Add flag -format to allow for output formatting

cmd/microdata/main.go

@@ -6,59 +6,88 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
-	"io"
 	"net/url"
 	"os"
+	"text/template"
 
 	"github.com/namsral/microdata"
 )
 
+var fnmap = template.FuncMap{
+	"jsonMarshal": jsonMarshal,
+}
+
 func main() {
 	var data *microdata.Microdata
 	var err error
 
 	baseURL := flag.String("base-url", "http://example.com", "base url to use for the data in the stdin stream.")
 	contentType := flag.String("content-type", "", "content type of the data in the stdin stream.")
+	// format := flag.String("format", "", "format for the output using the syntax of package html/template.")
+	format := flag.String("format", "", `alternate format for the output of the
+	microdata, using the syntax of package html/template. The default output is
+	equivalent to -f '{{. |jsonMarshal }}'. The struct being passed to the
+	template is:
+		
+		type Microdata struct
+			Items []*Item 'json:"items"'
+		}
+
+		type Item struct {
+			Types      []string    'json:"type"'
+			Properties PropertyMap 'json:"properties"'
+			Id         string      'json:"id,omitempty"'
+		}
+
+		type PropertyMap map[string]ValueList
+		
+		type ValueList []interface{}
+
+	The template function "jsonMarshal" calls json.Marshal
+`)
 
 	flag.Usage = func() {
 		fmt.Fprintf(os.Stderr, "Usage of %s [options] [url]:\n", os.Args[0])
 		flag.PrintDefaults()
-		fmt.Fprint(os.Stderr, "\nExtract the HTML Microdata from a HTML5 document.")
+		fmt.Fprint(os.Stderr, "\nExtract the HTML Microdata from a HTML5 document. Format to JSON or using the syntax of package html/template.")
 		fmt.Fprint(os.Stderr, " Provide an URL to a valid HTML5 document or stream a valid HTML5 document through stdin.\n")
 	}
 
 	flag.Parse()
 
-	// Args
-	if args := flag.Args(); len(args) > 0 {
-		urlStr := args[0]
-		data, err = microdata.ParseURL(urlStr)
+	// Fetch and parse microdata
+	switch len(flag.Args()) {
+	case 0:
+		u, err := url.Parse(*baseURL)
+		if err != nil {
+			fmt.Println(err)
+			os.Exit(1)
+		}
+		data, err = microdata.ParseHTML(os.Stdin, *contentType, u)
+		if err != nil {
+			fmt.Println(err)
+			os.Exit(1)
+		}
+	default:
+		data, err = microdata.ParseURL(flag.Args()[0])
 		if err != nil {
 			fmt.Println(err)
 			os.Exit(1)
 		}
-		printResult(os.Stdout, data)
-		return
 	}
 
-	// Stdin
-	r := os.Stdin
-	u, _ := url.Parse(*baseURL)
-	data, err = microdata.ParseHTML(r, *contentType, u)
-	if err != nil {
+	t := template.Must(template.New("format").Funcs(fnmap).Parse(*format))
+	if err := t.Execute(os.Stdout, data); err != nil {
 		fmt.Println(err)
 		os.Exit(1)
 	}
-	printResult(os.Stdout, data)
 }
 
-// printResult pretty formats and prints the given items in a JSON object.
-func printResult(w io.Writer, data *microdata.Microdata) {
+// jsonMarshal encodes the given data to JSON.
+func jsonMarshal(data interface{}) (string, error) {
 	b, err := json.MarshalIndent(data, "", "  ")
 	if err != nil {
-		fmt.Println(err)
-		os.Exit(1)
+		return "", err
 	}
-	w.Write(b)
-	w.Write([]byte("\n"))
+	return string(b), nil
 }