GenerateFileFromTemplate in generic pkg (#48)

* generic pkg

Signed-off-by: Alfredo Garo <[email protected]>

* PR feedback: no _

Signed-off-by: Alfredo Garo <[email protected]>

* PR feedback: generic to common

Signed-off-by: Alfredo Garo <[email protected]>

* PR feedback: Fallback to Default

Signed-off-by: Alfredo Garo <[email protected]>

.gitignore

@@ -1,3 +1,4 @@
 .vscode
 .DS_Store
-*.test
+*.test
+test/templates/generated_*

pkg/common/common.go

@@ -0,0 +1,94 @@
+/*
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package common provides functions and steps implementations not specifically related to Kubernetes nor AWS.
+package common
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"text/template"
+
+	"github.com/pkg/errors"
+	log "github.com/sirupsen/logrus"
+)
+
+type TemplateArgument struct {
+	Key                 string
+	EnvironmentVariable string
+	Default             string
+	Mandatory           bool
+}
+
+// GetValue returns the value of the Environment Variable defined by 'TemplateArgument.EnvironmentVariable'.
+// If 'TemplateArgument.EnvironmentVariable' is empty or the ENV. VAR. it defines is unset, 'TemplateArgument.Default' is returned.
+// That is, if 'TemplateArgument.Mandatory' is not 'true', in which case, an error is returned.
+func (ta TemplateArgument) GetValue() (string, error) {
+	if ta.Key == "" {
+		return "", errors.Errorf("'TemplateArgument.Key' can not be empty.")
+	} else if value, ok := os.LookupEnv(ta.EnvironmentVariable); ok {
+		return value, nil
+	} else if ta.Mandatory {
+		return "", errors.Errorf("'TemplateArgument.Mandatory'='true' but the Environment Variable '%s' defined by 'TemplateArgument.EnvironmentVariable' is not set", ta.EnvironmentVariable)
+	} else {
+		return ta.Default, nil
+	}
+}
+
+// TemplateArgumentsToMap uses the elements of 'templateArguments' to populate the key:value pairs of the returned map.
+// The key is the '.Key' variable of the corresponding element, and the value is the string returned by the 'GetValue' method of said element.
+func TemplateArgumentsToMap(templateArguments ...TemplateArgument) (map[string]string, error) {
+	args := map[string]string{}
+	for i, ta := range templateArguments {
+		value, err := ta.GetValue()
+		if err != nil {
+			return args, errors.Errorf("'templateArguments[%d].GetValue()' failed. 'templateArguments[%d]'='%v'. error: '%v'", i, i, ta, err)
+		}
+		args[ta.Key] = value
+	}
+	return args, nil
+}
+
+// GenerateFileFromTemplate applies the template defined in templatedFilePath to templateArgs.
+// The generated file will be named 'generated_<templated-file-base>' and it will be created in the same directory of the template.
+func GenerateFileFromTemplate(templatedFilePath string, templateArgs interface{}) (string, error) {
+	t, err := template.ParseFiles(templatedFilePath)
+	if err != nil {
+		return "", errors.Errorf("Error parsing templated file '%s': %v", templatedFilePath, err)
+	}
+
+	templatedFileDir := filepath.Dir(templatedFilePath)
+	templatedFileName := filepath.Base(templatedFilePath)
+	generatedFilePath := filepath.Join(templatedFileDir, "generated_"+templatedFileName)
+	f, err := os.Create(generatedFilePath)
+	if err != nil {
+		return "", errors.Errorf("Error creating generated file '%s': %v", generatedFilePath, err)
+	}
+	defer f.Close()
+
+	err = t.Execute(f, templateArgs)
+	if err != nil {
+		return "", errors.Errorf("Error executing template '%v' against '%s': %v", templateArgs, templatedFilePath, err)
+	}
+
+	generated, err := ioutil.ReadFile(generatedFilePath)
+	if err != nil {
+		return "", errors.Errorf("Error reading generated file '%s': %v", generatedFilePath, err)
+	}
+
+	log.Infof("Generated file '%s': \n %s", generatedFilePath, string(generated))
+
+	return generatedFilePath, nil
+}