from random import choice

import numpy

from cogent3.maths.stats.special import igam


try:
    from math import factorial
except ImportError:  # python version < 2.6
    from cogent3.maths.stats.special import Gamma

    factorial = lambda x: Gamma(x + 1)


def chi_square(x, p, df=1):
    """returns the chisquare statistic and it's probability"""
    N = len(x)
    end = N
    sim = numpy.logical_not(numpy.logical_xor(x[0 : end - p], x[p:end])) * 1
    s = ((numpy.ones((N - p,), float) - sim) ** 2).sum()
    D = s / (N - p)
    p_val = 1 - igam(df / 2.0, D / 2)
    return D, p_val


def g_statistic(X, p=None, idx=None):
    """
    return g statistic and p value
    arguments:
        X - the periodicity profile (e.g. DFT magnitudes, autocorrelation etc)
            X needs to contain only those period values being considered,
            i.e. only periods in the range [llim, ulim]
    """
    # X should be real
    X = abs(numpy.array(X))
    if p is None:
        power = X.max(0)
        idx = X.argmax(0)
    else:
        assert idx is not None
        power = X[idx]
    g_obs = power / X.sum()
    M = numpy.floor(1 / g_obs)
    pmax = len(X)

    result = numpy.zeros((int(M + 1),), float)
    pmax_fact = factorial(pmax)
    for index in range(1, min(pmax, int(M)) + 1):
        v = (-1) ** (index - 1) * pmax_fact / factorial(pmax - index) / factorial(index)
        v *= (1 - index * g_obs) ** (pmax - 1)
        result[index] = v

    p_val = result.sum()
    return g_obs, p_val


def seq_to_symbols(seq, motifs, motif_length, result=None):
    """return symbolic represetation of the sequence

    Parameters
    ----------
    seq
        a sequence
    motifs
        a list of sequence motifs
    motif_length
        length of first motif
    result : ndarray
        working array. Contents are reset to zero before encoding
    """
    if result is None:
        result = numpy.zeros(len(seq), numpy.uint8)
    else:
        result.fill(0)

    if motif_length is None:
        motif_length = len(motifs[0])

    for i in range(len(seq) - motif_length + 1):
        if seq[i : i + motif_length] in motifs:
            result[i] = 1

    return result


class SeqToSymbols(object):
    """class for converting all occurrences of motifs in passed sequence
    to 1/0 otherwise"""

    def __init__(self, motifs, length=None, motif_length=None):
        super(SeqToSymbols, self).__init__()
        if type(motifs) == str:
            motifs = [motifs]
        for i in range(len(motifs)):
            try:
                motifs[i] = motifs[i].encode("utf8")
            except AttributeError:
                pass
        self.motifs = motifs
        self.length = length
        self.motif_length = motif_length or len(motifs[0])
        self.working = None
        if length is not None:
            self.METHOD_NAME(length)

    def METHOD_NAME(self, length):
        """sets a result array for length"""
        self.working = numpy.zeros(length, numpy.uint8)
        self.length = length

    def __call__(self, seq, result=None):
        if result is None and self.working is None:
            self.METHOD_NAME(len(seq))
        elif self.working is not None:
            if len(seq) != self.working.shape[0]:
                self.METHOD_NAME(len(seq))

        result = self.working
        result.fill(0)
        if type(seq) == str:
            seq = seq.encode("utf8")
        elif type(seq) != bytes:
            seq = b"".join(seq)

        return seq_to_symbols(seq, self.motifs, self.motif_length, result)


def circular_indices(vector, start, length, num):
    """

    Parameters
    ----------
    vector : list[int]
        sequential integers
    start : int
        index to start sampling from
    length : int
        length of returned vector
    num : int
        k-mer size to support
    """
    if start > length:
        start = start - length

    if start + num < length:
        return vector[start : start + num]
    # get all till end, then from beginning
    return vector[start:] + vector[: start + num - length]


def sampled_places(block_size, length):
    """returns randomly sampled positions with block_size to make a new vector
    with length
    """
    # Main condition is to identify when a draw would run off end, we want to
    # draw from beginning
    num_seg, remainder = divmod(length, block_size)
    vector = list(range(length))
    result = []
    for _ in range(num_seg):
        i = choice(vector)
        result += circular_indices(vector, i, length, block_size)

    if remainder:
        result += circular_indices(vector, i + block_size, length, remainder)

    assert len(result) == length, len(result)
    return result


def blockwise_bootstrap(
    signal, calc, block_size, num_reps, seq_to_symbols=None, num_stats=None
):
    """returns observed statistic and the probability from the bootstrap
    test of observing more `power' by chance than that estimated from the
    observed signal

    Parameters
    ----------
    signal
        a series, can be a sequence object
    calc
        function to calculate the period power, e.g. ipdft, hybrid,
        auto_corr or any other statistic.
    block_size
        size of contiguous values for resampling
    num_reps
        number of randomly generated permutations
    seq_to_symbols
        function to convert a sequence to 1/0. If not
        provided, the raw data is used.
    num_stats
        the number of statistics being evaluated for each
        interation. Default to 1.

    """
    signal_length = len(signal)

    dtype = "c" if seq_to_symbols is not None else None
    signal = numpy.array(list(signal), dtype=dtype)

    if seq_to_symbols is not None:
        symbolic = seq_to_symbols(signal)
        data = symbolic
    else:
        data = signal

    obs_stat = calc(data)
    if seq_to_symbols is not None and sum(data) == 0:
        p = [numpy.array([1.0, 1.0, 1.0]), 1.0][num_stats == 1]

        return obs_stat, p

    if num_stats is None:
        try:
            num_stats = calc.get_num_stats()
        except AttributeError:
            num_stats = 1

    count = 0 if num_stats == 1 else numpy.zeros(num_stats)
    for _ in range(num_reps):
        # get sample positions
        sampled_indices = sampled_places(block_size, signal_length)
        new_signal = signal.take(sampled_indices)
        if seq_to_symbols is not None:
            symbolic = seq_to_symbols(new_signal)
            data = symbolic
        else:
            data = new_signal
        sim_stat = calc(data)
        # count if > than observed
        if num_stats > 1:
            count[sim_stat >= obs_stat] += 1
        elif sim_stat >= obs_stat:
            count += 1

    return obs_stat, count / num_reps