import hashlib


class AssetFingerprinter(object):
    """
    Get a unique hash for an asset file, so that it doesn't stay cached
    when it changes

    Usage:

        in the application
        template_data.asset_fingerprinter = AssetFingerprinter()

        where template data is how you pass variables to every template.

        in template.html:
        {{ asset_fingerprinter.get_url('stylesheets/application.css') }}

    * 'app/static' is assumed to be the root for all asset files
    """

    def __init__(self, asset_root="/static/", filesystem_path="app/static/"):
        self._cache = {}
        self._asset_root = asset_root
        self._filesystem_path = filesystem_path

    def get_url(self, asset_path, with_querystring_hash=True):
        if not with_querystring_hash:
            return self._asset_root + asset_path
        if asset_path not in self._cache:
            self._cache[asset_path] = (
                self._asset_root
                + asset_path
                + "?"
                + self.get_asset_fingerprint(self._filesystem_path + asset_path)
            )
        return self._cache[asset_path]

    def get_asset_fingerprint(self, asset_file_path):
        return hashlib.md5(  # nosec B324 - hash value is not verified, so md5 is fine
            self.get_asset_file_contents(asset_file_path)
        ).hexdigest()

    def get_asset_file_contents(self, asset_file_path):
        with open(asset_file_path, "rb") as asset_file:
            contents = asset_file.read()
        return contents


asset_fingerprinter = AssetFingerprinter()