accept -archive to push -f Done into -archive Done

cmd/main.go

@@ -30,6 +30,8 @@ func _main() error {
 
 	if config.target2 != "" {
 		return merge(&config)
+	} else if config.archive != "" {
+		return archive(&config)
 	} else {
 		if err := add(&config); err != nil {
 			return err
@@ -41,6 +43,60 @@ func _main() error {
 	}
 }
 
+func archive(config *config) error {
+	if config.archive == "" {
+		return nil
+	}
+
+	baseReader, err := filePathReader(config.target)
+	if err != nil {
+		return err
+	}
+	baseB, err := ioutil.ReadAll(baseReader)
+	if err != nil {
+		return err
+	}
+
+	archiveReader, err := filePathReader(config.archive)
+	if err != nil {
+		return err
+	}
+	archiveB, err := ioutil.ReadAll(archiveReader)
+	if err != nil {
+		return err
+	}
+
+	var base, archive pttodo.Root
+	if err := yaml.Unmarshal(baseB, &base); err != nil {
+		return err
+	}
+	if err := yaml.Unmarshal(archiveB, &archive); err != nil {
+		return err
+	}
+
+	archive.Done = append(archive.Done, base.Done...)
+	if tmppath2, err := marshalRootToTempFile(archive); err != nil {
+		return err
+	} else if config.dryRun {
+	} else if err := rename(tmppath2, config.archive); err != nil {
+		return err
+	}
+
+	base.Done = base.Done[:0]
+	if tmppath, err := marshalRootToTempFile(base); err != nil {
+		return err
+	} else if config.dryRun {
+		log.Println("===before===")
+		_dump(os.Stdout, []string{config.target}, config.tags, config.search, config.root)
+		log.Println("===after===")
+		_dump(os.Stdout, []string{tmppath}, config.tags, config.search, config.root)
+	} else if err := rename(tmppath, config.target); err != nil {
+		return err
+	}
+
+	return nil
+}
+
 func merge(config *config) error {
 	if config.target2 == "" {
 		return nil