from datetime import datetime, timedelta, time
import numpy as np
from collections import MutableMapping

import pandas.lib as lib
import pandas.tslib as tslib

from pandas.types.common import (_ensure_object,
                                 is_datetime64_ns_dtype,
                                 is_datetime64_dtype,
                                 is_datetime64tz_dtype,
                                 is_integer_dtype,
                                 is_list_like)
from pandas.types.generic import (ABCIndexClass, ABCSeries,
                                  ABCDataFrame)
from pandas.types.missing import notnull

import pandas.compat as compat
from pandas.util.decorators import deprecate_kwarg

_DATEUTIL_LEXER_SPLIT = None
try:
    # Since these are private methods from dateutil, it is safely imported
    # here so in case this interface changes, pandas will just fallback
    # to not using the functionality
    from dateutil.parser import _timelex

    if hasattr(_timelex, 'split'):
        def _lexer_split_from_str(dt_str):
            # The StringIO(str(_)) is for dateutil 2.2 compatibility
            return _timelex.split(compat.StringIO(str(dt_str)))

        _DATEUTIL_LEXER_SPLIT = _lexer_split_from_str
except (ImportError, AttributeError):
    pass


def _infer_tzinfo(start, end):
    def _infer(a, b):
        tz = a.tzinfo
        if b and b.tzinfo:
            if not (tslib.get_timezone(tz) == tslib.get_timezone(b.tzinfo)):
                raise AssertionError('Inputs must both have the same timezone,'
                                     ' {0} != {1}'.format(tz, b.tzinfo))
        return tz
    tz = None
    if start is not None:
        tz = _infer(start, end)
    elif end is not None:
        tz = _infer(end, start)
    return tz


def _guess_datetime_format(dt_str, dayfirst=False,
                           dt_str_parse=compat.parse_date,
                           dt_str_split=_DATEUTIL_LEXER_SPLIT):
    """
    Guess the datetime format of a given datetime string.

    Parameters
    ----------
    dt_str : string, datetime string to guess the format of
    dayfirst : boolean, default False
        If True parses dates with the day first, eg 20/01/2005
        Warning: dayfirst=True is not strict, but will prefer to parse
        with day first (this is a known bug).
    dt_str_parse : function, defaults to `compat.parse_date` (dateutil)
        This function should take in a datetime string and return
        a `datetime.datetime` guess that the datetime string represents
    dt_str_split : function, defaults to `_DATEUTIL_LEXER_SPLIT` (dateutil)
        This function should take in a datetime string and return
        a list of strings, the guess of the various specific parts
        e.g. '2011/12/30' -> ['2011', '/', '12', '/', '30']

    Returns
    -------
    ret : datetime format string (for `strftime` or `strptime`)
    """
    if dt_str_parse is None or dt_str_split is None:
        return None

    if not isinstance(dt_str, compat.string_types):
        return None

    day_attribute_and_format = (('day',), '%d', 2)

    # attr name, format, padding (if any)
    datetime_attrs_to_format = [
        (('year', 'month', 'day'), '%Y%m%d', 0),
        (('year',), '%Y', 0),
        (('month',), '%B', 0),
        (('month',), '%b', 0),
        (('month',), '%m', 2),
        day_attribute_and_format,
        (('hour',), '%H', 2),
        (('minute',), '%M', 2),
        (('second',), '%S', 2),
        (('microsecond',), '%f', 6),
        (('second', 'microsecond'), '%S.%f', 0),
    ]

    if dayfirst:
        datetime_attrs_to_format.remove(day_attribute_and_format)
        datetime_attrs_to_format.insert(0, day_attribute_and_format)

    try:
        parsed_datetime = dt_str_parse(dt_str, dayfirst=dayfirst)
    except:
        # In case the datetime can't be parsed, its format cannot be guessed
        return None

    if parsed_datetime is None:
        return None

    try:
        tokens = dt_str_split(dt_str)
    except:
        # In case the datetime string can't be split, its format cannot
        # be guessed
        return None

    format_guess = [None] * len(tokens)
    found_attrs = set()

    for attrs, attr_format, padding in datetime_attrs_to_format:
        # If a given attribute has been placed in the format string, skip
        # over other formats for that same underlying attribute (IE, month
        # can be represented in multiple different ways)
        if set(attrs) & found_attrs:
            continue

        if all(getattr(parsed_datetime, attr) is not None for attr in attrs):
            for i, token_format in enumerate(format_guess):
                token_filled = tokens[i].zfill(padding)
                if (token_format is None and
                        token_filled == parsed_datetime.strftime(attr_format)):
                    format_guess[i] = attr_format
                    tokens[i] = token_filled
                    found_attrs.update(attrs)
                    break

