# Note: This is a private API, internal to NixOS. Its interface is subject
# to change without notice.
#
# The result of this builder is a single disk image, partitioned like this:
#
#  * partition #1: a very small, 1MiB partition to leave room for Grub.
#
#  * partition #2: boot, a partition formatted with FAT to be used for /boot.
#      FAT is chosen to support EFI.
#
#  * partition #3: nixos, a partition dedicated to a zpool.
#
# This single-disk approach does not satisfy ZFS's requirements for autoexpand,
# however automation can expand it anyway. For example, with
# `services.zfs.expandOnBoot`.
{
  lib,
  pkgs,
  # The NixOS configuration to be installed onto the disk image.
  config,

  # size of the FAT partition, in megabytes.
  bootSize ? 1024

  , # memory allocated for virtualized build instance
  memSize ? 1024,

  # The size of the root partition, in megabytes.
  rootSize ? 2048,

  # The name of the ZFS pool
  rootPoolName ? "tank",

  # zpool properties
  rootPoolProperties ? {
    autoexpand = "on";
  },
  # pool-wide filesystem properties
  rootPoolFilesystemProperties ? {
    acltype = "posixacl";
    atime = "off";
    compression = "on";
    mountpoint = "legacy";
    xattr = "sa";
  },

  # datasets, with per-attribute options:
  # mount: (optional) mount point in the VM
  # properties: (optional) ZFS properties on the dataset, like filesystemProperties
  # Notes:
  # 1. datasets will be created from shorter to longer names as a simple topo-sort
  # 2. you should define a root's dataset's mount for `/`
  datasets ? { },

  # The files and directories to be placed in the target file system.
  # This is a list of attribute sets {source, target} where `source'
  # is the file system object (regular file or directory) to be
  # grafted in the file system at path `target'.
  contents ? [ ],

  # The initial NixOS configuration file to be copied to
  # /etc/nixos/configuration.nix. This configuration will be embedded
  # inside a configuration which includes the described ZFS fileSystems.
  configFile ? null,

  # Shell code executed after the VM has finished.
  postVM ? "",

  name ? "nixos-disk-image",

  # Disk image format, one of qcow2, qcow2-compressed, vdi, vpc, raw.
  format ? "raw",

  # Include a copy of Nixpkgs in the disk image
  includeChannel ? true,
}:
let
  formatOpt = if format == "qcow2-compressed" then "qcow2" else format;

  compress = lib.optionalString (format == "qcow2-compressed") "-c";

  filenameSuffix =
    "."
    + {
      qcow2 = "qcow2";
      vdi = "vdi";
      vpc = "vhd";
      raw = "img";
    }
    .${formatOpt} or formatOpt;
  rootFilename = "nixos.root${filenameSuffix}";

  # FIXME: merge with channel.nix / make-channel.nix.
  channelSources =
    let
      nixpkgs = lib.cleanSource pkgs.path;
    in
    pkgs.runCommand "nixos-${config.system.nixos.version}" { } ''
      mkdir -p $out
      cp -prd ${nixpkgs.outPath} $out/nixos
      chmod -R u+w $out/nixos
      if [ ! -e $out/nixos/nixpkgs ]; then
        ln -s . $out/nixos/nixpkgs
      fi
      rm -rf $out/nixos/.git
      echo -n ${config.system.nixos.versionSuffix} > $out/nixos/.version-suffix
    '';

  closureInfo = pkgs.closureInfo {
    rootPaths = [ config.system.build.toplevel ] ++ (lib.optional includeChannel channelSources);
  };

  modulesTree = pkgs.aggregateModules (
    with config.boot.kernelPackages;
    [
      kernel
      zfs
    ]
  );

  tools = lib.makeBinPath (
    with pkgs;
    [
      nixos-enter
      config.system.build.nixos-install
      dosfstools
      e2fsprogs
      gptfdisk
      nix
      parted
      util-linux
      zfs
    ]
  );

  hasDefinedMount = disk: ((disk.mount or null) != null);

  stringifyProperties =
    prefix: properties:
    lib.concatStringsSep " \\\n" (
      lib.mapAttrsToList (
        property: value: "${prefix} ${lib.escapeShellArg property}=${lib.escapeShellArg value}"
      ) properties
    );

  createDatasets =
    let
      datasetlist = lib.mapAttrsToList lib.nameValuePair datasets;
      sorted = lib.sort (
        left: right: (lib.stringLength left.name) < (lib.stringLength right.name)
      ) datasetlist;
      cmd =
        { name, value }:
        let
          properties = stringifyProperties "-o" (value.properties or { });
        in
        "zfs create -p ${properties} ${name}";
    in
    lib.concatMapStringsSep "\n" cmd sorted;

