.direnvrc

# Usage: use_nix [...]
#
# Load environment variables from `nix-shell`.
# If you have a `default.nix` or `shell.nix` one of these will be used and
# the derived environment will be stored at ./.direnv/env-<hash>
# and symlink to it will be created at ./.direnv/default.
# Dependencies are added to the GC roots, such that the environment remains persistent.
#
# The resulting environment is cached for better performance.
#
# To trigger switch to a different environment:
# `rm -f .direnv/default`
#
# To derive a new environment:
# `rm -rf .direnv/env-$(md5sum {shell,default}.nix 2> /dev/null | cut -c -32)`
#
# To remove cache:
# `rm -f .direnv/dump-*`
#
# To remove all environments:
# `rm -rf .direnv/env-*`
#
# To remove only old environments:
# `find .direnv -name 'env-*' -and -not -name `readlink .direnv/default` -exec rm -rf {} +`
#

set -eo pipefail

use_nix() {
	# define all local variables
	local shell f env_hash dir default wd drv dump path_backup
	local files_to_watch=()

        declare opt
        declare OPTARG
        declare OPTIND

	while getopts ":s:w:" opt; do
		case "${opt}" in
			s)
				shell="${OPTARG}"
				files_to_watch=("${files_to_watch[@]}" "${shell}")
				;;
			w)
				files_to_watch=("${files_to_watch[@]}" "${OPTARG}")
				;;
			:)
				>&2 echo "Invalid option: $OPTARG requires an argument"
				;;
			\?)
				>&2 echo "Invalid option: $OPTARG"
				exit 1
				;;
		esac
	done
	shift $((OPTIND -1))

	if [[ -z "${shell}" ]]; then
		>&2 echo "ERR: no shell was given"
		exit 1
	fi

	for f in "${files_to_watch[@]}"; do
		if ! [[ -f "${f}" ]]; then
			>&2 echo "cannot watch file ${f} because it does not exist"
			exit 1
		fi
	done

	# compute the hash of all the files that makes up the development environment
	env_hash="$(hashContents "${files_to_watch[@]}")"

	dir="$(direnv_layout_dir)"
	default="${dir}/default"
	if [[ ! -L "${default}" ]] || [[ ! -d $(readlink "${default}") ]]; then
		wd="${dir}/env-${env_hash}"
		mkdir -p "${wd}"

		drv="${wd}/env.drv"
		if [[ ! -f "${drv}" ]]; then
			log_status "use nix: deriving new environment"
			IN_NIX_SHELL=1 nix-instantiate --add-root "${drv}" --indirect "${shell}" > /dev/null
			nix-store -r $(nix-store --query --references "${drv}") --add-root "${wd}/dep" --indirect > /dev/null
		fi

		rm -f "${default}"
		ln -s $(basename "${wd}") "${default}"
	fi

	drv=$(readlink "${default}/env.drv")
	dump="${dir}/dump-$(hashFile ".envrc")-$(hashFile ${drv})"

	if [[ ! -f "${dump}" ]] || [[ "${XDG_CONFIG_DIR}/direnv/direnvrc" -nt "${dump}" ]]; then
		log_status "use nix: updating cache"

		old=$(find "${dir}" -name 'dump-*')
		nix-shell --pure "${drv}" --show-trace --run "$(join_args "$direnv" dump bash)" > "${dump}"
		rm -f ${old}
	fi

	# evaluate the dump created by nix-shell earlier, but have to merge the PATH
	# with the current PATH
	# NOTE: we eval the dump here as opposed to direnv_load it because we don't
	# want to persist environment variables coming from the shell at the time of
	# the dump. See https://github.com/direnv/direnv/issues/405 for context.
	path_backup="${PATH}"
	eval $(cat "${dump}")
	export PATH="${PATH}:${path_backup}"

	for f in "${files_to_watch[@]}"; do
		watch_file "${f}"
	done
}

hashContents() {
	if has md5sum; then
		cat "${@}" | md5sum | cut -c -32
	elif has md5; then
		cat "${@}" | md5 -q
	fi
}

hashFile() {
	if has md5sum; then
		md5sum "${@}" | cut -c -32
	elif has md5; then
		md5 -q "${@}"
	fi
}

fail() {
	log_error "${@}"
	exit 1
}

validateVersion() {
	local version="$("${direnv}" version)"
	local major="$(echo "${version}" | cut -d. -f1)"
	local minor="$(echo "${version}" | cut -d. -f2)"
	local patch="$(echo "${version}" | cut -d. -f3)"

	if [[ "${major}" -gt 2 ]]; then return 0; fi
	if [[ "${major}" -eq 2 ]] && [[ "${minor}" -gt 18 ]]; then return 0; fi
	if [[ "${major}" -eq 2 ]] && [[ "${minor}" -eq 18 ]] && [[ "${patch}" -ge 2 ]]; then return 0; fi
	return 1
}

if ! validateVersion; then
	echo "This .envrc requires direnv version 2.18.2 or above."
	exit 1
fi