    # Only consider it a valid guess if we have a year, month and day
    if len(set(['year', 'month', 'day']) & found_attrs) != 3:
        return None

    output_format = []
    for i, guess in enumerate(format_guess):
        if guess is not None:
            # Either fill in the format placeholder (like %Y)
            output_format.append(guess)
        else:
            # Or just the token separate (IE, the dashes in "01-01-2013")
            try:
                # If the token is numeric, then we likely didn't parse it
                # properly, so our guess is wrong
                float(tokens[i])
                return None
            except ValueError:
                pass

            output_format.append(tokens[i])

    guessed_format = ''.join(output_format)

    # rebuild string, capturing any inferred padding
    dt_str = ''.join(tokens)
    if parsed_datetime.strftime(guessed_format) == dt_str:
        return guessed_format


def _guess_datetime_format_for_array(arr, **kwargs):
    # Try to guess the format based on the first non-NaN element
    non_nan_elements = notnull(arr).nonzero()[0]
    if len(non_nan_elements):
        return _guess_datetime_format(arr[non_nan_elements[0]], **kwargs)


@deprecate_kwarg(old_arg_name='coerce', new_arg_name='errors',
                 mapping={True: 'coerce', False: 'raise'})
def to_datetime(arg, errors='raise', dayfirst=False, yearfirst=False,
                utc=None, box=True, format=None, exact=True, coerce=None,
                unit=None, infer_datetime_format=False):
    """
    Convert argument to datetime.

    Parameters
    ----------
    arg : string, datetime, list, tuple, 1-d array, Series

        .. versionadded: 0.18.1

           or DataFrame/dict-like

    errors : {'ignore', 'raise', 'coerce'}, default 'raise'

        - If 'raise', then invalid parsing will raise an exception
        - If 'coerce', then invalid parsing will be set as NaT
        - If 'ignore', then invalid parsing will return the input
    dayfirst : boolean, default False
        Specify a date parse order if `arg` is str or its list-likes.
        If True, parses dates with the day first, eg 10/11/12 is parsed as
        2012-11-10.
        Warning: dayfirst=True is not strict, but will prefer to parse
        with day first (this is a known bug, based on dateutil behavior).
    yearfirst : boolean, default False
        Specify a date parse order if `arg` is str or its list-likes.

        - If True parses dates with the year first, eg 10/11/12 is parsed as
          2010-11-12.
        - If both dayfirst and yearfirst are True, yearfirst is preceded (same
          as dateutil).

        Warning: yearfirst=True is not strict, but will prefer to parse
        with year first (this is a known bug, based on dateutil beahavior).

        .. versionadded: 0.16.1

    utc : boolean, default None
        Return UTC DatetimeIndex if True (converting any tz-aware
        datetime.datetime objects as well).
    box : boolean, default True

        - If True returns a DatetimeIndex
        - If False returns ndarray of values.
    format : string, default None
        strftime to parse time, eg "%d/%m/%Y", note that "%f" will parse
        all the way up to nanoseconds.
    exact : boolean, True by default

        - If True, require an exact format match.
        - If False, allow the format to match anywhere in the target string.

    unit : string, default 'ns'
        unit of the arg (D,s,ms,us,ns) denote the unit in epoch
        (e.g. a unix timestamp), which is an integer/float number.
    infer_datetime_format : boolean, default False
        If True and no `format` is given, attempt to infer the format of the
        datetime strings, and if it can be inferred, switch to a faster
        method of parsing them. In some cases this can increase the parsing
        speed by ~5-10x.

