feat: Add "countdown" subcommandHEADv1.1.0main

3 files changed, 123 insertions, 3 deletions

diff --git a/README.md b/README.md
index 3a2b891..92300bd 100644
--- a/README.md
+++ b/README.md
@@ -4,9 +4,10 @@ A digital clock that runs in your terminal, providing clock, alarm and timer.
 
 ## Features
 
-- **Clock Mode**: Digital display of current time (24-hour format)
-- **Alarm Mode**: Screen flashes at the specified time
-- **Timer Mode**: Countdown timer (up to 99 minutes)
+- Clock Mode: Digital display of current time (24-hour format)
+- Alarm Mode: Screen flashes at the specified time
+- Timer Mode: Countdown timer (up to 99 minutes)
+- Countdown Mode: Countdown from a specified duration to zero
 
 ## Installation
 
@@ -49,6 +50,19 @@ $ term-clock timer 90s    # 90-second timer
 $ term-clock timer 1h30m  # 1 hour 30 minutes timer (note: maximum 99 minutes)
 ```
 
+### Countdown Mode
+
+Counts down from the specified number of seconds to zero, displaying the remaining seconds.
+The screen flashes when the countdown reaches zero.
+
+```bash
+$ term-clock countdown 10    # Countdown from 10 seconds
+$ term-clock countdown 600   # Countdown from 600 seconds
+$ term-clock countdown 9999  # Countdown from 9999 seconds
+```
+
+Note: Maximum supported duration is 9999 seconds.
+
 ## How to Exit
 
 Press `Ctrl+C` or type `q` to exit.
diff --git a/cmd/countdown.go b/cmd/countdown.go
new file mode 100644
index 0000000..61cd929
--- /dev/null
+++ b/cmd/countdown.go
@@ -0,0 +1,105 @@
+package cmd
+
+import (
+	"log"
+	"math"
+	"strconv"
+	"time"
+
+	"github.com/spf13/cobra"
+
+	"github.com/nsfisis/term-clock/internal/term"
+)
+
+func drawCountdown(scr *term.Screen, leftSeconds int, bgStyle, fgStyle term.Style) {
+	if leftSeconds <= 0 {
+		if int(math.Abs(float64(leftSeconds)))%2 == 0 {
+			bgStyle, fgStyle = fgStyle, bgStyle
+		}
+		leftSeconds = 0
+	}
+
+	// Clear the entire screen.
+	scr.Clear(bgStyle)
+
+	// Calculate number of digits needed
+	numDigits := 1
+	if leftSeconds > 0 {
+		n := leftSeconds
+		numDigits = 0
+		for n > 0 {
+			numDigits++
+			n /= 10
+		}
+	}
+
+	scrW, scrH := scr.Size()
+	// Calculate square size based on number of digits
+	squareW := scrW / (numDigits*4 + 2)
+	squareH := min(scrH/(5+2), squareW)
+	if squareW > squareH*3/2 {
+		squareW = squareH * 3 / 2
+	}
+	xOffset := (scrW - squareW*numDigits*4) / 2
+	yOffset := (scrH - squareH*5) / 2
+
+	// Extract and display each digit
+	n := leftSeconds
+	for i := numDigits - 1; i >= 0; i-- {
+		digit := n % 10
+		term.DrawNumber(scr, digit, xOffset+squareW*i*4, yOffset, squareW, squareH, fgStyle)
+		n /= 10
+	}
+}
+
+func cmdCountdown(cmd *cobra.Command, args []string) {
+	totalSeconds, err := strconv.Atoi(args[0])
+	if err != nil {
+		log.Fatalf("%+v", err)
+	}
+
+	if totalSeconds > 9999 {
+		log.Fatal("Duration over 9999 seconds is not supported.")
+	}
+
+	scr, err := term.NewScreen()
+	if err != nil {
+		log.Fatalf("%+v", err)
+	}
+	defer scr.Close()
+
+	startTime := time.Now()
+
+	calcLeftSeconds := func(t time.Time) int {
+		elapsed := int(t.Sub(startTime).Seconds())
+		return totalSeconds - elapsed
+	}
+
+	drawCountdown(scr, calcLeftSeconds(time.Now()), term.BgStyle, term.FgStyle)
+
+	scr.OnResize(func() bool {
+		drawCountdown(scr, calcLeftSeconds(time.Now()), term.BgStyle, term.FgStyle)
+		return false
+	})
+	go scr.DoEventLoop()
+
+	t := time.NewTicker(1 * time.Second)
+	defer t.Stop()
+
+	for {
+		select {
+		case <-scr.QuitC:
+			return
+		case now := <-t.C:
+			drawCountdown(scr, calcLeftSeconds(now), term.BgStyle, term.FgStyle)
+			scr.Show()
+		}
+	}
+}
+
+var countdownCmd = &cobra.Command{
+	Use:   "countdown",
+	Short: "Countdown mode",
+	Run:   cmdCountdown,
+	Args:  cobra.ExactArgs(1),
+}
diff --git a/cmd/root.go b/cmd/root.go
index 5a91eae..e3aa309 100644
--- a/cmd/root.go
+++ b/cmd/root.go
@@ -16,6 +16,7 @@ var rootCmd = &cobra.Command{
 func init() {
 	rootCmd.AddCommand(alarmCmd)
 	rootCmd.AddCommand(clockCmd)
+	rootCmd.AddCommand(countdownCmd)
 	rootCmd.AddCommand(timerCmd)
 }