{ stdenv, xorgserver }:

# !!! What does this package do, and does it belong in Nixpkgs?

stdenv.mkDerivation {
  name = "xlaunch";
  inherit xorgserver;
  buildCommand = "
    cat << EOF > realizeuid.c
    #include <sys/types.h>
    #include <unistd.h>
    #include <stdio.h>
    int main(int argc, char ** argv, char ** envp)
    {
      uid_t a,b,c;
      int i;
      char *nargv[10000];
      char arg1 [10];
      nargv[0]=argv[0];
      for (i=1; i<=argc; i++){
        nargv[i+1]=argv[i];
      }
      nargv[1]=arg1;
      getresuid (&a,&b,&c);
      snprintf(arg1,8,\"%d\",a);
      setresuid(c,c,c);
      execve(\"\$out/libexec/xlaunch\", nargv, envp);
    }
EOF
    mkdir -p \$out/bin
    mkdir -p \$out/libexec
    gcc realizeuid.c -o \$out/bin/xlaunch
    echo '#! ${stdenv.shell}
      USER=\$(egrep '\\''^[-a-z0-9A-Z_]*:[^:]*:'\\''\$1'\\'':'\\'' /etc/passwd | sed -e '\\''s/:.*//'\\'' )
      shift
      case \"\$1\" in 
        :*) export _display=\"\$1\"; 
        shift
      esac
      _display=\${_display:-:0}
      _display=\${_display#:}
      echo Using :\$_display
      if [ -n \"\$DO_X_RESET\" ]; then 
        RESET_OPTION=\"-once\"
      else
        RESET_OPTION=\"-noreset\"
      fi;
      XCMD=\"\$(egrep \"^Environment=\" /etc/systemd/system/display-manager.service | sed -e \"s/Environment=/ export /\" | sed -e '\\''s/#.*//'\\'' ; echo export _XARGS_=\\\$\\( grep xserver_arguments \\\$SLIM_CFGFILE \\| sed -e s/xserver_arguments// \\| sed -e s/:0/:\${_display}/ \\| sed -e s/vt7/vt\$((7+_display))/ \\) ; echo ${xorgserver}/bin/X \\\$_XARGS_ \$RESET_OPTION )\" 
      PRE_XCMD=\"\$(egrep \"^ExecStartPre=\" /etc/systemd/system/display-manager.service | sed -e \"\s/ExecStartPre=//\")\"
      echo \"\$PRE_XCMD\" 
      echo \"\$PRE_XCMD\" | bash
      echo \"\$XCMD\" 
      echo \"\$XCMD\" | bash &
      while ! test -e /tmp/.X11-unix/X\$_display &>/dev/null ; do sleep 0.5; done
      su -l \${USER:-identityless-shelter} -c \"DISPLAY=:\$_display \$*\";
    ' >\$out/libexec/xlaunch
    chmod a+x \$out/libexec/xlaunch
  ";
  meta = {
    description = ''Wrapper to parse NixOS-specific X environment and launch a custom X session'';
    maintainers = [ stdenv.lib.maintainers.raskin ];
  };
}