import math

__all__ = [
    'e6', 'e12', 'e24', 'e48', 'e96', 'e192',
    'eng_str',
]


class ESeries(object):
    ROUND_CLOSEST = 1
    ROUND_UP = 2
    ROUND_DOWN = 3

    def __init__(self, series):
        self.series = series

    def closest(self, value, round_direction=ROUND_CLOSEST):
        if round_direction != ESeries.ROUND_CLOSEST:
            raise NotImplementedError("Only closest rounding is implemented for now")
        e = math.floor(math.log10(value))
        value = float(value / (10 ** e))

        return min(self.series, key=lambda v: abs(v - value)) * 10 ** e


# https://en.wikipedia.org/wiki/E-series_of_preferred_numbers
_e_series_24 = [1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0,
                3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1]
_e_series_12 = [v for i, v in enumerate(_e_series_24) if i % 2 == 0]
_e_series_6 = [v for i, v in enumerate(_e_series_24) if i % 4 == 0]

_e_series_192 = [
    1.00, 1.01, 1.02, 1.04, 1.05, 1.06, 1.07, 1.09, 1.10, 1.11,
    1.13, 1.14, 1.15, 1.17, 1.18, 1.20, 1.21, 1.23, 1.24, 1.26,
    1.27, 1.29, 1.30, 1.32, 1.33, 1.35, 1.37, 1.38, 1.40, 1.42,
    1.43, 1.45, 1.47, 1.49, 1.50, 1.52, 1.54, 1.56, 1.58, 1.60,
    1.62, 1.64, 1.65, 1.67, 1.69, 1.72, 1.74, 1.76, 1.78, 1.80,
    1.82, 1.84, 1.87, 1.89, 1.91, 1.93, 1.96, 1.98, 2.00, 2.03,
    2.05, 2.08, 2.10, 2.13, 2.15, 2.18, 2.21, 2.23, 2.26, 2.29,
    2.32, 2.34, 2.37, 2.40, 2.43, 2.46, 2.49, 2.52, 2.55, 2.58,
    2.61, 2.64, 2.67, 2.71, 2.74, 2.77, 2.80, 2.84, 2.87, 2.91,
    2.94, 2.98, 3.01, 3.05, 3.09, 3.12, 3.16, 3.20, 3.24, 3.28,
    3.32, 3.36, 3.40, 3.44, 3.48, 3.52, 3.57, 3.61, 3.65, 3.70,
    3.74, 3.79, 3.83, 3.88, 3.92, 3.97, 4.02, 4.07, 4.12, 4.17,
    4.22, 4.27, 4.32, 4.37, 4.42, 4.48, 4.53, 4.59, 4.64, 4.70,
    4.75, 4.81, 4.87, 4.93, 4.99, 5.05, 5.11, 5.17, 5.23, 5.30,
    5.36, 5.42, 5.49, 5.56, 5.62, 5.69, 5.76, 5.83, 5.90, 5.97,
    6.04, 6.12, 6.19, 6.26, 6.34, 6.42, 6.49, 6.57, 6.65, 6.73,
    6.81, 6.90, 6.98, 7.06, 7.15, 7.23, 7.32, 7.41, 7.50, 7.59,
    7.68, 7.77, 7.87, 7.96, 8.06, 8.16, 8.25, 8.35, 8.45, 8.56,
    8.66, 8.76, 8.87, 8.98, 9.09, 9.20, 9.31, 9.42, 9.53, 9.65,
    9.76, 9.88,
]
_e_series_96 = [v for i, v in enumerate(_e_series_192) if i % 2 == 0]
_e_series_48 = [v for i, v in enumerate(_e_series_192) if i % 4 == 0]

e6 = ESeries(_e_series_6)
e12 = ESeries(_e_series_12)
e24 = ESeries(_e_series_24)
e48 = ESeries(_e_series_48)
e96 = ESeries(_e_series_96)
e192 = ESeries(_e_series_192)


def eng_str(value, unit=None):
    if value == 0:
        s = '0' + (' ' + unit if unit is not None else '')
    else:
        big = ['k', 'M', 'G', 'T']
        small = ['m', 'u', 'n', 'p']

        if unit is not None:
            big = [' ' + unit] + [' ' + x + unit for x in big]
            small = [' ' + unit] + [' ' + x + unit for x in small]
        else:
            big = [''] + [' ' + x for x in big]
            small = [''] + [' ' + x for x in small]

        e_floor = math.floor(math.log10(value))

        div3 = math.floor(e_floor / 3)
        if div3 > 0:
            suffixes = big
            idx = int(div3)
        else:
            suffixes = small
            idx = int(-div3)

        if idx < len(suffixes):
            suffix = suffixes[idx]
            scale = 10 ** (div3 * 3)
            scaled = value / scale
        else:
            idx = len(suffixes) - 1
            suffix = suffixes[idx]
            scale = 10 ** (3 * idx)
            scaled = scale * value

        s = "{:1.3g}{}".format(scaled, suffix)

    return s