implement help; move 'no types' message up to gen out of typewriter

Author: clipperhouse

help.go

@@ -0,0 +1,31 @@
+package main
+
+import (
+	"os"
+	"text/template"
+)
+
+func help() error {
+	info := helpInfo{
+		Name:       os.Args[0],
+		CustomName: customName,
+	}
+
+	helpTmpl.Execute(out, info)
+	return nil
+}
+
+type helpInfo struct {
+	Name, CustomName string
+}
+
+var helpTmpl = template.Must(template.New("help").Parse(`
+Usage:
+  {{.Name}}           Generate files for types marked with +gen
+  {{.Name}} get       Download and install typewriters (standard or custom)
+  {{.Name}} list      List available typewriters (standard or custom)
+  {{.Name}} custom    Create a standard {{.CustomName}} file for importing custom typewriters
+  {{.Name}} help      Print usage
+
+Further details are available at http://clipperhouse.github.io/gen
+`))

main.go

@@ -20,10 +20,11 @@ func main() {
 	case "get":
 		runCmd(get)
 		// TODO: pass subsequent flags (such as -u) to get
+	case "help":
+		runCmd(help)
 	case "list":
 		runCmd(list)
 	}
-	// TODO: add help command
 	// TODO: verbosity?
 }
 

run.go

@@ -1,9 +1,15 @@
 package main
 
-import "github.com/clipperhouse/gen/typewriter"
+import (
+	"fmt"
+	"os"
+
+	"github.com/clipperhouse/gen/typewriter"
+)
 
 func run() error {
 	imports := []string{
+		`"fmt"`,
 		`"os"`,
 		`"github.com/clipperhouse/gen/typewriter"`,
 	}
@@ -18,6 +24,14 @@ func runStandard() error {
 		return err
 	}
 
+	if len(app.Types) == 0 {
+		return fmt.Errorf("No types marked with +gen were found. See http://clipperhouse.github.io/gen to get started, or type %s help.", os.Args[0])
+	}
+
+	if len(app.TypeWriters) == 0 {
+		return fmt.Errorf("No typewriters were imported. See http://clipperhouse.github.io/gen to get started, or type %s help.", os.Args[0])
+	}
+
 	if err := app.WriteAll(); err != nil {
 		return err
 	}
@@ -27,16 +41,31 @@ func runStandard() error {
 
 const runBody string = `
 func main() {
+	if err := gen(); err != nil {
+		os.Stderr.WriteString(err.Error() + "\n")
+		os.Exit(1)
+	}
+}
+
+func gen() error {
 	app, err := typewriter.NewApp("+gen")
 
 	if err != nil {
-		os.Stderr.WriteString(err.Error() + "\n")
-		os.Exit(1)
+		return err
+	}
+
+	if len(app.Types) == 0 {
+		return fmt.Errorf("No types marked with +gen were found. See http://clipperhouse.github.io/gen to get started, or type %s help.", os.Args[0])
+	}
+
+	if len(app.TypeWriters) == 0 {
+		return fmt.Errorf("No typewriters were imported. See http://clipperhouse.github.io/gen to get started, or type %s help.", os.Args[0])
 	}
 
 	if err := app.WriteAll(); err != nil {
-		os.Stderr.WriteString(err.Error() + "\n")
-		os.Exit(1)
+		return err
 	}
+
+	return nil
 }
 `

typewriter/app.go

@@ -38,10 +38,6 @@ func NewAppFiltered(directive string, filter func(os.FileInfo) bool) (*app, erro
 		return a, err
 	}
 
-	if len(typs) == 0 {
-		return a, fmt.Errorf("no types marked with %s were found, so there is nothing to gen. see http://clipperhouse.github.io/gen to get started.", directive)
-	}
-
 	a.Types = typs
 	a.TypeWriters = typeWriters
 	return a, nil