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'''
Classes:
    Metric - Abstract Base Class from which all metrics must inherit.
'''

from abc import ABCMeta, abstractmethod
import ocw.utils as utils
import numpy
import numpy.ma as ma
from scipy.stats import mstats

class Metric(object):
    '''Base Metric Class'''
    __metaclass__ = ABCMeta


class UnaryMetric(Metric):
    '''Abstract Base Class from which all unary metrics inherit.'''
    __metaclass__ = ABCMeta

    @abstractmethod
    def run(self, target_dataset):
        '''Run the metric for a given target dataset.

        :param target_dataset: The dataset on which the current metric will
            be run.
        :type target_dataset: :class:`dataset.Dataset`

        :returns: The result of evaluating the metric on the target_dataset.
        '''


class BinaryMetric(Metric):
    '''Abstract Base Class from which all binary metrics inherit.'''
    __metaclass__ = ABCMeta

    @abstractmethod
    def run(self, ref_dataset, target_dataset):
        '''Run the metric for the given reference and target datasets.

        :param ref_dataset: The Dataset to use as the reference dataset when
            running the evaluation.
        :type ref_dataset: :class:`dataset.Dataset`

        :param target_dataset: The Dataset to use as the target dataset when
            running the evaluation.
        :type target_dataset: :class:`dataset.Dataset`

        :returns: The result of evaluation the metric on the reference and 
            target dataset.
        '''


class Bias(BinaryMetric):
    '''Calculate the bias between a reference and target dataset.'''

    def run(self, ref_dataset, target_dataset):
        '''Calculate the bias between a reference and target dataset.

        .. note::
           Overrides BinaryMetric.run()

        :param ref_dataset: The reference dataset to use in this metric run.
        :type ref_dataset: :class:`dataset.Dataset`

        :param target_dataset: The target dataset to evaluate against the
            reference dataset in this metric run.
        :type target_dataset: :class:`dataset.Dataset`

        :returns: The difference between the reference and target datasets.
        :rtype: :class:`numpy.ndarray`
        '''
        return calc_bias(target_dataset.values,ref_dataset.values) 

class SpatialPatternTaylorDiagram(BinaryMetric):
    ''' Calculate the target to reference ratio of spatial standard deviation and pattern correlation'''

    def run(self, ref_dataset, target_dataset):
        '''Calculate two metrics to plot a Taylor diagram to compare spatial patterns      

        .. note::
           Overrides BinaryMetric.run() 
        
        :param ref_dataset: The reference dataset to use in this metric run.
        :type ref_dataset: :class:`dataset.Dataset`

        :param target_dataset: The target dataset to evaluate against the
            reference dataset in this metric run.
        :type target_dataset: :class:`dataset.Dataset`

        :returns: standard deviation ratio, pattern correlation coefficient
        :rtype: :float:'float','float' 
        '''
        return ma.array([calc_stddev_ratio(target_dataset.values, ref_dataset.values), calc_correlation(target_dataset.values, ref_dataset.values)])


class TemporalStdDev(UnaryMetric):
    '''Calculate the standard deviation over the time.'''

    def run(self, target_dataset):
        '''Calculate the temporal std. dev. for a datasets.

        .. note::
           Overrides UnaryMetric.run()

        :param target_dataset: The target_dataset on which to calculate the 
            temporal standard deviation.
        :type target_dataset: :class:`dataset.Dataset`

        :returns: The temporal standard deviation of the target dataset
        :rtype: :class:`ndarray`
        '''
        return calc_stddev(target_dataset.values, axis=0)


class StdDevRatio(BinaryMetric):
    '''Calculate the standard deviation ratio between two datasets.'''

    def run(self, ref_dataset, target_dataset):
        '''Calculate the standard deviation ratio.

        .. note::
            Overrides BinaryMetric.run()

        :param ref_dataset: The reference dataset to use in this metric run.
        :type ref_dataset: :class:`dataset.Dataset`

        :param target_dataset: The target dataset to evaluate against the
            reference dataset in this metric run.
        :type target_dataset: :class:`dataset.Dataset`

        :returns: The standard deviation ratio of the reference and target
        '''
       
        return calc_stddev_ratio(target_dataset.values, ref_dataset.values)


class PatternCorrelation(BinaryMetric):
    '''Calculate the correlation coefficient between two datasets'''

    def run(self, ref_dataset, target_dataset):
        '''Calculate the correlation coefficient between two dataset.

        .. note::
           Overrides BinaryMetric.run()

        :param ref_dataset: The reference dataset to use in this metric run.
        :type ref_dataset: :class:`dataset.Dataset`

        :param target_dataset: The target dataset to evaluate against the
            reference dataset in this metric run.
        :type target_dataset: :class:`dataset.Dataset`

        :returns: The correlation coefficient between a reference and target dataset.
        '''
        # stats.pearsonr returns correlation_coefficient, 2-tailed p-value
        # We only care about the correlation coefficient
        # Docs at http://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.pearsonr.html

        return calc_correlation(target_dataset.values, ref_dataset.values)


class TemporalCorrelation(BinaryMetric):
    '''Calculate the temporal correlation coefficients and associated
       confidence levels between two datasets, using Pearson's correlation.'''

    def run(self, reference_dataset, target_dataset):
        '''Calculate the temporal correlation coefficients and associated
           confidence levels between two datasets, using Pearson's correlation.

