visual polish: add pulsing start button and color-shifting progress ring

- Countdown ring interpolates green → yellow → red as timer progresses
- Start button pulses continuously to draw attention
- Pulse stops while dialog is shown and restarts on resume

app/src/main/java/com/example/countdowntimer/CountdownCanvasView.kt

@@ -47,6 +47,13 @@ class CountdownCanvasView @JvmOverloads constructor(
         invalidate()
     }
 
+    fun setColor(color: Int) {
+        if (ringPaint.color != color) {
+            ringPaint.color = color
+            invalidate()
+        }
+    }
+
     override fun onSizeChanged(w: Int, h: Int, oldw: Int, oldh: Int) {
         super.onSizeChanged(w, h, oldw, oldh)
         val inset = ringPaint.strokeWidth / 2f + 12f

app/src/main/java/com/example/countdowntimer/CountdownDialog.kt

@@ -3,6 +3,8 @@ package com.example.countdowntimer
 import android.app.Dialog
 import android.content.Context
 import android.content.SharedPreferences
+import androidx.core.content.ContextCompat
+import androidx.core.graphics.ColorUtils
 import android.media.AudioManager
 import android.media.ToneGenerator
 import android.os.Bundle
@@ -56,11 +58,28 @@ class CountdownDialog(
 
     private fun startTimer() {
         cvCountdown.setProgress(1f)
+        cvCountdown.setColor(ContextCompat.getColor(context, R.color.md_color_ring_progress))
         timer = object : CountDownTimer(durationMillis, 1000) {
             override fun onTick(millisUntilFinished: Long) {
                 val progress = millisUntilFinished.toFloat() / durationMillis
                 cvCountdown.setProgress(progress)
 
+                // Interpolate ring color: green → yellow at 50% → red at end
+                val green = android.graphics.Color.parseColor("#2E7D32")
+                val yellow = android.graphics.Color.parseColor("#FFC107")
+                val red = android.graphics.Color.parseColor("#F44336")
+                val ringColor = when {
+                    progress >= 0.5f -> {
+                        val t = (progress - 0.5f) * 2f
+                        ColorUtils.blendARGB(green, yellow, t)
+                    }
+                    else -> {
+                        val t = progress * 2f
+                        ColorUtils.blendARGB(yellow, red, t)
+                    }
+                }
+                cvCountdown.setColor(ringColor)
+
                 val secondsLeft = (millisUntilFinished / 1000).toInt() + 1
                 cvCountdown.setText(secondsLeft.toString())
 

app/src/main/java/com/example/countdowntimer/MainActivity.kt

@@ -11,6 +11,8 @@ import android.view.inputmethod.InputMethodManager
 import android.widget.Button
 import androidx.appcompat.app.AppCompatActivity
 import com.google.android.material.chip.ChipGroup
+import android.animation.ValueAnimator
+import android.view.animation.AnticipateOvershootInterpolator
 
 class MainActivity : AppCompatActivity() {
 
@@ -24,9 +26,11 @@ class MainActivity : AppCompatActivity() {
     private lateinit var btnDurationLabel: Button
     private lateinit var hsvDurationOptions: View
     private lateinit var chipGroup: ChipGroup
+    private lateinit var btnStart: View
     private lateinit var vibrator: Vibrator
     private var selectedDuration: Long = DEFAULT_DURATION
     private var lastSelectedChipId: Int = -1
+    private var pulseAnimator: ValueAnimator? = null
 
     private fun durationToChipId(duration: Long): Int = when (duration) {
         5000L -> R.id.chip5s
@@ -57,6 +61,30 @@ class MainActivity : AppCompatActivity() {
         }
     }
 
+    private fun startPulseAnimation() {
+        pulseAnimator = ValueAnimator.ofFloat(1f, 0.78f, 1f).apply {
+            duration = 1500
+            repeatMode = ValueAnimator.REVERSE
+            repeatCount = ValueAnimator.INFINITE
+            interpolator = AnticipateOvershootInterpolator(1f)
+            addUpdateListener { animation ->
+                val fraction = animation.animatedValue as Float
+                btnStart.scaleX = fraction
+                btnStart.scaleY = fraction
+                btnStart.alpha = fraction
+            }
+        }
+        pulseAnimator?.start()
+    }
+
+    private fun stopPulseAnimation() {
+        pulseAnimator?.cancel()
+        pulseAnimator = null
+        btnStart.scaleX = 1f
+        btnStart.scaleY = 1f
+        btnStart.alpha = 1f
+    }
+
     override fun onCreate(savedInstanceState: Bundle?) {
         super.onCreate(savedInstanceState)
         setContentView(R.layout.activity_main)
@@ -67,6 +95,7 @@ class MainActivity : AppCompatActivity() {
         btnDurationLabel = findViewById(R.id.btnDurationLabel)
         hsvDurationOptions = findViewById(R.id.hsvDurationOptions)
         chipGroup = findViewById(R.id.chipGroup)
+        btnStart = findViewById(R.id.btnStart)
         val vibratorManager = getSystemService(Context.VIBRATOR_MANAGER_SERVICE) as VibratorManager
         vibrator = vibratorManager.defaultVibrator
 
@@ -111,7 +140,22 @@ class MainActivity : AppCompatActivity() {
         findViewById<View>(R.id.chip30s).setOnClickListener { onChipClicked(R.id.chip30s) }
 
         findViewById<View>(R.id.btnStart).setOnClickListener {
+            stopPulseAnimation()
             CountdownDialog(this, selectedDuration, prefs).show()
         }
+
+        startPulseAnimation()
+    }
+
+    override fun onResume() {
+        super.onResume()
+        if (!isFinishing && !isDestroyed) {
+            startPulseAnimation()
+        }
+    }
+
+    override fun onPause() {
+        super.onPause()
+        stopPulseAnimation()
     }
 }