We are building a single-page web app in one file: index.html
 We have phaser.min.js already in the current directory, so we can load it via <script src="phaser.min.js"></script>
 The game: top-down alien shooter with WASD movement, aiming and firing, waves of aliens, health, score, increasing difficulty.
 Since we cannot use external assets, all graphics must be procedurally generated (using Phaser's graphics API or simple shapes).

 Steps:
 1. We'll create an index.html file that includes:
    - A <style> section for minimal CSS (to make the canvas fullscreen or centered)
    - A <script src="phaser.min.js"></script>
    - A <script> section for our game code

 2. In the game code, we'll set up a Phaser game configuration and define the game states.

 3. We'll have:
    - A player (a rectangle or circle) that can move with WASD.
    - The player can aim with the mouse and fire with a mouse click.
    - Aliens (enemies) that spawn in waves and move toward the player.
    - The player has health. When hit by an alien, health decreases.
    - The player can shoot aliens to gain score.
    - Each wave increases the number of aliens and their speed (difficulty).

 4. We'll use Phaser's built-in physics (Arcade Physics) for collisions and movement.

 5. We'll generate graphics for the player, bullets, and aliens using Phaser.Graphics or by using simple sprites with filled rectangles/circles.

 6. We'll display the health and score on the screen.

 Implementation:

  - Preload: Since we have no assets, preload might be empty.
  - Create:
      * Set up the world, physics, and initial game state.
      * Create the player (a sprite with a rectangle graphic) and set physics properties.
      * Set up the cursor keys for WASD and mouse for aiming and shooting.
      * Create groups for bullets and aliens.
      * Initialize score and health variables and display them as text.

  - Update:
      * Handle player movement based on WASD.
      * Rotate the player to face the mouse pointer.
      * Spawn aliens in waves (using a timer or wave counter).
      * Move aliens toward the player.
      * Check for collisions between bullets and aliens, and between aliens and the player.

  - Shooting:
      * On mouse click, create a bullet at the player's position and set its velocity toward the mouse pointer.

  - Waves:
      * After all aliens of a wave are killed, start the next wave with more aliens and faster movement.

 7. We'll write the entire code in one go in the <script> tag.

 Let's structure the code:

  - We'll use a module pattern to avoid polluting the global scope.

  - We'll create a game configuration object and start the game.

  - We'll define a main scene that contains preload, create, and update functions.

  - We'll use the following:
        var config = {
            type: Phaser.AUTO,
            width: 800,
            height: 600,
            physics: {
                default: 'arcade',
                arcade: {
                    gravity: { y: 0 },
                    debug: false
                }
            },
            scene: {
                preload: preload,
                create: create,
                update: update
            }
        };

        var game = new Phaser.Game(config);

  - Then define the preload, create, and update functions.

 8. We'll keep track of:
        player, cursors, aliens, bullets, score, health, waveNumber

 9. For generating graphics dynamically, we can create a function that returns a generated texture for a rectangle or circle.

 However, for simplicity, we can also use the graphics API to draw directly. But note: we want good performance, so we can create a texture once and reuse it.

 Alternatively, we can use the `this.add.rectangle` and `this.add.circle` methods for the player and aliens? But then we cannot set a texture.

 Another way: create a bitmap data and use it as a texture.

 Since we are not using images, let's create a function to generate a texture for a sprite:

        function createColoredRectangle(scene, width, height, color) {
            // Create a new BitmapData object
            var bmd = scene.add.bitmapData(width, height);
            bmd.fill(color);
            return bmd;
        }

 But note: we can also just use a filled rectangle without a texture? Actually, we can use:

        this.add.rectangle(x, y, width, height, color);

 But then we cannot use it as a physics body? Actually, we can:

        var player = this.add.rectangle(400, 300, 40, 40, 0x00ff00);
        this.physics.add.existing(player);

 However, the documentation says that we can add physics to any Game Object. But let's test:

        We can do: 
          var player = this.physics.add.sprite(400, 300, 'playerTexture');
        and then create the texture in the preload.

 Since we are generating, we can do:

        preload: function() {
            // Create a player texture
            var playerTexture = this.textures.createCanvas('playerTexture', 40, 40);
            var ctx = playerTexture.getContext();
            ctx.fillStyle = '#00ff00';
            ctx.fillRect(0, 0, 40, 40);
            playerTexture.refresh();

            // Similarly for alien and bullet.
        }

 But note: we are in preload, and we can draw on a canvas texture.

 Alternatively, we can create the textures in the create function? Actually, preload is for loading assets, and create is for creating the game world.

 Since we are generating, we can do it in preload.

 However, we are going to do it in create for simplicity because we don't have to wait for the preload to complete.

 But the Phaser way is to preload. So let's preload by generating the textures.

