feat(cli): limit output to specific objects only (grafana#30)

Allows to limit the processed objects using an `objectspec`.

Format: --target (-t) <kind>/<name>
Example: tk show --target=deployment/nginx

Can be used multiple times to use multiple objects

cmd/tk/workflow.go

@@ -9,9 +9,20 @@ import (
 	"github.com/grafana/tanka/pkg/cmp"
 	"github.com/posener/complete"
 	"github.com/spf13/cobra"
+	"github.com/spf13/pflag"
 	"golang.org/x/crypto/ssh/terminal"
 )
 
+type workflowFlagVars struct {
+	targets []string
+}
+
+func workflowFlags(fs *pflag.FlagSet) *workflowFlagVars {
+	v := workflowFlagVars{}
+	fs.StringSliceVarP(&v.targets, "target", "t", nil, "only use the specified objects (Format: <type>/<name>)")
+	return &v
+}
+
 func applyCmd() *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "apply [directory]",
@@ -21,13 +32,14 @@ func applyCmd() *cobra.Command {
 			"args": "baseDir",
 		},
 	}
+	vars := workflowFlags(cmd.Flags())
 	cmd.Run = func(cmd *cobra.Command, args []string) {
 		raw, err := evalDict(args[0])
 		if err != nil {
 			log.Fatalln("Evaluating jsonnet:", err)
 		}
 
-		desired, err := kube.Reconcile(raw)
+		desired, err := kube.Reconcile(raw, vars.targets...)
 		if err != nil {
 			log.Fatalln("Reconciling:", err)
 		}
@@ -52,6 +64,7 @@ func diffCmd() *cobra.Command {
 			"flags/diff-strategy": "diffStrategy",
 		},
 	}
+	vars := workflowFlags(cmd.Flags())
 	cmd.Run = func(cmd *cobra.Command, args []string) {
 		raw, err := evalDict(args[0])
 		if err != nil {
@@ -62,7 +75,7 @@ func diffCmd() *cobra.Command {
 			kube.Spec.DiffStrategy = cmd.Flag("diff-strategy").Value.String()
 		}
 
-		desired, err := kube.Reconcile(raw)
+		desired, err := kube.Reconcile(raw, vars.targets...)
 		if err != nil {
 			log.Fatalln("Reconciling:", err)
 		}
@@ -93,13 +106,14 @@ func showCmd() *cobra.Command {
 			"args": "baseDir",
 		},
 	}
+	vars := workflowFlags(cmd.Flags())
 	cmd.Run = func(cmd *cobra.Command, args []string) {
 		raw, err := evalDict(args[0])
 		if err != nil {
 			log.Fatalln("Evaluating jsonnet:", err)
 		}
 
-		state, err := kube.Reconcile(raw)
+		state, err := kube.Reconcile(raw, vars.targets...)
 		if err != nil {
 			log.Fatalln("Reconciling:", err)
 		}

pkg/kubernetes/kubernetes.go

@@ -2,10 +2,13 @@ package kubernetes
 
 import (
 	"bytes"
+	"fmt"
+	"strings"
 
 	"github.com/Masterminds/semver"
 	"github.com/pkg/errors"
 	"github.com/stretchr/objx"
+	funk "github.com/thoas/go-funk"
 	yaml "gopkg.in/yaml.v2"
 
 	"github.com/grafana/tanka/pkg/config/v1alpha1"
@@ -40,7 +43,7 @@ type Manifest map[string]interface{}
 
 // Reconcile receives the raw evaluated jsonnet as a marshaled json dict and
 // shall return it reconciled as a state object of the target system
-func (k *Kubernetes) Reconcile(raw map[string]interface{}) (state []Manifest, err error) {
+func (k *Kubernetes) Reconcile(raw map[string]interface{}, objectspecs ...string) (state []Manifest, err error) {
 	docs, err := walkJSON(raw, "")
 	out := make([]Manifest, 0, len(docs))
 	if err != nil {
@@ -51,6 +54,19 @@ func (k *Kubernetes) Reconcile(raw map[string]interface{}) (state []Manifest, er
 		m.Set("metadata.namespace", k.Spec.Namespace)
 		out = append(out, Manifest(m))
 	}
+
+	if len(objectspecs) > 0 {
+		out = funk.Filter(out, func(i interface{}) bool {
+			p := objectspec(i.(Manifest))
+			for _, o := range objectspecs {
+				if strings.EqualFold(p, o) {
+					return true
+				}
+			}
+			return false
+		}).([]Manifest)
+	}
+
 	return out, nil
 }
 
@@ -95,3 +111,10 @@ func (k *Kubernetes) Diff(state []Manifest) (string, error) {
 
 	return k.differs[k.Spec.DiffStrategy](yaml)
 }
+
+func objectspec(m Manifest) string {
+	return fmt.Sprintf("%s/%s",
+		m["kind"],
+		m["metadata"].(map[string]interface{})["name"],
+	)
+}