# Copyright (c) MONAI Consortium
# 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
#     http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from __future__ import annotations

from typing import TYPE_CHECKING, Any, Callable, Iterable, Sequence

import numpy as np
import torch
from monai.apps.vista3d.sampler import sample_prompt_pairs
from monai.engines.trainer import Trainer
from monai.engines.utils import IterationEvents, default_metric_cmp_fn, default_prepare_batch
from monai.inferers import Inferer, SimpleInferer
from monai.transforms import Transform
from monai.utils import IgniteInfo, RankFilter, min_version, optional_import
from monai.utils.enums import CommonKeys as Keys
from torch.optim.optimizer import Optimizer
from torch.utils.data import DataLoader

if TYPE_CHECKING:
    from ignite.engine import Engine, EventEnum
    from ignite.metrics import Metric
else:
    Engine, _ = optional_import("ignite.engine", IgniteInfo.OPT_IMPORT_VERSION, min_version, "Engine")
    Metric, _ = optional_import("ignite.metrics", IgniteInfo.OPT_IMPORT_VERSION, min_version, "Metric")
    EventEnum, _ = optional_import("ignite.engine", IgniteInfo.OPT_IMPORT_VERSION, min_version, "EventEnum")

__all__ = ["Vista3dTrainer"]


class Vista3dTrainer(Trainer):
    """
    Supervised detection training method with image and label, inherits from ``Trainer`` and ``Workflow``.
    Args:
        device: an object representing the device on which to run.
        max_epochs: the total epoch number for trainer to run.
        train_data_loader: Ignite engine use data_loader to run, must be Iterable or torch.DataLoader.
        detector: detector to train in the trainer, should be regular PyTorch `torch.nn.Module`.
        optimizer: the optimizer associated to the detector, should be regular PyTorch optimizer from `torch.optim`
            or its subclass.
        epoch_length: number of iterations for one epoch, default to `len(train_data_loader)`.
        non_blocking: if True and this copy is between CPU and GPU, the copy may occur asynchronously
            with respect to the host. For other cases, this argument has no effect.
        prepare_batch: function to parse expected data (usually `image`,`box`, `label` and other detector args)
            from `engine.state.batch` for every iteration, for more details please refer to:
            https://pytorch.org/ignite/generated/ignite.engine.create_supervised_trainer.html.
        iteration_update: the callable function for every iteration, expect to accept `engine`
            and `engine.state.batch` as inputs, return data will be stored in `engine.state.output`.
            if not provided, use `self._iteration()` instead. for more details please refer to:
            https://pytorch.org/ignite/generated/ignite.engine.engine.Engine.html.
        inferer: inference method that execute model forward on input data, like: SlidingWindow, etc.
        postprocessing: execute additional transformation for the model output data.
            Typically, several Tensor based transforms composed by `Compose`.
        key_train_metric: compute metric when every iteration completed, and save average value to
            engine.state.metrics when epoch completlabel_set = np.arange(output_classes).tolist().
            key_train_metric is the main metric to compare and save the checkpoint into files.
        additional_metrics: more Ignite metrics that also attach to Ignite Engine.
        metric_cmp_fn: function to compare current key metric with previous best key metric value,
            it must accept 2 args (current_metric, previous_best) and return a bool result: if `True`, will update
            `best_metric` and `best_metric_epoch` with current metric and epoch, default to `greater than`.
        train_handlers: every handler is a set of Ignite Event-Handlers, must have `attach` function, like:
            CheckpointHandler, StatsHandler, etc.
        amp: whether to enable auto-mixed-precision training, default is False.
        event_names: additional custom ignite events that will register to the engine.
            new events can be a list of str or `ignite.engine.events.EventEnum`.
        event_to_attr: a dictionary to map an event to a state attribute, then add to `engine.state`.
            for more details, check: https://pytorch.org/ignite/generated/ignite.engine.engine.Engine.html
            #ignite.engine.engine.Engine.register_events.
        decollate: whether to decollate the batch-first data to a list of data after model computation,
            recommend `decollate=True` when `postprocessing` uses components from `monai.transforms`.
            default to `True`.
        optim_set_to_none: when calling `optimizer.zero_grad()`, instead of setting to zero, set the grads to None.
            more details: https://pytorch.org/docs/stable/generated/torch.optim.Optimizer.zero_grad.html.
        to_kwargs: dict of other args for `prepare_batch` API when converting the input data, except for
            `device`, `non_blocking`.
        amp_kwargs: dict of the args for `torch.amp.autocast()` API, for more details:
            https://pytorch.org/docs/stable/amp.html#torch.amp.autocast.
    """

