# shellcheck shell=bash

_nix_import_env() {
  local env=$1

  local term_backup=$TERM path_backup=$PATH
  if [[ -n ${TMPDIR+x} ]]; then
    local tmp_backup=$TMPDIR
  fi
  local impure_ssl_cert_file=${SSL_CERT_FILE:-__UNSET__}
  local impure_nix_ssl_cert_file=${NIX_SSL_CERT_FILE:-__UNSET__}

  eval "$env"

  # `nix-shell --pure` sets invalid ssl certificate paths
  if [[ "${SSL_CERT_FILE:-}" = /no-cert-file.crt ]]; then
    if [[ $impure_ssl_cert_file == __UNSET__ ]]; then
      unset SSL_CERT_FILE
    else
      export SSL_CERT_FILE=$impure_ssl_cert_file
    fi
  fi

  if [[ "${NIX_SSL_CERT_FILE:-}" = /no-cert-file.crt ]]; then
    if [[ $impure_nix_ssl_cert_file == __UNSET__ ]]; then
      unset NIX_SSL_CERT_FILE
    else
      export NIX_SSL_CERT_FILE=${impure_nix_ssl_cert_file}
    fi
  fi

  export PATH=$PATH:$path_backup TERM=$term_backup
  if [[ -n ${tmp_backup+x} ]]; then
    export TMPDIR=${tmp_backup}
  else
    unset TMPDIR
  fi

  # misleading since we are in an impure shell now
  export IN_NIX_SHELL=impure
}

_nix_add_gcroot() {
  local storepath=$1
  local symlink=$2

  local stripped_pwd=${PWD/\//}
  local escaped_pwd=${stripped_pwd//-/--}
  local escaped_pwd=${escaped_pwd//\//-}
  ln -fs "$storepath" "$symlink"
  ln -fs "$symlink" "/nix/var/nix/gcroots/per-user/$USER/$escaped_pwd"
}

use_flake() {
  watch_file flake.nix
  watch_file flake.lock

  local profile="$(direnv_layout_dir)/flake-profile"
  local profile_rc="${profile}.rc"

  if [[ ! -e "$profile" ]] || \
    [[ ! -e "$profile_rc" ]] || \
    [[ "$HOME/.direnvrc" -nt "$profile_rc" ]] || \
    [[ .envrc -nt "$profile_rc" ]] || \
    [[ flake.nix -nt "$profile_rc" ]] || \
    [[ flake.lock -nt "$profile_rc" ]];
  then
    local tmp_profile="$(direnv_layout_dir)/flake-profile.$$"
    [[ -d "$(direnv_layout_dir)" ]] || mkdir "$(direnv_layout_dir)"
    local tmp_profile_rc=$(nix print-dev-env --profile "$tmp_profile")
    drv=$(realpath "$tmp_profile")
    echo "$tmp_profile_rc" > "$profile_rc"
    rm -f "$tmp_profile" "$tmp_profile"*
    _nix_add_gcroot "$drv" "$profile"
    log_status renewed cache
  else
    log_status using cached dev shell
  fi

  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=${TEMPDIR:-__UNSET__}
  eval "$(< "$profile_rc")"
  # nix print-env-dev will create a temporary directory and use it a TMPDIR,
  # we cannot rely on this directory beeing not deleted at some point,
  # hence we are just removing it right away.
  if [[ "$NIX_BUILD_TOP" == */nix-shell.* && -d "$NIX_BUILD_TOP" ]]; then
    rmdir "$NIX_BUILD_TOP"
  fi

  if [[ "$old_nix_build_top" == __UNSET__ ]]; then
    unset NIX_BUILD_TOP
  else
    export NIX_BUILD_TOP=$old_nix_build_top
  fi
  if [[ "$old_tmp" == __UNSET__ ]]; then
    unset TMP
  else
    export TMP=$old_temp
  fi
  if [[ "$old_tmpdir" == __UNSET__ ]]; then
    unset TMPDIR
  else
    export TMPDIR=$old_tmpdir
  fi
  if [[ "$old_temp" == __UNSET__ ]]; then
    unset TEMP
  else
    export TEMP=$old_temp
  fi
  if [[ "$old_tempdir" == __UNSET__ ]]; then
    unset TEMPDIR
  else
    export TEMPDIR=$old_tempdir
  fi
}

use_nix() {
  local path direnv_dir
  path=$(nix-instantiate --find-file nixpkgs)
  direnv_dir=$(direnv_layout_dir)

  if [[ "${direnv:-}" == "" ]]; then
    log_status "\$direnv environment variable was not defined. Was this script run inside direnv?"
  fi

  local version
  if [[ -f "${path}/.version-suffix" ]]; then
    version=$(< "${path}/.version-suffix")
  elif [[ -f "${path}/.git/HEAD" ]]; then
    local head
    read -r head < "${path}/.git/HEAD"
    local regex="ref: (.*)"
    if [[ "$head" =~  $regex ]]; then
      read -r version < ".git/${BASH_REMATCH[1]}"
    else
      version="$head"
    fi
  fi

  local cache="$direnv_dir/cache-${version:-unknown}"

  local update_drv=0
  if [[ ! -e "$cache" ]] || \
    [[ "$HOME/.direnvrc" -nt "$cache" ]] || \
    [[ .envrc -nt "$cache" ]] || \
    [[ default.nix -nt "$cache" ]] || \
    [[ shell.nix -nt "$cache" ]];
  then
    [[ -d "$direnv_dir" ]] || mkdir "$direnv_dir"
    local dump_cmd tmp
    dump_cmd="echo -n _____direnv_____; \"$direnv\" dump bash"
    tmp=$(nix-shell --show-trace --pure "$@" --run "$dump_cmd" \
              | grep -oP '(?<=_____direnv_____).*')
    echo "$tmp" > "$cache"
    update_drv=1
  else
    log_status using cached derivation
  fi

  log_status eval "$cache"
  read -r cache_content < "$cache"
  _nix_import_env "$cache_content"

  # This part is based on https://discourse.nixos.org/t/what-is-the-best-dev-workflow-around-nix-shell/418/4
  if [[ "${out:-}" != "" ]] && (( update_drv )); then
    local drv_link="${direnv_dir}/drv" drv
    drv=$(nix show-derivation "$out" | grep -E -o -m1 '/nix/store/.*.drv')
    _nix_add_gcroot "$drv" "$drv_link"
    log_status renewed cache and derivation link
  fi

  if [[ "$#" == 0 ]]; then
    watch_file default.nix
    watch_file shell.nix
  fi
}