"""Main entry point for the documentation build process."""

import os


def define_env(env):
    """Define custom environment variables for the documentation build process."""

    @env.macro
    def listimages(subdir):
        """Return a listing of all asset files in the provided subdir."""
        here = os.path.dirname(__file__)

        directory = os.path.join(here, 'docs', 'assets', 'images', subdir)

        assets = []

        allowed = ['.png', '.jpg']

        for asset in os.listdir(directory):
            if any(asset.endswith(x) for x in allowed):
                assets.append(os.path.join(subdir, asset))

        return assets
