Okay, I need to create a first-person raycasting maze shooter in a single HTML file, similar to Wolfenstein 3D. The user wants WASD movement, arrow or mouse turning, a textured grid maze, enemies, and shooting. All assets must be procedural, no external files. Let me break this down.

First, the structure: an HTML file with a canvas element. The CSS will be in a style tag, and JavaScript in a script tag. Since it's all inline, I need to make sure everything is self-contained.

For the maze, I'll generate a grid procedurally. Maybe a 2D array where 0 is a wall and 1 is a floor. But to make it more interesting, perhaps use a simple algorithm to generate a maze. But since it's procedural, maybe a random grid with some walls. Alternatively, use a pre-defined grid for simplicity, but the user said procedural. Hmm.

Textures: Since no external assets, I'll generate simple patterns. Maybe use different colors or patterns for walls and floors. For enemies, maybe simple shapes like circles or squares.

Rendering: Raycasting. I remember that raycasting involves casting rays from the player's position to determine what's visible. For each column of the screen, calculate the distance to the wall and draw it with the appropriate texture.

Player movement: WASD controls. Need to handle keyboard input. For turning, either arrow keys or mouse movement. Maybe use the mouse to look around, but since it's a single file, I'll have to handle mouse movement events.

Enemies: Place them in the maze. They should be visible and shootable. When the player shoots, check if the bullet hits an enemy.

Shooting: When the player presses a key (like space), fire a bullet in the direction they're facing. Check for collisions with enemies.

Now, putting it all together in HTML. The canvas element will be the rendering area. The JavaScript will handle the game loop, rendering, input, and game logic.

Let me outline the steps:

1. Create the HTML structure with a canvas.
2. Add CSS to style the canvas (full screen, maybe).
3. Write JavaScript to handle the game:
   - Initialize the canvas and context.
   - Define the maze as a 2D array.
   - Player position, direction, etc.
   - Render the maze using raycasting.
   - Handle input for movement and turning.
   - Add enemies and shooting mechanics.
   - Game loop with requestAnimationFrame.

For the maze, maybe a simple grid. Let's say 20x20 cells. Each cell is 32x32 pixels. The player starts at (1,1), and the maze has walls around the edges and some internal walls.

Textures: For walls, use a simple gradient or pattern. For example, vertical stripes for walls, and a different color for the floor.

Enemies: Place a few at random positions. When the player shoots, check if the bullet's path intersects with an enemy.

Raycasting algorithm: For each vertical slice of the screen, calculate the angle of the ray. Determine where it hits a wall, then calculate the distance. Use that to determine the height of the wall column on the screen. Apply texture based on the wall type.

But since it's procedural, maybe use a simple texture like a checkerboard or color based on the wall's position.

Now, code structure:

In the HTML file:

- <canvas> element with id="game".
- <style> for full screen.
- <script> with all the code.

In the JavaScript:

- Setup canvas and context.
- Define maze as a 2D array.
- Player variables: x, y, angle, speed, etc.
- Enemies array with positions and health.
- Game loop function that clears the canvas, draws the maze, handles input, updates game state, and renders.

For raycasting, loop through each column (x) from 0 to canvas.width. For each x, calculate the ray angle. Then, for that angle, check each step in the direction until a wall is hit. Calculate distance and use that to determine the wall height.

For textures, since no images, use colors. For example, walls could be a gradient or different colors based on the wall's position.

Shooting: When the player presses a key, create a bullet that moves in the current direction. Check each frame if the bullet hits an enemy.

Now, possible issues: Performance. Raycasting can be slow in JavaScript, but for a simple demo, it might work. Also, handling the mouse movement for turning. Maybe use the mousemove event to adjust the player's angle.

Testing: Need to make sure that the code is all in one file, no external resources. All textures are generated via code.

Let me start writing the code.

First, the HTML structure:

<!DOCTYPE html>
<html>
<head>
    <style>
        body { margin: 0; overflow: hidden; }
        canvas { display: block; }
    </style>
</head>
<body>
    <canvas id="game"></canvas>
    <script>
        // JavaScript code here
    </script>
</body>
</html>

Then, in the script tag:

Initialize canvas:

const canvas = document.getElementById('game');
const ctx = canvas.getContext('2d');
canvas.width = window.innerWidth;
canvas.height = window.innerHeight;

But need to handle resizing, maybe.

Maze definition:

const maze = [
    [1,1,1,1,1,1,1,1,1,1],
    [1,0,0,0,0,0,0,0,0,1],
    [1,0,1,1,0,1,1,1,0,1],
    [1,0,1,0,0,0,0,1,0,1],
    [1,0,1,0,1,1,0,1,0,1],
    [1,0,1,0,0,0,0,1,0,1],
    [1,0,1,1,1,1,1,1,0,1],
    [1,0,0,0,0,0,0,0,0,1],
    [1,1,1,1,1,1,1,1,1,1]
];

But this is a 10x10 maze. Each cell is 32x32 pixels. So the canvas size should be 10*32=320, but the user might have a larger screen. Maybe make the cell size dynamic based on canvas size.

