import copy

import torch
import torch.nn.functional as F
from torch import nn

from ..util import box_ops
from ..util.misc import (
    nested_tensor_from_tensor_list,
    accuracy,
    get_world_size,
    interpolate,
    is_dist_avail_and_initialized,
)
from .segmentation import dice_loss, sigmoid_focal_loss


class SetCriterion(nn.Module):
    """This class computes the loss for DETR.
    The process happens in two steps:
        1) we compute hungarian assignment between ground truth boxes and the outputs of the model
        2) we supervise each pair of matched ground-truth / prediction (supervise class and box)
    """

    def __init__(self, num_classes, matcher, weight_dict, eos_coef, losses):
        """Create the criterion.
        Parameters:
            num_classes: number of object categories, omitting the special no-object category
            matcher: module able to compute a matching between targets and proposals
            weight_dict: dict containing as key the names of the losses and as values their relative weight.
            eos_coef: relative classification weight applied to the no-object category
            losses: list of all the losses to be applied. See get_loss for list of available losses.
        """
        super().__init__()
        self.num_classes = num_classes
        self.matcher = matcher
        self.weight_dict = weight_dict
        self.eos_coef = eos_coef
        self.losses = losses
        empty_weight = torch.ones(self.num_classes + 1)
        empty_weight[-1] = self.eos_coef
        self.register_buffer("empty_weight", empty_weight)

    def loss_labels(self, outputs, targets, indices, num_boxes, log=True):
        """Classification loss (NLL)
        targets dicts must contain the key "labels" containing a tensor of dim [nb_target_boxes]
        """
        assert "pred_logits" in outputs
        # shape (batch_size, num_queries, NUM_CLASS + 1)
        src_logits = outputs["pred_logits"]
        # idx = (batch_idx, src_idx)
        #    batch_idx shape [\sum_b num_match_b]
        #    src_idx shape [\sum_b num_match_b]
        idx = self._get_src_permutation_idx(indices)
        # targets: List[Dict[str, torch.Tensor]]. Keys
        #   "labels": [NUM_BOX,]
        #   "boxes": [NUM_BOX, 4]
        # target_classes_o shape [batch_size * num_match]
        target_classes_o = torch.cat(
            [t["labels"][J] for t, (_, J) in zip(targets, indices)]
        )
        # shape (batch_size, num_queries)
        target_classes = torch.full(
            src_logits.shape[:2],
            self.num_classes,
            dtype=torch.int64,
            device=src_logits.device,
        )
        target_classes[idx] = target_classes_o

        loss_ce = F.cross_entropy(
            src_logits.transpose(1, 2), target_classes, self.empty_weight
        )
        losses = {"loss_ce": loss_ce}

        if log:
            # TODO this should probably be a separate loss, not hacked in this one here
            losses["class_error"] = 100 - accuracy(src_logits[idx], target_classes_o)[0]
        return losses

    @torch.no_grad()
    def loss_cardinality(self, outputs, targets, indices, num_boxes):
        """Compute the cardinality error, ie the absolute error in the number of predicted non-empty boxes
        This is not really a loss, it is intended for logging purposes only. It doesn't propagate gradients
        """
        pred_logits = outputs["pred_logits"]
        device = pred_logits.device
        tgt_lengths = torch.as_tensor(
            [len(v["labels"]) for v in targets], device=device
        )
        # Count the number of predictions that are NOT "no-object" (which is the last class)
        card_pred = (pred_logits.argmax(-1) != pred_logits.shape[-1] - 1).sum(1)
        card_err = F.l1_loss(card_pred.float(), tgt_lengths.float())
        losses = {"cardinality_error": card_err}
        return losses

    def loss_boxes(self, outputs, targets, indices, num_boxes):
        """Compute the losses related to the bounding boxes, the L1 regression loss and the GIoU loss
        targets dicts must contain the key "boxes" containing a tensor of dim [nb_target_boxes, 4]
        The target boxes are expected in format (center_x, center_y, w, h), normalized by the image size.
        """
        assert "pred_boxes" in outputs
        idx = self._get_src_permutation_idx(indices)
        # shape [\sum_b num_matches_b, 4]
        src_boxes = outputs["pred_boxes"][idx]
        # shape [\sum_b num_matches_b, 4]
        target_boxes = torch.cat(
            [t["boxes"][i] for t, (_, i) in zip(targets, indices)], dim=0
        )

        loss_bbox = F.l1_loss(src_boxes, target_boxes, reduction="none")

