feat(cmd): Add build Command to CLI Tool

cmd/substation/build.go

@@ -0,0 +1,105 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+
+	"github.com/spf13/cobra"
+)
+
+func init() {
+	rootCmd.AddCommand(buildCmd)
+	buildCmd.PersistentFlags().BoolP("recursive", "R", false, "recursively build all files")
+	buildCmd.PersistentFlags().StringToString("ext-str", nil, "set external variables")
+}
+
+var buildCmd = &cobra.Command{
+	Use:   "build [path]",
+	Short: "build configs",
+	Long: `'substation build' compiles configuration files.
+
+The 'recursive' flag can be used to build all files in a directory,
+and the current directory is used if no arg is provided.`,
+	Example: `  substation build [-R]
+  substation build [-R] /path/to/configs
+  substation build config.jsonnet
+`,
+	Args: cobra.MaximumNArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		// Default to current directory if no path is provided
+		path := "."
+		if len(args) > 0 {
+			path = args[0]
+		}
+
+		// Catches an edge case where the user is looking for help.
+		if path == "help" {
+			fmt.Printf("warning: %q matched no files\n", path)
+			return nil
+		}
+
+		m, err := cmd.PersistentFlags().GetStringToString("ext-str")
+		if err != nil {
+			return err
+		}
+
+		r, err := cmd.Flags().GetBool("recursive")
+		if err != nil {
+			return err
+		}
+
+		return buildPath(path, m, r)
+	},
+}
+
+func buildPath(arg string, extVars map[string]string, recursive bool) error {
+	// Handle cases where the path is a file.
+	//
+	// Only `.jsonnet` files are built.
+	if filepath.Ext(arg) == ".jsonnet" {
+		return buildFile(arg, extVars)
+	}
+
+	if err := filepath.WalkDir(arg, func(path string, d os.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if d.IsDir() {
+			if !recursive && path != arg {
+				return filepath.SkipDir
+			}
+
+			return nil
+		}
+
+		// Only `.jsonnet` files are built.
+		if filepath.Ext(path) != ".jsonnet" {
+			return nil
+		}
+
+		return buildFile(path, extVars)
+	}); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func buildFile(arg string, extVars map[string]string) error {
+	mem, err := compileFile(arg, extVars)
+	if err != nil {
+		return err
+	}
+
+	dir, fname := pathVars(arg)
+	if err := os.WriteFile(filepath.Join(dir, fname)+".json", []byte(mem), 0o644); err != nil {
+		return err
+	}
+
+	// Print the file that was built.
+	fmt.Println(arg)
+
+	return nil
+}

cmd/substation/main.go

@@ -2,6 +2,8 @@ package main
 
 import (
 	"os"
+	"path/filepath"
+	"strings"
 
 	"github.com/google/go-jsonnet"
 	"github.com/spf13/cobra"
@@ -27,8 +29,8 @@ func init() {
 	})
 }
 
-// buildFile returns JSON from a Jsonnet file.
-func buildFile(f string, extVars map[string]string) (string, error) {
+// compileFile returns JSON from a Jsonnet file.
+func compileFile(f string, extVars map[string]string) (string, error) {
 	vm := jsonnet.MakeVM()
 	for k, v := range extVars {
 		vm.ExtVar(k, v)
@@ -42,6 +44,15 @@ func buildFile(f string, extVars map[string]string) (string, error) {
 	return res, nil
 }
 
+// pathVars returns the directory and file name of a file path.
+func pathVars(p string) (string, string) {
+	dir, fn := filepath.Split(p)
+	ext := filepath.Ext(fn)
+	fn = strings.TrimSuffix(fn, ext)
+
+	return dir, fn
+}
+
 func main() {
 	err := rootCmd.Execute()
 	if err != nil {

cmd/substation/test.go

@@ -261,7 +261,7 @@ production resources, such as any enrichment or send transforms.
 				}
 
 				// If the Jsonnet cannot compile, then the file is invalid.
-				mem, err := buildFile(arg, m)
+				mem, err := compileFile(arg, m)
 				if err != nil {
 					fmt.Printf("?\t%s\t[config error]\n", arg)
 
@@ -332,7 +332,7 @@ production resources, such as any enrichment or send transforms.
 				}
 
 				// If the Jsonnet cannot compile, then the file is invalid.
-				mem, err := buildFile(entry, m)
+				mem, err := compileFile(entry, m)
 				if err != nil {
 					fmt.Printf("?\t%s\t[config error]\n", entry)