    Returns
    -------
    ret : datetime if parsing succeeded.
        Return type depends on input:

        - list-like: DatetimeIndex
        - Series: Series of datetime64 dtype
        - scalar: Timestamp

        In case when it is not possible to return designated types (e.g. when
        any element of input is before Timestamp.min or after Timestamp.max)
        return will have datetime.datetime type (or correspoding array/Series).

    Examples
    --------

    Assembling a datetime from multiple columns of a DataFrame. The keys can be
    common abbreviations like ['year', 'month', 'day', 'minute', 'second',
    'ms', 'us', 'ns']) or plurals of the same

    >>> df = pd.DataFrame({'year': [2015, 2016],
                           'month': [2, 3],
                           'day': [4, 5]})
    >>> pd.to_datetime(df)
    0   2015-02-04
    1   2016-03-05
    dtype: datetime64[ns]

    If a date that does not meet timestamp limitations, passing errors='coerce'
    will force to NaT. Furthermore this will force non-dates to NaT as well.

    >>> pd.to_datetime('13000101', format='%Y%m%d')
    datetime.datetime(1300, 1, 1, 0, 0)
    >>> pd.to_datetime('13000101', format='%Y%m%d', errors='coerce')
    NaT

    Passing infer_datetime_format=True can often-times speedup a parsing
    if its not an ISO8601 format exactly, but in a regular format.

    >>> s = pd.Series(['3/11/2000', '3/12/2000', '3/13/2000']*1000)

    >>> s.head()
    0    3/11/2000
    1    3/12/2000
    2    3/13/2000
    3    3/11/2000
    4    3/12/2000
    dtype: object

    >>> %timeit pd.to_datetime(s,infer_datetime_format=True)
    100 loops, best of 3: 10.4 ms per loop

    >>> %timeit pd.to_datetime(s,infer_datetime_format=False)
    1 loop, best of 3: 471 ms per loop

    """

    from pandas.tseries.index import DatetimeIndex

    tz = 'utc' if utc else None

    def _convert_listlike(arg, box, format, name=None, tz=tz):

        if isinstance(arg, (list, tuple)):
            arg = np.array(arg, dtype='O')

        # these are shortcutable
        if is_datetime64_ns_dtype(arg):
            if box and not isinstance(arg, DatetimeIndex):
                try:
                    return DatetimeIndex(arg, tz=tz, name=name)
                except ValueError:
                    pass

            return arg

        elif is_datetime64tz_dtype(arg):
            if not isinstance(arg, DatetimeIndex):
                return DatetimeIndex(arg, tz=tz, name=name)
            if utc:
                arg = arg.tz_convert(None).tz_localize('UTC')
            return arg

        elif unit is not None:
            if format is not None:
                raise ValueError("cannot specify both format and unit")
            arg = getattr(arg, 'values', arg)
            result = tslib.array_with_unit_to_datetime(arg, unit,
                                                       errors=errors)
            if box:
                if errors == 'ignore':
                    from pandas import Index
                    return Index(result)

                return DatetimeIndex(result, tz=tz, name=name)
            return result
        elif getattr(arg, 'ndim', 1) > 1:
            raise TypeError('arg must be a string, datetime, list, tuple, '
                            '1-d array, or Series')

        arg = _ensure_object(arg)
        require_iso8601 = False

        if infer_datetime_format and format is None:
            format = _guess_datetime_format_for_array(arg, dayfirst=dayfirst)

        if format is not None:
            # There is a special fast-path for iso8601 formatted
            # datetime strings, so in those cases don't use the inferred
            # format because this path makes process slower in this
            # special case
            format_is_iso8601 = _format_is_iso(format)
            if format_is_iso8601:
                require_iso8601 = not infer_datetime_format
                format = None

        try:
            result = None

            if format is not None:
                # shortcut formatting here
                if format == '%Y%m%d':
                    try:
                        result = _attempt_YYYYMMDD(arg, errors=errors)
                    except:
                        raise ValueError("cannot convert the input to "
                                         "'%Y%m%d' date format")

