from __future__ import absolute_import
from rllab2.misc.ext import compile_function, lazydict, flatten_tensor_variables
from rllab2.misc import logger
from rllab2.core.serializable import Serializable
import theano.tensor as TT
import theano
import numpy as np
import scipy.optimize


class PenaltyLbfgsOptimizer(Serializable):
    u"""
    Performs constrained optimization via penalized L-BFGS. The penalty term is adaptively adjusted to make sure that
    the constraint is satisfied.
    """

    def __init__(
            self,
            max_opt_itr=20,
            initial_penalty=1.0,
            min_penalty=1e-2,
            max_penalty=1e6,
            increase_penalty_factor=2,
            decrease_penalty_factor=0.5,
            max_penalty_itr=10,
            adapt_penalty=True):
        Serializable.quick_init(self, locals())
        self._max_opt_itr = max_opt_itr
        self._penalty = initial_penalty
        self._initial_penalty = initial_penalty
        self._min_penalty = min_penalty
        self._max_penalty = max_penalty
        self._increase_penalty_factor = increase_penalty_factor
        self._decrease_penalty_factor = decrease_penalty_factor
        self._max_penalty_itr = max_penalty_itr
        self._adapt_penalty = adapt_penalty

        self._opt_fun = None
        self._target = None
        self._max_constraint_val = None
        self._constraint_name = None

    def update_opt(self, loss, target, leq_constraint, inputs, constraint_name=u"constraint", *args, **kwargs):
        u"""
        :param loss: Symbolic expression for the loss function.
        :param target: A parameterized object to optimize over. It should implement methods of the
        :class:`rllab2.core.paramerized.Parameterized` class.
        :param leq_constraint: A constraint provided as a tuple (f, epsilon), of the form f(*inputs) <= epsilon.
        :param inputs: A list of symbolic variables as inputs
        :return: No return value.
        """
        constraint_term, constraint_value = leq_constraint
        penalty_var = TT.scalar(u"penalty")
        penalized_loss = loss + penalty_var * constraint_term

        self._target = target
        self._max_constraint_val = constraint_value
        self._constraint_name = constraint_name

        def get_opt_output():
            flat_grad = flatten_tensor_variables(theano.grad(
                penalized_loss, target.get_params(trainable=True), disconnected_inputs=u'ignore'
            ))
            return [penalized_loss.astype(u'float64'), flat_grad.astype(u'float64')]

        self._opt_fun = lazydict(
            f_loss=lambda: compile_function(inputs, loss, log_name=u"f_loss"),
            f_constraint=lambda: compile_function(inputs, constraint_term, log_name=u"f_constraint"),
            f_penalized_loss=lambda: compile_function(
                inputs=inputs + [penalty_var],
                outputs=[penalized_loss, loss, constraint_term],
                log_name=u"f_penalized_loss",
            ),
            f_opt=lambda: compile_function(
                inputs=inputs + [penalty_var],
                outputs=get_opt_output(),
                log_name=u"f_opt"
            )
        )

    def loss(self, inputs):
        return self._opt_fun[u"f_loss"](*inputs)

    def constraint_val(self, inputs):
        return self._opt_fun[u"f_constraint"](*inputs)

    def optimize(self, inputs):

        inputs = tuple(inputs)

        try_penalty = np.clip(
            self._penalty, self._min_penalty, self._max_penalty)

        penalty_scale_factor = None
        f_opt = self._opt_fun[u"f_opt"]
        f_penalized_loss = self._opt_fun[u"f_penalized_loss"]

        def gen_f_opt(penalty):
            def f(flat_params):
                self._target.set_param_values(flat_params, trainable=True)
                return f_opt(*(inputs + (penalty,)))
            return f

        cur_params = self._target.get_param_values(trainable=True).astype(u'float64')
        opt_params = cur_params

        for penalty_itr in xrange(self._max_penalty_itr):
            logger.log(u'trying penalty=%.3f...' % try_penalty)
            
            itr_opt_params, _, _ = scipy.optimize.fmin_l_bfgs_b(
                func=gen_f_opt(try_penalty), x0=cur_params,
                maxiter=self._max_opt_itr
            )

            _, try_loss, try_constraint_val = f_penalized_loss(*(inputs + (try_penalty,)))

            logger.log(u'penalty %f => loss %f, %s %f' %
                       (try_penalty, try_loss, self._constraint_name, try_constraint_val))

            # Either constraint satisfied, or we are at the last iteration already and no alternative parameter
            # satisfies the constraint
            if try_constraint_val < self._max_constraint_val or \
                    (penalty_itr == self._max_penalty_itr - 1 and opt_params is None):
                opt_params = itr_opt_params

            if not self._adapt_penalty:
                break

            # Decide scale factor on the first iteration, or if constraint violation yields numerical error
            if penalty_scale_factor is None or np.isnan(try_constraint_val):
                # Increase penalty if constraint violated, or if constraint term is NAN
                if try_constraint_val > self._max_constraint_val or np.isnan(try_constraint_val):
                    penalty_scale_factor = self._increase_penalty_factor
                else:
                    # Otherwise (i.e. constraint satisfied), shrink penalty
                    penalty_scale_factor = self._decrease_penalty_factor
                    opt_params = itr_opt_params
            else:
                # After the first iteration, the penalty is not None. Now whenever constraint is crossed, we stop adjust
                if penalty_scale_factor > 1 and \
                        try_constraint_val <= self._max_constraint_val:
                    break
                elif penalty_scale_factor < 1 and \
                        try_constraint_val >= self._max_constraint_val:
                    break

            # check if the penalty was already at the bounds. Otherwise update it. Here penalty_scale_fact is never None
            if try_penalty >= self._max_penalty and penalty_scale_factor > 1:
                logger.log(u'_max_penalty has already been tried!')
                self._penalty = try_penalty  # useless: if we were at max_penalty it means a previous itr already set it
                break
            elif try_penalty <= self._min_penalty and penalty_scale_factor < 1:
                logger.log(u'_min_penalty has already been tried!')
                self._penalty = try_penalty
                break
            else:
                try_penalty *= penalty_scale_factor
                try_penalty = np.clip(try_penalty, self._min_penalty, self._max_penalty)
                self._penalty = try_penalty

        self._target.set_param_values(opt_params, trainable=True)
