from __future__ import absolute_import
import theano
import theano.tensor as T
import numpy as np

from .utils.theano_utils import shared_zeros, shared_scalar
from six.moves import zip


def clip_norm(g, c, n):
    if c > 0:
        g = T.switch(T.ge(n, c), g * c / n, g)
    return g


def kl_divergence(p, p_hat):
    return p_hat - p + p * T.log(p / p_hat)


class Optimizer(object):
    def get_updates(self, params, constraints, loss):
        raise NotImplementedError

    def get_gradients(self, loss, params):

        grads = T.grad(loss, params)

        if hasattr(self, 'clipnorm') and self.clipnorm > 0:
            norm = T.sqrt(sum([T.sum(g ** 2) for g in grads]))
            grads = [clip_norm(g, self.clipnorm, norm) for g in grads]

        return grads

    def get_config(self):
        return {"name": self.__class__.__name__}


class SGD(Optimizer):

    def __init__(self, lr=0.01, momentum=0., decay=0., nesterov=False, *args, **kwargs):
        self.__dict__.update(kwargs)
        self.__dict__.update(locals())
        self.iterations = shared_scalar(0)

    def get_updates(self, params, constraints, loss):
        grads = self.get_gradients(loss, params)
        lr = self.lr * (1.0 / (1.0 + self.decay * self.iterations))
        updates = [(self.iterations, self.iterations + 1.)]

        for p, g, c in zip(params, grads, constraints):
            m = shared_zeros(p.get_value().shape) # momentum
            v = self.momentum * m - lr * g # velocity
            updates.append((m, v))

            if self.nesterov:
                new_p = p + self.momentum * v - lr * g
            else:
                new_p = p + v

            updates.append((p, c(new_p))) # apply constraints
        return updates

    def get_config(self):
        return {"name": self.__class__.__name__,
                "lr": self.lr,
                "momentum": self.momentum,
                "decay": self.decay,
                "nesterov": self.nesterov}


class RMSprop(Optimizer):
    def __init__(self, lr=0.001, rho=0.9, epsilon=1e-6, *args, **kwargs):
        self.__dict__.update(kwargs)
        self.__dict__.update(locals())

    def get_updates(self, params, constraints, loss):
        grads = self.get_gradients(loss, params)
        accumulators = [shared_zeros(p.get_value().shape) for p in params]
        updates = []

        for p, g, a, c in zip(params, grads, accumulators, constraints):
            new_a = self.rho * a + (1 - self.rho) * g ** 2 # update accumulator
            updates.append((a, new_a))

            new_p = p - self.lr * g / T.sqrt(new_a + self.epsilon)
            updates.append((p, c(new_p))) # apply constraints
        return updates

    def get_config(self):
        return {"name": self.__class__.__name__,
                "lr": self.lr,
                "rho": self.rho,
                "epsilon": self.epsilon}


class Adagrad(Optimizer):
    def __init__(self, lr=0.01, epsilon=1e-6, *args, **kwargs):
        self.__dict__.update(kwargs)
        self.__dict__.update(locals())

    def get_updates(self, params, constraints, loss):
        grads = self.get_gradients(loss, params)
        accumulators = [shared_zeros(p.get_value().shape) for p in params]
        updates = []

        for p, g, a, c in zip(params, grads, accumulators, constraints):
            new_a = a + g ** 2 # update accumulator
            updates.append((a, new_a))
            new_p = p - self.lr * g / T.sqrt(new_a + self.epsilon)
            updates.append((p, c(new_p))) # apply constraints
        return updates

    def get_config(self):
        return {"name": self.__class__.__name__,
                "lr": self.lr,
                "epsilon": self.epsilon}


class Adadelta(Optimizer):
    '''
        Reference: http://arxiv.org/abs/1212.5701
    '''
    def __init__(self, lr=1.0, rho=0.95, epsilon=1e-6, *args, **kwargs):
        self.__dict__.update(kwargs)
        self.__dict__.update(locals())

    def get_updates(self, params, constraints, loss):
        grads = self.get_gradients(loss, params)
        accumulators = [shared_zeros(p.get_value().shape) for p in params]
        delta_accumulators = [shared_zeros(p.get_value().shape) for p in params]
        updates = []

        for p, g, a, d_a, c in zip(params, grads, accumulators, delta_accumulators, constraints):
            new_a = self.rho * a + (1 - self.rho) * g ** 2 # update accumulator
            updates.append((a, new_a))

            # use the new accumulator and the *old* delta_accumulator
            update = g * T.sqrt(d_a + self.epsilon) / T.sqrt(new_a + self.epsilon)

            new_p = p - self.lr * update
            updates.append((p, c(new_p))) # apply constraints

            # update delta_accumulator
            new_d_a = self.rho * d_a + (1 - self.rho) * update ** 2
            updates.append((d_a, new_d_a))
        return updates

    def get_config(self):
        return {"name": self.__class__.__name__,
                "lr": self.lr,
                "rho": self.rho,
                "epsilon": self.epsilon}


class Adam(Optimizer):
    '''
        Reference: http://arxiv.org/abs/1412.6980

        Default parameters follow those provided in the original paper

        lambda is renamed kappa.
    '''
    def __init__(self, lr=0.001, beta_1=0.9, beta_2=0.999, epsilon=1e-8, kappa=1-1e-8, *args, **kwargs):
        self.__dict__.update(kwargs)
        self.__dict__.update(locals())
        self.iterations = shared_scalar(0)

    def get_updates(self, params, constraints, loss):
        grads = self.get_gradients(loss, params)
        updates = [(self.iterations, self.iterations+1.)]

        i = self.iterations
        beta_1_t = self.beta_1 * (self.kappa**i)

        # the update below seems missing from the paper, but is obviously required
        beta_2_t = self.beta_2 * (self.kappa**i)

        for p, g, c in zip(params, grads, constraints):
            m = theano.shared(p.get_value() * 0.) # zero init of moment
            v = theano.shared(p.get_value() * 0.) # zero init of velocity

            m_t = (beta_1_t * m) + (1 - beta_1_t) * g
            v_t = (beta_2_t * v) + (1 - beta_2_t) * (g**2)

            m_b_t = m_t / (1 - beta_1_t)
            v_b_t = v_t / (1 - beta_2_t)

            p_t = p - self.lr * m_b_t / (T.sqrt(v_b_t) + self.epsilon)

            updates.append((m, m_t))
            updates.append((v, v_t))
            updates.append((p, c(p_t))) # apply constraints
        return updates

    def get_config(self):
        return {"name": self.__class__.__name__,
                "lr": self.lr,
                "beta_1": self.beta_1,
                "beta_2": self.beta_2,
                "epsilon": self.epsilon,
                "kappa": self.kappa}

# aliases
sgd = SGD
rmsprop = RMSprop
adagrad = Adagrad
adadelta = Adadelta
adam = Adam

from .utils.generic_utils import get_from_module
def get(identifier, kwargs=None):
    return get_from_module(identifier, globals(), 'optimizer', instantiate=True, kwargs=kwargs)
