Support auto detection (#46)

internal/app/app.go

@@ -24,7 +24,7 @@ func Run(arguments []string, out io.Writer, version string) (err error) {
 
 	outputFormat := flag.String(
 		"format",
-		string(model.FormatGo),
+		string(model.FormatAutoDetect),
 		"output format: "+strings.Join(model.Formats(), ", "),
 	)
 	templateFile := flag.String(

internal/app/generator.go

@@ -3,6 +3,8 @@ package app
 import (
 	"fmt"
 	"io"
+	"path"
+	"strings"
 
 	"github.com/hedhyw/gherkingen/v2/internal/docplugin/goplugin"
 	"github.com/hedhyw/gherkingen/v2/internal/docplugin/multiplugin"
@@ -22,6 +24,10 @@ func runGenerator(
 		return err
 	}
 
+	if outputFormat == model.FormatAutoDetect {
+		outputFormat = detectFormat(templateFile)
+	}
+
 	inputSource, err := readInput(inputFile)
 	if err != nil {
 		return err
@@ -42,3 +48,15 @@ func runGenerator(
 
 	return nil
 }
+
+func detectFormat(templateFile string) model.Format {
+	templateFile = strings.ToLower(templateFile)
+	switch path.Ext(templateFile) {
+	case ".go":
+		return model.FormatGo
+	case ".tmpl":
+		return detectFormat(strings.TrimSuffix(templateFile, ".tmpl"))
+	default:
+		return model.FormatRaw
+	}
+}

internal/app/generator_test.go

@@ -0,0 +1,41 @@
+package app
+
+import (
+	"testing"
+
+	"github.com/hedhyw/gherkingen/v2/internal/model"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDetectFormat(t *testing.T) {
+	t.Parallel()
+
+	testCases := [...]struct {
+		Filename string
+		Expected model.Format
+	}{{
+		Filename: "example.go",
+		Expected: model.FormatGo,
+	}, {
+		Filename: "example.rb",
+		Expected: model.FormatRaw,
+	}, {
+		Filename: "example.json",
+		Expected: model.FormatRaw,
+	}, {
+		Filename: "example.GO",
+		Expected: model.FormatGo,
+	}, {
+		Filename: "example.go.tmpl",
+		Expected: model.FormatGo,
+	}, {
+		Filename: "example.rb.tmpl",
+		Expected: model.FormatRaw,
+	}}
+
+	for _, tc := range testCases {
+		actual := detectFormat(tc.Filename)
+		assert.Equal(t, tc.Expected, actual, tc.Filename)
+	}
+}

internal/model/enums.go

@@ -5,14 +5,16 @@ type Format string
 
 // Possible formats.
 const (
-	FormatJSON Format = "json"
-	FormatGo   Format = "go"
-	FormatRaw  Format = "raw"
+	FormatAutoDetect Format = "autodetect"
+	FormatJSON       Format = "json"
+	FormatGo         Format = "go"
+	FormatRaw        Format = "raw"
 )
 
 // Formats returns supported output formats.
 func Formats() []string {
 	return []string{
+		string(FormatAutoDetect),
 		string(FormatJSON),
 		string(FormatGo),
 		string(FormatRaw),

internal/model/enums_test.go

@@ -14,6 +14,7 @@ func TestFormats(t *testing.T) {
 	actualFormats := model.Formats()
 
 	expFormats := [...]string{
+		string(model.FormatAutoDetect),
 		string(model.FormatJSON),
 		string(model.FormatGo),
 		string(model.FormatRaw),