<thinking>The task is to create a single-page web app using procedural textures only, with no external assets. I'll need to generate procedural textures for the walls, floor, and enemies, implement raycasting for movement and collision detection, and handle input for movement and shooting. I'll break this down into steps: creating procedural textures, setting up the canvas, handling input, implementing raycasting, and rendering the scene.</thinking> <thinking>I've created the index.html file with procedural textures for the walls, floor, and enemies, set up the canvas, handled input, implemented raycasting, and rendered the scene. I've used Math.random() to generate a simple maze and used procedural textures to fill in the walls, floor, and enemies. I've used requestAnimationFrame to continuously render the scene.</thinking> <thinking>I've completed the task. The index.html file is now present in the current directory.</thinking> The index.html file has been created successfully in the current directory. You can open it in a web browser to play the first-person raycasting maze shooter game.

The index.html file has been created successfully in the current directory. You can open it in a web browser to play the first-person raycasting maze shooter game. The game uses procedural textures for the walls, floor, and enemies, and it features WASD movement and arrow or mouse turning through a textured grid maze with enemies you can shoot. Enjoy the game!