create internal/cnf generic loader

internal/cnf/common.go

@@ -4,16 +4,6 @@ import (
 	"io"
 )
 
-// Field generic representation (root, branch or leaf)
-type Field struct {
-	// Label of the current field
-	Label string
-	// Value of the current field
-	Value string
-	// Children of the current field or NIL if none
-	Children []Field
-}
-
 // ConfigurationFormat is the common interface for all configuration parser
 type ConfigurationFormat interface {
 	// Parse the given file

internal/cnf/loader.go

@@ -0,0 +1,81 @@
+package cnf
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+)
+
+var ErrUnknownExtension = errors.New("unknown extension format")
+
+// Load the current file and create the configuration format accordingly
+func Load(path string) (ConfigurationFormat, error) {
+
+	var confFormat ConfigurationFormat
+
+	// 1. check file
+	if _, err := os.Stat(path); os.IsNotExist(err) {
+		return nil, fmt.Errorf("cannot find file '%s'", path)
+	}
+
+	// 2. Try to load from extension
+	extension := filepath.Ext(path)
+	if len(extension) > 0 {
+
+		confFormat = loadFromExtension(extension)
+		if confFormat == nil {
+			return nil, ErrUnknownExtension
+		}
+
+		// open file
+		file, err := os.Open(path)
+		if err != nil {
+			return nil, err
+		}
+		defer file.Close()
+
+		// parse
+		err = confFormat.Parse(file)
+		if err != nil {
+			return nil, fmt.Errorf("cannot parse file as '%s' | %s", extension, err)
+		}
+
+		return confFormat, nil
+
+	}
+
+	// 3. open file
+	file, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer file.Close()
+
+	// 4. Try to guess from the content
+	confFormat = loadFromContent(file)
+	if confFormat == nil {
+		return nil, fmt.Errorf("cannot infer format from content")
+	}
+
+	return confFormat, nil
+}
+
+func loadFromExtension(ext string) ConfigurationFormat {
+
+	var confFormat ConfigurationFormat
+
+	// select configuration or fail if not known
+	switch ext {
+	case "json":
+		return new(Json)
+	default:
+		return nil
+	}
+
+}
+
+func loadFromContent(file io.Reader) ConfigurationFormat {
+	return nil
+}