# -*- coding: utf-8 -*-
from numba import njit
from numpy import copy, cos, exp
from pandas import Series
from pandas_ta._typing import DictLike, Int, IntFloat
from pandas_ta.utils import v_bool, v_offset, v_pos_default, v_series



# Ehlers's Super Smoother Filter
# http://traders.com/documentation/feedbk_docs/2014/01/traderstips.html
@njit(cache=True)
def nb_ssf(x, n, pi, sqrt2):
    m, ratio, result = x.size, sqrt2 / n, copy(x)
    a = exp(-pi * ratio)
    b = 2 * a * cos(180 * ratio)
    c = a * a - b + 1

    # result[:2] = x[:2]
    for i in range(2, m):
        result[i] = 0.5 * c * (x[i] + x[i - 1]) + b * result[i - 1] \
            - a * a * result[i - 2]

    return result


# John F. Ehlers's Super Smoother Filter by Everget (2 poles), Tradingview
# https://www.tradingview.com/script/VdJy0yBJ-Ehlers-Super-Smoother-Filter/
@njit(cache=True)
def nb_ssf_everget(x, n, pi, sqrt2):
    m, arg, result = x.size, pi * sqrt2 / n, copy(x)
    a = exp(-arg)
    b = 2 * a * cos(arg)

    # result[:2] = x[:2]
    for i in range(2, m):
        result[i] = 0.5 * (a * a - b + 1) * (x[i] + x[i - 1]) \
            + b * result[i - 1] - a * a * result[i - 2]

    return result


def ssf(
    close: Series, length: Int = None,
    everget: bool = None, pi: IntFloat = None, sqrt2: IntFloat = None,
    offset: Int = None, **kwargs: DictLike
) -> Series:
    """Ehlers's Super Smoother Filter

    This indicator, by John F. Ehlers's © 2013, is a (Recursive) Digital
    Filter that attempts to reduce lag and remove aliases. This version
    has two poles.

    Sources:
        * [mql5](https://www.mql5.com/en/code/588)
        * [traders.com](http://traders.com/documentation/feedbk_docs/2014/01/traderstips.html)
        * [tradingview](https://www.tradingview.com/script/VdJy0yBJ-Ehlers-Super-Smoother-Filter/)

    Parameters:
        close (Series): ```close``` Series
        length (int): The period. Default: ```20```
        everget (bool): Everget's implementation of ssf that uses pi
            instead of 180 for the b factor of ssf. Default: ```False```
        pi (float): The default is Ehlers's truncated value: ```3.14159```.
            Default: ```3.14159```
        sqrt2 (float): The default is Ehlers's truncated value: ```1.414```.
            Default: ```1.414```
        offset (int): Post shift. Default: ```0```

    Other Parameters:
        fillna (value): ```pd.DataFrame.fillna(value)```

    Returns:
        (Series): 1 column

    Note:
        * Everget's calculation on TradingView:
            ```pi=np.pi```, ```sqrt2=np.sqrt(2)```

    Danger:
        Possible Data Leak
    """
    # Validate
    length = v_pos_default(length, 20)
    close = v_series(close, length)

    if close is None:
        return

    pi = v_pos_default(pi, 3.14159)
    sqrt2 = v_pos_default(sqrt2, 1.414)
    everget = v_bool(everget, False)
    offset = v_offset(offset)

    # Calculate
    np_close = close.to_numpy()
    if everget:
        ssf = nb_ssf_everget(np_close, length, pi, sqrt2)
    else:
        ssf = nb_ssf(np_close, length, pi, sqrt2)
    ssf = Series(ssf, index=close.index)

    # Offset
    if offset != 0:
        ssf = ssf.shift(offset)

    # Fill
    if "fillna" in kwargs:
        ssf.fillna(kwargs["fillna"], inplace=True)

    # Name and Category
    ssf.name = f"SSF{'e' if everget else ''}_{length}"
    ssf.category = "overlap"

    return ssf