                # fallback
                if result is None:
                    try:
                        result = tslib.array_strptime(arg, format, exact=exact,
                                                      errors=errors)
                    except tslib.OutOfBoundsDatetime:
                        if errors == 'raise':
                            raise
                        result = arg
                    except ValueError:
                        # if format was inferred, try falling back
                        # to array_to_datetime - terminate here
                        # for specified formats
                        if not infer_datetime_format:
                            if errors == 'raise':
                                raise
                            result = arg

            if result is None and (format is None or infer_datetime_format):
                result = tslib.array_to_datetime(
                    arg,
                    errors=errors,
                    utc=utc,
                    dayfirst=dayfirst,
                    yearfirst=yearfirst,
                    require_iso8601=require_iso8601
                )

            if is_datetime64_dtype(result) and box:
                result = DatetimeIndex(result, tz=tz, name=name)
            return result

        except ValueError as e:
            try:
                values, tz = tslib.datetime_to_datetime64(arg)
                return DatetimeIndex._simple_new(values, name=name, tz=tz)
            except (ValueError, TypeError):
                raise e

    if arg is None:
        return arg
    elif isinstance(arg, tslib.Timestamp):
        return arg
    elif isinstance(arg, ABCSeries):
        from pandas import Series
        values = _convert_listlike(arg._values, False, format)
        return Series(values, index=arg.index, name=arg.name)
    elif isinstance(arg, (ABCDataFrame, MutableMapping)):
        return _assemble_from_unit_mappings(arg, errors=errors)
    elif isinstance(arg, ABCIndexClass):
        return _convert_listlike(arg, box, format, name=arg.name)
    elif is_list_like(arg):
        return _convert_listlike(arg, box, format)

    return _convert_listlike(np.array([arg]), box, format)[0]

# mappings for assembling units
_unit_map = {'year': 'year',
             'years': 'year',
             'month': 'month',
             'months': 'month',
             'day': 'day',
             'days': 'day',
             'hour': 'h',
             'hours': 'h',
             'minute': 'm',
             'minutes': 'm',
             'second': 's',
             'seconds': 's',
             'ms': 'ms',
             'millisecond': 'ms',
             'milliseconds': 'ms',
             'us': 'us',
             'microsecond': 'us',
             'microseconds': 'us',
             'ns': 'ns',
             'nanosecond': 'ns',
             'nanoseconds': 'ns'
             }


def _assemble_from_unit_mappings(arg, errors):
    """
    assemble the unit specifed fields from the arg (DataFrame)
    Return a Series for actual parsing

    Parameters
    ----------
    arg : DataFrame
    errors : {'ignore', 'raise', 'coerce'}, default 'raise'

        - If 'raise', then invalid parsing will raise an exception
        - If 'coerce', then invalid parsing will be set as NaT
        - If 'ignore', then invalid parsing will return the input

    Returns
    -------
    Series
    """
    from pandas import to_timedelta, to_numeric, DataFrame
    arg = DataFrame(arg)
    if not arg.columns.is_unique:
        raise ValueError("cannot assemble with duplicate keys")

    # replace passed unit with _unit_map
    def f(value):
        if value in _unit_map:
            return _unit_map[value]

        # m is case significant
        if value.lower() in _unit_map:
            return _unit_map[value.lower()]

        return value

    unit = {k: f(k) for k in arg.keys()}
    unit_rev = {v: k for k, v in unit.items()}

    # we require at least Ymd
    required = ['year', 'month', 'day']
    req = sorted(list(set(required) - set(unit_rev.keys())))
    if len(req):
        raise ValueError("to assemble mappings requires at "
                         "least that [year, month, day] be specified: "
                         "[{0}] is missing".format(','.join(req)))

    # keys we don't recognize
    excess = sorted(list(set(unit_rev.keys()) - set(_unit_map.values())))
    if len(excess):
        raise ValueError("extra keys have been passed "
                         "to the datetime assemblage: "
                         "[{0}]".format(','.join(excess)))

    def coerce(values):
        # we allow coercion to if errors allows
        values = to_numeric(values, errors=errors)

