]+)@auto-(\d{8}\.\d{4})-\d+[mwy]$`)
	snapshotFormat  = "20060102.1504"

	fetchRequestDurationMetric = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "ssh_fetch_duration_seconds",
		Help: "Time to fetch and parse snapshot age over SSH",
	})
	snapshotAgesMetric = prometheus.NewGaugeVec(
		prometheus.GaugeOpts{
			Name: "zfs_snapshot_age_seconds",
			Help: "Duration in seconds for most recent snapshot for `filesystem`",
		},
		[]string{"filesystem"},
	)
)

func init() {
	prometheus.MustRegister(fetchRequestDurationMetric)
	prometheus.MustRegister(snapshotAgesMetric)
}

func newPublicKey() ([]ssh.AuthMethod, error) {
	var signers []ssh.AuthMethod

	for _, path := range []string{
		filepath.Join(os.Getenv("HOME"), ".ssh", "id_dsa"),
		filepath.Join(os.Getenv("HOME"), ".ssh", "id_rsa"),
	} {

		// A public key may be used to authenticate against the remote
		// server by using an unencrypted PEM-encoded private key file.
		//
		// If you have an encrypted private key, the crypto/x509 package
		// can be used to decrypt it.
		key, err := ioutil.ReadFile(path)
		if err != nil {
			if os.IsNotExist(err) {
				continue
			}
			return nil, fmt.Errorf("unable to read private key %q: %v", path, err)
		}

		// Create the Signer for this private key.
		signer, err := ssh.ParsePrivateKey(key)
		if err != nil {
			return nil, fmt.Errorf("unable to parse private key %q: %v", path, err)
		}
		signers = append(signers, ssh.PublicKeys(signer))
	}
	if len(signers) == 0 {
		return nil, fmt.Errorf("no public keys configured")
	}
	return signers, nil
}

func updateMetrics(c *ssh.Client) error {
	now := time.Now()
	defer func() {
		delta := time.Since(now)
		fetchRequestDurationMetric.Set(delta.Seconds())
		glog.V(2).Infof("Update took %s", delta)
	}()
	// Each ClientConn can support multiple interactive sessions,
	// represented by a Session.
	s, err := c.NewSession()
	if err != nil {
		return fmt.Errorf("error creating new session: %v", err)
	}
	defer s.Close()

	glog.V(2).Infof("Running %q", snapshotListCmd)
	b, err := s.CombinedOutput(snapshotListCmd)
	if err != nil {
		return fmt.Errorf("error running %q: %v", snapshotListCmd, err)
	}
	scanner := bufio.NewScanner(bytes.NewReader(b))
	snapshotAges := map[string]time.Time{}
	for scanner.Scan() {
		l := scanner.Text()
		m := snapshotPattern.FindStringSubmatch(l)
		if len(m) == 3 {
			snapshot := m[1]
			t, err := time.Parse(snapshotFormat, m[2])
			if err != nil {
				glog.Errorf("Malformed time in snapshot %q: %v", m[2], err)
				continue
			}
			snapshotTime := snapshotAges[snapshot]
			if snapshotTime.Before(t) {
				snapshotAges[snapshot] = t
			}
		}
	}
	if err := scanner.Err(); err != nil {
		return fmt.Errorf("failed to scan response: %v", err)
	}

	for snapshot, snapshotTime := range snapshotAges {
		snapshotAgesMetric.WithLabelValues(snapshot).Set(now.Sub(snapshotTime).Seconds())
	}
	return nil
}

func main() {
	flag.Parse()
	defer glog.Flush()

	ams, err := newPublicKey()
	if err != nil {
		glog.Exitf("Error fetching public keys: %v", err)
	}

	// An SSH client is represented with a ClientConn.
	//
	// To authenticate with the remote server you must pass at least one
	// implementation of ClientAuth via the Auth field in ClientConfig.
	config := &ssh.ClientConfig{
		User: *user,
		Auth: ams,
		// TODO(wathiede); use FixedHostKey?
		HostKeyCallback: ssh.InsecureIgnoreHostKey(),
	}
	c, err := ssh.Dial("tcp", *host, config)
	if err != nil {
		glog.Exitf("Error dialing %q: %v", *host, err)
	}

	go func() {
		for {
			if err := updateMetrics(c); err != nil {
				glog.Errorf("Failed to update metrics: %v", err)
			}
			time.Sleep(*refreshInterval)
		}
	}()

	// Expose the registered metrics via HTTP.
	http.Handle("/metrics", promhttp.Handler())
	glog.Exitf("Failed to ListenAndServe: %v", http.ListenAndServe(*addr, nil))
}