# manual config
nix_version=2.3
nix_openpgp=B541D55301270E0BCF15CA5D8170B4726D7198DE
nixpkgs_channel=nixos-19.09-small
nixshell_sources=(shell.nix $(test ! -d shell || find shell -type f -not -name "*~" | sort))

# nix
if ! has nix || test "$(nix --version)" != "nix (Nix) $nix_version"
then log_status "installing Nix core tools"
	if test ! -e .config/nix/install -o ! -e .config/nix/install.asc
	then
		mkdir -p .config/nix
		(cd .config/nix; curl -OO https://nixos.org/releases/nix/nix-"$nix_version"/{install,install.asc})
		gpg2 --keyserver hkp://keys.gnupg.net --recv-keys "$nix_openpgp"
	fi
	test -e ~/.nix-profile/etc/profile.d/nix.sh || {
		gpg --verify .config/nix/install.asc
		sh .config/nix/install
	}
	. ~/.nix-profile/etc/profile.d/nix.sh
fi

# nixpkgs
if test ! -e .config/nixpkgs-channel/$nixpkgs_channel.nix
then log_status "installing nixpkgs from $nixpkgs_channel (This may take some time. To update: delete .config/nixpkgs-channel/$nixpkgs_channel.nix)"
  rev=$(curl -L https://nixos.org/channels/"$nixpkgs_channel"/git-revision | head -n1 | tr -dC 'a-z0-9')
  sha256=$(nix-prefetch-url --unpack https://github.com/NixOS/nixpkgs-channels/archive/"$rev".tar.gz)
  mkdir -p .config/nixpkgs-channel
  echo >.config/nixpkgs-channel/$nixpkgs_channel.nix "builtins.fetchTarball {url=\"https://github.com/NixOS/nixpkgs-channels/archive/$rev.tar.gz\"; sha256=\"$sha256\";}"
else log_status "using nixpkgs from $nixpkgs_channel"
fi
watch_file .config/nixpkgs-channel/$nixpkgs_channel.nix
# Get the store path of this nixpkgs,
# it will not be registered as a root for the garbage-collector
# but will be preserved as long as it is used by shell.nix
# which itself will produce a registered derivation.
nixpkgs=$(nix-instantiate --eval .config/nixpkgs-channel/$nixpkgs_channel.nix)
nixpkgs=${nixpkgs#'"'}
nixpkgs=${nixpkgs%'"'}
export NIX_PATH="${NIX_PATH:+$NIX_PATH:}nixpkgs=$nixpkgs"

# nix-shell
has shasum || fail "shasum is needed to cache environment"
for e in "${nixshell_sources[@]}"
do watch_file "$e"; done
hash=$(for e in "${nixshell_sources[@]}"; do shasum -a 256 "$e"; done | shasum -a 256 | cut -c -64)
if test -e ".cache/nix-shell/${hash}/dump"
then log_status "reusing .cache/nix-shell/$hash/"
else log_status "building .cache/nix-shell/$hash/"
  # Unregister previous derivations
  rm -rf ".cache/nix-shell"
  trap "rm -rf '$PWD/.cache/nix-shell'" EXIT
  mkdir -p ".cache/nix-shell/$hash"
  # Register the derivation as a root for the garbage-collector
  nix-instantiate >/dev/null ./shell.nix \
   --indirect --add-root .cache/nix-shell/"$hash"/shell.drv \
   ${TRACE:+--show-trace} \
   ${OFFLINE:+--option substituters ""}
  nix-store >/dev/null \
   --indirect --add-root .cache/nix-shell/"$hash"/shell.dep \
   ${OFFLINE:+--option substituters ""} \
   --realise $(nix-store --query --references .cache/nix-shell/"$hash"/shell.drv)
  # Dump the environment from within the nix-shell
  local dump
  dump="$(mktemp .cache/nix-shell/dump-XXXXXXXX)"
  if nix-shell ${TRACE:+--show-trace} --pure \
   --run "$(command -v direnv) dump" >"$dump" \
   ${OFFLINE:+--option substituters ""}
  then mv -f "$dump" .cache/nix-shell/"$hash"/dump
  else rm -f "$dump"; false
  fi
  trap "" EXIT
fi
# Load the cached environment
direnv_load cat .cache/nix-shell/"$hash"/dump
# Re-run the shellHook to update envvars like GPG_TTY
eval "$shellHook"