    def __init__(
        self,
        device: torch.device,
        max_epochs: int,
        train_data_loader: Iterable | DataLoader,
        network: torch.nn.Module,
        optimizer: Optimizer,
        loss_function: Callable,
        epoch_length: int | None = None,
        non_blocking: bool = False,
        prepare_batch: Callable = default_prepare_batch,
        iteration_update: Callable[[Engine, Any], Any] | None = None,
        inferer: Inferer | None = None,
        postprocessing: Transform | None = None,
        key_train_metric: dict[str, Metric] | None = None,
        additional_metrics: dict[str, Metric] | None = None,
        metric_cmp_fn: Callable = default_metric_cmp_fn,
        train_handlers: Sequence | None = None,
        amp: bool = False,
        event_names: list[str | EventEnum] | None = None,
        event_to_attr: dict | None = None,
        decollate: bool = True,
        optim_set_to_none: bool = False,
        to_kwargs: dict | None = None,
        amp_kwargs: dict | None = None,
        hyper_kwargs: dict | None = None,
    ) -> None:
        super().__init__(
            device=device,
            max_epochs=max_epochs,
            data_loader=train_data_loader,
            epoch_length=epoch_length,
            non_blocking=non_blocking,
            prepare_batch=prepare_batch,
            iteration_update=iteration_update,
            postprocessing=postprocessing,
            key_metric=key_train_metric,
            additional_metrics=additional_metrics,
            metric_cmp_fn=metric_cmp_fn,
            handlers=train_handlers,
            amp=amp,
            event_names=event_names,
            event_to_attr=event_to_attr,
            decollate=decollate,
            to_kwargs=to_kwargs,
            amp_kwargs=amp_kwargs,
        )

        self.network = network
        self.optimizer = optimizer
        self.loss_function = loss_function
        self.inferer = SimpleInferer() if inferer is None else inferer
        self.optim_set_to_none = optim_set_to_none
        self.hyper_kwargs = hyper_kwargs
        self.logger.addFilter(RankFilter())

    def _iteration(self, engine, batchdata: dict[str, torch.Tensor]):
        """
        Callback function for the Supervised Training processing logic of 1 iteration in Ignite Engine.
        Return below items in a dictionary:
            - IMAGE: image Tensor data for model input, already moved to device.
        Args:
            engine: `Vista3DTrainer` to execute operation for an iteration.
            batchdata: input data for this iteration, usually can be dictionary or tuple of Tensor data.
        Raises:
            ValueError: When ``batchdata`` is None.
        """

        if batchdata is None:
            raise ValueError("Must provide batch data for current iteration.")

        inputs, labels = engine.prepare_batch(batchdata, engine.state.device, engine.non_blocking, **engine.to_kwargs)
        engine.state.output = {Keys.IMAGE: inputs, Keys.LABEL: labels}

        label_set = engine.hyper_kwargs["label_set"]
        output_classes = engine.hyper_kwargs["output_classes"]
        if label_set is None:
            label_set = np.arange(output_classes).tolist()
        label_prompt, point, point_label, prompt_class = sample_prompt_pairs(
            labels,
            label_set,
            image_size=engine.hyper_kwargs["patch_size"],
            max_point=engine.hyper_kwargs["max_point"],
            max_prompt=engine.hyper_kwargs["max_prompt"],
            max_backprompt=engine.hyper_kwargs["max_backprompt"],
            max_foreprompt=engine.hyper_kwargs["max_foreprompt"],
            drop_label_prob=engine.hyper_kwargs["drop_label_prob"],
            drop_point_prob=engine.hyper_kwargs["drop_point_prob"],
            include_background=not engine.hyper_kwargs["exclude_background"],
        )

        def _compute_pred_loss():
            outputs = engine.network(
                input_images=inputs, point_coords=point, point_labels=point_label, class_vector=label_prompt
            )
            # engine.state.output[Keys.PRED] = outputs
            engine.fire_event(IterationEvents.FORWARD_COMPLETED)
            loss, loss_n = torch.tensor(0.0, device=engine.state.device), torch.tensor(0.0, device=engine.state.device)
            for id in range(len(prompt_class)):
                loss += engine.loss_function(outputs[[id]].float(), labels == prompt_class[id])
                loss_n += 1.0
            loss /= max(loss_n, 1.0)
            engine.state.output[Keys.LOSS] = loss
            outputs = None
            torch.cuda.empty_cache()
            engine.fire_event(IterationEvents.LOSS_COMPLETED)

        engine.network.train()
        engine.optimizer.zero_grad(set_to_none=engine.optim_set_to_none)

        if engine.amp and engine.scaler is not None:
            with torch.amp.autocast("cuda", **engine.amp_kwargs):
                _compute_pred_loss()
            engine.scaler.scale(engine.state.output[Keys.LOSS]).backward()
            engine.fire_event(IterationEvents.BACKWARD_COMPLETED)
            engine.scaler.step(engine.optimizer)
            engine.scaler.update()
        else:
            _compute_pred_loss()
            engine.state.output[Keys.LOSS].backward()
            engine.fire_event(IterationEvents.BACKWARD_COMPLETED)
            engine.optimizer.step()
        engine.fire_event(IterationEvents.MODEL_COMPLETED)
        return engine.state.output