 10. Steps for textures:

        preload: function() {
            // Player texture: green square
            this.textures.generate('player', {
                data: ['🟩'], // This is not going to work for a square? Let's use a canvas method.
                // Instead, let's use the canvas method.
            });

            // We can use the same method for all? Actually, we can generate via a function.

            // Alternatively, we can use the graphics API to draw and then generate a texture.

            // Since we are not loading anything, we can skip preload and create the textures in create.

            // But the Phaser documentation says we can create textures in create too.

            // Let's create the textures in create.

            // We'll skip preload entirely.
        }

        Then in create:

            // Create a texture for the player
            var graphics = this.add.graphics();
            graphics.fillStyle(0x00ff00, 1);
            graphics.fillRect(0, 0, 40, 40);
            var playerTexture = graphics.generateTexture('playerTexture', 40, 40);
            graphics.destroy();

            // Then create the sprite:
            player = this.physics.add.sprite(400, 300, 'playerTexture');

        But note: we can also use the graphics to draw the player? Actually, we want physics, so we need a sprite.

        Alternatively, we can use the `this.add.rectangle` and then enable physics on it? Let's check:

            var player = this.add.rectangle(400, 300, 40, 40, 0x00ff00);
            this.physics.add.existing(player);

        Then we can set the body as:

            player.body.setCollideWorldBounds(true);

        This should work.

        Similarly for aliens and bullets.

        We'll use rectangles for simplicity.

 11. Let's plan:

        Player: rectangle, green.
        Aliens: rectangle, red.
        Bullets: circle, yellow.

        We'll create groups for aliens and bullets.

 12. Code structure:

        var player;
        var cursors;
        var aliens;
        var bullets;
        var score = 0;
        var health = 100;
        var waveNumber = 1;
        var scoreText;
        var healthText;
        var waveText;

        function create() {
            // Set up the world
            // Create player
            player = this.add.rectangle(400, 300, 40, 40, 0x00ff00);
            this.physics.add.existing(player);
            player.body.setCollideWorldBounds(true);

            // Set up physics for groups
            aliens = this.physics.add.group();
            bullets = this.physics.add.group();

            // Set up keyboard input
            cursors = this.input.keyboard.createCursorKeys();
            // But we want WASD: we can use the key objects for W, A, S, D
            // Actually, we can use:
            keyW = this.input.keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.W);
            keyA = this.input.keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.A);
            keyS = this.input.keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.S);
            keyD = this.input.keyboard.addKey(Phaser.Input.Keyboard.KeyCodes.D);

            // Set up mouse input for shooting
            this.input.on('pointerdown', function (pointer) {
                // Create a bullet from player position
                var bullet = this.add.circle(player.x, player.y, 5, 0xffff00);
                this.physics.add.existing(bullet);
                bullets.add(bullet);

                // Set velocity toward the pointer
                var angle = Phaser.Math.Angle.Between(player.x, player.y, pointer.x, pointer.y);
                this.physics.velocityFromRotation(angle, 300, bullet.body.velocity);
            }, this);

            // Collisions
            this.physics.add.collider(bullets, aliens, function(bullet, alien) {
                bullet.destroy();
                alien.destroy();
                score += 10;
                scoreText.setText('Score: ' + score);
                // Check if all aliens are dead -> next wave
                if (aliens.countActive(true) === 0) {
                    nextWave.call(this);
                }
            });

            this.physics.add.collider(player, aliens, function(player, alien) {
                alien.destroy();
                health -= 10;
                healthText.setText('Health: ' + health);
                if (health <= 0) {
                    // Game over
                    // We can show a game over text and stop the game
                }
            });

            // Create text for score, health, wave
            scoreText = this.add.text(10, 10, 'Score: 0', { fontSize: '20px', fill: '#fff' });
            healthText = this.add.text(10, 40, 'Health: 100', { fontSize: '20px', fill: '#fff' });
            waveText = this.add.text(10, 70, 'Wave: 1', { fontSize: '20px', fill: '#fff' });

            // Start the first wave
            nextWave.call(this);
        }

        function nextWave() {
            // Increase wave number
            waveNumber++;
            waveText.setText('Wave: ' + waveNumber);

            // Spawn aliens: more aliens and faster as wave increases
            var numAliens = waveNumber * 5; // Example: 5, 10, 15, ...
            for (var i = 0; i < numAliens; i++) {
                // Spawn at random edge
                var x = Phaser.Math.Between(0, 800);
                var y = Phaser.Math.Between(0, 600);
                // But let's make them spawn off-screen? Or at the edges?
                // We'll spawn at the edges for now.
                var side = Phaser.Math.Between(0, 3);
                if (side === 0) { x = 0; }
                else if (side === 1) { x = 800; }
                else if (side === 2) { y = 0; }
                else { y = 600; }

                var alien = this.add.rectangle(x, y, 30, 30, 0xff0000);
                this.physics.add.existing(alien);
                aliens.add(alien);
            }

