Merge pull request #5 from vinted/feature/add_now_function

graphql-exporter: add NOW function

README.md

@@ -32,6 +32,9 @@ Exporter is designed to build and display metrics based on GraphQL query results
 }
 ```
 
+Query supports dynamic `datetime` field. It can be specified as template variable.
+For example when specified `{{NOW ""-1h"}}` query will generate `datetime` that existed one hour ago.
+
 Metrics results in:
 
 ```

config_example.json

@@ -4,7 +4,7 @@
   "CacheExpire": 0,
   "queries":[
     {
-      "query": "query {device_list {name serial custom_fields}}",
+      "query": "query {device_list {name serial custom_fields}} {{NOW "-1h"}}",
       "metrics": [
         {
           "description": "Deprecation date",

pkg/config/config.go

@@ -1,9 +1,13 @@
 package config
 
 import (
+	"bytes"
 	"encoding/json"
+	"fmt"
 	"log"
 	"os"
+	"text/template"
+	"time"
 )
 
 type Cfg struct {
@@ -30,6 +34,13 @@ var (
 	ConfigPath string
 )
 
+var funcMap = template.FuncMap{
+	"NOW": func(t string) (string, error) {
+		d, err := time.ParseDuration(t)
+		return time.Now().UTC().Add(d).Format(time.RFC3339), err
+	},
+}
+
 func Init(configPath string) error {
 	ConfigPath = configPath
 	content := []byte(`{}`)
@@ -43,7 +54,22 @@ func Init(configPath string) error {
 	if len(content) == 0 {
 		content = []byte(`{}`)
 	}
-	err = json.Unmarshal(content, &Config)
+
+	if err != nil {
+		return fmt.Errorf("%s", err)
+	}
+	tpl, err := template.New("query").Funcs(funcMap).Parse(string(content))
+	if err != nil {
+		return fmt.Errorf("%s", err)
+	}
+
+	var templateBuffer bytes.Buffer
+	err = tpl.Execute(&templateBuffer, nil)
+	if err != nil {
+		return fmt.Errorf("Template error %s", err)
+	}
+
+	err = json.Unmarshal(templateBuffer.Bytes(), &Config)
 	if err != nil {
 		return err
 	}