#!/nix/var/nix/profiles/execline/bin/execlineb -W

# Execute things in an ephemeral nix environment context, with similar
# syntax as `guix environment --ad-hoc`:
# nix-environment <package_1> [ ... <package_n> ] -- \
#   command [ <arg_1> [ ... <arg_n>]]

/nix/var/nix/profiles/execline/bin/define EL_BIN /nix/var/nix/profiles/execline/bin
${EL_BIN}/import PATH
${EL_BIN}/export PATH ${EL_BIN}:$PATH

${EL_BIN}/importas -i PACKAGE 1

ifelse {
  redirfd -w 1 /dev/null
  expr -- $PACKAGE != --
}
{
  ifelse {
    redirfd -w 1 /dev/null
    import \#
    expr $\# = 0
  }
  {
    fdmove 1 2
    echo "The '--' argument is required"
    exit 1
  }
  backtick PACKAGE_NETSTRING {
    execlineb -c "dollarat -d \"\"" $PACKAGE
  }
  multisubstitute {
    import PACKAGE_NETSTRING
    import -D "" NIX_ENVIRONMENT_PACKAGES
  }
  export NIX_ENVIRONMENT_PACKAGES ${NIX_ENVIRONMENT_PACKAGES}${PACKAGE_NETSTRING}
  importas -i SELF 0
  shift
  elgetpositionals
  emptyenv -P
  export PATH $PATH
  ${EL_BIN}/execlineb $SELF $@
}
shift
import -u -s -d "" NIX_ENVIRONMENT_PACKAGES
export PATH $PATH
nix-shell -p $NIX_ENVIRONMENT_PACKAGES --run
  "exec '${EL_BIN}/elgetpositionals' \\$@"