#!/usr/bin/env bash
# Enter the dev shell without re-fetching nixpkgs.
#
# flake.nix pins nixos-26.05. When the machine already has that revision in its
# store (NixOS systems built from the same channel usually do), pointing the
# input at the local path skips the tarball fetch entirely and makes
# `nix develop` near-instant. Falls back to the pinned input otherwise.
set -euo pipefail

local_nixpkgs=$(nix registry list 2>/dev/null |
	awk '$1 == "system" && $2 == "flake:nixpkgs" { print $3 }' |
	sed 's/?.*//')

args=()
if [[ -n ${local_nixpkgs} && -d ${local_nixpkgs#path:} ]]; then
	args=(--override-input nixpkgs "${local_nixpkgs}")
fi

exec nix develop "${args[@]}" --command "${@:-bash}"