fix(table): append headers/columns to zero sized string slice

There are many "interesting" cases:

- logical content is wider than display width (long lines).
  In this case, we truncate.
- logical content is smaller than display height (fewer lines
  than visible).
  In this case, we pad with empty lines up to the specified height.
- logical content is higher than display height (more lines than
  visible).
  In this case, we truncate.

- style specifies a width wider than the display width.
  In this case, we ignore the style width and
  fit in the display width.
- style specifies a height higher than the display height.
  Same as width, we ignore the style and fit in the display height.
- style specifies a narrower width or smaller height than the display.
  In this case we obey the style.

table/table.go

@@ -59,11 +59,11 @@ func DefaultKeyMap() KeyMap {
 		),
 		PageUp: key.NewBinding(
 			key.WithKeys("b", "pgup"),
-			key.WithHelp("b", "page up"),
+			key.WithHelp("b/pgup", "page up"),
 		),
 		PageDown: key.NewBinding(
-			key.WithKeys("f", "pgup", spacebar),
-			key.WithHelp("f", "page down"),
+			key.WithKeys("f", "pgdown", spacebar),
+			key.WithHelp("f/pgdn", "page down"),
 		),
 		HalfPageUp: key.NewBinding(
 			key.WithKeys("u", "ctrl+u"),
@@ -291,6 +291,12 @@ func (m Model) Cursor() int {
 	return m.cursor
 }
 
+// SetCursor sets the cursor position in the table.
+func (m *Model) SetCursor(n int) {
+	m.cursor = clamp(n, 0, len(m.rows)-1)
+	m.UpdateViewport()
+}
+
 // MoveUp moves the selection up by any number of row.
 // It can not go above the first row.
 func (m *Model) MoveUp(n int) {
@@ -340,7 +346,7 @@ func (m *Model) FromValues(value, separator string) {
 }
 
 func (m Model) headersView() string {
-	var s = make([]string, len(m.cols))
+	var s = make([]string, 0, len(m.cols))
 	for _, col := range m.cols {
 		style := lipgloss.NewStyle().Width(col.Width).MaxWidth(col.Width).Inline(true)
 		renderedCell := style.Render(runewidth.Truncate(col.Title, col.Width, "…"))
@@ -350,7 +356,7 @@ func (m Model) headersView() string {
 }
 
 func (m *Model) renderRow(rowID int) string {
-	var s = make([]string, len(m.cols))
+	var s = make([]string, 0, len(m.cols))
 	for i, value := range m.rows[rowID] {
 		style := lipgloss.NewStyle().Width(m.cols[i].Width).MaxWidth(m.cols[i].Width).Inline(true)
 		renderedCell := m.styles.Cell.Render(style.Render(runewidth.Truncate(value, m.cols[i].Width, "…")))

textarea/textarea.go

@@ -46,6 +46,14 @@ type KeyMap struct {
 	Paste                   key.Binding
 	WordBackward            key.Binding
 	WordForward             key.Binding
+	InputBegin              key.Binding
+	InputEnd                key.Binding
+
+	UppercaseWordForward  key.Binding
+	LowercaseWordForward  key.Binding
+	CapitalizeWordForward key.Binding
+
+	TransposeCharacterBackward key.Binding
 }
 
 // DefaultKeyMap is the default set of key bindings for navigating and acting
@@ -67,6 +75,14 @@ var DefaultKeyMap = KeyMap{
 	LineStart:               key.NewBinding(key.WithKeys("home", "ctrl+a")),
 	LineEnd:                 key.NewBinding(key.WithKeys("end", "ctrl+e")),
 	Paste:                   key.NewBinding(key.WithKeys("ctrl+v")),
+	InputBegin:              key.NewBinding(key.WithKeys("alt+<", "ctrl+home")),
+	InputEnd:                key.NewBinding(key.WithKeys("alt+>", "ctrl+end")),
+
+	CapitalizeWordForward: key.NewBinding(key.WithKeys("alt+c")),
+	LowercaseWordForward:  key.NewBinding(key.WithKeys("alt+l")),
+	UppercaseWordForward:  key.NewBinding(key.WithKeys("alt+u")),
+
+	TransposeCharacterBackward: key.NewBinding(key.WithKeys("ctrl+t")),
 }
 