        losses = {}
        losses["loss_bbox"] = loss_bbox.sum() / num_boxes

        loss_giou = 1 - torch.diag(
            box_ops.generalized_box_iou(
                box_ops.box_cxcywh_to_xyxy(src_boxes),
                box_ops.box_cxcywh_to_xyxy(target_boxes),
            )
        )
        losses["loss_giou"] = loss_giou.sum() / num_boxes
        return losses

    def loss_masks(self, outputs, targets, indices, num_boxes):
        """Compute the losses related to the masks: the focal loss and the dice loss.
        targets dicts must contain the key "masks" containing a tensor of dim [nb_target_boxes, h, w]
        """
        assert "pred_masks" in outputs

        src_idx = self._get_src_permutation_idx(indices)
        tgt_idx = self._get_tgt_permutation_idx(indices)
        src_masks = outputs["pred_masks"]
        src_masks = src_masks[src_idx]
        masks = [t["masks"] for t in targets]
        # TODO use valid to mask invalid areas due to padding in loss
        target_masks, valid = nested_tensor_from_tensor_list(masks).decompose()
        target_masks = target_masks.to(src_masks)
        target_masks = target_masks[tgt_idx]

        # upsample predictions to the target size
        src_masks = interpolate(
            src_masks[:, None],
            size=target_masks.shape[-2:],
            mode="bilinear",
            align_corners=False,
        )
        src_masks = src_masks[:, 0].flatten(1)

        target_masks = target_masks.flatten(1)
        target_masks = target_masks.view(src_masks.shape)
        losses = {
            "loss_mask": sigmoid_focal_loss(src_masks, target_masks, num_boxes),
            "loss_dice": dice_loss(src_masks, target_masks, num_boxes),
        }
        return losses

    def _get_src_permutation_idx(self, indices):
        # permute predictions following indices
        batch_idx = torch.cat(
            [torch.full_like(src, i) for i, (src, _) in enumerate(indices)]
        )  # shape [\sum_b num_match_b]
        src_idx = torch.cat([src for (src, _) in indices])  # shape [\sum_b num_match_b]
        return batch_idx, src_idx

    def _get_tgt_permutation_idx(self, indices):
        # permute targets following indices
        batch_idx = torch.cat(
            [torch.full_like(tgt, i) for i, (_, tgt) in enumerate(indices)]
        )  # shape [\sum_b num_match_b]
        tgt_idx = torch.cat([tgt for (_, tgt) in indices])  # shape [\sum_b num_match_b]
        return batch_idx, tgt_idx

    def get_loss(self, loss, outputs, targets, indices, num_boxes, **kwargs):
        loss_map = {
            "labels": self.loss_labels,
            "cardinality": self.loss_cardinality,
            "boxes": self.loss_boxes,
            "masks": self.loss_masks,
        }
        assert loss in loss_map, f"do you really want to compute {loss} loss?"
        return loss_map[loss](outputs, targets, indices, num_boxes, **kwargs)

    def _forward(self, outputs, outputs_without_aux, targets):

        # Retrieve the matching between the outputs of the last layer and the targets
        # A list where each item is [row_indices, col_indices]
        indices = self.matcher(outputs_without_aux, targets)

        # Compute the average number of target boxes accross all nodes, for normalization purposes
        num_boxes = sum(len(t["labels"]) for t in targets)
        num_boxes = torch.as_tensor(
            [num_boxes], dtype=torch.float, device=next(iter(outputs.values())).device
        )
        if is_dist_avail_and_initialized():
            torch.distributed.all_reduce(num_boxes)
        num_boxes = torch.clamp(num_boxes / get_world_size(), min=1).item()

        # Compute all the requested losses
        losses = {}
        for loss in self.losses:
            losses.update(self.get_loss(loss, outputs, targets, indices, num_boxes))

