#!/usr/bin/env python
# -*- encoding: utf-8 -*-
import torch

from colossalai.legacy.registry import HOOKS
from colossalai.legacy.trainer.hooks import BaseHook
from colossalai.logging import get_dist_logger
from colossalai.utils.checkpointing import save_checkpoint

from ._lr_scheduler_hook import LRSchedulerHook


@HOOKS.register_module
class SaveCheckpointHook(BaseHook):
    """Saves the model by interval in training process.

    Args:
       interval (int, optional): Number of epochs between saving the checkpoint, defaults to 1.
            if save_by_iter is True, this arg refers to the number of iters between saving.
       checkpoint_dir (str, optional): File name to save the checkpoint, defaults to None.
       model (torch.nn.Module, Optional): The model to save, defaults to None. When not passing,
            'trainer.engine.model' will be used. We encourage you to pass the model in it to avoid some
            unexpected bugs, especially when using **DDP**.
       save_by_iter (bool, optional): Whether saving the checkpoint by iter, default to False.
       priority (int, optional): Priority in the printing, hooks with small priority will be printed in front
            defaults to 10. If different hooks share same priority, the order of printing would
            depend on the hooks order in the hook list.
    """

    def __init__(self,
                 interval: int = 1,
                 checkpoint_dir: str = None,
                 model: torch.nn.Module = None,
                 save_by_iter: bool = False,
                 priority: int = 10):
        super().__init__(priority=priority)
        self.interval = interval
        self.checkpoint_dir = checkpoint_dir
        self.model = model
        self.save_by_iter = save_by_iter
        self.logger = get_dist_logger()

        # get lr scheduler from the LRSchedulerHook before train
        self._lr_scheduler = None

    def after_hook_is_attached(self, trainer):
        # get lr scheduler if exists
        for hook in trainer.hooks:
            if isinstance(hook, LRSchedulerHook):
                self._lr_scheduler = hook.lr_scheduler
                break
        self.model = self.model if self.model is not None else trainer.engine.model

    def after_train_iter(self, trainer, output, label, loss):
        """Saves the model after a training iter.
        """
        # save by interval
        if self.save_by_iter and trainer.cur_step % self.interval == 0:
            save_checkpoint(self.checkpoint_dir, trainer.cur_epoch, self.model, trainer.engine.optimizer,
                            self._lr_scheduler)
            self.logger.info(f'checkpoint for iteration {trainer.cur_step} is saved to {self.checkpoint_dir}',
                             ranks=[0])
        else:
            pass

    def after_train_epoch(self, trainer):
        """Saves the model after a training epoch.
        """
        # save by interval
        if trainer.cur_epoch % self.interval == 0:
            save_checkpoint(self.checkpoint_dir, trainer.cur_epoch, self.model, trainer.engine.optimizer,
                            self._lr_scheduler)
            self.logger.info(f'checkpoint for epoch {trainer.cur_epoch} is saved to {self.checkpoint_dir}', ranks=[0])