 // LineInfo is a helper for keeping track of line information regarding
@@ -117,10 +133,27 @@ type Model struct {
 	Err error
 
 	// General settings.
+
+	// Prompt is printed at the beginning of each line.
+	//
+	// When changing the value of Prompt after the model has been
+	// initialized, ensure that SetWidth() gets called afterwards.
+	//
+	// See also SetPromptFunc().
 	Prompt string
+
+	// Placeholder is the text displayed when the user
+	// hasn't entered anything yet.
 	Placeholder string
+
+	// ShowLineNumbers, if enabled, causes line numbers to be printed
+	// after the prompt.
 	ShowLineNumbers bool
+
+	// EndOfBufferCharacter is displayed at the end of the input.
 	EndOfBufferCharacter rune
+
+	// KeyMap encodes the keybindings recognized by the widget.
 	KeyMap KeyMap
 
 	// Styling. FocusedStyle and BlurredStyle are used to style the textarea in
@@ -140,6 +173,13 @@ type Model struct {
 	// accept. If 0 or less, there's no limit.
 	CharLimit int
 
+	// If promptFunc is set, it replaces Prompt as a generator for
+	// prompt strings at the beginning of each line.
+	promptFunc func(line int) string
+
+	// promptWidth is the width of the prompt.
+	promptWidth int
+
 	// width is the maximum number of characters that can be displayed at once.
 	// If 0 or less this setting is ignored.
 	width int
@@ -473,6 +513,24 @@ func (m *Model) deleteAfterCursor() {
 	m.SetCursor(len(m.value[m.row]))
 }
 
+// transposeLeft exchanges the runes at the cursor and immediately
+// before. No-op if the cursor is at the beginning of the line.  If
+// the cursor is not at the end of the line yet, moves the cursor to
+// the right.
+func (m *Model) transposeLeft() {
+	if m.col == 0 || len(m.value[m.row]) < 2 {
+		return
+	}
+	if m.col >= len(m.value[m.row]) {
+		m.SetCursor(m.col - 1)
+	}
+	m.value[m.row][m.col-1], m.value[m.row][m.col] =
+		m.value[m.row][m.col], m.value[m.row][m.col-1]
+	if m.col < len(m.value[m.row]) {
+		m.SetCursor(m.col + 1)
+	}
+}
+
 // deleteWordLeft deletes the word left to the cursor. Returns whether or not
 // the cursor blink should be reset.
 func (m *Model) deleteWordLeft() {
@@ -547,31 +605,50 @@ func (m *Model) deleteWordRight() {
 	m.SetCursor(oldCol)
 }
 
+// characterRight moves the cursor one character to the right.
+func (m *Model) characterRight() {
+	if m.col < len(m.value[m.row]) {
+		m.SetCursor(m.col + 1)
+	} else {
+		if m.row < len(m.value)-1 {
+			m.row++
+			m.CursorStart()
+		}
+	}
+}
+
+// characterLeft moves the cursor one character to the left.
+// If insideLine is set, the cursor is moved to the last
+// character in the previous line, instead of one past that.
+func (m *Model) characterLeft(insideLine bool) {
+	if m.col == 0 && m.row != 0 {
+		m.row--
+		m.CursorEnd()
+		if !insideLine {
+			return
+		}
+	}
+	if m.col > 0 {
+		m.SetCursor(m.col - 1)
+	}
+}
+
 // wordLeft moves the cursor one word to the left. Returns whether or not the
 // cursor blink should be reset. If input is masked, move input to the start
 // so as not to reveal word breaks in the masked input.
 func (m *Model) wordLeft() {
-	if m.col == 0 || len(m.value[m.row]) == 0 {
-		return
-	}
-
-	i := m.col - 1
-	for i >= 0 {
-		if unicode.IsSpace(m.value[m.row][min(i, len(m.value[m.row])-1)]) {
-			m.SetCursor(m.col - 1)
-			i--
-		} else {
+	for {
+		m.characterLeft(true /* insideLine */)
+		if m.col < len(m.value[m.row]) && !unicode.IsSpace(m.value[m.row][m.col]) {
 			break
 		}
 	}
 
