#!/usr/bin/env python
"""Translations of functions from Release 2.3 of the Cephes Math Library,
which is (c) Stephen L. Moshier 1984, 1995.
"""

from numpy import arctan as atan
from numpy import array, exp, sqrt

from cogent3.maths.stats.special import (
    MACHEP,
    MAXNUM,
    PI,
    SQRTH,
    betai,
    erf,
    erfc,
    expm1,
    fix_rounding_error,
    igam,
    igamc,
    igami,
    incbi,
    ln_binomial,
    log1p,
    ndtri,
)


# ndtri import b/c it should be available via this module


__author__ = "Rob Knight"
__copyright__ = "Copyright 2007-2020, The Cogent Project"
__credits__ = ["Rob Knight", "Sandra Smit", "Gavin Huttley", "Daniel McDonald"]
__license__ = "BSD-3"
__version__ = "2020.12.21a"
__maintainer__ = "Gavin Huttley"
__email__ = "Gavin.Huttley@anu.edu.au"
__status__ = "Production"

incbet = betai  # shouldn't have renamed it...

# Probability integrals: low gives left-hand tail, high gives right-hand tail.


def z_low(x):
    """Returns left-hand tail of z distribution (0 to x).

    x ranges from -infinity to +infinity; result ranges from 0 to 1

    See Cephes docs for details."""
    y = x * SQRTH
    z = abs(y)  # distribution is symmetric
    if z < SQRTH:
        return 0.5 + 0.5 * erf(y)
    else:
        if y > 0:
            return 1 - 0.5 * erfc(z)
        else:
            return 0.5 * erfc(z)


def z_high(x):
    """Returns right-hand tail of z distribution (0 to x).

    x ranges from -infinity to +infinity; result ranges from 0 to 1

    See Cephes docs for details."""
    y = x * SQRTH
    z = abs(y)
    if z < SQRTH:
        return 0.5 - 0.5 * erf(y)
    else:
        if x < 0:
            return 1 - 0.5 * erfc(z)
        else:
            return 0.5 * erfc(z)


def zprob(x):
    """Returns both tails of z distribution (-inf to -x, inf to x)."""
    return 2 * z_high(abs(x))


def chi_low(x, df):
    """Returns left-hand tail of chi-square distribution (0 to x), given df.

    x ranges from 0 to infinity.

    df, the degrees of freedom, ranges from 1 to infinity (assume integers).
    Typically, df is (r-1)*(c-1) for a r by c table.

    Result ranges from 0 to 1.

    See Cephes docs for details.
    """
    x = fix_rounding_error(x)
    if x < 0:
        raise ValueError("chi_low: x must be >= 0 (got %s)." % x)
    if df < 1:
        raise ValueError("chi_low: df must be >= 1 (got %s)." % df)
    return igam(df / 2, x / 2)


def chi_high(x, df):
    """Returns right-hand tail of chi-square distribution (x to infinity).

    df, the degrees of freedom, ranges from 1 to infinity (assume integers).
    Typically, df is (r-1)*(c-1) for a r by c table.

    Result ranges from 0 to 1.

    See Cephes docs for details.
    """
    x = fix_rounding_error(x)

    if x < 0:
        raise ValueError("chi_high: x must be >= 0 (got %s)." % x)
    if df < 1:
        raise ValueError("chi_high: df must be >= 1 (got %s)." % df)
    return igamc(df / 2, x / 2)


def t_low(t, df):
    """Returns left-hand tail of Student's t distribution (-infinity to x).

    df, the degrees of freedom, ranges from 1 to infinity.
    Typically, df is (n-1) for a sample size of n.

    Result ranges from 0 to 1.

    See Cephes docs for details.
    """
    if df < 1:
        raise ValueError("t_low: df must be >= 1 (got %s)." % df)
    return stdtr(df, t)


def t_high(t, df):
    """Returns right-hand tail of Student's t distribution (x to infinity).

    df, the degrees of freedom, ranges from 1 to infinity.
    Typically, df is (n-1) for a sample size of n.

    Result ranges from 0 to 1.

