add help command

cmd/help.go

@@ -0,0 +1,60 @@
+package lumecmd
+
+import (
+	"flag"
+	"fmt"
+)
+
+func init() {
+	var cmdName string = "help"
+	fs := flag.NewFlagSet(cmdName, flag.ExitOnError)
+
+	RegisterCommand(cmdName, Command{
+		Func:  HelpCmd,
+		Flags: fs,
+		Use:   "<command>",
+		Short: "Show help for a command",
+	})
+}
+
+func HelpCmd(args CmdArgs) (int, error) {
+	argv := args.Flags.Args()
+
+	if len(argv) == 0 {
+		printHelp(commandRegistry)
+	} else if len(argv) >= 1 {
+		subCmd, ok := commandRegistry[argv[0]]
+		if !ok {
+			fmt.Printf("unknown command: %s\n", argv[0])
+			return 1, nil
+		}
+
+		if subCmd.Use != "" {
+			fmt.Printf("usage:\n  lume %s %s\n", subCmd.Name, subCmd.Use)
+			fmt.Println()
+		}
+
+		fmt.Print("flags:\n")
+		subCmd.Flags.PrintDefaults()
+	}
+
+	return 0, nil
+}
+
+func printHelp(commands map[string]Command) {
+	var maxLen, cmdLen int
+	for _, c := range commands {
+		cmdLen = len(c.Name)
+		if cmdLen > maxLen {
+			maxLen = cmdLen
+		}
+	}
+
+	fmt.Printf("usage:\n  lume <command> [<args...>]")
+	fmt.Println()
+
+	fmt.Println("\ncommands:")
+	for _, c := range commands {
+		fmt.Printf("  %-*s    %s\n", maxLen, c.Name, c.Short)
+	}
+}