package main

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

	"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"
)

type ImageStatus struct {
	ContainerName   string
	Image           string
	Tag             string
	UpdateAvailable float64
	LocalDigest     string
	RemoteDigest    string
}

type StatusCache struct {
	sync.RWMutex
	Data      []ImageStatus
	LastCheck time.Time
}

var (
	cache             = &StatusCache{Data: []ImageStatus{}, LastCheck: time.Time{}}
	interval          = 6 * time.Hour // Default wird ggf. überschrieben durch CHECK_INTERVAL
	excludeContainers = map[string]struct{}{}
)

// Helper: image ohne ":tag" erhält "latest"
func normalizeImageTag(tag string) string {
	if !strings.Contains(tag, ":") {
		return tag + ":latest"
	}
	return tag
}

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
}

func checkImageUpdates() {
	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()

	containers, err := cli.ContainerList(ctx, container.ListOptions{All: false})
	if err != nil {
		log.Printf("Fehler beim ContainerList: %v", err)
		return
	}

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

	imageTagToDigest := make(map[string]string)
	for _, img := range images {
		for _, tag := range img.RepoTags {
			normalizedTag := normalizeImageTag(tag)
			if len(img.RepoDigests) > 0 {
				imageTagToDigest[normalizedTag] = extractDigest(img.RepoDigests[0])
			} else {
				imageTagToDigest[normalizedTag] = img.ID
			}
		}
	}
	for tag, digest := range imageTagToDigest {
		fmt.Printf("imageTagToDigest: %s -> %s\n", tag, digest)
	}

	results := make([]ImageStatus, 0)
	for _, ctr := range containers {
		containerName := "unknown"
		if len(ctr.Names) > 0 {
			containerName = strings.TrimPrefix(ctr.Names[0], "/")
		}

		// Überspringen, wenn im EXCLUDE_CONTAINERS enthalten
		if _, excluded := excludeContainers[containerName]; excluded {
			fmt.Printf("⏭️  Container '%s' ist ausgeschlossen.\n", containerName)
			continue
		}

		rawTag := normalizeImageTag(ctr.Image)
		localDigest := imageTagToDigest[rawTag]

		imageRef, err := toRegistryImage(rawTag)
		if err != nil {
			log.Printf("Ungültige Image-Referenz (%s): %v", rawTag, err)
			continue
		}
		refObj, err := ref.New(imageRef)
		if err != nil {
			log.Printf("Fehler beim Erzeugen der Referenz (%s): %v", rawTag, err)
			continue
		}
		desc, err := rc.ManifestHead(ctx, refObj)
		if err != nil {
			log.Printf("Remote-Manifest nicht gefunden (%s): %v", rawTag, err)
			continue
		}

		remoteDigest := desc.GetDigest().String()
		update := 0.0

		fmt.Printf("Container: %s\n", containerName)
		fmt.Printf("  Image:         %s\n", rawTag)
		fmt.Printf("  Local Digest:  %s\n", localDigest)
		fmt.Printf("  Remote Digest: %s\n", remoteDigest)

		if localDigest != remoteDigest {
			update = 1.0
			fmt.Println("  -> ⚠️  Update verfügbar!")
		} else {
			fmt.Println("  -> ✅ Kein Update erforderlich.")
		}

		imageName, imageTag := rawTag, "latest"
		if cp := strings.Split(rawTag, ":"); len(cp) == 2 {
			imageName, imageTag = cp[0], cp[1]
		}

		results = append(results, ImageStatus{
			ContainerName:   containerName,
			Image:           imageName,
			Tag:             imageTag,
			UpdateAvailable: update,
			LocalDigest:     localDigest,
			RemoteDigest:    remoteDigest,
		})
	}

	cache.Lock()
	cache.Data = results
	cache.LastCheck = time.Now()
	cache.Unlock()
}

type imageUpdateCollector struct {
	metric *prometheus.Desc
}

func newImageUpdateCollector() *imageUpdateCollector {
	return &imageUpdateCollector{
		metric: prometheus.NewDesc(
			"docker_image_update_available",
			"Ob ein Update für das verwendete Image eines laufenden Containers verfügbar ist (1 = Update)",
			[]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) {
	cache.RLock()
	defer cache.RUnlock()
	for _, stat := range cache.Data {
		ch <- prometheus.MustNewConstMetric(
			c.metric, prometheus.GaugeValue,
			stat.UpdateAvailable, stat.ContainerName, stat.Image, stat.Tag,
		)
	}
}

func loadIntervalFromEnv() {
	if val := os.Getenv("CHECK_INTERVAL"); val != "" {
		dur, err := time.ParseDuration(val)
		if err != nil {
			log.Printf("❌ Ungültiger CHECK_INTERVAL: %s – verwende Default (%s)", val, interval)
		} else {
			interval = dur
		}
	}
}

func loadExclusionsFromEnv() {
	raw := os.Getenv("EXCLUDE_CONTAINERS")
	if raw == "" {
		return
	}
	list := strings.Split(raw, ",")
	for _, name := range list {
		clean := strings.TrimSpace(name)
		if clean != "" {
			excludeContainers[clean] = struct{}{}
		}
	}
}

func main() {
	log.Println("🚀 Docker Image Update Exporter startet...")

	loadIntervalFromEnv()
	loadExclusionsFromEnv()
	log.Printf("🔁 Prüfintervall: %v", interval)
	if len(excludeContainers) > 0 {
		log.Printf("🙈 Ignorierte Container: %v", keys(excludeContainers))
	}

	go func() {
		for {
			checkImageUpdates()
			time.Sleep(interval)
		}
	}()

	checkImageUpdates()

	exporter := newImageUpdateCollector()
	prometheus.MustRegister(exporter)

	http.Handle("/metrics", promhttp.Handler())
	log.Fatal(http.ListenAndServe(":9788", nil))
}

func keys(m map[string]struct{}) []string {
	var result []string
	for k := range m {
		result = append(result, k)
	}
	return result
}