    See Cephes docs for details.
    """
    if df < 1:
        raise ValueError("t_high: df must be >= 1 (got %s)." % df)
    return stdtr(df, -t)  # distribution is symmetric


def tprob(t, df):
    """Returns both tails of t distribution (-infinity to -x, infinity to x)"""
    return 2 * t_high(abs(t), df)


def poisson_high(successes, mean):
    """Returns right tail of Poission distribution, Pr(X > x).

    successes ranges from 0 to infinity. mean must be positive.
    """
    return pdtrc(successes, mean)


def poisson_low(successes, mean):
    """Returns left tail of Poisson distribution, Pr(X <= x).

    successes ranges from 0 to infinity. mean must be positive.
    """
    return pdtr(successes, mean)


def poisson_exact(successes, mean):
    """Returns Poisson probablity for exactly Pr(X=successes).

    Formula is e^-(mean) * mean^(successes) / (successes)!
    """
    if successes == 0:
        return pdtr(0, mean)
    elif successes < mean:  # use left tail
        return pdtr(successes, mean) - pdtr(successes - 1, mean)
    else:  # successes > mean: use right tail
        return pdtrc(successes - 1, mean) - pdtrc(successes, mean)


def binomial_high(successes, trials, prob):
    """Returns right-hand binomial tail (X > successes) given prob(success)."""
    if -1 <= successes < 0:
        return 1
    return bdtrc(successes, trials, prob)


def binomial_low(successes, trials, prob):
    """Returns left-hand binomial tail (X <= successes) given prob(success)."""
    return bdtr(successes, trials, prob)


def binomial_exact(successes, trials, prob):
    """Returns binomial probability of exactly X successes.

    Works for integer and floating point values.

    Note: this function is only a probability mass function for integer
    values of 'trials' and 'successes', i.e. if you sum up non-integer
    values you probably won't get a sum of 1.
    """
    if (prob < 0) or (prob > 1):
        raise ValueError("Binomial prob must be between 0 and 1.")
    if (successes < 0) or (trials < successes):
        raise ValueError("Binomial successes must be between 0 and trials.")
    return exp(ln_binomial(successes, trials, prob))


def f_low(df1, df2, x):
    """Returns left-hand tail of f distribution (0 to x).

    x ranges from 0 to infinity.

    Result ranges from 0 to 1.

    See Cephes docs for details.
    """
    return fdtr(df1, df2, x)


def f_high(df1, df2, x):
    """Returns right-hand tail of f distribution (x to infinity).

    Result ranges from 0 to 1.

    See Cephes docs for details.
    """
    return fdtrc(df1, df2, x)


def fprob(dfn, dfd, F, side="right"):
    """Returns both tails of F distribution (-inf to F and F to inf)

    Use in case of two-tailed test. Usually this method is called by
    f_two_sample, so you don't have to worry about choosing the right side.

    side: right means return twice the right-hand tail of the F-distribution.
        Use in case var(a) > var (b)
          left means return twice the left-hand tail of the F-distribution.
        Use in case var(a) < var(b)
    """
    if F < 0:
        raise ValueError("fprob: F must be >= 0 (got %s)." % F)
    if side == "right":
        return 2 * f_high(dfn, dfd, F)
    elif side == "left":
        return 2 * f_low(dfn, dfd, F)
    else:
        raise ValueError("Not a valid value for side %s" % (side))


def stdtr(k, t):
    """Student's t distribution, -infinity to t.

    See Cephes docs for details.
    """
    if k <= 0:
        raise ValueError("stdtr: df must be > 0.")
    if t == 0:
        return 0.5
    if t < -2:
        rk = k
        z = rk / (rk + t * t)
        return 0.5 * betai(0.5 * rk, 0.5, z)
    # compute integral from -t to + t
    if t < 0:
        x = -t
    else:
        x = t

    rk = k  # degrees of freedom
    z = 1 + (x * x) / rk
    # test if k is odd or even
    if (k & 1) != 0:
        # odd k
        xsqk = x / sqrt(rk)
        p = atan(xsqk)
        if k > 1:
            f = 1
            tz = 1
            j = 3
            while (j <= (k - 2)) and ((tz / f) > MACHEP):
                tz *= (j - 1) / (z * j)
                f += tz
                j += 2
            p += f * xsqk / z
        p *= 2 / PI
    else:
        # even k
        f = 1
        tz = 1
        j = 2
        while (j <= (k - 2)) and ((tz / f) > MACHEP):
            tz *= (j - 1) / (z * j)
            f += tz
            j += 2
        p = f * x / sqrt(z * rk)
    # common exit
    if t < 0:
        p = -p  # note destruction of relative accuracy
    p = 0.5 + 0.5 * p
    return p


def bdtr(k, n, p):
    """Binomial distribution, 0 through k.

