feat: auto generate example env file (#647)

* feat: auto generate example env file

* refactor: simplify build paths func and better slice handling

* chore: forgot to stage everything

* chore: review comments

* refactor: remove square brackets because they mess up the syntax
highlighting

* refactor: use lowercase name to mark dynamic values

gen/gen_env.go

@@ -0,0 +1,137 @@
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"log/slog"
+	"os"
+	"reflect"
+	"strings"
+
+	"github.com/steveiliop56/tinyauth/internal/config"
+)
+
+type Path struct {
+	Name        string
+	Description string
+	Value       any
+}
+
+func generateExampleEnv() {
+	cfg := config.NewDefaultConfiguration()
+	paths := make([]Path, 0)
+
+	root := reflect.TypeOf(cfg).Elem()
+	rootValue := reflect.ValueOf(cfg).Elem()
+	rootPath := "TINYAUTH_"
+
+	buildPaths(root, rootValue, rootPath, &paths)
+	compiled := compileEnv(paths)
+
+	err := os.Remove(".env.example")
+	if err != nil {
+		slog.Error("failed to remove example env file", "error", err)
+		os.Exit(1)
+	}
+
+	err = os.WriteFile(".env.example", compiled, 0644)
+	if err != nil {
+		slog.Error("failed to write example env file", "error", err)
+		os.Exit(1)
+	}
+}
+
+func buildPaths(parent reflect.Type, parentValue reflect.Value, parentPath string, paths *[]Path) {
+	for i := 0; i < parent.NumField(); i++ {
+		field := parent.Field(i)
+		fieldType := field.Type
+		fieldValue := parentValue.Field(i)
+		switch fieldType.Kind() {
+		case reflect.Struct:
+			childPath := parentPath + strings.ToUpper(field.Name) + "_"
+			buildPaths(fieldType, fieldValue, childPath, paths)
+		case reflect.Map:
+			buildMapPaths(field, parentPath, paths)
+		case reflect.Bool, reflect.String, reflect.Slice, reflect.Int:
+			buildPath(field, fieldValue, parentPath, paths)
+		default:
+			slog.Info("unknown type", "type", fieldType.Kind())
+		}
+	}
+}
+
+func buildPath(field reflect.StructField, fieldValue reflect.Value, parent string, paths *[]Path) {
+	desc := field.Tag.Get("description")
+	yamlTag := field.Tag.Get("yaml")
+
+	// probably internal logic, should be skipped
+	if yamlTag == "-" {
+		return
+	}
+
+	defaultValue := fieldValue.Interface()
+
+	path := Path{
+		Name:        parent + strings.ToUpper(field.Name),
+		Description: desc,
+	}
+
+	switch fieldValue.Kind() {
+	case reflect.Slice:
+		sl, ok := defaultValue.([]string)
+		if !ok {
+			slog.Error("invalid default value", "value", defaultValue)
+			return
+		}
+		path.Value = strings.Join(sl, ",")
+	case reflect.String:
+		st, ok := defaultValue.(string)
+		if !ok {
+			slog.Error("invalid default value", "value", defaultValue)
+			return
+		}
+		// good idea to escape strings probably
+		if st != "" {
+			path.Value = fmt.Sprintf(`"%s"`, st)
+		} else {
+			path.Value = ""
+		}
+	default:
+		path.Value = defaultValue
+	}
+	*paths = append(*paths, path)
+}
+
+func buildMapPaths(field reflect.StructField, parentPath string, paths *[]Path) {
+	fieldType := field.Type
+
+	if fieldType.Key().Kind() != reflect.String {
+		slog.Info("unsupported map key type", "type", fieldType.Key().Kind())
+		return
+	}
+
+	mapPath := parentPath + strings.ToUpper(field.Name) + "_name_"
+	valueType := fieldType.Elem()
+
+	if valueType.Kind() == reflect.Struct {
+		zeroValue := reflect.New(valueType).Elem()
+		buildPaths(valueType, zeroValue, mapPath, paths)
+	}
+}
+
+func compileEnv(paths []Path) []byte {
+	buffer := bytes.Buffer{}
+	buffer.WriteString("# Tinyauth example configuration\n\n")
+
+	for _, path := range paths {
+		buffer.WriteString("# ")
+		buffer.WriteString(path.Description)
+		buffer.WriteString("\n")
+		buffer.WriteString(path.Name)
+		buffer.WriteString("=")
+		fmt.Fprintf(&buffer, "%v", path.Value)
+		buffer.WriteString("\n\n")
+	}
+
+	return buffer.Bytes()
+}