  mountDatasets =
    let
      datasetlist = lib.mapAttrsToList lib.nameValuePair datasets;
      mounts = lib.filter ({ value, ... }: hasDefinedMount value) datasetlist;
      sorted = lib.sort (
        left: right: (lib.stringLength left.value.mount) < (lib.stringLength right.value.mount)
      ) mounts;
      cmd =
        { name, value }:
        ''
          mkdir -p /mnt${lib.escapeShellArg value.mount}
          mount -t zfs ${name} /mnt${lib.escapeShellArg value.mount}
        '';
    in
    lib.concatMapStringsSep "\n" cmd sorted;

  unmountDatasets =
    let
      datasetlist = lib.mapAttrsToList lib.nameValuePair datasets;
      mounts = lib.filter ({ value, ... }: hasDefinedMount value) datasetlist;
      sorted = lib.sort (
        left: right: (lib.stringLength left.value.mount) > (lib.stringLength right.value.mount)
      ) mounts;
      cmd =
        { name, value }:
        ''
          umount /mnt${lib.escapeShellArg value.mount}
        '';
    in
    lib.concatMapStringsSep "\n" cmd sorted;

  fileSystemsCfgFile =
    let
      mountable = lib.filterAttrs (_: value: hasDefinedMount value) datasets;
    in
    pkgs.runCommand "filesystem-config.nix"
      {
        buildInputs = with pkgs; [
          jq
          nixpkgs-fmt
        ];
        filesystems = builtins.toJSON {
          fileSystems = lib.mapAttrs' (dataset: attrs: {
            name = attrs.mount;
            value = {
              fsType = "zfs";
              device = "${dataset}";
            };
          }) mountable;
        };
        passAsFile = [ "filesystems" ];
      }
      ''
        (
          echo "builtins.fromJSON '''"
          jq . < "$filesystemsPath"
          echo "'''"
        ) > $out

        nixpkgs-fmt $out
      '';

  mergedConfig =
    if configFile == null then
      fileSystemsCfgFile
    else
      pkgs.runCommand "configuration.nix"
        {
          buildInputs = with pkgs; [ nixpkgs-fmt ];
        }
        ''
          (
            echo '{ imports = ['
            printf "(%s)\n" "$(cat ${fileSystemsCfgFile})";
            printf "(%s)\n" "$(cat ${configFile})";
            echo ']; }'
          ) > $out

          nixpkgs-fmt $out
        '';

  image =
    (pkgs.vmTools.override {
      rootModules = [
        "zfs"
        "9p"
        "9pnet_virtio"
        "virtio_pci"
        "virtio_blk"
      ];
      kernel = modulesTree;
    }).runInLinuxVM
      (
        pkgs.runCommand name
          {
            inherit memSize;
            QEMU_OPTS = "-drive file=$rootDiskImage,if=virtio,cache=unsafe,werror=report";
            preVM = ''
              PATH=$PATH:${pkgs.qemu_kvm}/bin
              mkdir $out

              rootDiskImage=root.raw
              qemu-img create -f raw $rootDiskImage ${toString (bootSize + rootSize)}M
            '';

            postVM = ''
              ${
                if formatOpt == "raw" then
                  ''
                    mv $rootDiskImage $out/${rootFilename}
                  ''
                else
                  ''
                    ${pkgs.qemu_kvm}/bin/qemu-img convert -f raw -O ${formatOpt} ${compress} $rootDiskImage $out/${rootFilename}
                  ''
              }
              rootDiskImage=$out/${rootFilename}
              set -x
              ${postVM}
            '';
          }
          ''
            export PATH=${tools}:$PATH
            set -x

            cp -sv /dev/vda /dev/sda
            cp -sv /dev/vda /dev/xvda

            parted --script /dev/vda -- \
              mklabel gpt \
              mkpart no-fs 1MiB 2MiB \
              set 1 bios_grub on \
              align-check optimal 1 \
              mkpart primary fat32 2MiB ${toString bootSize}MiB \
              align-check optimal 2 \
              mkpart primary fat32 ${toString bootSize}MiB -1MiB \
              align-check optimal 3 \
              print

            sfdisk --dump /dev/vda


            zpool create \
              ${stringifyProperties "  -o" rootPoolProperties} \
              ${stringifyProperties "  -O" rootPoolFilesystemProperties} \
              ${rootPoolName} /dev/vda3
            parted --script /dev/vda -- print

            ${createDatasets}
            ${mountDatasets}

            mkdir -p /mnt/boot
            mkfs.vfat -n ESP /dev/vda2
            mount /dev/vda2 /mnt/boot

            mount

            # Install a configuration.nix
            mkdir -p /mnt/etc/nixos
            # `cat` so it is mutable on the fs
            cat ${mergedConfig} > /mnt/etc/nixos/configuration.nix

            export NIX_STATE_DIR=$TMPDIR/state
            nix-store --load-db < ${closureInfo}/registration

            nixos-install \
              --root /mnt \
              --no-root-passwd \
              --system ${config.system.build.toplevel} \
              --substituters "" \
              ${lib.optionalString includeChannel ''--channel ${channelSources}''}

            df -h

            umount /mnt/boot
            ${unmountDatasets}

            zpool export ${rootPoolName}
          ''
      );
in
image