refactor around config parsing

ocis-pkg/config/helpers.go

@@ -0,0 +1,80 @@
+package config
+
+import (
+	"io/fs"
+	"os"
+	"path/filepath"
+	"strings"
+
+	gofig "github.com/gookit/config/v2"
+	gooyaml "github.com/gookit/config/v2/yaml"
+)
+
+var (
+	defaultLocations = []string{
+		filepath.Join(os.Getenv("HOME"), "/.ocis/config"),
+		"/etc/ocis",
+		".config/",
+	}
+
+	// supportedExtensions is determined by gookit/config. For the purposes of the PR MVP we will focus on yaml, looking
+	// into extending it to all supported drivers.
+	supportedExtensions = []string{
+		"yaml",
+		"yml",
+	}
+)
+
+// DefaultConfigSources returns a slice with matched expected config files. It sugars coat several aspects of config file
+// management by assuming there are 3 default locations a config file could be.
+// It uses globbing to match a config file by name, and retrieve any supported extension supported by our drivers.
+// It sanitizes the output depending on the list of drivers provided.
+func DefaultConfigSources(filename string, drivers []string) []string {
+	var sources []string
+
+	for i := range defaultLocations {
+		_fs := os.DirFS(defaultLocations[i])
+		pattern := filename + ".*"
+		matched, _ := fs.Glob(_fs, pattern)
+		if len(matched) > 0 {
+			// prepend path to results
+			for j := 0; j < len(matched); j++ {
+				matched[j] = filepath.Join(defaultLocations[i], matched[j])
+			}
+		}
+		sources = append(sources, matched...)
+	}
+
+	return sanitizeExtensions(sources, drivers, func(a, b string) bool {
+		return strings.HasSuffix(filepath.Base(a), b)
+	})
+}
+
+// sanitizeExtensions removes elements from "set" which extensions are not in "ext".
+func sanitizeExtensions(set []string, ext []string, f func(a, b string) bool) []string {
+	var r []string
+	for i := 0; i < len(set); i++ {
+		for j := 0; j < len(ext); j++ {
+			if f(filepath.Base(set[i]), ext[j]) {
+				r = append(r, set[i])
+			}
+		}
+	}
+	return r
+}
+
+// BindSourcesToStructs assigns any config value from a config file / env variable to struct `dst`. Its only purpose
+// is to solely modify `dst`, not dealing with the config structs; and do so in a thread safe manner.
+func BindSourcesToStructs(extension string, dst interface{}) error {
+	sources := DefaultConfigSources(extension, supportedExtensions)
+	cnf := gofig.NewWithOptions("proxy", gofig.ParseEnv)
+	cnf.AddDriver(gooyaml.Driver)
+	_ = cnf.LoadFiles(sources...)
+
+	err := cnf.BindStruct("", &dst)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}