import os
from datetime import datetime, timedelta

from google.cloud.bigtable import Client

project_id = os.environ.get("GCP_PROJECT", "delphi-prod")
instance_id = os.environ.get("INSTANCE_ID", "delphi-consumer-analytics-hdd")
cluster_id = os.environ.get("CLUSTER_ID", "stg-delphi-ca-hdd-us-east4-b")
expiration_days = int(os.environ.get("EXPIRATION_DAYS", "1"))

client = Client(project=project_id, admin=True)
instance = client.instance(instance_id)


def get_backup_id(table_name: str) -> str:
    """Helper function, adds current date as a suffix to a given string

    :param table_name: The name of the table
    :return: table name with a current date
    """
    from time import gmtime, strftime

    return """{}-{}""".format(table_name, strftime("%m%d%Y", gmtime()))


def get_expire_time() -> datetime:
    """Helper function, returns current date +{expiration_days} days

    :return: datetime object, the current date +{expiration_days} days
    """
    date = datetime.now()
    date += timedelta(days=expiration_days)
    return date


def main(event, context):
    """Background Cloud Function to be triggered by Pub/Sub.
    Args:
         event (dict):  The dictionary with data specific to this type of
         event. The `data` field contains the PubsubMessage message. The
         `attributes` field will contain custom attributes if there are any.
         context (google.cloud.functions.Context): The Cloud Functions event
         metadata. The `event_id` field contains the Pub/Sub message ID. The
         `timestamp` field contains the publish time.
    """
    print(
        """This Function was triggered by messageId {} published at {}
        """.format(
            context.event_id, context.timestamp
        )
    )

    import base64
    import json

    if "data" in event:
        data = json.loads(base64.b64decode(event["data"]).decode("utf-8"))
        if "tables" in data:
            for table_id in data["tables"]:
                table = instance.table(table_id)
                if not table.exists():
                    raise Exception(f"Table {table_id} doesn't exists.")
                backup_id = get_backup_id(table_id)
                expire_time = get_expire_time()

                print(f"Backup for {table_id} has started.")
                backup = table.backup(backup_id, cluster_id, expire_time)
                backup.create()
                print(f"Backup has {table_id} finished.")
            return 0
        else:
            raise Exception("expected list of tables not found in data")
    else:
        raise Exception("data is missing")