Add Nomad provider

I modeled it off the Kubernetes provider a bit. It supports setting task
config at group and task levels using services and meta attributes.

internal/provider/nomad/task.go

@@ -0,0 +1,126 @@
+package nomad
+
+import (
+	"reflect"
+	"strings"
+
+	"github.com/crazy-max/diun/v4/internal/model"
+	"github.com/crazy-max/diun/v4/internal/provider"
+	nomad "github.com/hashicorp/nomad/api"
+)
+
+func parseServiceTags(tags []string) map[string]string {
+	labels := map[string]string{}
+
+	for _, tag := range tags {
+		tagParts := strings.SplitN(tag, "=", 2)
+		if len(tagParts) < 2 {
+			continue
+		}
+
+		labels[tagParts[0]] = tagParts[1]
+	}
+
+	return labels
+}
+
+func updateMap(m1, m2 map[string]string) map[string]string {
+	for key, value := range m2 {
+		m1[key] = value
+	}
+
+	return m1
+}
+
+func (c *Client) listTaskImages() []model.Image {
+	config := &nomad.Config{
+		Address:   c.config.Address,
+		Region:    c.config.Region,
+		SecretID:  c.config.SecretID,
+		Namespace: c.config.Namespace,
+	}
+
+	if *c.config.TLSInsecure {
+		config.TLSConfig.Insecure = true
+	}
+
+	client, err := nomad.NewClient(config)
+	if err != nil {
+		c.logger.Error().Err(err).Msg("Cannot create Nomad client")
+		return []model.Image{}
+	}
+
+	jobs, _, err := client.Jobs().List(nil)
+	if err != nil {
+		c.logger.Error().Err(err).Msg("Cannot list Nomad jobs")
+	}
+
+	var list []model.Image
+
+	for _, job := range jobs {
+		jobInfo, _, err := client.Jobs().Info(job.ID, nil)
+		if err != nil {
+			c.logger.Error().Err(err).Msg("Cannot get info for job")
+		}
+
+		for _, taskGroup := range jobInfo.TaskGroups {
+			// Get task group service labels
+			groupLabels := map[string]string{}
+			for _, service := range taskGroup.Services {
+				groupLabels = updateMap(groupLabels, parseServiceTags(service.Tags))
+			}
+
+			for _, task := range taskGroup.Tasks {
+				if task.Driver != "docker" {
+					continue
+				}
+
+				if taskImage, ok := task.Config["image"]; ok {
+					imageName := taskImage.(string)
+					if imageName == "${meta.connect.sidecar_image}" {
+						c.logger.Debug().
+							Str("job_id", job.ID).
+							Str("task_group", *taskGroup.Name).
+							Str("task_name", task.Name).
+							Msg("Skipping connect sidecar")
+						continue
+					}
+
+					// Get task service labels
+					labels := map[string]string{}
+					labels = updateMap(labels, groupLabels)
+					for _, service := range task.Services {
+						labels = updateMap(labels, parseServiceTags(service.Tags))
+					}
+
+					// Finally, merge task meta values
+					labels = updateMap(labels, task.Meta)
+
+					image, err := provider.ValidateImage(imageName, labels, *c.config.WatchByDefault)
+					if err != nil {
+						c.logger.Error().
+							Err(err).
+							Str("job_id", job.ID).
+							Str("task_group", *taskGroup.Name).
+							Str("task_name", task.Name).
+							Str("image_name", imageName).
+							Msg("Error validating image")
+						continue
+					} else if reflect.DeepEqual(image, model.Image{}) {
+						c.logger.Debug().
+							Str("job_id", job.ID).
+							Str("task_group", *taskGroup.Name).
+							Str("task_name", task.Name).
+							Str("image_name", imageName).
+							Msg("Watch disabled")
+						continue
+					}
+
+					list = append(list, image)
+				}
+			}
+		}
+	}
+
+	return list
+}