"""Theil Inequality metrics

"""
__author__ = "Sergio J. Rey <srey@asu.edu> "

from pysal.common import *
import numpy as np
__all__ = ['Theil', 'TheilD', 'TheilDSim']

SMALL = np.finfo('float').tiny


class Theil:
    """
    Classic Theil measure of inequality

        .. math::

            T = \sum_{i=1}^n \left( \\frac{y_i}{\sum_{i=1}^n y_i} \ln \left[ N \\frac{y_i}{\sum_{i=1}^n y_i}\\right] \\right)

    Parameters
    ----------
    y   : array (n,t) or (n,)
          with n taken as the observations across which inequality is
          calculated.  If y is (n,) then a scalar inequality value is
          determined. If y is (n,t) then an array of inequality values are
          determined, one value for each column in y.

    Attributes
    ----------

    T   : array (t,) or (1,)
          Theil's T for each column of y

    Notes
    -----
    This computation involves natural logs. To prevent ln[0] from occurring, a
    small value is added to each element of y before beginning the computation.

    Examples
    --------
    >>> import pysal
    >>> f=pysal.open(pysal.examples.get_path("mexico.csv"))
    >>> vnames=["pcgdp%d"%dec for dec in range(1940,2010,10)]
    >>> y=np.transpose(np.array([f.by_col[v] for v in vnames]))
    >>> theil_y=Theil(y)
    >>> theil_y.T
    array([ 0.20894344,  0.15222451,  0.10472941,  0.10194725,  0.09560113,
            0.10511256,  0.10660832])
    """

    def __init__(self, y):

        n = len(y)
        y = y + SMALL * (y == 0)  # can't have 0 values
        yt = y.sum(axis=0)
        s = y / (yt * 1.0)
        lns = np.log(n * s)
        slns = s * lns
        t = sum(slns)
        self.T = t


class TheilD:
    """Decomposition of Theil's T based on partitioning of
    observations into exhaustive and mutually exclusive groups

    Parameters
    ----------
    y         : array  (n,t) or (n, )
                with n taken as the observations across which inequality is
                calculated If y is (n,) then a scalar inequality value is
                determined. If y is (n,t) then an array of inequality values are
                determined, one value for each column in y.
    partition : array (n, )
                elements indicating which partition each observation belongs
                to. These are assumed to be exhaustive.

    Attributes
    ----------
    T  : array (n,t) or (n,)
         global inequality T
    bg : array (n,t) or (n,)
         between group inequality
    wg : array (n,t) or (n,)
         within group inequality

    Examples
    --------
    >>> import pysal
    >>> f=pysal.open(pysal.examples.get_path("mexico.csv"))
    >>> vnames=["pcgdp%d"%dec for dec in range(1940,2010,10)]
    >>> y=np.transpose(np.array([f.by_col[v] for v in vnames]))
    >>> regimes=np.array(f.by_col('hanson98'))
    >>> theil_d=TheilD(y,regimes)
    >>> theil_d.bg
    array([ 0.0345889 ,  0.02816853,  0.05260921,  0.05931219,  0.03205257,
            0.02963731,  0.03635872])
    >>> theil_d.wg
    array([ 0.17435454,  0.12405598,  0.0521202 ,  0.04263506,  0.06354856,
            0.07547525,  0.0702496 ])
   """
    def __init__(self, y, partition):
        groups = np.unique(partition)
        T = Theil(y).T
        ytot = y.sum(axis=0)

        #group totals
        gtot = np.array([y[partition == gid].sum(axis=0) for gid in groups])
        mm = np.dot

        if ytot.size == 1:  # y is 1-d
            sg = gtot / (ytot * 1.)
            sg.shape = (sg.size, 1)
        else:
            sg = mm(gtot, np.diag(1. / ytot))
        ng = np.array([sum(partition == gid) for gid in groups])
        ng.shape = (ng.size,)  # ensure ng is 1-d
        n = y.shape[0]
        # between group inequality
        bg = np.multiply(sg, np.log(mm(np.diag(n * 1. / ng), sg))).sum(axis=0)
        self.T = T
        self.bg = bg
        self.wg = T - bg


class TheilDSim:
    """Random permutation based inference on Theil's inequality decomposition.

    Provides for computationally based inference regarding the inequality
    decomposition using random spatial permutations. [1]_

    Parameters
    ----------
    y            : array  (n,t) or (n, )
                   with n taken as the observations across which inequality is
                   calculated If y is (n,) then a scalar inequality value is
                   determined. If y is (n,t) then an array of inequality values are
                   determined, one value for each column in y.
    partition    : array (n, )
                   elements indicating which partition each observation belongs
                   to. These are assumed to be exhaustive.
    permutations : int
                   Number of random spatial permutations for computationally
                   based inference on the decomposition.

    Attributes
    ----------

    observed   : array (n,t) or (n,)
                 TheilD instance for the observed data.

    bg         : array (permutations+1,t)
                 between group inequality

    bg_pvalue  : array (t,1)
                 p-value for the between group measure.  Measures the
                 percentage of the realized values that were greater than
                 or equal to the observed bg value. Includes the observed
                 value.

    wg         : array (size=permutations+1)
                 within group inequality Depending on the shape of y, 1 or 2-dimensional

    Examples
    --------
    >>> import pysal
    >>> f=pysal.open(pysal.examples.get_path("mexico.csv"))
    >>> vnames=["pcgdp%d"%dec for dec in range(1940,2010,10)]
    >>> y=np.transpose(np.array([f.by_col[v] for v in vnames]))
    >>> regimes=np.array(f.by_col('hanson98'))
    >>> np.random.seed(10)
    >>> theil_ds=TheilDSim(y,regimes,999)
    >>> theil_ds.bg_pvalue
    array([ 0.4  ,  0.344,  0.001,  0.001,  0.034,  0.072,  0.032])

    References
    ----------
    .. [1] Rey, S.J. (2004) "Spatial analysis of regional economic growth,
       inequality and change," in  M.F. Goodchild and D.G. Jannelle (eds.)
       Spatially Integrated Social Science. Oxford University Press: Oxford.
       Pages 280-299.

    """
    def __init__(self, y, partition, permutations=99):

        observed = TheilD(y, partition)
        bg_ct = observed.bg == observed.bg  # already have one extreme value
        bg_ct = bg_ct * 1.0
        results = [observed]
        for perm in range(permutations):
            yp = np.random.permutation(y)
            t = TheilD(yp, partition)
            bg_ct += (1.0 * t.bg >= observed.bg)
            results.append(t)
        self.results = results
        self.T = observed.T
        self.bg_pvalue = bg_ct / (permutations * 1.0 + 1)
        self.bg = np.array([r.bg for r in results])
        self.wg = np.array([r.wg for r in results])

