{ config, lib, pkgs, ... }:

with lib;

let

  cfg = config.virtualbox;

in {

  options = {
    virtualbox = {
      baseImageSize = mkOption {
        type = types.str;
        default = "10G";
        description = ''
          The size of the VirtualBox base image. The size string should be on
          a format the qemu-img command accepts.
        '';
      };
    };
  };

  config = {
    system.build.virtualBoxImage =
      pkgs.vmTools.runInLinuxVM (
        pkgs.runCommand "virtualbox-image"
          { memSize = 768;
            preVM =
              ''
                mkdir $out
                diskImage=$out/image
                ${pkgs.vmTools.qemu}/bin/qemu-img create -f raw $diskImage "${cfg.baseImageSize}"
                mv closure xchg/
              '';
            postVM =
              ''
                echo "creating VirtualBox disk image..."
                ${pkgs.vmTools.qemu}/bin/qemu-img convert -f raw -O vdi $diskImage $out/disk.vdi
                rm $diskImage
              '';
            buildInputs = [ pkgs.utillinux pkgs.perl ];
            exportReferencesGraph =
              [ "closure" config.system.build.toplevel ];
          }
          ''
            # Create a single / partition.
            ${pkgs.parted}/sbin/parted /dev/vda mklabel msdos
            ${pkgs.parted}/sbin/parted /dev/vda -- mkpart primary ext2 1M -1s
            . /sys/class/block/vda1/uevent
            mknod /dev/vda1 b $MAJOR $MINOR
  
            # Create an empty filesystem and mount it.
            ${pkgs.e2fsprogs}/sbin/mkfs.ext4 -L nixos /dev/vda1
            ${pkgs.e2fsprogs}/sbin/tune2fs -c 0 -i 0 /dev/vda1
            mkdir /mnt
            mount /dev/vda1 /mnt
  
            # The initrd expects these directories to exist.
            mkdir /mnt/dev /mnt/proc /mnt/sys
            mount --bind /proc /mnt/proc
            mount --bind /dev /mnt/dev
            mount --bind /sys /mnt/sys
  
            # Copy all paths in the closure to the filesystem.
            storePaths=$(perl ${pkgs.pathsFromGraph} /tmp/xchg/closure)
  
            echo "filling Nix store..."
            mkdir -p /mnt/nix/store
            set -f
            cp -prd $storePaths /mnt/nix/store/
  
            mkdir -p /mnt/etc/nix
            echo 'build-users-group = ' > /mnt/etc/nix/nix.conf
  
            # Register the paths in the Nix database.
            printRegistration=1 perl ${pkgs.pathsFromGraph} /tmp/xchg/closure | \
                chroot /mnt ${config.nix.package}/bin/nix-store --load-db
  
            # Create the system profile to allow nixos-rebuild to work.
            chroot /mnt ${config.nix.package}/bin/nix-env \
                -p /nix/var/nix/profiles/system --set ${config.system.build.toplevel}
  
            # `nixos-rebuild' requires an /etc/NIXOS.
            mkdir -p /mnt/etc/nixos
            touch /mnt/etc/NIXOS
  
            # `switch-to-configuration' requires a /bin/sh
            mkdir -p /mnt/bin
            ln -s ${config.system.build.binsh}/bin/sh /mnt/bin/sh
  
            # Generate the GRUB menu.
            ln -s vda /dev/sda
            chroot /mnt ${config.system.build.toplevel}/bin/switch-to-configuration boot
  
            umount /mnt/proc /mnt/dev /mnt/sys
            umount /mnt
          ''
      );
  
    system.build.virtualBoxOVA = pkgs.runCommand "virtualbox-ova"
      { buildInputs = [ pkgs.linuxPackages.virtualbox ];
        vmName = "NixOS ${config.system.nixosVersion} (${pkgs.stdenv.system})";
        fileName = "nixos-${config.system.nixosVersion}-${pkgs.stdenv.system}.ova";
      }
      ''
        echo "creating VirtualBox VM..."
        export HOME=$PWD
        VBoxManage createvm --name "$vmName" --register \
          --ostype ${if pkgs.stdenv.system == "x86_64-linux" then "Linux26_64" else "Linux26"}
        VBoxManage modifyvm "$vmName" \
          --memory 1536 --acpi on --vram 10 \
          --nictype1 virtio --nic1 nat \
          --audiocontroller ac97 --audio alsa \
          --rtcuseutc on \
          --usb on --mouse usbtablet
        VBoxManage storagectl "$vmName" --name SATA --add sata --portcount 4 --bootable on --hostiocache on
        VBoxManage storageattach "$vmName" --storagectl SATA --port 0 --device 0 --type hdd \
          --medium ${config.system.build.virtualBoxImage}/disk.vdi
  
        echo "exporting VirtualBox VM..."
        mkdir -p $out
        VBoxManage export "$vmName" --output "$out/$fileName"
      '';
  
    fileSystems."/".device = "/dev/disk/by-label/nixos";
  
    boot.loader.grub.version = 2;
    boot.loader.grub.device = "/dev/sda";
  
    services.virtualboxGuest.enable = true;
  };
}