Refactor TUI rendering handling and general cleanup

Improves render handling by moving the responsibility of laying out the
whole UI from each view and into the main `tui` model. Our `ViewModel`
interface has now diverged from bubbletea's `Model` and introduces
individual `Header`, `Content`, and `Footer` methods for rendering those
UI elements.

Also moved away from using value receivers on our Update and View
functions (as is common across Bubbletea) to pointer receivers, which
cleaned up some of the weirder aspects of the code (e.g. before we
essentially had no choice but to do our rendering in `Update` in order
to calculate and update the final height of the main content's
`viewport`).

pkg/tui/views/conversations/conversations.go

@@ -27,29 +27,24 @@ type (
 )
 
 type Model struct {
-	*shared.ViewState
-	shared.Sections
-
-	App    *model.AppModel
-	cursor int
+	App   *model.AppModel
+	width int
+	height int
 
+	cursor      int
 	itemOffsets []int // conversation y offsets
 
 	content       viewport.Model
 	confirmPrompt bubbles.ConfirmPrompt
 }
 
-func Conversations(app *model.AppModel, shared shared.ViewState) Model {
+func Conversations(app *model.AppModel) *Model {
+	viewport.New(0, 0)
 	m := Model{
-		App:       app,
-		ViewState: &shared,
-		content:   viewport.New(0, 0),
+		App:     app,
+		content: viewport.New(0, 0),
 	}
-	return m
-}
-
-func (m Model) Initialized() bool {
-	return m.ViewState.Initialized
+	return &m
 }
 
 func (m *Model) handleInput(msg tea.KeyMsg) tea.Cmd {
@@ -129,12 +124,11 @@ func (m *Model) handleInput(msg tea.KeyMsg) tea.Cmd {
 	return nil
 }
 
-func (m Model) Init() tea.Cmd {
-	m.ViewState.Initialized = true
-	return m.loadConversations()
+func (m *Model) Init() tea.Cmd {
+	return nil
 }
 
-func (m Model) Update(msg tea.Msg) (shared.ViewModel, tea.Cmd) {
+func (m *Model) Update(msg tea.Msg) (shared.ViewModel, tea.Cmd) {
 	isInput := false
 	inputHandled := false
 
@@ -144,15 +138,14 @@ func (m Model) Update(msg tea.Msg) (shared.ViewModel, tea.Cmd) {
 		isInput = true
 		cmd := m.handleInput(msg)
 		if cmd != nil {
-			inputHandled = true
 			cmds = append(cmds, cmd)
+			inputHandled = true
 		}
 	case shared.MsgViewEnter:
 		cmds = append(cmds, m.loadConversations())
 		m.content.SetContent(m.renderConversationList())
 	case tea.WindowSizeMsg:
-		m.Width, m.Height = msg.Width, msg.Height
-		m.content.Width = msg.Width
+		m.width, m.height = msg.Width, msg.Height
 		m.content.SetContent(m.renderConversationList())
 	case msgConversationsLoaded:
 		m.App.Conversations = msg
@@ -171,26 +164,13 @@ func (m Model) Update(msg tea.Msg) (shared.ViewModel, tea.Cmd) {
 	}
 
 	if !isInput || !inputHandled {
-		var cmd tea.Cmd
-		m.content, cmd = m.content.Update(msg)
+		content, cmd := m.content.Update(msg)
+		m.content = content
 		if cmd != nil {
 			cmds = append(cmds, cmd)
 		}
 	}
 
-	if m.Width > 0 {
-		wrap := lipgloss.NewStyle().Width(m.Width)
-		m.Header = m.headerView()
-		m.Footer = "" // TODO: "Press ? for help"
-		if m.confirmPrompt.Focused() {
-			m.Footer = wrap.Render(m.confirmPrompt.View())
-		}
-		m.Error = tuiutil.ErrorBanner(m.Err, m.Width)
-		fixedHeight := tuiutil.Height(m.Header) + tuiutil.Height(m.Error) + tuiutil.Height(m.Footer)
-		m.content.Height = m.Height - fixedHeight
-		m.Content = m.content.View()
-	}
-
 	if len(cmds) > 0 {
 		return m, tea.Batch(cmds...)
 	}
@@ -218,32 +198,22 @@ func (m *Model) deleteConversation(conv api.Conversation) tea.Cmd {
 	}
 }
 
-func (m Model) View() string {
-	if m.Width == 0 {
-		return ""
-	}
-	sections := make([]string, 0, 6)
-
-	if m.Header != "" {
-		sections = append(sections, m.Header)
-	}
-
-	sections = append(sections, m.Content)
-	if m.Error != "" {
-		sections = append(sections, m.Error)
-	}
-
-	if m.Footer != "" {
-		sections = append(sections, m.Footer)
-	}
-
-	return lipgloss.JoinVertical(lipgloss.Left, sections...)
-}
-
-func (m *Model) headerView() string {
+func (m *Model) Header(width int) string {
 	titleStyle := lipgloss.NewStyle().Bold(true)
 	header := titleStyle.Render("Conversations")
-	return styles.Header.Width(m.Width).Render(header)
+	return styles.Header.Width(width).Render(header)
+}
+
+func (m *Model) Content(width int, height int) string {
+	m.content.Width, m.content.Height = width, height
+	return m.content.View()
+}
+
+func (m *Model) Footer(width int) string {
+	if m.confirmPrompt.Focused() {
+		return lipgloss.NewStyle().Width(width).Render(m.confirmPrompt.View())
+	}
+	return ""
 }
 
 func (m *Model) renderConversationList() string {
@@ -321,7 +291,7 @@ func (m *Model) renderConversationList() string {
 			tStyle = tStyle.Inherit(selectedStyle)
 		}
 
-		title := tStyle.Width(m.Width - 3).PaddingLeft(2).Render(c.Conv.Title)
+		title := tStyle.Width(m.width - 3).PaddingLeft(2).Render(c.Conv.Title)
 		if i == m.cursor {
 			title = ">" + title[1:]
 		}