-	for i >= 0 {
-		if !unicode.IsSpace(m.value[m.row][min(i, len(m.value[m.row])-1)]) {
-			m.SetCursor(m.col - 1)
-			i--
-		} else {
+	for m.col > 0 {
+		if unicode.IsSpace(m.value[m.row][m.col-1]) {
 			break
 		}
+		m.SetCursor(m.col - 1)
 	}
 }
 
@@ -579,28 +656,54 @@ func (m *Model) wordLeft() {
 // cursor blink should be reset. If the input is masked, move input to the end
 // so as not to reveal word breaks in the masked input.
 func (m *Model) wordRight() {
-	if m.col >= len(m.value[m.row]) || len(m.value[m.row]) == 0 {
-		return
+	m.doWordRight(func(int, int) { /* nothing */ })
 }
 
-	i := m.col
-	for i < len(m.value[m.row]) {
-		if unicode.IsSpace(m.value[m.row][i]) {
-			m.SetCursor(m.col + 1)
-			i++
-		} else {
+func (m *Model) doWordRight(fn func(charIdx int, pos int)) {
+	// Skip spaces forward.
+	for {
+		if m.col < len(m.value[m.row]) && !unicode.IsSpace(m.value[m.row][m.col]) {
 			break
 		}
+		if m.row == len(m.value)-1 && m.col == len(m.value[m.row]) {
+			// End of text.
+			break
+		}
+		m.characterRight()
+	}
+
+	charIdx := 0
+	for m.col < len(m.value[m.row]) {
+		if unicode.IsSpace(m.value[m.row][m.col]) {
+			break
+		}
+		fn(charIdx, m.col)
+		m.SetCursor(m.col + 1)
+		charIdx++
+	}
 }
 
-	for i < len(m.value[m.row]) {
-		if !unicode.IsSpace(m.value[m.row][i]) {
-			m.SetCursor(m.col + 1)
-			i++
-		} else {
-			break
+// uppercaseRight changes the word to the right to uppercase.
+func (m *Model) uppercaseRight() {
+	m.doWordRight(func(_ int, i int) {
+		m.value[m.row][i] = unicode.ToUpper(m.value[m.row][i])
+	})
 }
+
+// lowercaseRight changes the word to the right to lowercase.
+func (m *Model) lowercaseRight() {
+	m.doWordRight(func(_ int, i int) {
+		m.value[m.row][i] = unicode.ToLower(m.value[m.row][i])
+	})
 }
+
+// capitalizeRight changes the word to the right to title case.
+func (m *Model) capitalizeRight() {
+	m.doWordRight(func(charIdx int, i int) {
+		if charIdx == 0 {
+			m.value[m.row][i] = unicode.ToTitle(m.value[m.row][i])
+		}
+	})
 }
 
 // LineInfo returns the number of characters from the start of the
@@ -662,6 +765,18 @@ func (m Model) Width() int {
 	return m.width
 }
 
