#  Copyright 2019-2020 The Lux Authors.
#
#  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 pandas as pd
import lux


def date_formatter(time_stamp, ldf):
    """
    Given a numpy timestamp and ldf, inspects which date granularity is appropriate and reformats timestamp accordingly

    Example
    ----------
    For changing granularity the results differ as so.
    days: '2020-01-01' -> '2020-1-1'
    months: '2020-01-01' -> '2020-1'
    years: '2020-01-01' -> '2020'

    Parameters
    ----------
    time_stamp: np.datetime64
            timestamp object holding the date information
    ldf : lux.core.frame
            LuxDataFrame with a temporal field

    Returns
    -------
    date_str: str
            A reformatted version of the time_stamp according to granularity
    """

    inverted_data_type = lux.config.executor.invert_data_type(ldf.data_type)
    # TODO: method for data_type_lookup to data_type
    datetime = pd.to_datetime(time_stamp)
    if inverted_data_type["temporal"]:
        # assumes only one temporal column, may need to change this function to recieve multiple temporal columns in the future
        date_column = ldf[inverted_data_type["temporal"][0]]

    granularity = compute_date_granularity(date_column)
    date_str = ""
    if granularity == "year":
        date_str += str(datetime.year)
    elif granularity == "month":
        date_str += str(datetime.year) + "-" + str(datetime.month)
    elif granularity == "day":
        date_str += str(datetime.year) + "-" + str(datetime.month) + "-" + str(datetime.day)
    else:
        # non supported granularity
        return datetime.date()

    return date_str


def compute_date_granularity(date_column: pd.core.series.Series):
    """
    Given a temporal column (pandas.core.series.Series), finds out the granularity of dates.

    Example
    ----------
    ['2018-01-01', '2019-01-02', '2018-01-03'] -> "day"
    ['2018-01-01', '2019-02-01', '2018-03-01'] -> "month"
    ['2018-01-01', '2019-01-01', '2020-01-01'] -> "year"

    Parameters
    ----------
    date_column: pandas.core.series.Series
            Column series with datetime type

    Returns
    -------
    field: str
            A str specifying the granularity of dates for the inspected temporal column
    """
    # supporting a limited set of Vega-Lite TimeUnit (https://vega.github.io/vega-lite/docs/timeunit.html)
    # corresponding to Pandas timescales
    date_fields = ["day", "month", "year", "dayofweek"]
    date_index = pd.DatetimeIndex(date_column)
    for field in date_fields:
        # can be changed to sum(getattr(date_index, field)) != 0
        if hasattr(date_index, field) and len(getattr(date_index, field).unique()) != 1:
            return field
    return "year"  # if none, then return year by default


def is_datetime_series(series: pd.Series) -> bool:

    """
    Check if the Series object is of datetime type

    Parameters
    ----------
    series : pd.Series

    Returns
    -------
    is_date: bool
    """
    return pd.api.types.is_datetime64_any_dtype(series) or pd.api.types.is_period_dtype(series)


def is_datetime_string(string: str) -> bool:
    """
    Check if the string is date-like.

    Parameters
    ----------
    string : str

    Returns
    -------
    is_date: bool
    """
    from dateutil.parser import parse

    try:
        parse(string)
        return True

    except ValueError:
        return False
