"""Utility functions and classes for the stix2 library."""

import datetime as dt
import json

from dateutil import parser
import pytz

# Sentinel value for properties that should be set to the current time.
# We can't use the standard 'default' approach, since if there are multiple
# timestamps in a single object, the timestamps will vary by a few microseconds.
NOW = object()


class STIXdatetime(dt.datetime):
    def __new__(cls, *args, **kwargs):
        precision = kwargs.pop('precision', None)
        if isinstance(args[0], dt.datetime):  # Allow passing in a datetime object
            dttm = args[0]
            args = (dttm.year,)
            kwargs['month'] = dttm.month
            kwargs['day'] = dttm.day
            kwargs['hour'] = dttm.hour
            kwargs['minute'] = dttm.minute
            kwargs['second'] = dttm.second
            kwargs['microsecond'] = dttm.microsecond
            kwargs['tzinfo'] = dttm.tzinfo
        self = dt.datetime.__new__(cls, *args, **kwargs)
        self.precision = precision
        return self


def get_timestamp():
    return STIXdatetime.now(tz=pytz.UTC)


def format_datetime(dttm):
    # 1. Convert to timezone-aware
    # 2. Convert to UTC
    # 3. Format in ISO format
    # 4. Ensure correct precision
    # 4a. Add subsecond value if non-zero and precision not defined
    # 5. Add "Z"

    if dttm.tzinfo is None or dttm.tzinfo.utcoffset(dttm) is None:
        # dttm is timezone-naive; assume UTC
        zoned = pytz.utc.localize(dttm)
    else:
        zoned = dttm.astimezone(pytz.utc)
    ts = zoned.strftime("%Y-%m-%dT%H:%M:%S")
    ms = zoned.strftime("%f")
    precision = getattr(dttm, "precision", None)
    if precision:
        if precision == "millisecond":
            ts = ts + '.' + ms[:3]
    elif zoned.microsecond > 0:
        ts = ts + '.' + ms.rstrip("0")
    return ts + "Z"


def parse_into_datetime(value, precision=None):
    if isinstance(value, dt.date):
        if hasattr(value, 'hour'):
            ts = value
        else:
            # Add a time component
            ts = dt.datetime.combine(value, dt.time(0, 0, tzinfo=pytz.utc))
    else:
        # value isn't a date or datetime object so assume it's a string
        try:
            parsed = parser.parse(value)
        except (TypeError, ValueError):
            # Unknown format
            raise ValueError("must be a datetime object, date object, or "
                             "timestamp string in a recognizable format.")
        if parsed.tzinfo:
            ts = parsed.astimezone(pytz.utc)
        else:
            # Doesn't have timezone info in the string; assume UTC
            ts = pytz.utc.localize(parsed)

    # Ensure correct precision
    if not precision:
        return ts
    ms = ts.microsecond
    if precision == 'millisecond':
        ms_len = len(str(ms))
        if ms_len > 3:
            # Truncate to millisecond precision
            return ts.replace(microsecond=(ts.microsecond // (10 ** (ms_len - 3))))
    return STIXdatetime(ts, precision=precision)


def get_dict(data):
    """Return data as a dictionary.
    Input can be a dictionary, string, or file-like object.
    """

    if type(data) is dict:
        return data
    else:
        try:
            return json.loads(data)
        except TypeError:
            pass
        try:
            return json.load(data)
        except AttributeError:
            pass
        try:
            return dict(data)
        except (ValueError, TypeError):
            raise ValueError("Cannot convert '%s' to dictionary." % str(data))