From c3d531f8f28e8b69a7ab91c6e9c96ef0db1d0287 Mon Sep 17 00:00:00 2001
From: Chris Church <chris.church@patientco.com>
Date: Thu, 18 May 2017 13:59:09 -0400
Subject: [PATCH] add-json-support: added support for both YAML and JSON values
 for input to a template

---
 tpl.go      | 51 +++++++++++++++++++++++++++++++++++++++------------
 tpl_test.go | 28 ++++++++++++++++++++++++++--
 2 files changed, 65 insertions(+), 14 deletions(-)

diff --git a/tpl.go b/tpl.go
index 563d847..497eb70 100644
--- a/tpl.go
+++ b/tpl.go
@@ -2,6 +2,8 @@ package main
 
 import (
 	"bytes"
+	"encoding/json"
+	"flag"
 	"fmt"
 	"io"
 	"log"
@@ -14,33 +16,58 @@ import (
 // Reads a YAML document from the values_in stream, uses it as values
 // for the tpl_files templates and writes the executed templates to
 // the out stream.
-func ExecuteTemplates(values_in io.Reader, out io.Writer, tpl_files ...string) error {
+func ExecuteTemplates(values map[string]interface{}, out io.Writer, tpl_files ...string) error {
 	tpl, err := template.ParseFiles(tpl_files...)
 	if err != nil {
 		return fmt.Errorf("Error parsing template(s): %v", err)
 	}
 
-	buf := bytes.NewBuffer(nil)
-	_, err = io.Copy(buf, values_in)
+	err = tpl.Execute(out, values)
 	if err != nil {
-		return fmt.Errorf("Failed to read standard input: %v", err)
+		return fmt.Errorf("Failed to parse standard input: %v", err)
 	}
+	return nil
+}
 
-	var values map[string]interface{}
-	err = yaml.Unmarshal(buf.Bytes(), &values)
+func ParseValues(values_in io.Reader, format string) (map[string]interface{}, error) {
+	buf := bytes.NewBuffer(nil)
+	_, err := io.Copy(buf, values_in)
 	if err != nil {
-		return fmt.Errorf("Failed to parse standard input: %v", err)
+		return nil, fmt.Errorf("Failed to read standard input: %v", err)
 	}
 
-	err = tpl.Execute(out, values)
-	if err != nil {
-		return fmt.Errorf("Failed to parse standard input: %v", err)
+	var values map[string]interface{}
+
+	switch format {
+	case "json":
+		err = json.Unmarshal(buf.Bytes(), &values)
+		if err != nil {
+			return nil, fmt.Errorf("Failed to parse standard input: %v", err)
+		}
+	case "yaml":
+		err = yaml.Unmarshal(buf.Bytes(), &values)
+		if err != nil {
+			return nil, fmt.Errorf("Failed to parse standard input: %v", err)
+		}
+	default:
+		return nil, fmt.Errorf("Unknown format: %s", format)
 	}
-	return nil
+
+	return values, nil
+
 }
 
 func main() {
-	err := ExecuteTemplates(os.Stdin, os.Stdout, os.Args[1:]...)
+	format := flag.String("format", "yaml", "format of input values: yaml or json")
+	flag.Parse()
+
+	values, err := ParseValues(os.Stdin, *format)
+	if err != nil {
+		log.Println(err)
+		os.Exit(1)
+	}
+
+	err = ExecuteTemplates(values, os.Stdout, flag.Args()...)
 	if err != nil {
 		log.Println(err)
 		os.Exit(1)
diff --git a/tpl_test.go b/tpl_test.go
index e08291e..b9aee0b 100644
--- a/tpl_test.go
+++ b/tpl_test.go
@@ -10,11 +10,12 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
-func TestYamlTemplate(t *testing.T) {
+func TestTemplate(t *testing.T) {
 	type io struct {
 		Input    string
 		Template string
 		Output   string
+		Format   string
 	}
 
 	tests := []io{
@@ -22,16 +23,37 @@ func TestYamlTemplate(t *testing.T) {
 			Input:    "test: value",
 			Template: "{{.test}}",
 			Output:   "value",
+			Format:   "yaml",
 		},
 		io{
 			Input:    "name: Max\nage: 15",
 			Template: "Hello {{.name}}, of {{.age}} years old",
 			Output:   "Hello Max, of 15 years old",
+			Format:   "yaml",
 		},
 		io{
 			Input:    "legumes:\n  - potato\n  - onion\n  - cabbage",
 			Template: "Legumes:{{ range $index, $el := .legumes}}{{if $index}},{{end}} {{$el}}{{end}}",
 			Output:   "Legumes: potato, onion, cabbage",
+			Format:   "yaml",
+		},
+		io{
+			Input:    "{\"test\": \"value\"}",
+			Template: "{{.test}}",
+			Output:   "value",
+			Format:   "json",
+		},
+		io{
+			Input:    "{\"name\": \"Max\", \"age\": 15}",
+			Template: "Hello {{.name}}, of {{.age}} years old",
+			Output:   "Hello Max, of 15 years old",
+			Format:   "json",
+		},
+		io{
+			Input:    "{\"legumes\": [\"potato\", \"onion\", \"cabbage\"]}",
+			Template: "Legumes:{{ range $index, $el := .legumes}}{{if $index}},{{end}} {{$el}}{{end}}",
+			Output:   "Legumes: potato, onion, cabbage",
+			Format:   "json",
 		},
 	}
 
@@ -45,7 +67,9 @@ func TestYamlTemplate(t *testing.T) {
 		tpl_file.Close()
 
 		output := bytes.NewBuffer(nil)
-		err = ExecuteTemplates(strings.NewReader(test.Input), output,
+		values, err := ParseValues(strings.NewReader(test.Input), test.Format)
+		assert.Nil(t, err)
+		err = ExecuteTemplates(values, output,
 			tpl_file.Name())
 		assert.Nil(t, err)