    Uses formula bdtr(k, n, p) = betai(n-k, k+1, 1-p)

    See Cephes docs for details.
    """
    p = fix_rounding_error(p)
    if (p < 0) or (p > 1):
        raise ValueError("Binomial p must be between 0 and 1.")
    if (k < 0) or (n < k):
        raise ValueError("Binomial k must be between 0 and n.")
    if k == n:
        return 1
    dn = n - k
    if k == 0:
        return pow(1 - p, dn)
    else:
        return betai(dn, k + 1, 1 - p)


def bdtrc(k, n, p):
    """Complement of binomial distribution, k+1 through n.

    Uses formula bdtrc(k, n, p) = betai(k+1, n-k, p)

    See Cephes docs for details.
    """
    p = fix_rounding_error(p)
    if (p < 0) or (p > 1):
        raise ValueError("Binomial p must be between 0 and 1.")
    if (k < 0) or (n < k):
        raise ValueError("Binomial k must be between 0 and n.")
    if k == n:
        return 0
    dn = n - k
    if k == 0:
        if p < 0.01:
            dk = -expm1(dn * log1p(-p))
        else:
            dk = 1 - pow(1.0 - p, dn)
    else:
        dk = k + 1
        dk = betai(dk, dn, p)
    return dk


def pdtr(k, m):
    """Returns sum of left tail of Poisson distribution, 0 through k.

    See Cephes docs for details.
    """
    if k < 0:
        raise ValueError("Poisson k must be >= 0.")
    if m < 0:
        raise ValueError("Poisson m must be >= 0.")
    return igamc(k + 1, m)


def pdtrc(k, m):
    """Returns sum of right tail of Poisson distribution, k+1 through infinity.

    See Cephes docs for details.
    """
    if k < 0:
        raise ValueError("Poisson k must be >= 0.")
    if m < 0:
        raise ValueError("Poisson m must be >= 0.")
    return igam(k + 1, m)


def fdtr(a, b, x):
    """Returns left tail of F distribution, 0 to x.

    See Cephes docs for details.
    """
    if min(a, b) < 1:
        raise ValueError("F a and b (degrees of freedom) must both be >= 1.")
    if x < 0:
        raise ValueError("F distribution value of f must be >= 0.")
    w = a * x
    w /= float(b + w)
    return betai(0.5 * a, 0.5 * b, w)


def fdtrc(a, b, x):
    """Returns right tail of F distribution, x to infinity.

    See Cephes docs for details.
    """
    if min(a, b) < 1:
        raise ValueError("F a and b (degrees of freedom) must both be >= 1.")
    if x < 0:
        raise ValueError("F distribution value of f must be >= 0.")
    w = float(b) / (b + a * x)
    return betai(0.5 * b, 0.5 * a, w)


def gdtr(a, b, x):
    """Returns integral from 0 to x of Gamma distribution with params a and b."""
    if x < 0.0:
        raise ZeroDivisionError("x must be at least 0.")
    return igam(b, a * x)


def gdtrc(a, b, x):
    """Returns integral from x to inf of Gamma distribution with params a and b."""
    if x < 0.0:
        raise ZeroDivisionError("x must be at least 0.")
    return igamc(b, a * x)


# note: ndtri for the normal distribution is already imported


def chdtri(df, y):
    """Returns inverse of chi-squared distribution."""
    y = fix_rounding_error(y)
    if y < 0.0 or y > 1.0 or df < 1.0:
        raise ZeroDivisionError("y must be between 0 and 1; df >= 1")
    return 2 * igami(0.5 * df, y)


def stdtri(k, p):
    """Returns inverse of Student's t distribution. k = df."""
    p = fix_rounding_error(p)
    # handle easy cases
    if k <= 0 or p < 0.0 or p > 1.0:
        raise ZeroDivisionError("k must be >= 1, p between 1 and 0.")
    rk = k
    # handle intermediate values
    if p > 0.25 and p < 0.75:
        if p == 0.5:
            return 0.0
        z = 1.0 - 2.0 * p
        z = incbi(0.5, 0.5 * rk, abs(z))
        t = sqrt(rk * z / (1.0 - z))
        if p < 0.5:
            t = -t
        return t
    # handle extreme values
    rflg = -1
    if p >= 0.5:
        p = 1.0 - p
        rflg = 1
    z = incbi(0.5 * rk, 0.5, 2.0 * p)

    if MAXNUM * z < rk:
        return rflg * MAXNUM
    t = sqrt(rk / z - rk)
    return rflg * t


def pdtri(k, p):
    """Inverse of Poisson distribution.

