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"""Utilities for creating a virtual environment"""
import os
from typing import List, Optional

import jinja2

from airflow.utils.process_utils import execute_in_subprocess


def _generate_virtualenv_cmd(tmp_dir: str, python_bin: str, system_site_packages: bool) -> List[str]:
    cmd = ['virtualenv', tmp_dir]
    if system_site_packages:
        cmd.append('--system-site-packages')
    if python_bin is not None:
        cmd.append('--python={}'.format(python_bin))
    return cmd


def _generate_pip_install_cmd(tmp_dir: str, requirements: List[str]) -> Optional[List[str]]:
    if not requirements:
        return None
    # direct path alleviates need to activate
    cmd = ['{}/bin/pip'.format(tmp_dir), 'install']
    return cmd + requirements


def prepare_virtualenv(
    venv_directory: str,
    python_bin: str,
    system_site_packages: bool,
    requirements: List[str]
) -> str:
    """
    Creates a virtual environment and installs the additional python packages

    :param venv_directory: The path for directory where the environment will be created
    :type venv_directory: str
    :param python_bin: Path for python binary
    :type python_bin: str
    :param system_site_packages: Whether to include system_site_packages in your virtualenv.
        See virtualenv documentation for more information.
    :type system_site_packages: bool
    :param requirements: List of additional python packages
    :type requirements: List[str]
    :return: Path to a binary file with Python in a virtual environment.
    :rtype: str
    """
    virtualenv_cmd = _generate_virtualenv_cmd(venv_directory, python_bin, system_site_packages)
    execute_in_subprocess(virtualenv_cmd)
    pip_cmd = _generate_pip_install_cmd(venv_directory, requirements)
    if pip_cmd:
        execute_in_subprocess(pip_cmd)

    return '{}/bin/python'.format(venv_directory)


def write_python_script(jinja_context: dict, filename: str):
    """
    Renders the python script to a file to execute in the virtual environment.

    :param jinja_context: The jinja context variables to unpack and replace with its placeholders in the
        template file.
    :type jinja_context: dict
    :param filename: The name of the file to dump the rendered script to.
    :type filename: str
    """
    template_loader = jinja2.FileSystemLoader(searchpath=os.path.dirname(__file__))
    template_env = jinja2.Environment(
        loader=template_loader,
        undefined=jinja2.StrictUndefined
    )
    template = template_env.get_template('python_virtualenv_script.jinja2')
    template.stream(**jinja_context).dump(filename)
