# manual config
nix_version=2.3
nix_openpgp=B541D55301270E0BCF15CA5D8170B4726D7198DE
nixpkgs_channel=nixos-19.09-small
nixshell_sources=(.envrc 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=\"$sha256\";}"
else log_status "using nixpkgs from .config/nixpkgs-channel/$nixpkgs_channel.nix"
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=${nixpkgs%'"'}
#export NIX_PATH="nixpkgs=$nixpkgs${NIX_PATH:+:$NIX_PATH}"

# nix-shell
has shasum || { log_error "shasum is needed to cache environment"; return 1; }
for e in "${nixshell_sources[@]}"
do watch_file "$e"; done
hash=$(shasum -a 256 "${nixshell_sources[@]}" | shasum -a 256 | cut -c -64)
if test -e ".cache/nix-shell/$hash/dump"
then
  log_status "reusing .cache/nix-shell/$hash/"
  # Load the cached environment
  direnv_load cat .cache/nix-shell/"$hash"/dump
  # Re-run the shellHook to update envvars like GPG_TTY,
  # and run gpg-connect-agent updatestartuptty /bye
  eval "$shellHook"
else log_status "building .cache/nix-shell/$hash/"
  mkdir -p ".cache/nix-shell/$hash"
  local dump="$(mktemp .cache/nix-shell/$hash/dump-XXXXXXXX)"
  # Register the derivation as a root for the garbage-collector,
  # then cache a dump of the environment from within the nix-shell,
  # then unregister previous derivations,
  # then load the cached environment.
  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) &&
  nix-shell >"$dump" ${TRACE:+--show-trace} --pure \
  --run "$(join_args "$direnv" dump)" \
   ${OFFLINE:+--option substituters ""} &&
  mv -f "$dump" .cache/nix-shell/"$hash"/dump &&
  find .cache/nix-shell -mindepth 1 -maxdepth 1 -not -name "$hash" -exec rm -rf {} + &&
  direnv_load cat .cache/nix-shell/"$hash"/dump || {
    rm -rf "$PWD/.cache/nix-shell/$hash"
    log_error "cannot build shell.nix"
    return 1
  }
fi