"""
@author: Junguang Jiang
@contact: JiangJunguang1123@outlook.com
"""
from typing import Optional, Sequence
import torch
import torch.nn as nn

from common.modules.classifier import Classifier as ClassifierBase
from ..modules.grl import GradientReverseLayer
from ..modules.kernels import GaussianKernel
from .dan import _update_index_matrix


__all__ = ['JointMultipleKernelMaximumMeanDiscrepancy', 'ImageClassifier']



class JointMultipleKernelMaximumMeanDiscrepancy(nn.Module):
    r"""The Joint Multiple Kernel Maximum Mean Discrepancy (JMMD) used in
    `Deep Transfer Learning with Joint Adaptation Networks (ICML 2017) <https://arxiv.org/abs/1605.06636>`_

    Given source domain :math:`\mathcal{D}_s` of :math:`n_s` labeled points and target domain :math:`\mathcal{D}_t`
    of :math:`n_t` unlabeled points drawn i.i.d. from P and Q respectively, the deep networks will generate
    activations in layers :math:`\mathcal{L}` as :math:`\{(z_i^{s1}, ..., z_i^{s|\mathcal{L}|})\}_{i=1}^{n_s}` and
    :math:`\{(z_i^{t1}, ..., z_i^{t|\mathcal{L}|})\}_{i=1}^{n_t}`. The empirical estimate of
    :math:`\hat{D}_{\mathcal{L}}(P, Q)` is computed as the squared distance between the empirical kernel mean
    embeddings as

    .. math::
        \hat{D}_{\mathcal{L}}(P, Q) &=
        \dfrac{1}{n_s^2} \sum_{i=1}^{n_s}\sum_{j=1}^{n_s} \prod_{l\in\mathcal{L}} k^l(z_i^{sl}, z_j^{sl}) \\
        &+ \dfrac{1}{n_t^2} \sum_{i=1}^{n_t}\sum_{j=1}^{n_t} \prod_{l\in\mathcal{L}} k^l(z_i^{tl}, z_j^{tl}) \\
        &- \dfrac{2}{n_s n_t} \sum_{i=1}^{n_s}\sum_{j=1}^{n_t} \prod_{l\in\mathcal{L}} k^l(z_i^{sl}, z_j^{tl}). \\

    Args:
        kernels (tuple(tuple(torch.nn.Module))): kernel functions, where `kernels[r]` corresponds to kernel :math:`k^{\mathcal{L}[r]}`.
        linear (bool): whether use the linear version of JAN. Default: False
        thetas (list(Theta): use adversarial version JAN if not None. Default: None

    Inputs:
        - z_s (tuple(tensor)): multiple layers' activations from the source domain, :math:`z^s`
        - z_t (tuple(tensor)): multiple layers' activations from the target domain, :math:`z^t`

    Shape:
        - :math:`z^{sl}` and :math:`z^{tl}`: :math:`(minibatch, *)`  where * means any dimension
        - Outputs: scalar

    .. note::
        Activations :math:`z^{sl}` and :math:`z^{tl}` must have the same shape.

    .. note::
        The kernel values will add up when there are multiple kernels for a certain layer.

    Examples::

        >>> feature_dim = 1024
        >>> batch_size = 10
        >>> layer1_kernels = (GaussianKernel(alpha=0.5), GaussianKernel(1.), GaussianKernel(2.))
        >>> layer2_kernels = (GaussianKernel(1.), )
        >>> loss = JointMultipleKernelMaximumMeanDiscrepancy((layer1_kernels, layer2_kernels))
        >>> # layer1 features from source domain and target domain
        >>> z1_s, z1_t = torch.randn(batch_size, feature_dim), torch.randn(batch_size, feature_dim)
        >>> # layer2 features from source domain and target domain
        >>> z2_s, z2_t = torch.randn(batch_size, feature_dim), torch.randn(batch_size, feature_dim)
        >>> output = loss((z1_s, z2_s), (z1_t, z2_t))
    """

    def __init__(self, kernels: Sequence[Sequence[nn.Module]], linear: Optional[bool] = True, thetas: Sequence[nn.Module] = None):
        super(JointMultipleKernelMaximumMeanDiscrepancy, self).__init__()
        self.kernels = kernels
        self.index_matrix = None
        self.linear = linear
        if thetas:
            self.thetas = thetas
        else:
            self.thetas = [nn.Identity() for _ in kernels]

    def forward(self, z_s: torch.Tensor, z_t: torch.Tensor) -> torch.Tensor:
        batch_size = int(z_s[0].size(0))
        self.index_matrix = _update_index_matrix(batch_size, self.index_matrix, self.linear).to(z_s[0].device)

        kernel_matrix = torch.ones_like(self.index_matrix)
        for layer_z_s, layer_z_t, layer_kernels, theta in zip(z_s, z_t, self.kernels, self.thetas):
            layer_features = torch.cat([layer_z_s, layer_z_t], dim=0)
            layer_features = theta(layer_features)
            kernel_matrix *= sum(
                [kernel(layer_features) for kernel in layer_kernels])  # Add up the matrix of each kernel

        # Add 2 / (n-1) to make up for the value on the diagonal
        # to ensure loss is positive in the non-linear version
        loss = (kernel_matrix * self.index_matrix).sum() + 2. / float(batch_size - 1)
        return loss


class Theta(nn.Module):
    """
    maximize loss respect to :math:`\theta`
    minimize loss respect to features
    """
    def __init__(self, dim: int):
        super(Theta, self).__init__()
        self.grl1 = GradientReverseLayer()
        self.grl2 = GradientReverseLayer()
        self.layer1 = nn.Linear(dim, dim)
        nn.init.eye_(self.layer1.weight)
        nn.init.zeros_(self.layer1.bias)

    def forward(self, features: torch.Tensor) -> torch.Tensor:
        features = self.grl1(features)
        return self.grl2(self.layer1(features))


class ImageClassifier(ClassifierBase):
    def __init__(self, backbone: nn.Module, num_classes: int, bottleneck_dim: Optional[int] = 256, **kwargs):
        bottleneck = nn.Sequential(
            # nn.AdaptiveAvgPool2d(output_size=(1, 1)),
            # nn.Flatten(),
            nn.Linear(backbone.out_features, bottleneck_dim),
            nn.BatchNorm1d(bottleneck_dim),
            nn.ReLU(),
            nn.Dropout(0.5)
        )
        super(ImageClassifier, self).__init__(backbone, num_classes, bottleneck, bottleneck_dim, **kwargs)