#   Copyright (c) 2020 PaddlePaddle Authors. All Rights Reserve.
#
# 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.

import os
import sys
import time
import copy

import logging
import datetime

import paddle
from paddle.distributed import ParallelEnv

from ..datasets.builder import build_dataloader
from ..models.builder import build_model
from ..utils.visual import tensor2img, save_image
from ..utils.filesystem import makedirs, save, load
from ..utils.timer import TimeAverager
from ..utils.profiler import add_profiler_step


class IterLoader:

    def __init__(self, dataloader):
        self._dataloader = dataloader
        self.iter_loader = iter(self._dataloader)
        self._epoch = 1
        self._inner_iter = 0

    @property
    def epoch(self):
        return self._epoch

    def __next__(self):
        try:
            if sys.platform == "Windows" and self._inner_iter == len(
                    self._dataloader) - 1:
                self._inner_iter = 0
                raise StopIteration
            data = next(self.iter_loader)
        except StopIteration:
            self._epoch += 1
            self.iter_loader = iter(self._dataloader)
            data = next(self.iter_loader)

        self._inner_iter += 1
        return data

    def __len__(self):
        return len(self._dataloader)


class Trainer:
    """
    # trainer calling logic:
    #
    #                build_model                               ||    model(BaseModel)
    #                     |                                    ||
    #               build_dataloader                           ||    dataloader
    #                     |                                    ||
    #               model.setup_lr_schedulers                  ||    lr_scheduler
    #                     |                                    ||
    #               model.setup_optimizers                     ||    optimizers
    #                     |                                    ||
    #     train loop (model.setup_input + model.train_iter)    ||    train loop
    #                     |                                    ||
    #         print log (model.get_current_losses)             ||
    #                     |                                    ||
    #         save checkpoint (model.nets)                     \/
    """

    def __init__(self, cfg):
        # base config
        self.logger = logging.getLogger(__name__)
        self.cfg = cfg
        self.output_dir = cfg.output_dir
        self.max_eval_steps = cfg.model.get('max_eval_steps', None)

        self.local_rank = ParallelEnv().local_rank
        self.world_size = ParallelEnv().nranks
        self.log_interval = cfg.log_config.interval
        self.visual_interval = cfg.log_config.visiual_interval
        self.weight_interval = cfg.snapshot_config.interval

        self.start_epoch = 1
        self.current_epoch = 1
        self.current_iter = 1
        self.inner_iter = 1
        self.batch_id = 0
        self.global_steps = 0

        # build model
        self.model = build_model(cfg.model)

        # build metrics
        self.metrics = None
        self.is_save_img = True
        validate_cfg = cfg.get('validate', None)
        if validate_cfg and 'metrics' in validate_cfg:
            self.metrics = self.model.setup_metrics(validate_cfg['metrics'])
        if validate_cfg and 'save_img' in validate_cfg:
            self.is_save_img = validate_cfg['save_img']

        self.enable_visualdl = cfg.get('enable_visualdl', False)
        if self.enable_visualdl:
            import visualdl
            self.vdl_logger = visualdl.LogWriter(logdir=cfg.output_dir)

        # build train dataloader
        self.train_dataloader = build_dataloader(cfg.dataset.train)
        self.iters_per_epoch = len(self.train_dataloader)

        # build lr scheduler
        # TODO: has a better way?
        if 'lr_scheduler' in cfg and 'iters_per_epoch' in cfg.lr_scheduler:
            cfg.lr_scheduler.iters_per_epoch = self.iters_per_epoch
        self.lr_schedulers = self.model.setup_lr_schedulers(cfg.lr_scheduler)

        # build optimizers
        self.optimizers = self.model.setup_optimizers(self.lr_schedulers,
                                                      cfg.optimizer)

