Add timer countdown example

examples/countdown/main.go

@@ -0,0 +1,70 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	tea "github.com/charmbracelet/bubbletea"
+)
+
+var (
+	duration = time.Second * 10
+	interval = time.Millisecond
+)
+
+func main() {
+	m := model{
+		timeout: time.Now().Add(duration),
+	}
+
+	if err := tea.NewProgram(m).Start(); err != nil {
+		fmt.Println("Oh no, it didn't work:", err)
+		os.Exit(1)
+	}
+}
+
+type tickMsg time.Time
+
+type model struct {
+	timeout  time.Time
+	lastTick time.Time
+}
+
+func (m model) Init() tea.Cmd {
+	return m.tick()
+}
+
+func (m model) Update(msg tea.Msg) (tea.Model, tea.Cmd) {
+	switch msg := msg.(type) {
+
+	case tickMsg:
+		t := time.Time(msg)
+		if t.After(m.timeout) {
+			return m, tea.Quit
+		}
+		m.lastTick = t
+		return m, m.tick()
+
+	case tea.KeyMsg:
+		switch msg.String() {
+		case "ctrl+c", "q":
+			return m, tea.Quit
+		}
+	}
+
+	return m, nil
+}
+
+func (m model) View() string {
+	t := m.timeout.Sub(m.lastTick).Milliseconds()
+	secs := t / 1000
+	millis := t % 1000 / 10
+	return fmt.Sprintf("This program will quit in %02d:%02d\n", secs, millis)
+}
+
+func (m model) tick() tea.Cmd {
+	return tea.Tick(time.Duration(interval), func(t time.Time) tea.Msg {
+		return tickMsg(t)
+	})
+}