echoerr() {
  printf "\033[0;31m%s\033[0m" "$1" >&2
}

ensure_python_build_installed() {
  if [ ! -f "$(python_build_path)" ]; then
    download_python_build
  fi
}

download_python_build() {
  echo "Downloading python-build..." >&2
  local pyenv_url="https://github.com/pyenv/pyenv.git"
  git clone $pyenv_url "$(pyenv_path)"
}

python_build_path() {
  echo "$(pyenv_path)/plugins/python-build/bin/python-build"
}

update_python_build() {
  cd "$(pyenv_path)" && git fetch && git reset --hard origin/master > /dev/null 2>&1
}

pyenv_path() {
  echo "$(dirname $(dirname $0))/pyenv"
}

pyenv_update_timestamp_path() {
  echo "$(dirname $(dirname "$0"))/pyenv_last_update"
}

pyenv_should_update() {
  update_timeout=3600
  update_timestamp_path=$(pyenv_update_timestamp_path)

  if [ ! -f "$update_timestamp_path" ]; then
    return 0
  fi

  last_update=$(cat "$update_timestamp_path")
  current_timestamp=$(date +%s)
  invalidated_at=$(($last_update + $update_timeout))

  [ $invalidated_at -lt $current_timestamp ]
}

install_or_update_python_build() {
  if [ ! -f "$(python_build_path)" ]; then
    download_python_build
  elif pyenv_should_update; then
    update_python_build
    date +%s > "$(pyenv_update_timestamp_path)"
  fi
}