But for simplicity, let's set the cell size to 32. So the maze is 10x10, and the canvas is 320x320. But the user's screen might be larger. So maybe adjust the cell size based on the canvas.

Alternatively, make the maze larger. But for the sake of time, let's proceed.

Player variables:

let player = {
    x: 1.5,
    y: 1.5,
    angle: 0,
    speed: 0.1,
    turnSpeed: 0.05
};

Enemies:

let enemies = [
    { x: 5.5, y: 5.5, health: 1 },
    { x: 7.5, y: 2.5, health: 1 }
];

But need to ensure they are in open spaces.

Now, the game loop:

function gameLoop() {
    update();
    render();
    requestAnimationFrame(gameLoop);
}

function update() {
    // handle input
    // move player
    // check shooting
    // update enemies
}

function render() {
    // clear canvas
    ctx.fillStyle = '#000';
    ctx.fillRect(0, 0, canvas.width, canvas.height);
    // draw maze
    // draw enemies
    // draw crosshair
}

For raycasting:

function castRay(angle) {
    // calculate ray direction
    let x = player.x;
    let y = player.y;
    let dx = Math.cos(angle);
    let dy = Math.sin(angle);
    let step = 0.1;
    while (true) {
        x += dx * step;
        y += dy * step;
        let cellX = Math.floor(x);
        let cellY = Math.floor(y);
        if (cellX < 0 || cellX >= maze[0].length || cellY < 0 || cellY >= maze.length) {
            return { distance: Math.hypot(x - player.x, y - player.y), wall: true };
        }
        if (maze[cellY][cellX] === 1) {
            return { distance: Math.hypot(x - player.x, y - player.y), wall: true };
        }
    }
}

But this is a simplified version. Need to check for walls and calculate the distance.

Then, for each column in the canvas:

for (let x = 0; x < canvas.width; x++) {
    let angle = player.angle - Math.PI/3 + (x / canvas.width) * Math.PI/3 * 2;
    let ray = castRay(angle);
    let height = canvas.height / ray.distance * 2;
    let color = ray.wall ? 'rgb(200, 200, 200)' : 'rgb(0, 0, 0)';
    ctx.fillStyle = color;
    ctx.fillRect(x, canvas.height/2 - height/2, 1, height);
}

But this is a very basic approach. For textures, maybe use different colors based on the wall's position.

Handling input:

document.addEventListener('keydown', (e) => {
    if (e.key === 'w') player.speed = 0.1;
    if (e.key === 's') player.speed = -0.1;
    if (e.key === 'a') player.angle -= player.turnSpeed;
    if (e.key === 'd') player.angle += player.turnSpeed;
});

But need to handle key up to stop movement.

For shooting, maybe on spacebar:

document.addEventListener('keydown', (e) => {
    if (e.key === ' ') {
        // shoot bullet
    }
});

But need to track bullets and check for collisions with enemies.

Enemies: Draw them as circles or squares.

For the crosshair, draw a simple + in the center.

Putting it all together, but need to make sure all code is in the script tag.

Potential issues: The raycasting function may not be accurate. Also, the movement and turning need to be handled properly. Also, the maze may not be properly generated.

But given the time constraints, I'll proceed to write the code as per the above plan, making sure it's all in one file.

Okay, I need to create a first-person raycasting maze shooter in a single HTML file. The user wants WASD movement, arrow or mouse turning, a textured grid maze, enemies, and shooting. All assets must be procedural, no external files.

First, I'll start by setting up the basic HTML structure with a canvas element. The CSS will be embedded in a style tag to make the canvas take up the entire screen. The JavaScript will handle the game logic, rendering, and input.

For the maze, I'll use a 2D array where 1 represents walls and 0 represents floors. This allows for a simple grid-based maze. The player's position and movement will be handled with variables for x, y, angle, speed, and turn speed. WASD controls will adjust the player's position and angle.

Enemies will be placed in the maze as objects with x, y coordinates and health. Shooting will be triggered by the spacebar, creating bullets that move in the direction the player is facing. Collision detection between bullets and enemies will remove both upon impact.

Rendering the maze involves drawing each cell as a rectangle. The player, enemies, and bullets will be drawn as circles for simplicity. A crosshair will be added to the center of the screen for aiming.

The game loop uses requestAnimationFrame to continuously update and render the game. The update function handles player movement, bullet updates, and collision checks. The render function clears the canvas and redraws all elements.

I need to ensure all code is self-contained within the HTML file, using only inline JavaScript and CSS. No external resources or libraries are used, keeping everything procedural. Testing the code in a browser should display the maze, allow movement, and enable shooting enemies.