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

/**** 
* Classes
****/ 
// Alien
var Alien = Container.expand(function () {
	var self = Container.call(this);
	var alien = self.attachAsset('alien', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.width = alien.width;
	self.height = alien.height;
	self.speedX = 0;
	self.speedY = 0.8;
	self.shootCooldown = 0;
	self.row = 0;
	self.col = 0;
	self.alive = true;
	self.update = function () {
		self.x += self.speedX;
		self.y += self.speedY;
		if (self.shootCooldown > 0) self.shootCooldown -= 1;
	};
	// Flash when hit
	self.flash = function () {
		tween(self, {
			alpha: 0.3
		}, {
			duration: 60,
			onFinish: function onFinish() {
				tween(self, {
					alpha: 1
				}, {
					duration: 100
				});
			}
		});
	};
	return self;
});
// Alien Bullet
var AlienBullet = Container.expand(function () {
	var self = Container.call(this);
	var bullet = self.attachAsset('alienBullet', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.width = bullet.width;
	self.height = bullet.height;
	self.speedY = 14;
	self.update = function () {
		self.y += self.speedY;
	};
	return self;
});
// Hero Bullet
var HeroBullet = Container.expand(function () {
	var self = Container.call(this);
	var bullet = self.attachAsset('heroBullet', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.width = bullet.width;
	self.height = bullet.height;
	self.speedY = -22;
	self.update = function () {
		self.y += self.speedY;
	};
	return self;
});
// Hero Ship
var HeroShip = Container.expand(function () {
	var self = Container.call(this);
	var ship = self.attachAsset('heroShip', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.width = ship.width;
	self.height = ship.height;
	self.lives = 1;
	self.fireCooldown = 0;
	self.powerLevel = 1;
	self.invincible = false;
	self.invincibleTimer = 0;
	// Flash when hit
	self.flash = function () {
		tween(self, {
			alpha: 0.3
		}, {
			duration: 80,
			onFinish: function onFinish() {
				tween(self, {
					alpha: 1
				}, {
					duration: 120
				});
			}
		});
	};
	// Power up
	self.upgrade = function () {
		if (self.powerLevel < 3) {
			self.powerLevel += 1;
			LK.effects.flashObject(self, 0xaa66ff, 400);
		}
	};
	// Invincibility after hit
	self.setInvincible = function (duration) {
		self.invincible = true;
		self.invincibleTimer = duration;
		tween(self, {
			alpha: 0.5
		}, {
			duration: 100
		});
	};
	// Called every tick
	self.update = function () {
		if (self.invincible) {
			self.invincibleTimer -= 1;
			if (self.invincibleTimer <= 0) {
				self.invincible = false;
				self.alpha = 1;
			}
		}
		if (self.fireCooldown > 0) self.fireCooldown -= 1;
	};
	return self;
});
// Powerup
var Powerup = Container.expand(function () {
	var self = Container.call(this);
	var p = self.attachAsset('powerup', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.width = p.width;
	self.height = p.height;
	self.speedY = 7;
	self.update = function () {
		self.y += self.speedY;
	};
	return self;
});

/**** 
* Initialize Game
****/ 
var game = new LK.Game({
	backgroundColor: 0x000000
});

/**** 
* Game Code
****/ 
// Music
// Sound effects
// Power-up: purple ellipse
// Alien bullet: red box
// Hero bullet: yellow box
// Alien: green ellipse
// Hero ship: blue box
// Game area
var GAME_WIDTH = 2048;
var GAME_HEIGHT = 2732;
// Play music
LK.playMusic('bgmusic');
// Score
var score = 0;
var scoreTxt = new Text2('0', {
	size: 120,
	fill: 0xFFFFFF
});
scoreTxt.anchor.set(0.5, 0);
