command: produce help output from flags (#39)

internal/command/cmd.go

@@ -0,0 +1,22 @@
+package command
+
+import (
+	"errors"
+
+	"github.com/shoenig/ssh-key-sync/internal/config"
+	"github.com/shoenig/ssh-key-sync/internal/netapi"
+	"github.com/shoenig/ssh-key-sync/internal/ssh"
+)
+
+func Start(args []string) error {
+	arguments := config.ParseArguments(args[0], args[1:])
+	if arguments.GitHubUser == "" {
+		arguments.Usage()
+		return errors.New("missing required argument(s)")
+	}
+
+	reader := ssh.NewKeysReader()
+	githubClient := netapi.NewGithubClient(arguments)
+	exe := NewExec(arguments.Verbose, reader, githubClient)
+	return exe.Execute(arguments)
+}

internal/config/arguments.go

@@ -27,6 +27,12 @@ type Arguments struct {
 
 	GitHubUser string
 	GitHubAPI  string
+
+	usage func()
+}
+
+func (a Arguments) Usage() {
+	a.usage()
 }
 
 func defaultUser() string {
@@ -37,7 +43,7 @@ func defaultUser() string {
 }
 
 func ParseArguments(program string, args []string) Arguments {
-	flags := flag.NewFlagSet(program, flag.PanicOnError)
+	flags := flag.NewFlagSet(program, flag.ContinueOnError)
 	var arguments Arguments
 
 	flags.BoolVar(
@@ -69,5 +75,6 @@ func ParseArguments(program string, args []string) Arguments {
 	)
 
 	_ = flags.Parse(args)
+	arguments.usage = flags.Usage
 	return arguments
 }

main.go

@@ -1,26 +1,15 @@
 package main
 
 import (
+	"fmt"
 	"os"
 
 	"github.com/shoenig/ssh-key-sync/internal/command"
-	"github.com/shoenig/ssh-key-sync/internal/config"
-	"github.com/shoenig/ssh-key-sync/internal/logs"
-	"github.com/shoenig/ssh-key-sync/internal/netapi"
-	"github.com/shoenig/ssh-key-sync/internal/ssh"
 )
 
 func main() {
-	logger := logs.New(true)
-	args := config.ParseArguments(os.Args[0], os.Args[1:])
-	if args.GitHubUser == "" {
-		logger.Fatal("ssh-key-sync requires --github-user")
+	if err := command.Start(os.Args); err != nil {
+		fmt.Println("[fatal]", err)
+		os.Exit(1)
 	}
-
-	reader := ssh.NewKeysReader()
-	githubClient := netapi.NewGithubClient(args)
-	exec := command.NewExec(args.Verbose, reader, githubClient)
-	if err := exec.Execute(args); err != nil {
-		logger.Fatalf("ssh-key-sync failed with error: %s", err)
-	}
-}
+ }