{pkgs, config, ...}:

###### implementation

let
  inherit (pkgs) e2fsprogs;
  mountPoints = map (fs: fs.mountPoint) fileSystems;
  fileSystems = config.fileSystems;
  devices = map (fs: if fs ? device then fs.device else "LABEL=" + fs.label) fileSystems;
  fsTypes = map (fs: if fs ? fsType then fs.fsType else "auto") fileSystems;
  optionss = map (fs: if fs ? options then fs.options else "defaults") fileSystems;
  autocreates = map (fs: if fs ? autocreate then fs.autocreate else "0") fileSystems;
  mount = config.system.sbin.mount;

  job = ''
  start on startup
  start on new-devices
  start on ip-up
  
  script
    PATH=${e2fsprogs}/sbin:$PATH
  
    mountPoints=(${toString mountPoints})  
    devices=(${toString devices})
    fsTypes=(${toString fsTypes})
    optionss=(${toString optionss})
    autocreates=(${toString autocreates})
  
    newDevices=1
  
    # If we mount any file system, we repeat this loop, because new
    # mount opportunities may have become available (such as images
    # for loopback mounts).
  
    while test -n "$newDevices"; do
  
      newDevices=
  
      for ((n = 0; n < ''${#mountPoints[*]}; n++)); do
        mountPoint=''${mountPoints[$n]}
        device=''${devices[$n]}
        fsType=''${fsTypes[$n]}
        options=''${optionss[$n]}
        autocreate=''${autocreates[$n]}
  
        isLabel=
        if echo "$device" | grep -q '^LABEL='; then isLabel=1; fi
  
        isPseudo=
        if test "$fsType" = "nfs" || test "$fsType" = "tmpfs" ||
          test "$fsType" = "ext3cow"; then isPseudo=1; fi
  
        if ! test -n "$isLabel" -o -n "$isPseudo" -o -e "$device"; then
            echo "skipping $device, doesn't exist (yet)"
            continue
        fi
  
        # !!! quick hack: if mount point already exists, try a
        # remount to change the options but nothing else.
        if cat /proc/mounts | grep -F -q " $mountPoint "; then
            echo "remounting $device on $mountPoint"
            ${mount}/bin/mount -t "$fsType" \
                -o remount,"$options" \
                "$device" "$mountPoint" || true
            continue
        fi
  
        # If $device is already mounted somewhere else, unmount it first.
        # !!! Note: we use /etc/mtab, not /proc/mounts, because mtab
        # contains more accurate info when using loop devices.
  
        # !!! not very smart about labels yet; should resolve the label somehow.
        if test -z "$isLabel" -a -z "$isPseudo"; then
  
          device=$(readlink -f "$device")
  
          prevMountPoint=$(
              cat /etc/mtab \
              | grep "^$device " \
              | sed 's|^[^ ]\+ \+\([^ ]\+\).*|\1|' \
          )
  
          if test "$prevMountPoint" = "$mountPoint"; then
              echo "remounting $device on $mountPoint"
              ${mount}/bin/mount -t "$fsType" \
                  -o remount,"$options" \
                  "$device" "$mountPoint" || true
              continue
          fi
  
          if test -n "$prevMountPoint"; then
              echo "unmount $device from $prevMountPoint"
              ${mount}/bin/umount "$prevMountPoint" || true
          fi
  
        fi
  
        echo "mounting $device on $mountPoint"
  
        # !!! should do something with the result; also prevent repeated fscks.
        if test -z "$isPseudo"; then
            fsck -a "$device" || true
        fi
  
        if test "$autocreate" = 1; then mkdir -p "$mountPoint"; fi
  
        if ${mount}/bin/mount -t "$fsType" -o "$options" "$device" "$mountPoint"; then
            newDevices=1
        fi
  
      done
  
    done
  
  end script
  '';
in

{
  services = {
    extraJobs = [{
      name = "filesystems";
      inherit job;
    }];
  };
}