        # setup amp train
        self.scalers = self.setup_amp_train() if self.cfg.amp else None

        # multiple gpus prepare
        if ParallelEnv().nranks > 1:
            self.distributed_data_parallel()

        # evaluate only
        if not cfg.is_train:
            return

        self.epochs = cfg.get('epochs', None)
        if self.epochs:
            self.total_iters = self.epochs * self.iters_per_epoch
            self.by_epoch = True
        else:
            self.by_epoch = False
            self.total_iters = cfg.total_iters

        if self.by_epoch:
            self.weight_interval *= self.iters_per_epoch

        self.validate_interval = -1
        if cfg.get('validate', None) is not None:
            self.validate_interval = cfg.validate.get('interval', -1)

        self.time_count = {}
        self.best_metric = {}
        self.model.set_total_iter(self.total_iters)
        self.profiler_options = cfg.profiler_options

    def setup_amp_train(self):
        """ decerate model, optimizer and return a list of GradScaler """
        self.logger.info('use AMP to train. AMP level = {}'.format(
            self.cfg.amp_level))

        # need to decorate model and optim if amp_level == 'O2'
        if self.cfg.amp_level == 'O2':
            nets, optimizers = list(self.model.nets.values()), list(
                self.optimizers.values())
            nets, optimizers = paddle.amp.decorate(models=nets,
                                                   optimizers=optimizers,
                                                   level='O2',
                                                   save_dtype='float32')
            for i, (k, _) in enumerate(self.model.nets.items()):
                self.model.nets[k] = nets[i]
            for i, (k, _) in enumerate(self.optimizers.items()):
                self.optimizers[k] = optimizers[i]

        scalers = [
            paddle.amp.GradScaler(init_loss_scaling=1024)
            for i in range(len(self.optimizers))
        ]

        return scalers

    def distributed_data_parallel(self):
        paddle.distributed.init_parallel_env()
        find_unused_parameters = self.cfg.get('find_unused_parameters', False)
        for net_name, net in self.model.nets.items():
            self.model.nets[net_name] = paddle.DataParallel(
                net, find_unused_parameters=find_unused_parameters)

    def learning_rate_scheduler_step(self):
        if isinstance(self.model.lr_scheduler, dict):
            for lr_scheduler in self.model.lr_scheduler.values():
                lr_scheduler.step()
        elif isinstance(self.model.lr_scheduler,
                        paddle.optimizer.lr.LRScheduler):
            self.model.lr_scheduler.step()
        else:
            raise ValueError(
                'lr schedulter must be a dict or an instance of LRScheduler')

    def train(self):
        reader_cost_averager = TimeAverager()
        batch_cost_averager = TimeAverager()

        iter_loader = IterLoader(self.train_dataloader)

        # set model.is_train = True
        self.model.setup_train_mode(is_train=True)
        while self.current_iter < (self.total_iters + 1):
            self.current_epoch = iter_loader.epoch
            self.inner_iter = self.current_iter % self.iters_per_epoch

            add_profiler_step(self.profiler_options)

            start_time = step_start_time = time.time()
            data = next(iter_loader)
            reader_cost_averager.record(time.time() - step_start_time)
            # unpack data from dataset and apply preprocessing
            # data input should be dict
            self.model.setup_input(data)

            if self.cfg.amp:
                self.model.train_iter_amp(self.optimizers, self.scalers,
                                          self.cfg.amp_level)  # amp train
            else:
                self.model.train_iter(self.optimizers)  # norm train

            batch_cost_averager.record(
                time.time() - step_start_time,
                num_samples=self.cfg['dataset']['train'].get('batch_size', 1))

            step_start_time = time.time()

            if self.current_iter % self.log_interval == 0:
                self.data_time = reader_cost_averager.get_average()
                self.step_time = batch_cost_averager.get_average()
                self.ips = batch_cost_averager.get_ips_average()
                self.print_log()

                reader_cost_averager.reset()
                batch_cost_averager.reset()

            if self.current_iter % self.visual_interval == 0 and self.local_rank == 0:
                self.visual('visual_train')

            self.learning_rate_scheduler_step()

            if self.validate_interval > -1 and self.current_iter % self.validate_interval == 0:
                self.test()

            if self.current_iter % self.weight_interval == 0:
                self.save(self.current_iter, 'weight', keep=-1)
                self.save(self.current_iter)

            self.current_iter += 1

    def test(self):
        if not hasattr(self, 'test_dataloader'):
            self.test_dataloader = build_dataloader(self.cfg.dataset.test,
                                                    is_train=False)
        iter_loader = IterLoader(self.test_dataloader)
        if self.max_eval_steps is None:
            self.max_eval_steps = len(self.test_dataloader)

        if self.metrics:
            for metric in self.metrics.values():
                metric.reset()

