chore: tidy up pkgs (#636)

for readability and towards potentially making helmfile usable as a go library

pkg/tmpl/file_renderer.go

@@ -0,0 +1,78 @@
+package tmpl
+
+import (
+	"bytes"
+	"io/ioutil"
+
+	"fmt"
+	"strings"
+)
+
+type FileRenderer struct {
+	ReadFile func(string) ([]byte, error)
+	Context  *Context
+	Data     interface{}
+}
+
+func NewFileRenderer(readFile func(filename string) ([]byte, error), basePath string, data interface{}) *FileRenderer {
+	return &FileRenderer{
+		ReadFile: readFile,
+		Context: &Context{
+			basePath: basePath,
+			readFile: readFile,
+		},
+		Data: data,
+	}
+}
+
+func NewFirstPassRenderer(basePath string, data interface{}) *FileRenderer {
+	return &FileRenderer{
+		ReadFile: ioutil.ReadFile,
+		Context: &Context{
+			preRender: true,
+			basePath:  basePath,
+			readFile:  ioutil.ReadFile,
+		},
+		Data: data,
+	}
+}
+
+func (r *FileRenderer) RenderTemplateFileToBuffer(file string) (*bytes.Buffer, error) {
+	content, err := r.ReadFile(file)
+	if err != nil {
+		return nil, err
+	}
+
+	return r.RenderTemplateContentToBuffer(content)
+}
+
+func (r *FileRenderer) RenderToBytes(path string) ([]byte, error) {
+	var yamlBytes []byte
+	splits := strings.Split(path, ".")
+	if len(splits) > 0 && splits[len(splits)-1] == "gotmpl" {
+		yamlBuf, err := r.RenderTemplateFileToBuffer(path)
+		if err != nil {
+			return nil, fmt.Errorf("failed to render [%s], because of %v", path, err)
+		}
+		yamlBytes = yamlBuf.Bytes()
+	} else {
+		var err error
+		yamlBytes, err = r.ReadFile(path)
+		if err != nil {
+			return nil, fmt.Errorf("failed to load [%s]: %v", path, err)
+		}
+	}
+	return yamlBytes, nil
+}
+
+func (r *FileRenderer) RenderTemplateContentToBuffer(content []byte) (*bytes.Buffer, error) {
+	return r.Context.RenderTemplateToBuffer(string(content), r.Data)
+}
+
+func (r *FileRenderer) RenderTemplateContentToString(content []byte) (string, error) {
+	buf, err := r.Context.RenderTemplateToBuffer(string(content), r.Data)
+	if err != nil {
+		return "", err
+	}
+	return buf.String(), nil
+}