LK.gui.top.addChild(scoreTxt);
// Wave
var wave = 1;
var waveTxt = new Text2('Wave 1', {
	size: 70,
	fill: 0xAAFFFF
});
waveTxt.anchor.set(0.5, 0);
LK.gui.top.addChild(waveTxt);
waveTxt.y = 120;
// Hero
var hero = new HeroShip();
game.addChild(hero);
hero.x = GAME_WIDTH / 2;
hero.y = GAME_HEIGHT - 220;
// Bullets, aliens, powerups
var heroBullets = [];
var alienBullets = [];
var aliens = [];
var powerups = [];
// Dragging
var dragNode = null;
// Alien formation
function spawnWave(waveNum) {
	// Remove old aliens
	for (var i = aliens.length - 1; i >= 0; i--) {
		aliens[i].destroy();
		aliens.splice(i, 1);
	}
	// Formation: rows, cols, spacing
	var rows = Math.min(2 + waveNum, 6);
	var cols = Math.min(4 + waveNum * 2, 10);
	var spacingX = 160;
	var spacingY = 140;
	var startX = (GAME_WIDTH - (cols - 1) * spacingX) / 2;
	var startY = 220 + (waveNum - 1) * 30;
	for (var r = 0; r < rows; r++) {
		for (var c = 0; c < cols; c++) {
			var alien = new Alien();
			alien.x = startX + c * spacingX;
			alien.y = startY + r * spacingY;
			alien.row = r;
			alien.col = c;
			alien.speedX = Math.sin((r * cols + c + waveNum) * 0.7) * 1.5 + (Math.random() - 0.5) * 0.5;
			alien.speedY = 0.7 + 0.1 * waveNum + (Math.random() - 0.5) * 0.2;
			alien.shootCooldown = 60 + Math.floor(Math.random() * 60);
			aliens.push(alien);
			game.addChild(alien);
		}
	}
	waveTxt.setText('Wave ' + waveNum);
}
// Powerup spawn
function maybeSpawnPowerup(x, y) {
	if (Math.random() < 0.18) {
		var p = new Powerup();
		p.x = x;
		p.y = y;
		powerups.push(p);
		game.addChild(p);
	}
}
// Fire hero bullets
function fireHeroBullets() {
	if (hero.fireCooldown > 0) return;
	var b;
	if (hero.powerLevel === 1) {
		b = new HeroBullet();
		b.x = hero.x;
		b.y = hero.y - hero.height / 2 - 10;
		heroBullets.push(b);
		game.addChild(b);
	} else if (hero.powerLevel === 2) {
		b = new HeroBullet();
		b.x = hero.x - 38;
		b.y = hero.y - hero.height / 2 - 10;
		heroBullets.push(b);
		game.addChild(b);
		b = new HeroBullet();
		b.x = hero.x + 38;
		b.y = hero.y - hero.height / 2 - 10;
		heroBullets.push(b);
		game.addChild(b);
	} else if (hero.powerLevel >= 3) {
		b = new HeroBullet();
		b.x = hero.x - 60;
		b.y = hero.y - hero.height / 2 - 10;
		heroBullets.push(b);
		game.addChild(b);
		b = new HeroBullet();
		b.x = hero.x;
		b.y = hero.y - hero.height / 2 - 10;
		heroBullets.push(b);
		game.addChild(b);
		b = new HeroBullet();
		b.x = hero.x + 60;
		b.y = hero.y - hero.height / 2 - 10;
		heroBullets.push(b);
		game.addChild(b);
	}
	hero.fireCooldown = 12;
	LK.getSound('shoot').play();
}
// Fire alien bullet
function fireAlienBullet(alien) {
	var b = new AlienBullet();
	b.x = alien.x;
	b.y = alien.y + alien.height / 2 + 10;
	alienBullets.push(b);
	game.addChild(b);
	LK.getSound('alienShoot').play();
}
// Move handler (drag hero)
function handleMove(x, y, obj) {
	if (dragNode) {
		// Clamp to game area, avoid top 100px (menu)
		var nx = Math.max(hero.width / 2, Math.min(GAME_WIDTH - hero.width / 2, x));
		var ny = Math.max(GAME_HEIGHT - 600, Math.min(GAME_HEIGHT - hero.height / 2, y));
		dragNode.x = nx;
		dragNode.y = ny;
	}
}
game.move = handleMove;
game.down = function (x, y, obj) {
	// Only drag if touch is on hero
	var local = hero.toLocal(game.toGlobal({
		x: x,
		y: y
	}));
	if (local.x > -hero.width / 2 && local.x < hero.width / 2 && local.y > -hero.height / 2 && local.y < hero.height / 2) {
		dragNode = hero;
		handleMove(x, y, obj);
	}
};
game.up = function (x, y, obj) {
