# Copyright 2022 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import random
import string
import pandas as pd
from google.cloud import bigquery

random.seed(1236)

# Generate a uuid of a specifed length(default=8)
def generate_uuid(length: int = 8) -> str:
    return "".join(random.choices(string.ascii_lowercase + string.digits, k=length))


def download_bq_table(bq_table_uri: str) -> pd.DataFrame:
    """This function downloads a BigQuery table and returns a dataframe

    Args:
        bq_table_uri (str): BigQuery uri of the table

    Returns:
        pd.DataFrame: table data in dataframe format
    """
    # Remove bq:// prefix if present
    prefix = "bq://"
    if bq_table_uri.startswith(prefix):
        bq_table_uri = bq_table_uri[len(prefix) :]

    client = bigquery.Client()

    table = client.get_table(bq_table_uri)
    rows = client.list_rows(table)

    return rows.to_dataframe()


def save_dataframe_to_bigquery(dataframe: pd.DataFrame, table_name: str) -> str:
    """This function loads a dataframe to a new bigquery table

    Args:
        dataframe (pd.Dataframe): dataframe to be loaded to bigquery
        table_name (str): name of the bigquery table that is being created

    Returns:
        str: table id of the destination bigquery table
    """
    client = bigquery.Client()
    project_id = client.project
    dataset_id = generate_uuid()

    bq_dataset = bigquery.Dataset(f"{project_id}.{dataset_id}")
    bq_dataset = client.create_dataset(bq_dataset, exists_ok=True)

    job_config = bigquery.LoadJobConfig(
        # Specify a (partial) schema. All columns are always written to the
        # table. The schema is used to assist in data type definitions.
        schema=[
            bigquery.SchemaField("date", bigquery.enums.SqlTypeNames.DATE),
        ],
        # Optionally, set the write disposition. BigQuery appends loaded rows
        # to an existing table by default, but with WRITE_TRUNCATE write
        # disposition it replaces the table with the loaded data.
        write_disposition="WRITE_TRUNCATE",
    )

    # Reference: https://cloud.google.com/bigquery/docs/samples/bigquery-load-table-dataframe
    job = client.load_table_from_dataframe(
        dataframe=dataframe,
        destination=f"{project_id}.{dataset_id}.{table_name}",
        job_config=job_config,
    )

    job.result()

    return str(job.destination)