        .. note::
           Overrides BinaryMetric.run()

        :param reference_dataset: The reference dataset to use in this metric
            run
        :type reference_dataset: :class:`dataset.Dataset`

        :param target_dataset: The target dataset to evaluate against the
            reference dataset in this metric run
        :type target_dataset: :class:`dataset.Dataset`

        :returns: A 2D array of temporal correlation coefficients and a 2D
            array of confidence levels associated with the temporal correlation
            coefficients
        '''
        num_times, num_lats, num_lons = reference_dataset.values.shape
        coefficients = ma.zeros([num_lats, num_lons])
        for i in numpy.arange(num_lats):
            for j in numpy.arange(num_lons):
                coefficients[i, j] = calc_correlation(
                        target_dataset.values[:, i, j],
                        reference_dataset.values[:, i, j])
        return coefficients 


class TemporalMeanBias(BinaryMetric):
    '''Calculate the bias averaged over time.'''

    def run(self, ref_dataset, target_dataset):
        '''Calculate the bias averaged over time.

        .. note::
           Overrides BinaryMetric.run()

        :param ref_dataset: The reference dataset to use in this metric run.
        :type ref_dataset: :class:`dataset.Dataset`

        :param target_dataset: The target dataset to evaluate against the
            reference dataset in this metric run.
        :type target_dataset: :class:`dataset.Dataset`

        :returns: The mean bias between a reference and target dataset over time.
        '''

        return calc_bias(target_dataset.values,ref_dataset.values, average_over_time=True) 

class RMSError(BinaryMetric):
    '''Calculate the Root Mean Square Difference (RMS Error), with the mean
       calculated over time and space.'''

    def run(self, reference_dataset, target_dataset):
        '''Calculate the Root Mean Square Difference (RMS Error), with the mean
           calculated over time and space.

        .. note::
           Overrides BinaryMetric.run()

        :param reference_dataset: The reference dataset to use in this metric
            run
        :type reference_dataset: :class:`dataset.Dataset`

        :param target_dataset: The target dataset to evaluate against the
            reference dataset in this metric run
        :type target_dataset: :class:`dataset.Dataset`

        :returns: The RMS error, with the mean calculated over time and space
        '''

        return calc_rmse(target_dataset.values, reference_dataset.values)

def calc_bias(target_array, reference_array, average_over_time = False):
    ''' Calculate difference between two arrays

    :param target_array: an array to be evaluated, as model output
    :type target_array: :class:'numpy.ma.core.MaskedArray'

    :param reference_array: an array of reference dataset
    :type reference_array: :class:'numpy.ma.core.MaskedArray'

    :param average_over_time: if True, calculated bias is averaged for the axis=0
    :type average_over_time: 'bool'

    :returns: Biases array of the target dataset
    :rtype: :class:'numpy.ma.core.MaskedArray'
    '''
    
    bias = target_array - reference_array
    if average_over_time:
        return ma.average(bias, axis=0)
    else:
        return bias

def calc_stddev(array, axis=None):
    ''' Calculate a sample standard deviation of an array along the array

    :param array: an array to calculate sample standard deviation
    :type array: :class:'numpy.ma.core.MaskedArray'
    
    :param axis: Axis along which the sample standard deviation is computed.
    :type axis: 'int'

    :returns: sample standard deviation of array
    :rtype: :class:'numpy.ma.core.MaskedArray'
    '''

    if isinstance(axis, int):
        return ma.std(array, axis=axis, ddof=1)
    else:
        return ma.std(array, ddof=1)
        

def calc_stddev_ratio(target_array, reference_array):
    ''' Calculate ratio of standard deivations of the two arrays

    :param target_array: an array to be evaluated, as model output
    :type target_array: :class:'numpy.ma.core.MaskedArray'

    :param reference_array: an array of reference dataset
    :type reference_array: :class:'numpy.ma.core.MaskedArray'

    :param average_over_time: if True, calculated bias is averaged for the axis=0
    :type average_over_time: 'bool'

    :returns: (standard deviation of target_array)/(standard deviation of reference array)
    :rtype: :class:'float'
    '''

    return calc_stddev(target_array)/calc_stddev(reference_array)

def calc_correlation(target_array, reference_array):
    '''Calculate the correlation coefficient between two arrays.

    :param target_array: an array to be evaluated, as model output
    :type target_array: :class:'numpy.ma.core.MaskedArray'

    :param reference_array: an array of reference dataset
    :type reference_array: :class:'numpy.ma.core.MaskedArray'

    :returns: pearson's correlation coefficient between the two input arrays
    :rtype: :class:'numpy.ma.core.MaskedArray'
    '''

    return mstats.pearsonr(reference_array.flatten(), target_array.flatten())[0]  
       
def calc_rmse(target_array, reference_array):
    ''' Calculate ratio of standard deivations of the two arrays

    :param target_array: an array to be evaluated, as model output
    :type target_array: :class:'numpy.ma.core.MaskedArray'

    :param reference_array: an array of reference dataset
    :type reference_array: :class:'numpy.ma.core.MaskedArray'

    :param average_over_time: if True, calculated bias is averaged for the axis=0
    :type average_over_time: 'bool'

    :returns: root mean square error
    :rtype: :class:'float'
    '''

    return (ma.mean((calc_bias(target_array, reference_array))**2))**0.5