+// moveToBegin moves the cursor to the beginning of the input.
+func (m *Model) moveToBegin() {
+	m.row = 0
+	m.SetCursor(0)
+}
+
+// moveToEnd moves the cursor to the end of the input.
+func (m *Model) moveToEnd() {
+	m.row = len(m.value) - 1
+	m.SetCursor(len(m.value[m.row]))
+}
+
 // SetWidth sets the width of the textarea to fit exactly within the given width.
 // This means that the textarea will account for the width of the prompt and
 // whether or not line numbers are being shown.
@@ -682,10 +797,26 @@ func (m *Model) SetWidth(w int) {
 	// Account for base style borders and padding.
 	inputWidth -= m.style.Base.GetHorizontalFrameSize()
 
-	inputWidth -= rw.StringWidth(m.Prompt)
+	if m.promptFunc == nil {
+		m.promptWidth = rw.StringWidth(m.Prompt)
+	}
+
+	inputWidth -= m.promptWidth
 	m.width = clamp(inputWidth, minWidth, maxWidth)
 }
 
+// SetPromptFunc supersedes the Prompt field and sets a dynamic prompt
+// instead.
+// If the function returns a prompt that is shorter than the
+// specified promptWidth, it will be padded to the left.
+// If it returns a prompt that is longer, display artifacts
+// may occur; the caller is responsible for computing an adequate
+// promptWidth.
+func (m *Model) SetPromptFunc(promptWidth int, fn func(lineIdx int) string) {
+	m.promptFunc = fn
+	m.promptWidth = promptWidth
+}
+
 // Height returns the current height of the textarea.
 func (m Model) Height() int {
 	return m.height
@@ -774,14 +905,7 @@ func (m Model) Update(msg tea.Msg) (Model, tea.Cmd) {
 		case key.Matches(msg, m.KeyMap.LineStart):
 			m.CursorStart()
 		case key.Matches(msg, m.KeyMap.CharacterForward):
-			if m.col < len(m.value[m.row]) {
-				m.SetCursor(m.col + 1)
-			} else {
-				if m.row < len(m.value)-1 {
-					m.row++
-					m.CursorStart()
-				}
-			}
+			m.characterRight()
 		case key.Matches(msg, m.KeyMap.LineNext):
 			m.CursorDown()
 		case key.Matches(msg, m.KeyMap.WordForward):
@@ -789,18 +913,24 @@ func (m Model) Update(msg tea.Msg) (Model, tea.Cmd) {
 		case key.Matches(msg, m.KeyMap.Paste):
 			return m, Paste
 		case key.Matches(msg, m.KeyMap.CharacterBackward):
-			if m.col == 0 && m.row != 0 {
-				m.row--
-				m.CursorEnd()
-				break
-			}
-			if m.col > 0 {
-				m.SetCursor(m.col - 1)
-			}
+			m.characterLeft(false /* insideLine */)
 		case key.Matches(msg, m.KeyMap.LinePrevious):
 			m.CursorUp()
 		case key.Matches(msg, m.KeyMap.WordBackward):
 			m.wordLeft()
+		case key.Matches(msg, m.KeyMap.InputBegin):
+			m.moveToBegin()
+		case key.Matches(msg, m.KeyMap.InputEnd):
+			m.moveToEnd()
+		case key.Matches(msg, m.KeyMap.LowercaseWordForward):
+			m.lowercaseRight()
+		case key.Matches(msg, m.KeyMap.UppercaseWordForward):
+			m.uppercaseRight()
+		case key.Matches(msg, m.KeyMap.CapitalizeWordForward):
+			m.capitalizeRight()
+		case key.Matches(msg, m.KeyMap.TransposeCharacterBackward):
+			m.transposeLeft()
+
 		default:
 			if m.CharLimit > 0 && rw.StringWidth(m.Value()) >= m.CharLimit {
 				break
@@ -848,6 +978,7 @@ func (m Model) View() string {
 
 	var newLines int
 
+	displayLine := 0
 	for l, line := range m.value {
 		wrappedLines := wrap(line, m.width)
 
