Add countdown timer and alarm functionality

Author: Richiealx

Sprint-3/alarmclock/alarmclock.js

@@ -1,10 +1,114 @@
-function setAlarm() {}
+// Store the current countdown value in seconds
+let remainingSeconds = 0;
+
+// Store the timer ID so an existing timer can be cleared
+let countdownTimerId = null;
+
+/**
+ * Converts a number of seconds into mm:ss format.
+ * Example:
+ * 19 -> 00:19
+ * 119 -> 01:59
+ */
+function formatTime(totalSeconds) {
+  const minutes = Math.floor(totalSeconds / 60);
+  const seconds = totalSeconds % 60;
+
+  const formattedMinutes = String(minutes).padStart(2, "0");
+  const formattedSeconds = String(seconds).padStart(2, "0");
+
+  return `${formattedMinutes}:${formattedSeconds}`;
+}
+
+/**
+ * Updates the heading text with the current remaining time.
+ */
+function updateHeading() {
+  const heading = document.getElementById("timeRemaining");
+  heading.innerText = `Time Remaining: ${formatTime(remainingSeconds)}`;
+}
+
+/**
+ * Resets the background colour to the default state.
+ */
+function resetBackground() {
+  document.body.classList.remove("alarm-finished");
+}
+
+/**
+ * Changes the background colour when the timer reaches zero.
+ */
+function showAlarmFinishedState() {
+  document.body.classList.add("alarm-finished");
+}
+
+/**
+ * Stops any existing countdown timer.
+ */
+function stopCountdown() {
+  if (countdownTimerId !== null) {
+    clearInterval(countdownTimerId);
+    countdownTimerId = null;
+  }
+}
+
+/**
+ * Starts the countdown timer and updates the heading every second.
+ */
+function startCountdown() {
+  countdownTimerId = setInterval(() => {
+    if (remainingSeconds > 0) {
+      remainingSeconds -= 1;
+      updateHeading();
+    }
+
+    if (remainingSeconds === 0) {
+      stopCountdown();
+      showAlarmFinishedState();
+      playAlarm();
+    }
+  }, 1000);
+}
+
+/**
+ * Reads the value from the input, updates the heading,
+ * resets the background, stops any existing alarm sound,
+ * and starts the countdown.
+ */
+function setAlarm() {
+  const input = document.getElementById("alarmSet");
+  const inputValue = Number(input.value);
+
+  // Prevent invalid negative values
+  if (Number.isNaN(inputValue) || inputValue < 0) {
+    return;
+  }
+
+  // Stop any previous countdown before starting a new one
+  stopCountdown();
+
+  // Stop any alarm sound that may already be playing
+  pauseAlarm();
+
+  // Reset the page state for a new alarm
+  resetBackground();
+
+  // Store the new number of seconds and update the heading immediately
+  remainingSeconds = Math.floor(inputValue);
+  updateHeading();
+
+  // Start counting down every second
+  startCountdown();
+}
 
 // DO NOT EDIT BELOW HERE
 
 var audio = new Audio("alarmsound.mp3");
 
 function setup() {
+  // Make the alarm loop continuously until stopped
+  audio.loop = true;
+
   document.getElementById("set").addEventListener("click", () => {
     setAlarm();
   });