config.nix

{ lib, stdenv }:

{ paths, disabledDefaultBackends ? [] }:

with lib;
let
installSanePath = path: ''
      if [ -e "${path}/lib/sane" ]; then
        find "${path}/lib/sane" -maxdepth 1 -not -type d | while read backend; do
          symlink "$backend" "$out/lib/sane/$(basename "$backend")"
        done
      fi

      if [ -e "${path}/etc/sane.d" ]; then
        find "${path}/etc/sane.d" -maxdepth 1 -not -type d | while read conf; do
          name="$(basename $conf)"
          if [ "$name" = "dll.conf" ] || [ "$name" = "saned.conf" ] || [ "$name" = "net.conf" ]; then
            cat "$conf" >> "$out/etc/sane.d/$name"
          else
            symlink "$conf" "$out/etc/sane.d/$name"
          fi
        done
      fi

      if [ -e "${path}/etc/sane.d/dll.d" ]; then
        find "${path}/etc/sane.d/dll.d" -maxdepth 1 -not -type d | while read conf; do
          symlink "$conf" "$out/etc/sane.d/dll.d/$(basename $conf)"
        done
      fi
    '';
    disableBackend = backend: ''
      grep -q '${backend}' $out/etc/sane.d/dll.conf || { echo '${backend} is not a default plugin in $SANE_CONFIG_DIR/dll.conf'; exit 1; }
      substituteInPlace $out/etc/sane.d/dll.conf --replace '${backend}' '# ${backend} disabled in nixos config'
    '';
in
stdenv.mkDerivation {
  name = "sane-config";
  dontUnpack = true;

  installPhase = ''
    function symlink () {
      local target=$1 linkname=$2
      if [ -e "$linkname" ]; then
        echo "warning: conflict for $linkname. Overriding $(readlink $linkname) with $target."
      fi
      ln -sfn "$target" "$linkname"
    }

    mkdir -p $out/etc/sane.d $out/etc/sane.d/dll.d $out/lib/sane
  ''
  + (concatMapStrings installSanePath paths)
  + (concatMapStrings disableBackend disabledDefaultBackends);
}