#!/usr/bin/env bash

# The below code is taken largely from nix-direnv.
# nix-direnv's license is replicated below:
# 
# Copyright (c) 2019 Nix community projects
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

_nix_export_or_unset() {
  local key=$1 value=$2
  if [[ $value == __UNSET__ ]]; then
    unset "$key"
  else
    export "$key=$value"
  fi
}

use_flake_env() {
  local old_nix_build_top=${NIX_BUILD_TOP:-__UNSET__}
  local old_tmp=${TMP:-__UNSET__}
  local old_tmpdir=${TMPDIR:-__UNSET__}
  local old_temp=${TEMP:-__UNSET__}
  local old_tempdir=${TEMPDIR:-__UNSET__}
  local old_xdg_data_dirs=${XDG_DATA_DIRS:-}

  local ld
  ld=$(direnv_layout_dir)
  export direnv

  local flake_reference="${1:-"."}"
  shift

  eval "$(@flake_env@ "$ld" "$flake_reference" "$@")"

  export -n direnv

  # `nix print-dev-env` will create a temporary directory and use it as TMPDIR
  # We cannot rely on this directory being available at all times,
  # as it may be garbage collected.
  # Instead - just remove it immediately.
  # Use recursive & force as it may not be empty.
  if [[ -n ${NIX_BUILD_TOP+x} && $NIX_BUILD_TOP == */nix-shell.* && -d $NIX_BUILD_TOP ]]; then
    rm -rf "$NIX_BUILD_TOP"
  fi

  _nix_export_or_unset NIX_BUILD_TOP "$old_nix_build_top"
  _nix_export_or_unset TMP "$old_tmp"
  _nix_export_or_unset TMPDIR "$old_tmpdir"
  _nix_export_or_unset TEMP "$old_temp"
  _nix_export_or_unset TEMPDIR "$old_tempdir"
  local new_xdg_data_dirs=${XDG_DATA_DIRS:-}
  export XDG_DATA_DIRS=
  local IFS=:
  for dir in $new_xdg_data_dirs${old_xdg_data_dirs:+:}$old_xdg_data_dirs; do
    dir="${dir%/}" # remove trailing slashes
    if [[ :$XDG_DATA_DIRS: == *:$dir:* ]]; then
      continue # already present, skip
    fi
    XDG_DATA_DIRS="$XDG_DATA_DIRS${XDG_DATA_DIRS:+:}$dir"
  done
}