        # set model.is_train = False
        self.model.setup_train_mode(is_train=False)

        for i in range(self.max_eval_steps):
            if self.max_eval_steps < self.log_interval or i % self.log_interval == 0:
                self.logger.info('Test iter: [%d/%d]' %
                                 (i * self.world_size,
                                  self.max_eval_steps * self.world_size))

            data = next(iter_loader)
            self.model.setup_input(data)
            self.model.test_iter(metrics=self.metrics)

            if self.is_save_img:
                visual_results = {}
                current_paths = self.model.get_image_paths()
                current_visuals = self.model.get_current_visuals()

                if len(current_visuals) > 0 and list(
                        current_visuals.values())[0].shape == 4:
                    num_samples = list(current_visuals.values())[0].shape[0]
                else:
                    num_samples = 1

                for j in range(num_samples):
                    if j < len(current_paths):
                        short_path = os.path.basename(current_paths[j])
                        basename = os.path.splitext(short_path)[0]
                    else:
                        basename = '{:04d}_{:04d}'.format(i, j)
                    for k, img_tensor in current_visuals.items():
                        name = '%s_%s' % (basename, k)
                        if len(img_tensor.shape) == 4:
                            visual_results.update({name: img_tensor[j]})
                        else:
                            visual_results.update({name: img_tensor})

                self.visual('visual_test',
                            visual_results=visual_results,
                            step=self.batch_id,
                            is_save_image=True)

        if self.metrics:
            for metric_name, metric in self.metrics.items():
                self.logger.info("Metric {}: {:.4f}".format(
                    metric_name, metric.accumulate()))

    def print_log(self):
        losses = self.model.get_current_losses()

        message = ''
        if self.by_epoch:
            message += 'Epoch: %d/%d, iter: %d/%d ' % (
                self.current_epoch, self.epochs, self.inner_iter,
                self.iters_per_epoch)
        else:
            message += 'Iter: %d/%d ' % (self.current_iter, self.total_iters)

        message += f'lr: {self.current_learning_rate:.3e} '

        for k, v in losses.items():
            message += '%s: %.3f ' % (k, v)
            if self.enable_visualdl:
                self.vdl_logger.add_scalar(k, v, step=self.global_steps)

        if hasattr(self, 'step_time'):
            message += 'batch_cost: %.5f sec ' % self.step_time

        if hasattr(self, 'data_time'):
            message += 'reader_cost: %.5f sec ' % self.data_time

        if hasattr(self, 'ips'):
            message += 'ips: %.5f images/s ' % self.ips

        if hasattr(self, 'step_time'):
            eta = self.step_time * (self.total_iters - self.current_iter)
            eta = eta if eta > 0 else 0

            eta_str = str(datetime.timedelta(seconds=int(eta)))
            message += f'eta: {eta_str}'

        # print the message
        self.logger.info(message)

    @property
    def current_learning_rate(self):
        for optimizer in self.model.optimizers.values():
            return optimizer.get_lr()

    def visual(self,
               results_dir,
               visual_results=None,
               step=None,
               is_save_image=False):
        """
        visual the images, use visualdl or directly write to the directory
        Parameters:
            results_dir (str)     --  directory name which contains saved images
            visual_results (dict) --  the results images dict
            step (int)            --  global steps, used in visualdl
            is_save_image (bool)  --  weather write to the directory or visualdl
        """
        self.model.compute_visuals()

        if visual_results is None:
            visual_results = self.model.get_current_visuals()

        min_max = self.cfg.get('min_max', None)
        if min_max is None:
            min_max = (-1., 1.)

