We need to create a single HTML file with canvas full-screen, fluid simulation with dye, interactive mouse drag pushes swirling colored dye.

Implement simple fluid simulation like Jos Stam stable fluids using Navier-Stokes, but can approximate with a simple implementation (e.g., based on a grid, velocity field, density field). Use JavaScript.

Full-screen canvas: set width/height to window.innerWidth/innerHeight, resize.

Implement fluid simulation with arrays for velocity (u,v) and density. Use time step, diffusion, viscosity. Use a standard stable fluids implementation.

Implement mouse drag: on mouse move with button down, add velocity at mouse position, add density of some dye color.

Add swirling colors: could have multiple dye components (e.g., three for RGB). Or store scalar density and map to color.

Simplify: use a single density for each pixel, with color derived from a hue based on time or something.

But requirement: swirling colored dye. Could have multiple dye sources with different colors. For simplicity, generate random hue for each injection.

Implement addDensity(x,y,amount) and addVelocity(x,y, amountX, amountY). We'll have array size N = 128 (grid). resolution adapt to screen.

Implementation: Use arrays of size (N+2)*(N+2) for each field to incorporate boundaries.

Implement functions: set_bnd, lin_solve, diffuse, advect, project.

I'll write all in JS within script tag.

Add main loop: requestAnimationFrame for updates.

Rendering: for each cell, draw a rectangle (or image) scaled to canvas. Better to use ImageData to set pixel colors from density*color.

We'll have a color field per cell (maybe store r,g,b). For injection, add to each component.

Simplify: store separate arrays for r,g,b densities.

Implement adding density of random color per mouse drag: generate hue, convert to rgb, add to respective density components.

Implement clearing, etc.

Now we need to write index.html in current dir.

Proceed to write file.