/**** 
* Plugins
****/ 
var tween = LK.import("@upit/tween.v1");

/**** 
* Classes
****/ 
// Asteroid class
var Asteroid = Container.expand(function () {
	var self = Container.call(this);
	// Attach asteroid asset
	var asteroidGraphics = self.attachAsset('asteroid', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	// Set asteroid speed
	self.speed = 3;
	// Update function called every game tick
	self.update = function () {
		// Move asteroid based on speed
		self.y += self.speed;
		// Destroy asteroid when it gets out of player screen
		if (self.y > 2732) {
			self.destroy();
		}
		// Check for collision with player
		if (self.intersects(player)) {
			// Trigger game over when asteroid hits player
			LK.showGameOver();
		}
	};
});
// Bullet class
var Bullet = Container.expand(function () {
	var self = Container.call(this);
	// Attach bullet asset
	var bulletGraphics = self.attachAsset('bullet', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	// Set bullet speed
	self.speed = -14;
	// Update function called every game tick
	self.update = function () {
		self.y += self.speed;
		// Check for collision with enemy and asteroid
		var targets = game.children.filter(function (child) {
			return child instanceof Enemy || child instanceof Asteroid;
		});
		for (var i = 0; i < targets.length; i++) {
			var target = targets[i];
			if (self.intersects(target)) {
				// Destroy target and bullet on collision
				target.destroy();
				self.destroy();
				// Increase score by 100 points when target dies
				LK.setScore(LK.getScore() + 100);
				// Update the scoreboard
				scoreTxt.setText(LK.getScore());
				// Add a blasting effect
				var blast = self.attachAsset('blast', {
					anchorX: 0.5,
					anchorY: 0.5
				});
				blast.x = self.x;
				blast.y = self.y;
				game.addChild(blast);
				// Destroy the blast effect after a short delay
				LK.setTimeout(function () {
					blast.destroy();
				}, 500);
				break;
			}
		}
		// Destroy bullet when it gets out of player screen
		if (self.y < 0 || self.y > 2732) {
			self.destroy();
		}
	};
});
// Enemy class
var Enemy = Container.expand(function () {
	var self = Container.call(this);
	// Attach enemy asset
	var enemyGraphics = self.attachAsset('enemy', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	// Set enemy speed
	self.speed = 5;
	// Update function called every game tick
	self.update = function () {
		// Move enemy based on speed
		self.y += self.speed;
		// Destroy enemy when it gets out of player screen
		if (self.y > 2732) {
			self.destroy();
		}
		// Enemy fires a bullet every 60 ticks
		if (LK.ticks % 60 == 0) {
			var enemyBullet = game.addChild(new EnemyBullet());
			// Set bullet initial position to enemy's position
			enemyBullet.x = self.x;
			enemyBullet.y = self.y;
			// Set bullet speed to move downwards
			enemyBullet.speed = 6;
		}
	};
});
// EnemyBullet class
var EnemyBullet = Container.expand(function () {
	var self = Container.call(this);
	// Attach bullet asset
	var bulletGraphics = self.attachAsset('bullet', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	// Set bullet speed
	self.speed = 5;
	// Update function called every game tick
	self.update = function () {
		self.y += self.speed;
		// Check for collision with player
		if (self.intersects(player)) {
			// Add a blasting effect
			var blast = self.attachAsset('blast', {
				anchorX: 0.5,
				anchorY: 0.5
			});
			blast.x = player.x;
			blast.y = player.y;
			game.addChild(blast);
			// Destroy the blast effect after a short delay
			LK.setTimeout(function () {
				blast.destroy();
			}, 500);
			// Trigger game over when bullet hits player
			LK.showGameOver();
		}
	};
});
// Player class
var Player = Container.expand(function () {
	var self = Container.call(this);
	// Attach player asset
	var playerGraphics = self.attachAsset('player', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	// Set player speed
	self.speed = 5;
	// Update function called every game tick
	self.update = function () {
		// Player movement is handled in game.move event
	};
});

/**** 
* Initialize Game
****/ 
//<Assets used in the game will automatically appear here>
//<Write imports for supported plugins here>
var game = new LK.Game();

/**** 
* Game Code
****/ 
//<Assets used in the game will automatically appear here>
//<Write imports for supported plugins here>
//<Assets used in the game will automatically appear here>
//<Write imports for supported plugins here>
var background = game.attachAsset('background', {
	anchorX: 0.5,
	anchorY: 0.5,
	x: 1024,
	y: 1366
});
// Create a scoreboard and display it on the screen
var scoreTxt = new Text2('0', {
	size: 150,
	fill: 0xFFFFFF
});
scoreTxt.anchor.set(0.5, 0);
LK.gui.top.addChild(scoreTxt);
game.update = function () {
	// Spawn an enemy and an asteroid every 60 ticks
	if (LK.ticks % 60 == 0) {
		var enemy = game.addChild(new Enemy());
		// Set enemy initial position
		enemy.x = Math.random() * 2048;
		enemy.y = 0;
		var asteroid = game.addChild(new Asteroid());
		// Set asteroid initial position
		asteroid.x = Math.random() * 2048;
		asteroid.y = 0;
	}
	// Move the background downwards smoothly
	tween(background, {
		y: background.y + 2732
	}, {
		duration: 1000,
		onComplete: function onComplete() {
			// Loop the background
			background.y = 0;
		}
	});
};
var player = game.addChild(new Player());
// Set player initial position
player.x = 1024;
player.y = 2732 - player.height / 2 - 500;
// Add mouse move event to the game
game.move = function (x, y, obj) {
	// Move player on both x and y axis
	player.x = x;
	player.y = y;
};
game.down = function (x, y, obj) {
	// Create a bullet instance
	var bullet = game.addChild(new Bullet());
	// Set bullet initial position to player's position
	bullet.x = player.x;
	bullet.y = player.y;
};
// Update the scoreboard every game tick
scoreTxt.setText(LK.getScore());

===================================================================
--- original.js
+++ change.js
@@ -165,12 +165,12 @@
 
 /**** 
 * Game Code
 ****/ 
-//<Write imports for supported plugins here>
 //<Assets used in the game will automatically appear here>
 //<Write imports for supported plugins here>
 //<Assets used in the game will automatically appear here>
+//<Write imports for supported plugins here>
 var background = game.attachAsset('background', {
 	anchorX: 0.5,
 	anchorY: 0.5,
 	x: 1024,
@@ -198,21 +198,14 @@
 	// Move the background downwards smoothly
 	tween(background, {
 		y: background.y + 2732
 	}, {
-		duration: 1000
+		duration: 1000,
+		onComplete: function onComplete() {
+			// Loop the background
+			background.y = 0;
+		}
 	});
-	// Spawn and loop the background when the previous one ends
-	if (background.y >= 2732) {
-		var newBackground = game.attachAsset('background', {
-			anchorX: 0.5,
-			anchorY: 0.5,
-			x: 1024,
-			y: 0
-		});
-		game.addChild(newBackground);
-		background = newBackground;
-	}
 };
 var player = game.addChild(new Player());
 // Set player initial position
 player.x = 1024;