        # In case of auxiliary losses, we repeat this process with the output of each intermediate layer.
        if "aux_outputs" in outputs:
            for i, aux_outputs in enumerate(outputs["aux_outputs"]):
                indices = self.matcher(aux_outputs, targets)
                for loss in self.losses:
                    if loss == "masks":
                        # Intermediate masks losses are too costly to compute, we ignore them.
                        continue
                    kwargs = {}
                    if loss == "labels":
                        # Logging is enabled only for the last layer
                        kwargs = {"log": False}
                    l_dict = self.get_loss(
                        loss, aux_outputs, targets, indices, num_boxes, **kwargs
                    )
                    l_dict = {k + f"_{i}": v for k, v in l_dict.items()}
                    losses.update(l_dict)
        return losses

    def forward(self, outputs, targets):
        """This performs the loss computation.
        Parameters:
             outputs: dict of tensors, see the output specification of the model for the format
             targets: list of dicts, such that len(targets) == batch_size.
                      The expected keys in each dict depends on the losses applied, see each loss' doc
        """
        # "pred_logits" shape (B, S, NUM_CLASS + 1)
        # "pred_boxes" shape (B, S, 4)
        outputs_without_aux = {k: v for k, v in outputs.items() if k != "aux_outputs"}
        return self._forward(outputs, outputs_without_aux, targets)


class FocalLossSetCriterion(SetCriterion):
    """This class computes the loss for DETR.
    The process happens in two steps:
        1) we compute hungarian assignment between ground truth boxes and the outputs of the model
        2) we supervise each pair of matched ground-truth / prediction (supervise class and box)
    """

    def __init__(self, num_classes, matcher, weight_dict, losses, focal_alpha=0.25):
        """Create the criterion.
        Parameters:
            num_classes: number of object categories, omitting the special no-object category
            matcher: module able to compute a matching between targets and proposals
            weight_dict: dict containing as key the names of the losses and as values their relative weight.
            losses: list of all the losses to be applied. See get_loss for list of available losses.
            focal_alpha: alpha in Focal Loss
        """
        super().__init__(num_classes, matcher, weight_dict, 0, losses)
        self.focal_alpha = focal_alpha

    def loss_labels(self, outputs, targets, indices, num_boxes, log=True):
        """Classification loss (NLL)
        targets dicts must contain the key "labels" containing a tensor of dim [nb_target_boxes]
        """
        assert "pred_logits" in outputs
        src_logits = outputs["pred_logits"]

        idx = self._get_src_permutation_idx(indices)
        target_classes_o = torch.cat(
            [t["labels"][J] for t, (_, J) in zip(targets, indices)]
        )
        target_classes = torch.full(
            src_logits.shape[:2],
            self.num_classes,
            dtype=torch.int64,
            device=src_logits.device,
        )
        target_classes[idx] = target_classes_o

        target_classes_onehot = torch.zeros(
            [src_logits.shape[0], src_logits.shape[1], src_logits.shape[2] + 1],
            dtype=src_logits.dtype,
            layout=src_logits.layout,
            device=src_logits.device,
        )
        target_classes_onehot.scatter_(2, target_classes.unsqueeze(-1), 1)

        target_classes_onehot = target_classes_onehot[:, :, :-1]
        loss_ce = (
            sigmoid_focal_loss(
                src_logits,
                target_classes_onehot,
                num_boxes,
                alpha=self.focal_alpha,
                gamma=2,
            )
            * src_logits.shape[1]
        )
        losses = {"loss_ce": loss_ce}

        if log:
            # TODO this should probably be a separate loss, not hacked in this one here
            losses["class_error"] = 100 - accuracy(src_logits[idx], target_classes_o)[0]
        return losses

    def forward(self, outputs, targets):
        """This performs the loss computation.
        Parameters:
             outputs: dict of tensors, see the output specification of the model for the format
             targets: list of dicts, such that len(targets) == batch_size.
                      The expected keys in each dict depends on the losses applied, see each loss' doc
        """
        outputs_without_aux = {
            k: v
            for k, v in outputs.items()
            if k != "aux_outputs" and k != "enc_outputs"
        }

        losses = self._forward(outputs, outputs_without_aux, targets)

        if "enc_outputs" in outputs:
            num_boxes = sum(len(t["labels"]) for t in targets)

            enc_outputs = outputs["enc_outputs"]
            bin_targets = copy.deepcopy(targets)
            for bt in bin_targets:
                bt["labels"] = torch.zeros_like(bt["labels"])
            indices = self.matcher(enc_outputs, bin_targets)
            for loss in self.losses:
                if loss == "masks":
                    # Intermediate masks losses are too costly to compute, we ignore them.
                    continue
                kwargs = {}
                if loss == "labels":
                    # Logging is enabled only for the last layer
                    kwargs["log"] = False
                l_dict = self.get_loss(
                    loss, enc_outputs, bin_targets, indices, num_boxes, **kwargs
                )
                l_dict = {k + "_enc": v for k, v in l_dict.items()}
                losses.update(l_dict)

        return losses