            // Set aliens to move toward the player
            aliens.children.iterate(function (alien) {
                // Move toward the player
                this.physics.moveToObject(alien, player, 100 + waveNumber * 10); // Speed increases with wave
            }, this);
        }

        function update() {
            // Player movement
            player.body.setVelocity(0);

            if (keyW.isDown) {
                player.body.setVelocityY(-200);
            } else if (keyS.isDown) {
                player.body.setVelocityY(200);
            }

            if (keyA.isDown) {
                player.body.setVelocityX(-200);
            } else if (keyD.isDown) {
                player.body.setVelocityX(200);
            }

            // Rotate player to face the mouse
            var pointer = this.input.activePointer;
            var angle = Phaser.Math.Angle.Between(player.x, player.y, pointer.x, pointer.y);
            player.rotation = angle + Math.PI/2; // Adjust because rectangle's default rotation is 0 pointing right? We want to point up? Actually, we can set the origin to center and then rotate.

            // But note: the rectangle doesn't have a rotation by default? Actually, it does. We can set the rotation.

            // Alternatively, we can use a sprite and set the texture to a rectangle? Then rotation would work.

            // Since we are using a rectangle, it doesn't have a natural forward direction? We can rotate it, but it's a square so it doesn't matter.

            // We'll skip rotation for the player? Or we can use a sprite with a generated texture that has a direction? 

            // Let's change the player to a sprite with a generated texture that is a triangle? So we can see the direction.

            // But the requirement says procedurally generated, so we can do:

            // In create, we generate a triangle for the player?

            // We'll stick with a rectangle and skip rotation for now? Or we can rotate the rectangle to face the mouse? It will look the same.

            // Actually, rotating a rectangle will look like a diamond? We want the player to face the mouse? We can use a circle for the player? Then rotation doesn't matter.

            // We'll change the player to a circle? Then we don't need to rotate.

            // Alternatively, we can draw a rectangle and then set the rotation? It will still be a rectangle, but rotated.

            // We'll keep it as a rectangle and rotate it to face the mouse? Then we can see the direction.

            // We'll set the rotation: 
            player.rotation = angle; // This will rotate the rectangle.

            // But note: the rectangle's origin is at the top-left? We want to rotate around the center.

            // We can set the origin to 0.5,0.5
            // We should set the origin in the create function for the player:
            player.setOrigin(0.5, 0.5);

            // Then rotation will be around the center.

            // We'll do that.

            // Also, we are moving the player with velocity, and the rotation doesn't affect movement? Correct, we are setting velocity independently.

            // So we are good.

            // Also, we are creating bullets from the player's center and they shoot in the direction of the mouse? Yes.

        }

 13. We'll adjust the player creation:

        player = this.add.rectangle(400, 300, 40, 40, 0x00ff00);
        player.setOrigin(0.5, 0.5); // Center the origin for rotation
        this.physics.add.existing(player);

 14. We'll also adjust the alien creation similarly? We don't rotate aliens, so we don't need to set origin? But we can set it to 0.5 for consistency.

        var alien = this.add.rectangle(x, y, 30, 30, 0xff0000);
        alien.setOrigin(0.5,0.5);
        this.physics.add.existing(alien);

 15. For bullets, we set the origin to 0.5 by default? Because circle is drawn from center.

 16. We also need to handle the game over condition.

        In the collision between player and alien, after reducing health:

            if (health <= 0) {
                // Game over
                this.physics.pause(); // Stop physics
                player.setTint(0xff0000); // Show red to indicate death
                // Show game over text
                var gameOverText = this.add.text(400, 300, 'Game Over', { fontSize: '64px', fill: '#ff0000' });
                gameOverText.setOrigin(0.5);
            }

 17. We'll also need to destroy the player? Or just stop.

 18. We'll write the entire index.html file with the above code.

 19. We'll also add some CSS to make the canvas centered.

        <style>
            body {
                margin: 0;
                padding: 0;
                display: flex;
                justify-content: center;
                align-items: center;
                height: 100vh;
                background-color: #000;
            }
        </style>

 20. The HTML structure:

        <!DOCTYPE html>
        <html>
        <head>
            <title>Alien Shooter</title>
            <style> ... </style>
            <script src="phaser.min.js"></script>
        </head>
        <body>
            <script>
                // Our game code
            </script>
        </body>
        </html>

 21. Let's write the code accordingly.

 Note: We are writing the entire game in one script tag.

 We'll write the code in a single script tag.

 Let's code accordingly.