# Copyright (c) Open-MMLab. All rights reserved.
import os.path as osp
import time
import warnings

import torch

import mmcv
from .base_runner import BaseRunner
from .checkpoint import save_checkpoint
from .utils import get_host_info


class EpochBasedRunner(BaseRunner):
    """Epoch-based Runner.

    This runner train models epoch by epoch.
    """

    def train(self, data_loader, **kwargs):
        self.model.train()
        self.mode = 'train'
        self.data_loader = data_loader
        self._max_iters = self._max_epochs * len(data_loader)
        self.call_hook('before_train_epoch')
        time.sleep(2)  # Prevent possible deadlock during epoch transition
        for i, data_batch in enumerate(data_loader):
            self._inner_iter = i
            self.call_hook('before_train_iter')
            if self.batch_processor is None:
                outputs = self.model.train_step(data_batch, self.optimizer,
                                                **kwargs)
            else:
                outputs = self.batch_processor(
                    self.model, data_batch, train_mode=True, **kwargs)
            if not isinstance(outputs, dict):
                raise TypeError('"batch_processor()" or "model.train_step()"'
                                ' must return a dict')
            if 'log_vars' in outputs:
                self.log_buffer.update(outputs['log_vars'],
                                       outputs['num_samples'])
            self.outputs = outputs
            self.call_hook('after_train_iter')
            self._iter += 1

        self.call_hook('after_train_epoch')
        self._epoch += 1

    def val(self, data_loader, **kwargs):
        self.model.eval()
        self.mode = 'val'
        self.data_loader = data_loader
        self.call_hook('before_val_epoch')
        time.sleep(2)  # Prevent possible deadlock during epoch transition
        for i, data_batch in enumerate(data_loader):
            self._inner_iter = i
            self.call_hook('before_val_iter')
            with torch.no_grad():
                if self.batch_processor is None:
                    outputs = self.model.val_step(data_batch, self.optimizer,
                                                  **kwargs)
                else:
                    outputs = self.batch_processor(
                        self.model, data_batch, train_mode=False, **kwargs)
            if not isinstance(outputs, dict):
                raise TypeError('"batch_processor()" or "model.val_step()"'
                                ' must return a dict')
            if 'log_vars' in outputs:
                self.log_buffer.update(outputs['log_vars'],
                                       outputs['num_samples'])
            self.outputs = outputs
            self.call_hook('after_val_iter')

        self.call_hook('after_val_epoch')

    def run(self, data_loaders, workflow, max_epochs, **kwargs):
        """Start running.

        Args:
            data_loaders (list[:obj:`DataLoader`]): Dataloaders for training
                and validation.
            workflow (list[tuple]): A list of (phase, epochs) to specify the
                running order and epochs. E.g, [('train', 2), ('val', 1)] means
                running 2 epochs for training and 1 epoch for validation,
                iteratively.
            max_epochs (int): Total training epochs.
        """
        assert isinstance(data_loaders, list)
        assert mmcv.is_list_of(workflow, tuple)
        assert len(data_loaders) == len(workflow)

        self._max_epochs = max_epochs
        for i, flow in enumerate(workflow):
            mode, epochs = flow
            if mode == 'train':
                self._max_iters = self._max_epochs * len(data_loaders[i])
                break

        work_dir = self.work_dir if self.work_dir is not None else 'NONE'
        self.logger.info('Start running, host: %s, work_dir: %s',
                         get_host_info(), work_dir)
        self.logger.info('workflow: %s, max: %d epochs', workflow, max_epochs)
        self.call_hook('before_run')

        while self.epoch < max_epochs:
            for i, flow in enumerate(workflow):
                mode, epochs = flow
                if isinstance(mode, str):  # self.train()
                    if not hasattr(self, mode):
                        raise ValueError(
                            f'runner has no method named "{mode}" to run an '
                            'epoch')
                    epoch_runner = getattr(self, mode)
                else:
                    raise TypeError(
                        'mode in workflow must be a str, but got {}'.format(
                            type(mode)))

                for _ in range(epochs):
                    if mode == 'train' and self.epoch >= max_epochs:
                        break
                    epoch_runner(data_loaders[i], **kwargs)

        time.sleep(1)  # wait for some hooks like loggers to finish
        self.call_hook('after_run')

    def save_checkpoint(self,
                        out_dir,
                        filename_tmpl='epoch_{}.pth',
                        save_optimizer=True,
                        meta=None,
                        create_symlink=True):
        """Save the checkpoint.

        Args:
            out_dir (str): The directory that checkpoints are saved.
            filename_tmpl (str, optional): The checkpoint filename template,
                which contains a placeholder for the epoch number.
                Defaults to 'epoch_{}.pth'.
            save_optimizer (bool, optional): Whether to save the optimizer to
                the checkpoint. Defaults to True.
            meta (dict, optional): The meta information to be saved in the
                checkpoint. Defaults to None.
            create_symlink (bool, optional): Whether to create a symlink
                "latest.pth" to point to the latest checkpoint.
                Defaults to True.
        """
        if meta is None:
            meta = dict(epoch=self.epoch + 1, iter=self.iter)
        else:
            meta.update(epoch=self.epoch + 1, iter=self.iter)

        filename = filename_tmpl.format(self.epoch + 1)
        filepath = osp.join(out_dir, filename)
        optimizer = self.optimizer if save_optimizer else None
        save_checkpoint(self.model, filepath, optimizer=optimizer, meta=meta)
        # in some environments, `os.symlink` is not supported, you may need to
        # set `create_symlink` to False
        if create_symlink:
            mmcv.symlink(filename, osp.join(out_dir, 'latest.pth'))


class Runner(EpochBasedRunner):
    """Deprecated name of EpochBasedRunner."""

    def __init__(self, *args, **kwargs):
        warnings.warn(
            'Runner was deprecated, please use EpochBasedRunner instead')
        super().__init__(*args, **kwargs)