        image_num = self.cfg.get('image_num', None)
        if (image_num is None) or (not self.enable_visualdl):
            image_num = 1
        for label, image in visual_results.items():
            image_numpy = tensor2img(image, min_max, image_num)
            if (not is_save_image) and self.enable_visualdl:
                self.vdl_logger.add_image(
                    results_dir + '/' + label,
                    image_numpy,
                    step=step if step else self.global_steps,
                    dataformats="HWC" if image_num == 1 else "NCHW")
            else:
                if self.cfg.is_train:
                    if self.by_epoch:
                        msg = 'epoch%.3d_' % self.current_epoch
                    else:
                        msg = 'iter%.3d_' % self.current_iter
                else:
                    msg = ''
                makedirs(os.path.join(self.output_dir, results_dir))
                img_path = os.path.join(self.output_dir, results_dir,
                                        msg + '%s.png' % (label))
                save_image(image_numpy, img_path)

    def save(self, epoch, name='checkpoint', keep=1):
        if self.local_rank != 0:
            return

        assert name in ['checkpoint', 'weight']

        state_dicts = {}
        if self.by_epoch:
            save_filename = 'epoch_%s_%s.pdparams' % (
                epoch // self.iters_per_epoch, name)
        else:
            save_filename = 'iter_%s_%s.pdparams' % (epoch, name)

        os.makedirs(self.output_dir, exist_ok=True)
        save_path = os.path.join(self.output_dir, save_filename)
        for net_name, net in self.model.nets.items():
            state_dicts[net_name] = net.state_dict()

        if name == 'weight':
            save(state_dicts, save_path)
            return

        state_dicts['epoch'] = epoch

        for opt_name, opt in self.model.optimizers.items():
            state_dicts[opt_name] = opt.state_dict()

        save(state_dicts, save_path)

        if keep > 0:
            try:
                if self.by_epoch:
                    checkpoint_name_to_be_removed = os.path.join(
                        self.output_dir, 'epoch_%s_%s.pdparams' %
                        ((epoch - keep * self.weight_interval) //
                         self.iters_per_epoch, name))
                else:
                    checkpoint_name_to_be_removed = os.path.join(
                        self.output_dir, 'iter_%s_%s.pdparams' %
                        (epoch - keep * self.weight_interval, name))

                if os.path.exists(checkpoint_name_to_be_removed):
                    os.remove(checkpoint_name_to_be_removed)

            except Exception as e:
                self.logger.info('remove old checkpoints error: {}'.format(e))

    def resume(self, checkpoint_path):
        state_dicts = load(checkpoint_path)
        if state_dicts.get('epoch', None) is not None:
            self.start_epoch = state_dicts['epoch'] + 1
            self.global_steps = self.iters_per_epoch * state_dicts['epoch']

            self.current_iter = state_dicts['epoch'] + 1

        for net_name, net in self.model.nets.items():
            net.set_state_dict(state_dicts[net_name])

        for opt_name, opt in self.model.optimizers.items():
            opt.set_state_dict(state_dicts[opt_name])

    def load(self, weight_path):
        state_dicts = load(weight_path)

        def is_dict_in_dict_weight(state_dict):
            if isinstance(state_dict, dict) and len(state_dict) > 0:
                val = list(state_dict.values())[0]
                if isinstance(val, dict):
                    return True
                else:
                    return False
            else:
                return False

        if is_dict_in_dict_weight(state_dicts):
            for net_name, net in self.model.nets.items():
                if net_name in state_dicts:
                    net.set_state_dict(state_dicts[net_name])
                    self.logger.info(
                        'Loaded pretrained weight for net {}'.format(net_name))
                else:
                    self.logger.warning(
                        'Can not find state dict of net {}. Skip load pretrained weight for net {}'
                        .format(net_name, net_name))
        else:
            assert len(self.model.nets
                       ) == 1, 'checkpoint only contain weight of one net, \
                                                but model contains more than one net!'

            net_name, net = list(self.model.nets.items())[0]
            net.set_state_dict(state_dicts)
            self.logger.info(
                'Loaded pretrained weight for net {}'.format(net_name))

    def close(self):
        """
        when finish the training need close file handler or other.
        """
        if self.enable_visualdl:
            self.vdl_logger.close()