Okay, the user wants a Tetris game in a single HTML file with all the features. Let me start by outlining the structure. I need HTML, CSS, and JavaScript all in one file. The canvas will be the main element for rendering the game.

First, I'll set up the HTML structure with a canvas element and elements for the next piece and score. Then, the CSS will style the canvas and the UI elements. The JavaScript will handle the game logic.

For the tetrominoes, I'll define each shape using matrices. The rotation logic needs to handle the rotation of each piece, making sure it stays within bounds and doesn't collide with other pieces. The game loop will handle the falling of pieces, line clearing, and increasing the speed as the game progresses.

The next-piece preview will require a separate canvas or div to display the next shape. The score will increment based on the number of lines cleared, with increasing points for more lines at once.

I'll need to handle keyboard inputs for moving and rotating the pieces. Collision detection is crucial to check if a piece can move or rotate without overlapping existing blocks.

Putting it all together, I'll write the JavaScript functions for creating the game board, drawing the pieces, updating the game state, and handling user input. The game loop will use requestAnimationFrame for smooth animation.

Finally, I'll ensure that all the code is self-contained within the HTML file, with no external dependencies. Testing each part as I go to make sure everything works together.

Okay, the user wanted a Tetris game in a single HTML file. I used the write function to create index.html with all the necessary HTML, CSS, and JavaScript. The file includes a canvas for the game, a scoreboard, and next-piece preview. The JavaScript handles game logic like piece movement, rotation, collision detection, line clearing, and scoring. I made sure everything is self-contained without external resources. Now, the index.html is ready, and the user can open it in a browser to play the game.