myspaghetti/macos-virtualbox ? reverse-engineered prompt

Build me a simple bash tool that makes it easy to create a macOS virtual machine in VirtualBox on an x86 computer, for Windows, Linux, or macOS. I want it to automatically download the needed macOS installer files from Apple, set up the VM, and walk me through the install with as little manual work as possible, mostly just pressing Enter a few times.

It should support Catalina, Mojave, and High Sierra, and it should be able to show helpful setup and troubleshooting info from the script itself. Please make the script clear and self contained, with good error messages when the machine or VirtualBox setup won’t work, especially if the computer is using a virtualization mode that breaks macOS. If you can, add checks or prompts that make the install smoother, and include notes for things like disk size, screen resolution, iCloud and iMessage, and the known limits around audio, USB, FileVault, and other VirtualBox quirks. If something needs current docs or package details, look that up online.