#!/usr/bin/env sh

ISO_PATH="/path/to/centos.iso" # Must be an absolute path.
USB_NAME="<USB>"
USB_PATH="/Volumes/$USB_NAME" # Must be an absolute path

# Mounting the ISO requires a privileged container.
docker run --rm -it --privileged \
           -v "$ISO_PATH":/centos.iso \
           -v "$USB_PATH":/usb \
            centos bash -c "
  echo -e '\033[0;32mInstalling Dependencies...\033[0m'
  sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-*
  sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-*
  yum install -y grub2 grub2-efi-x64-modules rsync genisoimage
  
  # Mount the ISO at /mnt to access its contents.
  mount -o ro /centos.iso /mnt
  ISO_NAME=\$(isoinfo -d -i /centos.iso | grep -i 'Volume id:' | cut -d' ' -f3-)
  
  # Store the name of the ISO for later
  ISO_NAME=\$(isoinfo -d -i /centos.iso | grep -i 'Volume id:' | cut -d' ' -f3-)

  # Copy the contents of the ISO to the USB drive
  echo -e '\033[0;32mCopying ISO contents...\033[0m'
  rsync -ra --info=progress2 /mnt/. /usb/

  # Generate a EFI boot image that can be used on Macs. It may be possible to
  # shorten this but it works.
  # This is adapted from https://unix.stackexchange.com/a/273334
  echo -e '\033[0;32mCreating EFI boot image...\033[0m'
  grub2-mkimage -O x86_64-efi -o /usb/EFI/BOOT/BOOTX64.EFI -p /efi/grub \
    disk part_msdos part_gpt linux loopback normal configfile test search \
    search_fs_uuid search_fs_file true iso9660 test  search_label efi_uga \
    efi_gop gfxterm gfxmenu gfxterm_menu fat ext2 ntfs cat echo ls memdisk tar

  # Replace the default boot drive name with the actual boot drive name.
  echo -e '\033[0;32mFixing grub.cfg...\033[0m'
  sed -i \"s/\$ISO_NAME/$USB_NAME/g\" /usb/EFI/BOOT/grub.cfg
  
  umount /mnt
"