    Finds Poission mean such that integral from 0 to k is p.
    """
    p = fix_rounding_error(p)
    if k < 0 or p < 0.0 or p >= 1.0:
        raise ZeroDivisionError("k must be >=0, p between 1 and 0.")
    v = k + 1
    return igami(v, p)


def bdtri(k, n, y):
    """Inverse of binomial distribution.

    Finds binomial p such that sum of terms 0-k reaches cum probability y.
    """
    y = fix_rounding_error(y)
    if y < 0.0 or y > 1.0:
        raise ZeroDivisionError("y must be between 1 and 0.")
    if k < 0 or n <= k:
        raise ZeroDivisionError("k must be between 0 and n")
    dn = n - k
    if k == 0:
        if y > 0.8:
            p = -expm1(log1p(y - 1.0) / dn)
        else:
            p = 1.0 - y ** (1.0 / dn)
    else:
        dk = k + 1
        p = incbet(dn, dk, 0.5)
        if p > 0.5:
            p = incbi(dk, dn, 1.0 - y)
        else:
            p = 1.0 - incbi(dn, dk, y)
    return p


def gdtri(a, b, y):
    """Returns Gamma such that y is the probability in the integral.

    WARNING: if 1-y == 1, gives incorrect result. The scipy implementation
    gets around this by using cdflib, which is in Fortran. Until someone
    gets around to translating that, only use this function for values of
    p greater than 1e-15 or so!
    """
    y = fix_rounding_error(y)
    if y < 0.0 or y > 1.0 or a <= 0.0 or b < 0.0:
        raise ZeroDivisionError("a and b must be non-negative, y from 0 to 1.")
    return igami(b, 1.0 - y) / a


def fdtri(a, b, y):
    """Returns inverse of F distribution."""
    y = fix_rounding_error(y)
    if a < 1.0 or b < 1.0 or y <= 0.0 or y > 1.0:
        raise ZeroDivisionError("y must be between 0 and 1; a and b >= 1")
    y = 1.0 - y
    # Compute probability for x = 0.5
    w = incbet(0.5 * b, 0.5 * a, 0.5)
    # If that is greater than y, then the solution w < .5.
    # Otherwise, solve at 1-y to remove cancellation in (b - b*w).
    if w > y or y < 0.001:
        w = incbi(0.5 * b, 0.5 * a, y)
        x = (b - b * w) / (a * w)
    else:
        w = incbi(0.5 * a, 0.5 * b, 1.0 - y)
        x = b * w / (a * (1.0 - w))
    return x


def probability_points(n):
    """return series of n probabilities

    Returns
    -------
    Numpy array of probabilities

    Notes
    -----
    Useful for plotting probability distributions
    """
    assert n > 0, f"{n} must be > 0"
    adj = 0.5 if n > 10 else 3 / 8
    denom = n if n > 10 else n + 1 - 2 * adj
    return array([(i - adj) / denom for i in range(1, n + 1)])


def theoretical_quantiles(n, dist, *args):
    """returns theoretical quantiles from dist

    Parameters
    ----------
    n : int
        number of elements
    dist : str
        one of 'normal', 'chisq', 't', 'uniform'

    Returns
    -------
    Numpy array of quantiles
    """
    dist = dist.lower()
    funcs = dict(
        normal=ndtri,
        chisq=chdtri,
        t=stdtri,
    )

    if dist != "uniform" and dist not in funcs:
        raise ValueError(f"'{dist} not in {list(funcs)}")

    probs = probability_points(n)
    if dist == "uniform":
        return probs

    func = funcs[dist]

    if not args:
        return array([func(p) for p in probs])

    return array([func(*(args + (p,))) for p in probs])