	dragNode = null;
};
// Tap to shoot
game.tap = function (x, y, obj) {
	fireHeroBullets();
};
// Main update
game.update = function () {
	// Hero update
	hero.update();
	// Fire hero bullets automatically if holding
	if (dragNode === hero && LK.ticks % 6 === 0) {
		fireHeroBullets();
	}
	// Update hero bullets
	for (var i = heroBullets.length - 1; i >= 0; i--) {
		var b = heroBullets[i];
		b.update();
		// Off screen
		if (b.y < -b.height) {
			b.destroy();
			heroBullets.splice(i, 1);
			continue;
		}
		// Hit alien
		for (var j = aliens.length - 1; j >= 0; j--) {
			var a = aliens[j];
			if (a.alive && b.intersects(a)) {
				a.flash();
				a.alive = false;
				a.destroy();
				aliens.splice(j, 1);
				b.destroy();
				heroBullets.splice(i, 1);
				score += 100;
				scoreTxt.setText(score);
				maybeSpawnPowerup(a.x, a.y);
				LK.getSound('explosion').play();
				break;
			}
		}
	}
	// Update alien bullets
	for (var i = alienBullets.length - 1; i >= 0; i--) {
		var b = alienBullets[i];
		b.update();
		if (b.y > GAME_HEIGHT + b.height) {
			b.destroy();
			alienBullets.splice(i, 1);
			continue;
		}
		// Hit hero
		if (!hero.invincible && b.intersects(hero)) {
			hero.flash();
			hero.setInvincible(60);
			b.destroy();
			alienBullets.splice(i, 1);
			LK.effects.flashScreen(0xff0000, 400);
			LK.getSound('explosion').play();
			// Game over
			LK.showGameOver();
			return;
		}
	}
	// Update aliens
	for (var i = aliens.length - 1; i >= 0; i--) {
		var a = aliens[i];
		a.update();
		// Fire bullet
		if (a.shootCooldown <= 0 && Math.random() < 0.012 + 0.002 * wave) {
			fireAlienBullet(a);
			a.shootCooldown = 60 + Math.floor(Math.random() * 60);
		}
		// Off screen (bottom)
		if (a.y > GAME_HEIGHT - 200) {
			LK.effects.flashScreen(0xff0000, 800);
			LK.showGameOver();
			return;
		}
		// Bounce alien off left/right borders
		if (a.x - a.width / 2 <= 0 && a.speedX < 0) {
			a.x = a.width / 2;
			a.speedX = -a.speedX;
		}
		if (a.x + a.width / 2 >= GAME_WIDTH && a.speedX > 0) {
			a.x = GAME_WIDTH - a.width / 2;
			a.speedX = -a.speedX;
		}
		// Remove alien if it goes off screen at the top
		if (a.y < -a.height) {
			a.destroy();
			aliens.splice(i, 1);
			continue;
		}
	}
	// Update powerups
	for (var i = powerups.length - 1; i >= 0; i--) {
		var p = powerups[i];
		p.update();
		if (p.y > GAME_HEIGHT + p.height) {
			p.destroy();
			powerups.splice(i, 1);
			continue;
		}
		// Collect
		if (p.intersects(hero)) {
			hero.upgrade();
			LK.getSound('powerup').play();
			p.destroy();
			powerups.splice(i, 1);
		}
	}
	// Next wave
	if (aliens.length === 0) {
		wave += 1;
		spawnWave(wave);
	}
};
// Start first wave
spawnWave(wave);
// Initial score
scoreTxt.setText(score);

===================================================================
--- original.js
+++ change.js
@@ -390,10 +390,19 @@
 			LK.effects.flashScreen(0xff0000, 800);
 			LK.showGameOver();
 			return;
 		}
-		// Remove alien if it goes off screen at the top or sides
-		if (a.x < -a.width || a.x > GAME_WIDTH + a.width || a.y < -a.height) {
+		// Bounce alien off left/right borders
+		if (a.x - a.width / 2 <= 0 && a.speedX < 0) {
+			a.x = a.width / 2;
+			a.speedX = -a.speedX;
+		}
+		if (a.x + a.width / 2 >= GAME_WIDTH && a.speedX > 0) {
+			a.x = GAME_WIDTH - a.width / 2;
+			a.speedX = -a.speedX;
+		}
+		// Remove alien if it goes off screen at the top
+		if (a.y < -a.height) {
 			a.destroy();
 			aliens.splice(i, 1);
 			continue;
 		}