add dump refereence env provider

provider/env/provider.go

@@ -3,10 +3,14 @@ package env
 import (
 	"context"
 	"fmt"
+	"io"
 	"os"
 	"strings"
 
 	"gitoa.ru/go-4devs/config"
+	"gitoa.ru/go-4devs/config/definition/option"
+	"gitoa.ru/go-4devs/config/key"
+	"gitoa.ru/go-4devs/config/param"
 	"gitoa.ru/go-4devs/config/value"
 )
 
@@ -42,15 +46,68 @@ type Provider struct {
 	prefix string
 }
 
+func (p *Provider) Key(path ...string) string {
+	return p.prefix + p.key(path...)
+}
+
 func (p *Provider) Name() string {
 	return p.name
 }
 
 func (p *Provider) Value(_ context.Context, path ...string) (config.Value, error) {
-	name := p.prefix + p.key(path...)
+	if val, ok := os.LookupEnv(p.Key(path...)); ok {
-	if val, ok := os.LookupEnv(name); ok {
 		return value.JString(val), nil
 	}
 
 	return nil, fmt.Errorf("%v:%w", p.Name(), config.ErrNotFound)
 }
+
+func (p *Provider) DumpReference(_ context.Context, w io.Writer, opt config.Options) error {
+	return p.writeOptions(w, opt)
+}
+
+func (p *Provider) writeOptions(w io.Writer, opt config.Options, key ...string) error {
+	for idx, option := range opt.Options() {
+		if err := p.writeOption(w, option, key...); err != nil {
+			return fmt.Errorf("option[%d]:%w", idx, err)
+		}
+	}
+
+	return nil
+}
+
+func (p *Provider) writeOption(w io.Writer, opt config.Option, keys ...string) error {
+	if desc := param.Description(opt); desc != "" {
+		if _, derr := fmt.Fprintf(w, "# %v.\n", desc); derr != nil {
+			return fmt.Errorf("write description:%w", derr)
+		}
+	}
+
+	var err error
+
+	switch one := opt.(type) {
+	case config.Group:
+		err = p.writeOptions(w, one, append(keys, one.Name())...)
+	case config.Options:
+		err = p.writeOptions(w, one, keys...)
+	default:
+		def, dok := option.DataDefaut(opt)
+
+		prefix := ""
+		if !dok || key.IsWild(keys...) {
+			prefix = "#"
+		}
+
+		if !dok {
+			def = ""
+		}
+
+		_, err = fmt.Fprintf(w, "%s%s=%v\n", prefix, p.Key(append(keys, one.Name())...), def)
+	}
+
+	if err != nil {
+		return fmt.Errorf("%w", err)
+	}
+
+	return nil
+}

provider/env/provider_test.go

@@ -1,10 +1,17 @@
 package env_test
 
 import (
+	"bytes"
+	"context"
 	"testing"
 
+	"gitoa.ru/go-4devs/config"
+	"gitoa.ru/go-4devs/config/definition/group"
+	"gitoa.ru/go-4devs/config/definition/option"
+	"gitoa.ru/go-4devs/config/definition/proto"
 	"gitoa.ru/go-4devs/config/provider/env"
 	"gitoa.ru/go-4devs/config/test"
+	"gitoa.ru/go-4devs/config/test/require"
 )
 
 func TestProvider(t *testing.T) {
@@ -19,3 +26,35 @@ func TestProvider(t *testing.T) {
 	}
 	test.Run(t, provider, read)
 }
+
+func TestProvider_DumpReference(t *testing.T) {
+	t.Parallel()
+
+	const expect = `# configure log.
+# level.
+FDEVS_CONFIG_LOG_LEVEL=info
+# configure log service.
+# level.
+#FDEVS_CONFIG_LOG_{SERVICE}_LEVEL=
+`
+
+	ctx := context.Background()
+	prov := env.New("fdevs", "config")
+	buf := bytes.NewBuffer(nil)
+
+	require.NoError(t, prov.DumpReference(ctx, buf, testOptions(t)))
+	require.Equal(t, buf.String(), expect)
+}
+
+func testOptions(t *testing.T) config.Options {
+	t.Helper()
+
+	return group.New("test", "test",
+		group.New("log", "configure log",
+			option.String("level", "level", option.Default("info")),
+			proto.New("service", "configure log service",
+				option.String("level", "level"),
+			),
+		),
+	)
+}