X-Git-Url: http://git.giacomolli.uk/onechat/blobdiff_plain/6844f8c992ec4e276a3a0d93b544de0127eebbd2..723f6e18adc6482ed913e1618c8a76e981720c2b:/memory.go?ds=sidebyside

diff --git a/memory.go b/memory.go
index c9fe1c5..a240b6c 100644
--- a/memory.go
+++ b/memory.go
@@ -149,6 +149,11 @@ func (m *Memory) AppendDated(kind, text, date string) (Message, error) {
 	m.mutex.Lock()
 	defer m.mutex.Unlock()
 
+	return m.appendDated(kind, text, date)
+}
+
+// appendDated appends under the memory lock and updates the views and builds.
+func (m *Memory) appendDated(kind, text, date string) (Message, error) {
 	message, err := m.log.AppendDated(kind, text, date)
 	if err != nil {
 		return Message{}, fmt.Errorf("append dated log message: %w", err)
@@ -172,6 +177,44 @@ func (m *Memory) AppendDated(kind, text, date string) (Message, error) {
 	return message, nil
 }
 
+// AppendOnce appends a queued message. prepare saves its log ID before the
+// append, under the memory lock. A saved ID permits recovery after a stop
+// between that save and the append, without a second log entry. prepare must
+// not call Memory. The caller stops delivery after a failed append.
+func (m *Memory) AppendOnce(kind, text string, id *int, prepare func(int) error) (Message, error) {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	if id != nil && *id < m.log.Len() {
+		message, err := m.log.Message(*id)
+		if err != nil {
+			return Message{}, fmt.Errorf("read queued message: %w", err)
+		}
+
+		if message.Kind != kind || message.Text != text {
+			return Message{}, errors.New("queued message does not match its log entry")
+		}
+
+		return message, nil
+	}
+
+	if id != nil && *id != m.log.Len() {
+		return Message{}, errors.New("queued message is beyond the log")
+	}
+
+	err := prepare(m.log.Len())
+	if err != nil {
+		return Message{}, fmt.Errorf("prepare queued message: %w", err)
+	}
+
+	message, err := m.appendDated(kind, text, "")
+	if err != nil {
+		return Message{}, fmt.Errorf("append queued message: %w", err)
+	}
+
+	return message, nil
+}
+
 // children reads the two children of the node key.
 func (m *Memory) children(key NodeKey) (Node, Node, error) {
 	var children [2]Node