basic functionality

.gitignore

@@ -4,6 +4,7 @@
 *.dll
 *.so
 *.dylib
+gotlet
 
 # Test binary, built with `go test -c`
 *.test

README.md

@@ -1,2 +1,138 @@
 # gotlet
 Simple Templating command line tool using go template engine
+
+## Instalation
+```
+chmod +x ./gotlet
+mv ./gotlet /usr/local/bin/gotlet
+```
+
+## Example usage:
+
+```
+./gotlet -t deployment.yaml -d data.yaml -v
+```
+
+## Flags:
+- `-t` Specify the template file path (required)
+- `-d` Specify the data file path containing the variables in Yaml (optional, if not specified you have only environment variables to include)
+- `-p` A prefix for filtering which env variables to include
+- `-o` Output file path (default: result.yaml)
+- `-v` Print out the result in stdout 
+
+## Template Engine Reference: 
+To use a variable, eighter from environment variables or the specified use the following syntax which is standard go template syntax.
+
+``` 
+statictext {{ .variable_name }} static text
+```
+Nested variables:
+```
+statictext {{ .variable_name.sub_var_name }} static text
+```
+Environment variables:
+```
+statictext {{ .USER }} static text
+```
+Iterate in a key-value dictionary
+```
+env: 
+{{range $key, $value := .environment_variables}}
+    - name: {{ $key }}
+      value: {{ $value }} 
+{{end}}
+```
+
+Read more at [official go documents](https://pkg.go.dev/text/template)
+
+## Sample
+This is a basic variable file:
+> Note that variables root element is required and MUST be `variables`
+```yaml
+variables:
+  service_name: nginx
+  version: 2
+  component: front-end
+  port: 80
+  frontend_max_replicas: 3
+  frontend_image: "nginx:latest"
+  environment_variables:
+    environment: production
+    api_url: "https://api.url.com"
+    project_name: website
+```
+This is a sample template file which is a kubernetes deployment
+```yaml
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: {{.service_name}}-{{.component}}-{{.version}}
+  labels:
+    app: {{.service_name}}
+    component: {{.component}}
+    version: {{.version}}
+spec:
+  strategy:
+    type: RollingUpdate
+    rollingUpdate:
+      maxUnavailable: 2
+      maxSurge: {{ .frontend_max_replicas }}
+    spec:
+      containers:
+        - name: {{.service_name}}
+          image: {{.frontend_image}}
+          imagePullPolicy: IfNotPresent
+          ports:
+            - containerPort: {{.ops_port}}
+          env: {{range $key, $value := .environment_variables}}
+            - name: {{ $key }}
+              value: {{ $value }} {{end}} 
+
+```
+
+running this command would generate this file:
+```
+./gotlet -t ./examples/template.yaml -d ./examples/variables.yaml -o export.yaml
+```
+```yaml
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: nginx-front-end-2
+  labels:
+    app: nginx
+    component: front-end
+    version: 2
+spec:
+  strategy:
+    type: RollingUpdate
+    rollingUpdate:
+      maxUnavailable: 2
+      maxSurge: 3
+    spec:
+      containers:
+        - name: nginx
+          image: nginx:latest
+          imagePullPolicy: IfNotPresent
+          ports:
+            - containerPort: <no value>
+          env: 
+            - name: api_url
+              value: https://api.url.com 
+            - name: environment
+              value: production 
+            - name: project_name
+              value: website  
+
+```
+
+## Build from source
+To run on your local machine (you need go 1.18+ installed)
+```
+go build .
+```
+
+To run on a linux server or a linux pipeline runner:
+```
+GOOS=linux GOARCH=amd64 go build -o gotlet-amd64-linux main.go
+```

examples/template.yaml

@@ -0,0 +1,24 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: {{.service_name}}-{{.component}}-{{.version}}
+  labels:
+    app: {{.service_name}}
+    component: {{.component}}
+    version: {{.version}}
+spec:
+  strategy:
+    type: RollingUpdate
+    rollingUpdate:
+      maxUnavailable: 2
+      maxSurge: {{ .frontend_max_replicas }}
+    spec:
+      containers:
+        - name: {{.service_name}}
+          image: {{.frontend_image}}
+          imagePullPolicy: IfNotPresent
+          ports:
+            - containerPort: {{.ops_port}}
+          env: {{range $key, $value := .environment_variables}}
+            - name: {{ $key }}
+              value: {{ $value }} {{end}} 

