New static configuration loading system.

Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>

pkg/cli/file_finder.go

@@ -0,0 +1,50 @@
+package cli
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// Finder holds a list of file paths.
+type Finder struct {
+	BasePaths  []string
+	Extensions []string
+}
+
+// Find returns the first valid existing file among configFile
+// and the paths already registered with Finder.
+func (f Finder) Find(configFile string) (string, error) {
+	paths := f.getPaths(configFile)
+
+	for _, filePath := range paths {
+		fp := os.ExpandEnv(filePath)
+
+		_, err := os.Stat(fp)
+		if os.IsNotExist(err) {
+			continue
+		}
+		if err != nil {
+			return "", err
+		}
+
+		return filepath.Abs(fp)
+	}
+
+	return "", nil
+}
+
+func (f Finder) getPaths(configFile string) []string {
+	var paths []string
+	if strings.TrimSpace(configFile) != "" {
+		paths = append(paths, configFile)
+	}
+
+	for _, basePath := range f.BasePaths {
+		for _, ext := range f.Extensions {
+			paths = append(paths, basePath+"."+ext)
+		}
+	}
+
+	return paths
+}