"""Fast scalar path for oggm.utils.floatyear_to_date (same algorithm, plain Python).

Arrays and return_day=True still go to the original. patch() installs it where
FlowlineModel.get_mb and get_days_of_month look it up.
"""
import bisect
import math

import numpy as np
from oggm import utils
from oggm.utils import _funcs

_orig = _funcs.floatyear_to_date
_CUM = [31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365]
_ONE_M = math.nextafter(1.0, 0.0)


def fast_floatyear_to_date(yr, return_day=False):
    if return_day or np.ndim(yr) != 0:
        return _orig(yr, return_day=return_day)
    yr = float(yr)
    y = math.floor(yr)
    f = min(max(yr - y, 0.0), _ONE_M)
    leap = (y % 4 == 0) and ((y % 100 != 0) or (y % 400 == 0))
    n = 365 + leap
    d = min(max(round(f * n), 0), n - 1)          # round() is half-to-even, like np.rint
    if y + d / n > yr:
        d = min(max(d - 1, 0), n - 1)
    doy = d + 1
    adj = doy - (1 if (leap and doy > 59) else 0)
    return np.int64(y), np.int64(bisect.bisect_left(_CUM, adj) + 1)


def patch():
    utils.floatyear_to_date = fast_floatyear_to_date
    _funcs.floatyear_to_date = fast_floatyear_to_date