examples/variables.yaml

@@ -0,0 +1,11 @@
+variables:
+  service_name: nginx
+  version: 2
+  component: front-end
+  port: 80
+  frontend_max_replicas: 3
+  frontend_image: "nginx:latest"
+  environment_variables:
+    environment: production
+    api_url: "https://api.url.com"
+    project_name: website

go.mod

@@ -0,0 +1,5 @@
+module gotlet
+
+go 1.18
+
+require gopkg.in/yaml.v3 v3.0.1

go.sum

@@ -0,0 +1,4 @@
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

main.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"gotlet/pkg/colors"
+	"io/ioutil"
+	"os"
+)
+
+func main() {
+	if len(flag.Args()) == 0 {
+		fmt.Println("gotlet renders your variables into a template file.")
+	}
+
+	templateFile := flag.String("t", "", "Specify the template file path")
+	envPrefix := flag.String("p", "", "A prefix for filtering which env variables to include")
+	dataFile := flag.String("d", "", "Specify the data file containing the variables in Yaml")
+	outputPath := flag.String("o", "result.yaml", "Output file path")
+	printOutput := flag.Bool("v", false, "Print out the result in stdout")
+
+	flag.Parse()
+
+	if *templateFile == "" {
+		fmt.Println(colors.Red + "- The template file path is required, use -t flag")
+		os.Exit(1)
+	}
+
+	if *envPrefix == "" {
+		fmt.Println(colors.Yellow, "- No env variable prefix specified, loading all env variables.\n"+
+			"\tThis is not recommended, use -p flag to specify", colors.Reset)
+	}
+
+	data := &Model{
+		Variables: make(map[string]any),
+	}
+
+	err := getVariables(data, *dataFile)
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	addEnvVariables(data, *envPrefix)
+
+	result, err := renderTemplate(*templateFile, data)
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	if *outputPath != "" {
+		err = ioutil.WriteFile(*outputPath, result, 0644)
+		if err != nil {
+			fmt.Println(err)
+			os.Exit(1)
+		}
+	}
+
+	if *printOutput {
+		fmt.Println(string(result))
+	}
+}

pkg/colors/colors.go

@@ -0,0 +1,11 @@
+package colors
+
+var Reset = "\033[0m"
+var Red = "\033[31m"
+var Green = "\033[32m"
+var Yellow = "\033[33m"
+var Blue = "\033[34m"
+var Purple = "\033[35m"
+var Cyan = "\033[36m"
+var Gray = "\033[37m"
+var White = "\033[97m"

render.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"bytes"
+	"io/ioutil"
+	"text/template"
+)
+
+type Model struct {
+	Variables map[string]any
+}
+
+func renderTemplate(templateFile string, data *Model) ([]byte, error) {
+	originalContent, err := ioutil.ReadFile(templateFile)
+	if err != nil {
+		return nil, err
+	}
+
+	tmpl := template.New(templateFile)
+
+	t, err := tmpl.Parse(string(originalContent))
+	if err != nil {
+		return nil, err
+	}
+
+	renderedContent := new(bytes.Buffer)
+	err = t.Execute(renderedContent, data.Variables)
+	if err != nil {
+		return nil, err
+	}
+
+	return renderedContent.Bytes(), nil
+}

variables.go

@@ -0,0 +1,55 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+	"strings"
+
+	"gopkg.in/yaml.v3"
+)
+
+func getVariables(data *Model, variablesFile string) error {
+	if variablesFile != "" {
+		err := readVariables(data, variablesFile)
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func addEnvVariables(data *Model, envPrefix string) {
+	envs := envToMap()
+	for k, v := range envs {
+		if strings.HasPrefix(k, envPrefix) {
+			data.Variables[k] = v
+		}
+	}
+}
+
+func readVariables(m *Model, variables string) error {
+	yamlFile, err := ioutil.ReadFile(variables)
+	if err != nil {
+		return err
+	}
+
+	err = yaml.Unmarshal(yamlFile, m)
+	if err != nil {
+		return fmt.Errorf("yamlFile.Unmarshal error   #%w ", err)
+	}
+
+	return nil
+}
+
+func envToMap() map[string]string {
+	envMap := make(map[string]string)
+
+	for _, v := range os.Environ() {
+		splitV := strings.SplitN(v, "=", 2)
+		envMap[splitV[0]] = splitV[1]
+	}
+
+	return envMap
+}