# coding=utf-8
# Copyright 2022 Meta Platforms, Inc. and The HuggingFace Inc. team. All rights reserved.
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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
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#     http://www.apache.org/licenses/LICENSE-2.0
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""" PyTorch ConvNext model."""

from dataclasses import dataclass
from typing import Optional, Tuple

import torch
import torch.utils.checkpoint
from torch import nn
from torch.nn import BCEWithLogitsLoss, CrossEntropyLoss, MSELoss

from ...activations import ACT2FN
from ...file_utils import (
    ModelOutput,
    add_code_sample_docstrings,
    add_start_docstrings,
    add_start_docstrings_to_model_forward,
)
from ...modeling_utils import PreTrainedModel
from ...utils import logging
from .configuration_convnext import ConvNextConfig


logger = logging.get_logger(__name__)

# General docstring
_CONFIG_FOR_DOC = "ConvNextConfig"
_FEAT_EXTRACTOR_FOR_DOC = "ConvNextFeatureExtractor"

# Base docstring
_CHECKPOINT_FOR_DOC = "facebook/convnext-tiny-224"
_EXPECTED_OUTPUT_SHAPE = [1, 768, 7, 7]

# Image classification docstring
_IMAGE_CLASS_CHECKPOINT = "facebook/convnext-tiny-224"
_IMAGE_CLASS_EXPECTED_OUTPUT = "tabby, tabby cat"

CONVNEXT_PRETRAINED_MODEL_ARCHIVE_LIST = [
    "facebook/convnext-tiny-224",
    # See all ConvNext models at https://huggingface.co/models?filter=convnext
]


@dataclass
class ConvNextEncoderOutput(ModelOutput):
    """
    Class for [`ConvNextEncoder`]'s outputs, with potential hidden states (feature maps).

    Args:
        last_hidden_state (`torch.FloatTensor` of shape `(batch_size, num_channels, height, width)`):
            Last hidden states (final feature map) of the last stage of the model.
        hidden_states (`tuple(torch.FloatTensor)`, *optional*, returned when `output_hidden_states=True` is passed or when `config.output_hidden_states=True`):
            Tuple of `torch.FloatTensor` (one for the output of the embeddings + one for the output of each stage) of
            shape `(batch_size, num_channels, height, width)`. Hidden-states (also called feature maps) of the model at
            the output of each stage.
    """

    last_hidden_state: torch.FloatTensor = None
    hidden_states: Optional[Tuple[torch.FloatTensor]] = None


@dataclass
class ConvNextModelOutput(ModelOutput):
    """
    Class for [`ConvNextModel`]'s outputs, with potential hidden states (feature maps).

    Args:
        last_hidden_state (`torch.FloatTensor` of shape `(batch_size, num_channels, height, width)`):
            Last hidden states (final feature map) of the last stage of the model.
        pooler_output (`torch.FloatTensor` of shape `(batch_size, config.dim[-1])`):
            Global average pooling of the last feature map followed by a layernorm.
        hidden_states (`tuple(torch.FloatTensor)`, *optional*, returned when `output_hidden_states=True` is passed or when `config.output_hidden_states=True`):
            Tuple of `torch.FloatTensor` (one for the output of the embeddings + one for the output of each stage) of
            shape `(batch_size, num_channels, height, width)`. Hidden-states (also called feature maps) of the model at
            the output of each stage.
    """

    last_hidden_state: torch.FloatTensor = None
    pooler_output: Optional[torch.FloatTensor] = None
    hidden_states: Optional[Tuple[torch.FloatTensor]] = None


@dataclass
class ConvNextClassifierOutput(ModelOutput):
    """
    Class for [`ConvNextForImageClassification`]'s outputs, with potential hidden states (feature maps).

    Args:
        loss (`torch.FloatTensor` of shape `(1,)`, *optional*, returned when `labels` is provided):
            Classification (or regression if config.num_labels==1) loss.
        logits (`torch.FloatTensor` of shape `(batch_size, config.num_labels)`):
            Classification (or regression if config.num_labels==1) scores (before SoftMax).
        hidden_states (`tuple(torch.FloatTensor)`, *optional*, returned when `output_hidden_states=True` is passed or when `config.output_hidden_states=True`):
            Tuple of `torch.FloatTensor` (one for the output of the embeddings + one for the output of each stage) of
            shape `(batch_size, num_channels, height, width)`. Hidden-states (also called feature maps) of the model at
            the output of each stage.
    """

    loss: Optional[torch.FloatTensor] = None
    logits: torch.FloatTensor = None
    hidden_states: Optional[Tuple[torch.FloatTensor]] = None


# Stochastic depth implementation
# Taken from https://github.com/rwightman/pytorch-image-models/blob/master/timm/models/layers/drop.py
def drop_path(x, drop_prob: float = 0.0, training: bool = False):
    """
    Drop paths (Stochastic Depth) per sample (when applied in main path of residual blocks). This is the same as the
    DropConnect impl I created for EfficientNet, etc networks, however, the original name is misleading as 'Drop
    Connect' is a different form of dropout in a separate paper... See discussion:
    https://github.com/tensorflow/tpu/issues/494#issuecomment-532968956 ... I've opted for changing the layer and
    argument names to 'drop path' rather than mix DropConnect as a layer name and use 'survival rate' as the argument.
    """
    if drop_prob == 0.0 or not training:
        return x
    keep_prob = 1 - drop_prob
    shape = (x.shape[0],) + (1,) * (x.ndim - 1)  # work with diff dim tensors, not just 2D ConvNets
    random_tensor = keep_prob + torch.rand(shape, dtype=x.dtype, device=x.device)
    random_tensor.floor_()  # binarize
    output = x.div(keep_prob) * random_tensor
    return output


class ConvNextDropPath(nn.Module):
    """Drop paths (Stochastic Depth) per sample (when applied in main path of residual blocks)."""