        # prevent overflow in case of int8 or int16
        if is_integer_dtype(values):
            values = values.astype('int64', copy=False)
        return values

    values = (coerce(arg[unit_rev['year']]) * 10000 +
              coerce(arg[unit_rev['month']]) * 100 +
              coerce(arg[unit_rev['day']]))
    try:
        values = to_datetime(values, format='%Y%m%d', errors=errors)
    except (TypeError, ValueError) as e:
        raise ValueError("cannot assemble the "
                         "datetimes: {0}".format(e))

    for u in ['h', 'm', 's', 'ms', 'us', 'ns']:
        value = unit_rev.get(u)
        if value is not None and value in arg:
            try:
                values += to_timedelta(coerce(arg[value]),
                                       unit=u,
                                       errors=errors)
            except (TypeError, ValueError) as e:
                raise ValueError("cannot assemble the datetimes "
                                 "[{0}]: {1}".format(value, e))

    return values


def _attempt_YYYYMMDD(arg, errors):
    """ try to parse the YYYYMMDD/%Y%m%d format, try to deal with NaT-like,
        arg is a passed in as an object dtype, but could really be ints/strings
        with nan-like/or floats (e.g. with nan)

    Parameters
    ----------
    arg : passed value
    errors : 'raise','ignore','coerce'
    """

    def calc(carg):
        # calculate the actual result
        carg = carg.astype(object)
        parsed = lib.try_parse_year_month_day(carg / 10000,
                                              carg / 100 % 100,
                                              carg % 100)
        return tslib.array_to_datetime(parsed, errors=errors)

    def calc_with_mask(carg, mask):
        result = np.empty(carg.shape, dtype='M8[ns]')
        iresult = result.view('i8')
        iresult[~mask] = tslib.iNaT
        result[mask] = calc(carg[mask].astype(np.float64).astype(np.int64)).\
            astype('M8[ns]')
        return result

    # try intlike / strings that are ints
    try:
        return calc(arg.astype(np.int64))
    except:
        pass

    # a float with actual np.nan
    try:
        carg = arg.astype(np.float64)
        return calc_with_mask(carg, notnull(carg))
    except:
        pass

    # string with NaN-like
    try:
        mask = ~lib.ismember(arg, tslib._nat_strings)
        return calc_with_mask(arg, mask)
    except:
        pass

    return None


def _format_is_iso(f):
    """
    Does format match the iso8601 set that can be handled by the C parser?
    Generally of form YYYY-MM-DDTHH:MM:SS - date separator can be different
    but must be consistent.  Leading 0s in dates and times are optional.
    """
    iso_template = '%Y{date_sep}%m{date_sep}%d{time_sep}%H:%M:%S.%f'.format
    excluded_formats = ['%Y%m%d', '%Y%m', '%Y']

    for date_sep in [' ', '/', '\\', '-', '.', '']:
        for time_sep in [' ', 'T']:
            if (iso_template(date_sep=date_sep,
                             time_sep=time_sep
                             ).startswith(f) and f not in excluded_formats):
                return True
    return False


def parse_time_string(arg, freq=None, dayfirst=None, yearfirst=None):
    """
    Try hard to parse datetime string, leveraging dateutil plus some extra
    goodies like quarter recognition.

    Parameters
    ----------
    arg : compat.string_types
    freq : str or DateOffset, default None
        Helps with interpreting time string if supplied
    dayfirst : bool, default None
        If None uses default from print_config
    yearfirst : bool, default None
        If None uses default from print_config

    Returns
    -------
    datetime, datetime/dateutil.parser._result, str
    """
    from pandas.core.config import get_option
    if not isinstance(arg, compat.string_types):
        return arg

    from pandas.tseries.offsets import DateOffset
    if isinstance(freq, DateOffset):
        freq = freq.rule_code

    if dayfirst is None:
        dayfirst = get_option("display.date_dayfirst")
    if yearfirst is None:
        yearfirst = get_option("display.date_yearfirst")

    return tslib.parse_datetime_string_with_reso(arg, freq=freq,
                                                 dayfirst=dayfirst,
                                                 yearfirst=yearfirst)


