defer db.Close and yaml writes to disk if $W

main.go

@@ -19,6 +19,7 @@ type (
 		LastAnswer(string, string) (string, Answer)
 		Answer(string) Answer
 		PushAnswer(string, string, string, bool) error
+		Close()
 	}
 	Question struct {
 		Q     string
@@ -49,6 +50,7 @@ func Main() error {
 	if err != nil {
 		return err
 	}
+	defer db.Close()
 	user := os.Getenv("USER")
 	for q, _ := range db.HistoryOf(user) {
 		if time.Until(db.Next(user, q)) > 0 {

yamldb.go

@@ -10,6 +10,7 @@ import (
 
 type (
 	yamlDB struct {
+		addr      string
 		Knowledge knowledge
 		Users     map[string]user
 		Cadence   []duration
@@ -29,6 +30,7 @@ type (
 
 func newYamlDB(p string) (yamlDB, error) {
 	db := yamlDB{
+		addr: p,
 		Knowledge: knowledge{
 			Questions: map[string]Question{},
 			Answers:   map[string]Answer{},
@@ -44,6 +46,22 @@ func newYamlDB(p string) (yamlDB, error) {
 	return db, nil
 }
 
+func (db yamlDB) Close() {
+	if os.Getenv("W") == "" {
+		return
+	}
+	b, err := yaml.Marshal(db)
+	if err != nil {
+		panic(err)
+	}
+	if err := os.Rename(db.addr, db.addr+".bak"); err != nil {
+		panic(err)
+	}
+	if err := os.WriteFile(db.addr, b, os.ModePerm); err != nil {
+		panic(err)
+	}
+}
+
 func (db yamlDB) HistoryOf(user string) map[string][]History {
 	result := map[string][]History{}
 	for k, v := range db.Users[user].History {