"""Implementations of discrete distributions."""

import torch

from torch.nn import functional as F

import nsf.nsf_utils as nsf_utils

from nsf.nde import distributions


class ConditionalIndependentBernoulli(distributions.Distribution):
    """An independent Bernoulli whose parameters are functions of a context."""

    def __init__(self, shape, context_encoder=None):
        """Constructor.

        Args:
            shape: list, tuple or torch.Size, the shape of the input variables.
            context_encoder: callable or None, encodes the context to the distribution parameters.
                If None, defaults to the identity function.
        """
        super().__init__()
        self._shape = torch.Size(shape)
        if context_encoder is None:
            self._context_encoder = lambda x: x
        else:
            self._context_encoder = context_encoder

    def _compute_params(self, context):
        """Compute the logits from context."""
        if context is None:
            raise ValueError('Context can\'t be None.')

        logits = self._context_encoder(context)
        if logits.shape[0] != context.shape[0]:
            raise RuntimeError(
                'The batch dimension of the parameters is inconsistent with the input.')

        return logits.reshape(logits.shape[0], *self._shape)

    def _log_prob(self, inputs, context):
        if inputs.shape[1:] != self._shape:
            raise ValueError('Expected input of shape {}, got {}'.format(
                self._shape, inputs.shape[1:]))

        # Compute parameters.
        logits = self._compute_params(context)
        assert logits.shape == inputs.shape

        # Compute log prob.
        log_prob = -inputs * F.softplus(-logits) - (1.0 - inputs) * F.softplus(logits)
        log_prob = nsf_utils.sum_except_batch(log_prob, num_batch_dims=1)
        return log_prob

    def _sample(self, num_samples, context):
        # Compute parameters.
        logits = self._compute_params(context)
        probs = torch.sigmoid(logits)
        probs = nsf_utils.repeat_rows(probs, num_samples)

        # Generate samples.
        context_size = context.shape[0]
        noise = torch.rand(context_size * num_samples, *self._shape)
        samples = (noise < probs).float()
        return nsf_utils.split_leading_dim(samples, [context_size, num_samples])

    def _mean(self, context):
        logits = self._compute_params(context)
        return torch.sigmoid(logits)