DateParseError = tslib.DateParseError
normalize_date = tslib.normalize_date


# Fixed time formats for time parsing
_time_formats = ["%H:%M", "%H%M", "%I:%M%p", "%I%M%p",
                 "%H:%M:%S", "%H%M%S", "%I:%M:%S%p", "%I%M%S%p"]


def _guess_time_format_for_array(arr):
    # Try to guess the format based on the first non-NaN element
    non_nan_elements = notnull(arr).nonzero()[0]
    if len(non_nan_elements):
        element = arr[non_nan_elements[0]]
        for time_format in _time_formats:
            try:
                datetime.strptime(element, time_format)
                return time_format
            except ValueError:
                pass

    return None


def to_time(arg, format=None, infer_time_format=False, errors='raise'):
    """
    Parse time strings to time objects using fixed strptime formats ("%H:%M",
    "%H%M", "%I:%M%p", "%I%M%p", "%H:%M:%S", "%H%M%S", "%I:%M:%S%p",
    "%I%M%S%p")

    Use infer_time_format if all the strings are in the same format to speed
    up conversion.

    Parameters
    ----------
    arg : string in time format, datetime.time, list, tuple, 1-d array,  Series
    format : str, default None
        Format used to convert arg into a time object.  If None, fixed formats
        are used.
    infer_time_format: bool, default False
        Infer the time format based on the first non-NaN element.  If all
        strings are in the same format, this will speed up conversion.
    errors : {'ignore', 'raise', 'coerce'}, default 'raise'
        - If 'raise', then invalid parsing will raise an exception
        - If 'coerce', then invalid parsing will be set as None
        - If 'ignore', then invalid parsing will return the input

    Returns
    -------
    datetime.time
    """
    from pandas.core.series import Series

    def _convert_listlike(arg, format):

        if isinstance(arg, (list, tuple)):
            arg = np.array(arg, dtype='O')

        elif getattr(arg, 'ndim', 1) > 1:
            raise TypeError('arg must be a string, datetime, list, tuple, '
                            '1-d array, or Series')

        arg = _ensure_object(arg)

        if infer_time_format and format is None:
            format = _guess_time_format_for_array(arg)

        times = []
        if format is not None:
            for element in arg:
                try:
                    times.append(datetime.strptime(element, format).time())
                except (ValueError, TypeError):
                    if errors == 'raise':
                        raise ValueError("Cannot convert %s to a time with "
                                         "given format %s" % (element, format))
                    elif errors == 'ignore':
                        return arg
                    else:
                        times.append(None)
        else:
            formats = _time_formats[:]
            format_found = False
            for element in arg:
                time_object = None
                for time_format in formats:
                    try:
                        time_object = datetime.strptime(element,
                                                        time_format).time()
                        if not format_found:
                            # Put the found format in front
                            fmt = formats.pop(formats.index(time_format))
                            formats.insert(0, fmt)
                            format_found = True
                        break
                    except (ValueError, TypeError):
                        continue

                if time_object is not None:
                    times.append(time_object)
                elif errors == 'raise':
                    raise ValueError("Cannot convert arg {arg} to "
                                     "a time".format(arg=arg))
                elif errors == 'ignore':
                    return arg
                else:
                    times.append(None)

        return times

    if arg is None:
        return arg
    elif isinstance(arg, time):
        return arg
    elif isinstance(arg, Series):
        values = _convert_listlike(arg._values, format)
        return Series(values, index=arg.index, name=arg.name)
    elif isinstance(arg, ABCIndexClass):
        return _convert_listlike(arg, format)
    elif is_list_like(arg):
        return _convert_listlike(arg, format)

    return _convert_listlike(np.array([arg]), format)[0]


def format(dt):
    """Returns date in YYYYMMDD format."""
    return dt.strftime('%Y%m%d')

OLE_TIME_ZERO = datetime(1899, 12, 30, 0, 0, 0)


def ole2datetime(oledt):
    """function for converting excel date to normal date format"""
    val = float(oledt)

    # Excel has a bug where it thinks the date 2/29/1900 exists
    # we just reject any date before 3/1/1900.
    if val < 61:
        raise ValueError("Value is outside of acceptable range: %s " % val)

    return OLE_TIME_ZERO + timedelta(days=val)