@@ -858,7 +989,10 @@ func (m Model) View() string {
 		}
 
 		for wl, wrappedLine := range wrappedLines {
-			s.WriteString(style.Render(m.style.Prompt.Render(m.Prompt)))
+			prompt := m.getPromptString(displayLine)
+			prompt = m.style.Prompt.Render(prompt)
+			s.WriteString(style.Render(prompt))
+			displayLine++
 
 			if m.ShowLineNumbers {
 				if wl == 0 {
@@ -907,7 +1041,10 @@ func (m Model) View() string {
 	// Always show at least `m.Height` lines at all times.
 	// To do this we can simply pad out a few extra new lines in the view.
 	for i := 0; i < m.height; i++ {
-		s.WriteString(m.style.Prompt.Render(m.Prompt))
+		prompt := m.getPromptString(displayLine)
+		prompt = m.style.Prompt.Render(prompt)
+		s.WriteString(prompt)
+		displayLine++
 
 		if m.ShowLineNumbers {
 			lineNumber := m.style.EndOfBuffer.Render((fmt.Sprintf(m.lineNumberFormat, string(m.EndOfBufferCharacter))))
@@ -920,6 +1057,19 @@ func (m Model) View() string {
 	return m.style.Base.Render(m.viewport.View())
 }
 
+func (m Model) getPromptString(displayLine int) (prompt string) {
+	prompt = m.Prompt
+	if m.promptFunc == nil {
+		return prompt
+	}
+	prompt = m.promptFunc(displayLine)
+	pl := rw.StringWidth(prompt)
+	if pl < m.promptWidth {
+		prompt = fmt.Sprintf("%*s%s", m.promptWidth-pl, "", prompt)
+	}
+	return prompt
+}
+
 // placeholderView returns the prompt and placeholder view, if any.
 func (m Model) placeholderView() string {
 	var (
@@ -928,7 +1078,8 @@ func (m Model) placeholderView() string {
 		style = m.style.Placeholder.Inline(true)
 	)
 
-	prompt := m.style.Prompt.Render(m.Prompt)
+	prompt := m.getPromptString(0)
+	prompt = m.style.Prompt.Render(prompt)
 	s.WriteString(m.style.CursorLine.Render(prompt))
 
 	if m.ShowLineNumbers {
@@ -945,6 +1096,8 @@ func (m Model) placeholderView() string {
 	// The rest of the new lines
 	for i := 1; i < m.height; i++ {
 		s.WriteRune('\n')
+		prompt := m.getPromptString(i)
+		prompt = m.style.Prompt.Render(prompt)
 		s.WriteString(prompt)
 
 		if m.ShowLineNumbers {

viewport/viewport.go

@@ -350,18 +350,23 @@ func (m Model) View() string {
 		return strings.Repeat("\n", max(0, m.Height-1))
 	}
 
-	lines := m.visibleLines()
-
-	// Fill empty space with newlines
-	extraLines := ""
-	if len(lines) < m.Height {
-		extraLines = strings.Repeat("\n", max(0, m.Height-len(lines)))
+	w, h := m.Width, m.Height
+	if sw := m.Style.GetWidth(); sw != 0 {
+		w = min(w, sw)
 	}
-
+	if sh := m.Style.GetHeight(); sh != 0 {
+		h = min(h, sh)
+	}
+	contentWidth := w - m.Style.GetHorizontalFrameSize()
+	contentHeight := h - m.Style.GetVerticalFrameSize()
+	contents := lipgloss.NewStyle().
+		Height(contentHeight).    // pad to height.
+		MaxHeight(contentHeight). // truncate height if taller.
+		MaxWidth(contentWidth).   // truncate width.
+		Render(strings.Join(m.visibleLines(), "\n"))
 	return m.Style.Copy().
-		UnsetWidth().
-		UnsetHeight().
-		Render(strings.Join(lines, "\n") + extraLines)
+		UnsetWidth().UnsetHeight(). // Style size already applied in contents.
+		Render(contents)
 }
 
 func clamp(v, low, high int) int {