feat: allow querying single tag

main.go

@@ -18,10 +18,11 @@ type Image struct {
 
 func main() {
 	var unknownMarker string
+	var query string
 
 	var rootCmd = &cobra.Command{
 		Use:   "dockerfile-image-tags",
-		Short: "List images & tags used in a Dockerfile.",
+		Short: "List or query images & tags used in a Dockerfile.",
 		Args:  cobra.MaximumNArgs(1),
 		Run: func(cmd *cobra.Command, args []string) {
 			file, err := getInput(args)
@@ -44,10 +45,21 @@ func main() {
 				log.Fatalf("Could not serialize images as JSON: %s\n", err)
 			}
 
-			fmt.Println(string(val))
+			if query == "" {
+				fmt.Println(string(val))
+			} else {
+				tag, err := getSingleTag(images, query)
+
+				if err != nil {
+					log.Fatalf("Could not find image in Dockerfile: %s", query)
+				}
+
+				fmt.Println(tag)
+			}
 		},
 	}
 	rootCmd.Flags().StringVarP(&unknownMarker, "unknown-marker", "m", "?", "string to use to indicate unknown tags")
+	rootCmd.Flags().StringVarP(&query, "query", "q", "", "single image to return tag for (first occurrence)")
 
 	if err := rootCmd.Execute(); err != nil {
 		log.Fatal(err)
@@ -94,3 +106,13 @@ func getTags(commands []dockerfile.Command, unknownMarker string) []Image {
 
 	return images
 }
+
+func getSingleTag(images []Image, query string) (string, error) {
+	for _, i := range images {
+		if i.Name == query {
+			return i.Tag, nil
+		}
+	}
+
+	return "", fmt.Errorf("could not find image %s in list", query)
+}

main_test.go

@@ -27,3 +27,36 @@ func TestParsing(t *testing.T) {
 
 	assert.Equal(t, expected, tags)
 }
+
+func TestQuery(t *testing.T) {
+	cases := []struct {
+		query string
+		match bool
+		tag   string
+	}{
+		{query: "foo", match: false, tag: ""},
+		{query: "viaductoss/ksops", match: true, tag: "v3.0.0"},
+		{query: "golang", match: true, tag: "1.17.0-alpine"},
+		{query: "common", match: true, tag: "?"},
+	}
+
+	commands, err := dockerfile.ParseFile("tests/Dockerfile.1")
+
+	if err != nil {
+		t.Errorf("Could not open Dockerfile.1: %s", err)
+	}
+
+	tags := getTags(commands, "?")
+
+	for _, c := range cases {
+		result, err := getSingleTag(tags, c.query)
+
+		if c.match {
+			assert.NoError(t, err, "must match %v", c.query)
+			assert.Equal(t, result, c.tag)
+		} else {
+			assert.Error(t, err, "must not match %v", c.query)
+			assert.Equal(t, result, "")
+		}
+	}
+}