    def __init__(self, drop_prob=None):
        super().__init__()
        self.drop_prob = drop_prob

    def forward(self, x):
        return drop_path(x, self.drop_prob, self.training)


class ConvNextLayerNorm(nn.Module):
    r"""LayerNorm that supports two data formats: channels_last (default) or channels_first.
    The ordering of the dimensions in the inputs. channels_last corresponds to inputs with shape (batch_size, height,
    width, channels) while channels_first corresponds to inputs with shape (batch_size, channels, height, width).
    """

    def __init__(self, normalized_shape, eps=1e-6, data_format="channels_last"):
        super().__init__()
        self.weight = nn.Parameter(torch.ones(normalized_shape))
        self.bias = nn.Parameter(torch.zeros(normalized_shape))
        self.eps = eps
        self.data_format = data_format
        if self.data_format not in ["channels_last", "channels_first"]:
            raise NotImplementedError(f"Unsupported data format: {self.data_format}")
        self.normalized_shape = (normalized_shape,)

    def forward(self, x):
        if self.data_format == "channels_last":
            x = torch.nn.functional.layer_norm(x, self.normalized_shape, self.weight, self.bias, self.eps)
        elif self.data_format == "channels_first":
            u = x.mean(1, keepdim=True)
            s = (x - u).pow(2).mean(1, keepdim=True)
            x = (x - u) / torch.sqrt(s + self.eps)
            x = self.weight[:, None, None] * x + self.bias[:, None, None]
        return x


class ConvNextEmbeddings(nn.Module):
    """This class is comparable to (and inspired by) the SwinEmbeddings class
    found in src/transformers/models/swin/modeling_swin.py.
    """

    def __init__(self, config):
        super().__init__()
        self.patch_embeddings = nn.Conv2d(
            config.num_channels, config.hidden_sizes[0], kernel_size=config.patch_size, stride=config.patch_size
        )
        self.layernorm = ConvNextLayerNorm(config.hidden_sizes[0], eps=1e-6, data_format="channels_first")

    def forward(self, pixel_values):
        embeddings = self.patch_embeddings(pixel_values)
        embeddings = self.layernorm(embeddings)
        return embeddings


class ConvNextLayer(nn.Module):
    """This corresponds to the `Block` class in the original implementation.

    There are two equivalent implementations: [DwConv, LayerNorm (channels_first), Conv, GELU,1x1 Conv]; all in (N, C,
    H, W) (2) [DwConv, Permute to (N, H, W, C), LayerNorm (channels_last), Linear, GELU, Linear]; Permute back

    The authors used (2) as they find it slightly faster in PyTorch.

    Args:
        config ([`ConvNextConfig`]): Model configuration class.
        dim (`int`): Number of input channels.
        drop_path (`float`): Stochastic depth rate. Default: 0.0.
    """

    def __init__(self, config, dim, drop_path=0):
        super().__init__()
        self.dwconv = nn.Conv2d(dim, dim, kernel_size=7, padding=3, groups=dim)  # depthwise conv
        self.layernorm = ConvNextLayerNorm(dim, eps=1e-6)
        self.pwconv1 = nn.Linear(dim, 4 * dim)  # pointwise/1x1 convs, implemented with linear layers
        self.act = ACT2FN[config.hidden_act]
        self.pwconv2 = nn.Linear(4 * dim, dim)
        self.layer_scale_parameter = (
            nn.Parameter(config.layer_scale_init_value * torch.ones((dim)), requires_grad=True)
            if config.layer_scale_init_value > 0
            else None
        )
        self.drop_path = ConvNextDropPath(drop_path) if drop_path > 0.0 else nn.Identity()

    def forward(self, hidden_states):
        input = hidden_states
        x = self.dwconv(hidden_states)
        x = x.permute(0, 2, 3, 1)  # (N, C, H, W) -> (N, H, W, C)
        x = self.layernorm(x)
        x = self.pwconv1(x)
        x = self.act(x)
        x = self.pwconv2(x)
        if self.layer_scale_parameter is not None:
            x = self.layer_scale_parameter * x
        x = x.permute(0, 3, 1, 2)  # (N, H, W, C) -> (N, C, H, W)

        x = input + self.drop_path(x)
        return x


class ConvNextStage(nn.Module):
    """ConvNeXT stage, consisting of an optional downsampling layer + multiple residual blocks.

    Args:
        config ([`ConvNextConfig`]): Model configuration class.
        in_channels (`int`): Number of input channels.
        out_channels (`int`): Number of output channels.
        depth (`int`): Number of residual blocks.
        drop_path_rates(`List[float]`): Stochastic depth rates for each layer.
    """