Add LastMessageAt field to conversation

Replaced `LatestConversationMessages` with `LoadConversationList`, which
utilizes `LastMessageAt` for much faster conversation loading in the
conversation listing TUI and `lmcli list` command.

pkg/conversation/conversation.go

@@ -17,6 +17,7 @@ type Conversation struct {
 	SelectedRootID *uint
 	SelectedRoot   *Message  `gorm:"foreignKey:SelectedRootID"`
 	RootMessages   []Message `gorm:"-:all"`
+	LastMessageAt  time.Time
 }
 
 type MessageMeta struct {

pkg/conversation/repo.go

@@ -15,8 +15,7 @@ import (
 // Repo exposes low-level message and conversation management. See
 // Service for high-level helpers
 type Repo interface {
-	// LatestConversationMessages returns a slice of all conversations ordered by when they were last updated (newest to oldest)
-	LatestConversationMessages() ([]Message, error)
+	LoadConversationList() (ConversationList, error)
 
 	FindConversationByShortName(shortName string) (*Conversation, error)
 	ConversationShortNameCompletions(search string) []string
@@ -72,25 +71,40 @@ func NewRepo(db *gorm.DB) (Repo, error) {
 	return &repo{db, _sqids}, nil
 }
 
-func (s *repo) LatestConversationMessages() ([]Message, error) {
-	var latestMessages []Message
+type conversationListItem struct {
+	ID            uint
+	ShortName     string
+	Title         string
+	LastMessageAt time.Time
+}
 
-	subQuery := s.db.Model(&Message{}).
-		Select("MAX(created_at) as max_created_at, conversation_id").
-		Group("conversation_id")
+type ConversationList struct {
+	Total int
+	Items []conversationListItem
+}
 
-	err := s.db.Model(&Message{}).
-		Joins("JOIN (?) as sub on messages.conversation_id = sub.conversation_id AND messages.created_at = sub.max_created_at", subQuery).
-		Group("messages.conversation_id").
-		Order("created_at DESC").
-		Preload("Conversation.SelectedRoot").
-		Find(&latestMessages).Error
+// LoadConversationList loads existing conversations, ordered by the date
+// of their latest message, from most recent to oldest.
+func (s *repo) LoadConversationList() (ConversationList, error) {
+	list := ConversationList{}
 
+	var convos []Conversation
+	err := s.db.Order("last_message_at DESC").Find(&convos).Error
 	if err != nil {
-		return nil, err
+		return list, err
 	}
 
-	return latestMessages, nil
+	for _, c := range convos {
+		list.Items = append(list.Items, conversationListItem{
+			ID:            c.ID,
+			ShortName:     c.ShortName.String,
+			Title:         c.Title,
+			LastMessageAt: c.LastMessageAt,
+		})
+	}
+
+	list.Total = len(list.Items)
+	return list, nil
 }
 
 func (s *repo) FindConversationByShortName(shortName string) (*Conversation, error) {
@@ -220,6 +234,9 @@ func (s *repo) Reply(to *Message, messages ...Message) ([]Message, error) {
 			savedMessages = append(savedMessages, message)
 			currentParent = &message
 		}
+
+		to.Conversation.LastMessageAt = savedMessages[len(savedMessages)-1].CreatedAt
+		s.UpdateConversation(to.Conversation)
 		return nil
 	})
 
@@ -427,10 +444,7 @@ func (s *repo) StartConversation(messages ...Message) (*Conversation, []Message,
 	// Update conversation's selected root message
 	conversation.RootMessages = []Message{messages[0]}
 	conversation.SelectedRoot = &messages[0]
-	err = s.UpdateConversation(conversation)
-	if err != nil {
-		return nil, nil, err
-	}
+	conversation.LastMessageAt = messages[0].CreatedAt
 
 	// Add additional replies to conversation
 	if len(messages) > 1 {
@@ -439,10 +453,12 @@ func (s *repo) StartConversation(messages ...Message) (*Conversation, []Message,
 			return nil, nil, err
 		}
 		messages = append([]Message{messages[0]}, newMessages...)
+		conversation.LastMessageAt = messages[len(messages)-1].CreatedAt
 	}
-	return conversation, messages, nil
-}
 
+	err = s.UpdateConversation(conversation)
+	return conversation, messages, err
+}
 
 // CloneConversation clones the given conversation and all of its meesages
 func (s *repo) CloneConversation(toClone Conversation) (*Conversation, uint, error) {