Add commands for toggling the altscreen (#62)

* Add commands EnterAltScreen and ExitAltScreen for toggling the altscreen
* Add altscreen toggling example
* ignore .idea

Co-authored-by: Christian Rocha <christian@rocha.is>

examples/altscreen-toggle/main.go

@@ -0,0 +1,76 @@
+package main
+
+import (
+	"fmt"
+	"os"
+
+	tea "github.com/charmbracelet/bubbletea"
+	"github.com/muesli/termenv"
+)
+
+var (
+	color   = termenv.ColorProfile().Color
+	keyword = termenv.Style{}.Foreground(color("204")).Background(color("235")).Styled
+)
+
+type model struct {
+	altscreen bool
+	quitting  bool
+}
+
+func (m model) Init() tea.Cmd {
+	return nil
+}
+
+func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
+	switch msg := msg.(type) {
+	case tea.KeyMsg:
+		switch msg.String() {
+		case "q", "ctrl+c", "esc":
+			m.quitting = true
+			return m, tea.Quit
+		case " ":
+			var cmd tea.Cmd
+			if m.altscreen {
+				cmd = tea.ExitAltScreen
+			} else {
+				cmd = tea.EnterAltScreen
+			}
+			m.altscreen = !m.altscreen
+			return m, cmd
+		}
+	}
+	return m, nil
+}
+
+func (m model) View() string {
+	if m.quitting {
+		return "Bye!\n"
+	}
+
+	const (
+		altscreenMode = " altscreen mode "
+		inlineMode    = " inline mode "
+	)
+
+	var mode, otherMode string
+	if m.altscreen {
+		mode = altscreenMode
+		otherMode = inlineMode
+	} else {
+		mode = inlineMode
+		otherMode = altscreenMode
+	}
+
+	return fmt.Sprintf(
+		"\n  You're in %s. Press %s to swich to %s.\n\n  To exit press %s.\n",
+		keyword(mode), keyword(" space "), keyword(otherMode), keyword(" q "),
+	)
+}
+
+func main() {
+	if err := tea.NewProgram(model{}).Start(); err != nil {
+		fmt.Println("Error running program:", err)
+		os.Exit(1)
+	}
+}