#
# Copyright 2013 Quantopian, Inc.
#
# 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 numpy as np
import pandas as pd

import pandas_datareader.data as pd_reader


def get_benchmark_returns(symbol, first_date, last_date):
    """
    Get a Series of benchmark returns from Google associated with `symbol`.
    Default is `SPY`.

    Parameters
    ----------
    symbol : str
        Benchmark symbol for which we're getting the returns.
    first_date : pd.Timestamp
        First date for which we want to get data.
    last_date : pd.Timestamp
        Last date for which we want to get data.

    The furthest date that Google goes back to is 1993-02-01. It has missing
    data for 2008-12-15, 2009-08-11, and 2012-02-02, so we add data for the
    dates for which Google is missing data.

    We're also limited to 4000 days worth of data per request. If we make a
    request for data that extends past 4000 trading days, we'll still only
    receive 4000 days of data.

    first_date is **not** included because we need the close from day N - 1 to
    compute the returns for day N.
    """
    if symbol == '^GSPC':
        symbol = 'spy'

    data = pd_reader.DataReader(
        symbol,
        'google',
        first_date,
        last_date
    )

    data = data['Close']

    data[pd.Timestamp('2008-12-15')] = np.nan
    data[pd.Timestamp('2009-08-11')] = np.nan
    data[pd.Timestamp('2012-02-02')] = np.nan

    data = data.fillna(method='ffill')

    return data.sort_index().tz_localize('UTC').pct_change(1).iloc[1:]