import zipfile
import os

from pip._internal import main as pip_main


def create_dependency_layer():
    """
    Installs dependencies in a target directory and then
    packages it into a zip file that can be used by CDK
    to create Lambda dependency layer
    """

    # file paths
    requirements_file_path = "requirements.txt"
    target_directory = "python"
    zip_file_path = "dependency-layer.zip"

    # change directory so that relative paths work
    cwd = os.getcwd()
    os.chdir("lambda")

    # create new dependency zip only if it doesn't exist
    if not os.path.isfile(zip_file_path):

        pip_main(
            [
                "install",
                "-r",
                requirements_file_path,
                "--target",
                target_directory,
            ]
        )

        # package dependencies as a zip file
        dep_zip = zipfile.ZipFile(zip_file_path, "w", zipfile.ZIP_DEFLATED)

        for root, dirs, files in os.walk(target_directory):
            for file in files:
                dep_zip.write(os.path.join(root, file))

        dep_zip.close()

    # change directory back
    os.chdir(cwd)


if __name__ == "__main__":
    create_dependency_layer()