package main

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"regexp"
	"strings"
	"sync"

	"github.com/docker/docker/api/types/container"
	"github.com/docker/docker/api/types/image"
	"github.com/docker/docker/client"
	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promhttp"
	"github.com/regclient/regclient"
	"github.com/regclient/regclient/types/ref"
)

func toRegistryImage(imageTag string) (string, error) {
	r := regexp.MustCompile(`^(?:(?P<registry>[^/]+)/)?(?P<repo>[^:]+)(?::(?P<tag>.+))?$`)
	match := r.FindStringSubmatch(imageTag)
	if len(match) == 0 {
		return "", fmt.Errorf("Image-Tag nicht erkannt: %s", imageTag)
	}
	registry := match[r.SubexpIndex("registry")]
	repo := match[r.SubexpIndex("repo")]
	tag := match[r.SubexpIndex("tag")]
	if registry == "" {
		registry = "registry-1.docker.io"
	}
	if tag == "" {
		tag = "latest"
	}
	return fmt.Sprintf("%s/%s:%s", registry, repo, tag), nil
}

func extractDigest(s string) string {
	for _, part := range strings.Split(s, "@") {
		if strings.HasPrefix(part, "sha256:") {
			return part
		}
	}
	return s
}

type imageUpdateCollector struct {
	metric *prometheus.Desc
}

func newImageUpdateCollector() *imageUpdateCollector {
	return &imageUpdateCollector{
		metric: prometheus.NewDesc(
			"docker_image_update_available",
			"Ob Update für das lokale Docker-Image des laufenden Containers für das Tag im Registry verfügbar ist (1=Update, 0=aktuell)",
			[]string{"container_name", "image", "tag"},
			nil,
		),
	}
}

func (c *imageUpdateCollector) Describe(ch chan<- *prometheus.Desc) {
	ch <- c.metric
}

func (c *imageUpdateCollector) Collect(ch chan<- prometheus.Metric) {
	ctx := context.Background()
	cli, err := client.NewClientWithOpts(client.FromEnv)
	if err != nil {
		log.Printf("Fehler bei Docker-Client: %v", err)
		return
	}
	defer cli.Close()
	rc := regclient.New()

	// Hole nur aktive (laufende) Container
	containers, err := cli.ContainerList(ctx, container.ListOptions{All: false})
	if err != nil {
		log.Printf("Fehler bei ContainerList: %v", err)
		return
	}

	images, err := cli.ImageList(ctx, image.ListOptions{All: true})
	if err != nil {
		log.Printf("Fehler bei ImageList: %v", err)
		return
	}

	imageTagToDigest := make(map[string]string)
	for _, img := range images {
		for _, tag := range img.RepoTags {
			if len(img.RepoDigests) > 0 {
				imageTagToDigest[tag] = extractDigest(img.RepoDigests[0])
			} else {
				imageTagToDigest[tag] = img.ID
			}
		}
	}

	var wg sync.WaitGroup
	for _, ctr := range containers {
		tag := ctr.Image

		imageRef, err := toRegistryImage(tag)
		if err != nil {
			log.Printf("ImageRef-Fehler bei %s: %v", tag, err)
			continue
		}
		localDigest := imageTagToDigest[tag]

		wg.Add(1)
		go func(ctr container.Summary, tag, localDigest, imageRef string) {
			defer wg.Done()
			refObj, err := ref.New(imageRef)
			if err != nil {
				log.Printf("ImageRef (regclient) ungültig (%s): %v", tag, err)
				return
			}
			desc, err := rc.ManifestHead(ctx, refObj)
			if err != nil {
				log.Printf("Remote-Manifest nicht gefunden (%s): %v", tag, err)
				return
			}
			remoteDigest := desc.GetDigest().String()

			fmt.Printf("Container: %s\n  Image: %s\n  Local Digest:  %s\n  Remote Digest: %s\n", ctr.Names[0], tag, localDigest, remoteDigest)
			var update float64 = 0
			if localDigest != remoteDigest {
				fmt.Println("  -> Update verfügbar!")
				update = 1
			} else {
				fmt.Println("  -> Kein Update verfügbar.")
			}
			// Labels container_name, image, tag
			labelImg, labelTag := tag, "latest"
			if cp := strings.Split(tag, ":"); len(cp) == 2 {
				labelImg, labelTag = cp[0], cp[1]
			}
			ch <- prometheus.MustNewConstMetric(
				c.metric, prometheus.GaugeValue,
				update, ctr.Names[0], labelImg, labelTag,
			)
		}(ctr, tag, localDigest, imageRef)
	}
	wg.Wait()
}

func main() {
	log.Println("Starte Prometheus Exporter für laufende Container-Images (Port 9788)...")
	exporter := newImageUpdateCollector()
	prometheus.MustRegister(exporter)
	http.Handle("/metrics", promhttp.Handler())
	log.Fatal(http.ListenAndServe(":9788", nil))
}