tui: cache highlighted messages

Syntax highlighting is fairly expensive, and this means we no longer
need to do syntax highlighting on the entire conversaion each time a new
message chunk is received

pkg/tui/tui.go

@@ -43,6 +43,7 @@ type model struct {
 	// ui state
 	focus          focusState
 	status         string   // a general status message
+	highlightCache []string // a cache of syntax highlighted message content
 
 	// ui elements
 	content viewport.Model
@@ -132,15 +133,15 @@ func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 		m.conversation = (*models.Conversation)(msg)
 		cmd = m.loadMessages(m.conversation)
 	case msgMessagesLoaded:
-		m.messages = []models.Message(msg)
+		m.setMessages(msg)
 		m.updateContent()
 	case msgResponseChunk:
 		chunk := string(msg)
 		last := len(m.messages) - 1
 		if last >= 0 && m.messages[last].Role == models.MessageRoleAssistant {
-			m.messages[last].Content += chunk
+			m.setMessageContents(last, m.messages[last].Content+chunk)
 		} else {
-			m.messages = append(m.messages, models.Message{
+			m.addMessage(models.Message{
 				Role:    models.MessageRoleAssistant,
 				Content: chunk,
 			})
@@ -155,9 +156,9 @@ func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
 			panic("Unexpected messages length handling msgReply")
 		}
 		if reply.Role == models.MessageRoleToolCall && m.messages[last].Role == models.MessageRoleAssistant {
-			m.messages[last] = reply
+			m.setMessage(last, reply)
 		} else if reply.Role != models.MessageRoleAssistant {
-			m.messages = append(m.messages, reply)
+			m.addMessage(reply)
 		}
 		m.updateContent()
 		cmd = m.waitForReply()
@@ -239,7 +240,7 @@ func (m *model) handleInputKey(msg tea.KeyMsg) tea.Cmd {
 			return nil
 		}
 		m.input.SetValue("")
-		m.messages = append(m.messages, models.Message{
+		m.addMessage(models.Message{
 			Role:    models.MessageRoleUser,
 			Content: userInput,
 		})
@@ -322,6 +323,40 @@ func (m *model) promptLLM() tea.Cmd {
 	}
 }
 
+func (m *model) setMessages(messages []models.Message) {
+	m.messages = messages
+	m.highlightCache = make([]string, len(messages))
+	for i, msg := range m.messages {
+		highlighted, _ := m.ctx.Chroma.HighlightS(msg.Content)
+		m.highlightCache[i] = highlighted
+	}
+}
+
+func (m *model) setMessage(i int, msg models.Message) {
+	if i >= len(m.messages) {
+		panic("i out of range")
+	}
+	highlighted, _ := m.ctx.Chroma.HighlightS(msg.Content)
+	m.messages[i] = msg
+	m.highlightCache[i] = highlighted
+}
+
+func (m *model) addMessage(msg models.Message) {
+	highlighted, _ := m.ctx.Chroma.HighlightS(msg.Content)
+	m.messages = append(m.messages, msg)
+	m.highlightCache = append(m.highlightCache, highlighted)
+}
+
+func (m *model) setMessageContents(i int, content string) {
+	if i >= len(m.messages) {
+		panic("i out of range")
+	}
+	highlighted, _ := m.ctx.Chroma.HighlightS(content)
+	m.messages[i].Content = content
+	m.highlightCache[i] = highlighted
+}
+
+// render the conversation into the main viewport
 func (m *model) updateContent() {
 	sb := strings.Builder{}
 	msgCnt := len(m.messages)
@@ -342,10 +377,22 @@ func (m *model) updateContent() {
 			icon = "🔧"
 		}
 
-		sb.WriteString(fmt.Sprintf("%s\n\n", style.Render(icon + friendly)))
+		// write message heading with space for content
+		header := fmt.Sprintf("%s\n\n", style.Render(icon+friendly))
+		sb.WriteString(header)
+
+		// TODO: render something for tool calls/results?
+
+		// write message contents
+		var highlighted string
+		if m.highlightCache[i] == "" {
+			highlighted = message.Content
+		} else {
+			highlighted = m.highlightCache[i]
+		}
+		contents := messageStyle.Width(m.content.Width - 5).Render(highlighted)
+		sb.WriteString(contents)
 
-		highlighted, _ := m.ctx.Chroma.HighlightS(message.Content)
-		sb.WriteString(messageStyle.Width(m.content.Width - 5).Render(highlighted))
 		if i < msgCnt-1 {
 			sb.WriteString("\n\n")
 		}
@@ -389,7 +436,6 @@ func (m *model) footerView() string {
 	}
 
 	footer := lipgloss.JoinHorizontal(lipgloss.Center, left, padding, right)
-
 	return footerStyle.Width(m.content.Width).Render(footer)
 }