Option to load tempate variables from json file (#98)

DOCS.md

@@ -186,6 +186,33 @@ Build finished for *{{tpl.app}}* - *{{tpl.env}}*
 {{/success}}
 ```
 
+Example configuration with a custom message template, with extra vars loaded from file (e.g. from previous build steps):
+
+```diff
+  - name: send telegram notification
+    image: appleboy/drone-telegram
+    settings:
+      token: xxxxxxxxxx
+      to: telegram_user_id
++     template_vars_file: build_report.json
++     message: >
++       {{#success build.status}}
++         build {{build.number}} succeeded, artefact version = {{tpl.artefact_version}}.
++       {{else}}
++         build {{build.number}} failed. Fix me please.
++       {{/success}}
+```
+
+Where `build_report.json` is:
+
+```
+{
+  ...
+  "artefact_version": "0.2.3452"
+  ...
+}
+```
+
 Example configuration with a custom socks5 URL:
 
 ```diff
@@ -215,6 +242,9 @@ message_file
 template_vars
 : define additional template vars. Example: `var1: hello` can be used within the template as `tpl.var1`
 
+template_vars_file
+: load additional template vars from json file. Example: given file content `{"var1":"hello"}`, variable can be used within the template as `tpl.var1`
+
 photo
 : local file path
 

main.go

@@ -54,6 +54,11 @@ func main() {
 			Usage:  "additional template vars to be used in message, as JSON string",
 			EnvVar: "PLUGIN_TEMPLATE_VARS,TELEGRAM_TEMPLATE_VARS,INPUT_TEMPLATE_VARS",
 		},
+		cli.StringFlag{
+			Name:   "template.vars.file",
+			Usage:  "load additional template vars to be used in message, from json file",
+			EnvVar: "PLUGIN_TEMPLATE_VARS_FILE,TELEGRAM_TEMPLATE_VARS_FILE",
+		},
 		cli.StringSliceFlag{
 			Name:   "photo",
 			Usage:  "send photo message",
@@ -304,6 +309,7 @@ func run(c *cli.Context) error {
 			Message:          c.String("message"),
 			MessageFile:      c.String("message.file"),
 			TemplateVars:     c.String("template.vars"),
+			TemplateVarsFile: c.String("template.vars.file"),
 			Photo:            c.StringSlice("photo"),
 			Document:         c.StringSlice("document"),
 			Sticker:          c.StringSlice("sticker"),

plugin.go

@@ -74,6 +74,7 @@ type (
 		To               []string
 		Message          string
 		MessageFile      string
+		TemplateVarsFile string
 		TemplateVars     string
 		Photo            []string
 		Document         []string
@@ -283,6 +284,25 @@ func (p Plugin) Exec() (err error) {
 		}
 	}
 
+	if p.Config.TemplateVarsFile != "" {
+		content, err := ioutil.ReadFile(p.Config.TemplateVarsFile)
+		if err != nil {
+			return fmt.Errorf("unable to read file with template vars '%s': %v", p.Config.TemplateVarsFile, err)
+		}
+		var vars = make(map[string]string)
+		if err = json.Unmarshal(content, &vars); err != nil {
+			return fmt.Errorf("unable to unmarshall template vars from JSON file '%s': %v", p.Config.TemplateVarsFile, err)
+		}
+		// Merging templates variables from file to the variables form plugin settings (variables from file takes precedence)
+		if p.Tpl == nil {
+			p.Tpl = vars
+		} else {
+			for k, v := range vars {
+				p.Tpl[k] = v
+			}
+		}
+	}
+
 	var proxyURL *url.URL
 	if proxyURL, err = url.Parse(p.Config.Socks5); err != nil {
 		return fmt.Errorf("unable to unmarshall socks5 proxy url from string '%s': %v", p.Config.Socks5, err)

plugin_test.go

@@ -387,6 +387,37 @@ func TestTemplateVars(t *testing.T) {
 	assert.Nil(t, err)
 }
 
+func TestTemplateVarsFile(t *testing.T) {
+	plugin := Plugin{
+		Repo: Repo{
+			Name:      "go-hello",
+			Namespace: "appleboy",
+		},
+		Commit: Commit{
+			Sha:     "e7c4f0a63ceeb42a39ac7806f7b51f3f0d204fd2",
+			Author:  "Bo-Yi Wu",
+			Branch:  "master",
+			Message: "This is a test commit msg",
+		},
+		Build: Build{
+			Number: 101,
+			Status: "success",
+			Link:   "https://github.com/appleboy/go-hello",
+		},
+
+		Config: Config{
+			Token:            os.Getenv("TELEGRAM_TOKEN"),
+			To:               []string{os.Getenv("TELEGRAM_TO")},
+			Format:           formatMarkdown,
+			MessageFile:      "tests/message_template.txt",
+			TemplateVarsFile: "tests/vars.json",
+		},
+	}
+
+	err := plugin.Exec()
+	assert.Nil(t, err)
+}
+
 func TestProxySendMessage(t *testing.T) {
 	plugin := Plugin{
 		Repo: Repo{

tests/vars.json

@@ -0,0 +1 @@
+{"env":"testing","version":"1.2.0-SNAPSHOT"}