feat: add animated-counter component for dynamic values

closes #1

README.md

@@ -1,6 +1,6 @@
 # Compound Interest Calculator
 
-A minimal compound interest calculator that displays the total return of a compounded investment over a specified time period.
+A minimal compound interest investment calculator that displays the total returns over a specified time period, interest rate and compounding frequency.
 
 
 [![Deployment](https://github.com/rocktimsaikia/compound-interest-calculator/actions/workflows/deploy.yml/badge.svg)](https://github.com/rocktimsaikia/compound-interest-calculator/actions/workflows/deploy.yml)

src/App.tsx

@@ -1,5 +1,6 @@
 import { useEffect, useState } from "react";
 import compounder from "compounder";
+import AnimatedCounter from "./components/animated-counter";
 
 type CompoundingFrequency = "quarterly" | "semi-annually" | "annually";
 
@@ -196,15 +197,21 @@ export default function App() {
 				<div className="mt-24 grid grid-cols-3 text-center">
 					<div>
 						<p className="text-gray-500">Principal Amount</p>
-						<p>₹{principalAmount.toLocaleString("en-IN")}</p>
+						<div>
+							₹ <AnimatedCounter start={principalAmount} locale="en-IN" />
+						</div>
 					</div>
 					<div>
 						<p className="text-gray-500">Total Interest</p>
-						<p>₹{totalInterest.toLocaleString("en-IN")}</p>
+						<p>
+							₹ <AnimatedCounter start={totalInterest} locale="en-IN" />
+						</p>
 					</div>
 					<div>
 						<p className="text-gray-500">Total Amount</p>
-						<p>₹{totalAmount.toLocaleString("en-IN")}</p>
+						<p>
+							₹ <AnimatedCounter start={totalAmount} locale="en-IN" />
+						</p>
 					</div>
 				</div>
 			</div>

src/components/animated-counter.tsx

@@ -0,0 +1,46 @@
+import { useEffect, useRef, useState } from "react";
+
+interface Props {
+	start: number;
+	duration?: number;
+	locale?: string;
+}
+
+export default function AnimatedCounter({
+	start,
+	duration = 200,
+	locale,
+}: Props) {
+	const [count, setCount] = useState(start); // State to keep track of the current count
+	const prevStartRef = useRef(start); // Ref to store the previous start value
+
+	// Update the previous start value when start changes
+	useEffect(() => {
+		prevStartRef.current = start;
+	}, [start]);
+
+	// Previous start value
+	const prevStart = prevStartRef.current;
+
+	// Animate the count when the start value changes
+	useEffect(() => {
+		// If start value changes, animate the count
+		if (prevStart !== start) {
+			let startTimestamp: DOMHighResTimeStamp;
+
+			const step = (timestamp: DOMHighResTimeStamp) => {
+				if (!startTimestamp) startTimestamp = timestamp;
+				const progress = Math.min((timestamp - startTimestamp) / duration, 1); // Calculate progress
+				setCount(Math.floor(progress * (start - prevStart) + prevStart)); // Update count based on progress
+
+				if (progress < 1) {
+					window.requestAnimationFrame(step); // Continue animation
+				}
+			};
+
+			window.requestAnimationFrame(step); // Start animation
+		}
+	}, [start, duration]);
+
+	return <span>{locale ? count.toLocaleString(locale) : count}</span>; // Render the current count
+}