import os
import time
from collections import OrderedDict

import torch
from torch.utils.data.distributed import DistributedSampler

from lib.train.admin import AverageMeter, StatValue
from lib.train.admin import TensorboardWriter
from lib.train.data.wandb_logger import WandbWriter
from lib.train.trainers import BaseTrainer
from lib.utils.misc import get_world_size


class LTRTrainer(BaseTrainer):
    def __init__(self, actor, loaders, optimizer, settings, lr_scheduler=None):
        """
        Args:
            actor: The actor for training the network.
            loaders: List of dataset loaders, e.g. [train_loader, val_loader].
                     In each epoch, the trainer runs one epoch for each loader.
            optimizer: The optimizer used for training, e.g. Adam.
            settings: Training settings.
            lr_scheduler: Learning rate scheduler.
        """

        super().__init__(actor, loaders, optimizer, settings, lr_scheduler)

        self._set_default_settings()

        # Initialize statistics variables
        self.stats = OrderedDict({loader.name: None for loader in self.loaders})

        # Initialize tensorboard and wandb
        self.wandb_writer = None
        if settings.local_rank in [-1, 0]:
            tensorboard_writer_dir = os.path.join(self.settings.env.tensorboard_dir, self.settings.project_path)
            if not os.path.exists(tensorboard_writer_dir):
                os.makedirs(tensorboard_writer_dir)
            self.tensorboard_writer = TensorboardWriter(tensorboard_writer_dir, [l.name for l in loaders])

            if settings.use_wandb:
                world_size = get_world_size()
                cur_train_samples = self.loaders[0].dataset.samples_per_epoch * max(0, self.epoch - 1)
                interval = (world_size * settings.batchsize)  # * interval
                self.wandb_writer = WandbWriter(settings.project_path[6:], {}, tensorboard_writer_dir,
                                                cur_train_samples, interval)

        self.move_data_to_gpu = getattr(settings, 'move_data_to_gpu', True)
        self.settings = settings

    def _set_default_settings(self):
        # Dict of all default values
        default = {'print_interval': 10,
                   'print_stats': None,
                   'description': ''}

        for param, default_value in default.items():
            if getattr(self.settings, param, None) is None:
                setattr(self.settings, param, default_value)

    def cycle_dataset(self, loader):
        """
        Do a cycle of training or validation.
        """

        self.actor.train(loader.training)
        torch.set_grad_enabled(loader.training)

        self._init_timing()

        for i, data in enumerate(loader, 1):
            self.data_read_done_time = time.time()
            # Get inputs
            if self.move_data_to_gpu:
                data = data.to(self.device)

            self.data_to_gpu_time = time.time()

            data['epoch'] = self.epoch
            data['settings'] = self.settings
            # Forward pass
            loss, stats = self.actor(data)

            # Backward pass and update weights
            if loader.training:
                self.optimizer.zero_grad()
                loss.backward()
                if self.settings.grad_clip_norm > 0:
                    torch.nn.utils.clip_grad_norm_(self.actor.net.parameters(), self.settings.grad_clip_norm)
                self.optimizer.step()

            # Update statistics
            batch_size = data['template_images'].shape[loader.stack_dim]
            self._update_stats(stats, batch_size, loader)

            # Print statistics
            self._print_stats(i, loader, batch_size)

            # Update wandb status
            if self.wandb_writer is not None and i % self.settings.print_interval == 0:
                if self.settings.local_rank in [-1, 0]:
                    self.wandb_writer.write_log(self.stats, self.epoch)

    def train_epoch(self):
        """
        Do one epoch for each loader.
        """

        for loader in self.loaders:
            if self.epoch % loader.epoch_interval == 0:
                # Set epoch
                if isinstance(loader.sampler, DistributedSampler):
                    loader.sampler.set_epoch(self.epoch)
                self.cycle_dataset(loader)

        self._stats_new_epoch()
        if self.settings.local_rank in [-1, 0]:
            self._write_tensorboard()

    def _init_timing(self):
        self.num_frames = 0
        self.start_time = time.time()
        self.prev_time = self.start_time
        self.avg_date_time = 0
        self.avg_gpu_trans_time = 0
        self.avg_forward_time = 0

    def _update_stats(self, new_stats: OrderedDict, batch_size, loader):
        # Initialize stats if not initialized yet
        if loader.name not in self.stats.keys() or self.stats[loader.name] is None:
            self.stats[loader.name] = OrderedDict({name: AverageMeter() for name in new_stats.keys()})

        # Add lr state
        if loader.training:
            lr_list = self.lr_scheduler.get_last_lr()
            for i, lr in enumerate(lr_list):
                var_name = 'LearningRate/group{}'.format(i)
                if var_name not in self.stats[loader.name].keys():
                    self.stats[loader.name][var_name] = StatValue()
                self.stats[loader.name][var_name].update(lr)

        for name, val in new_stats.items():
            if name not in self.stats[loader.name].keys():
                self.stats[loader.name][name] = AverageMeter()
            self.stats[loader.name][name].update(val, batch_size)

    def _print_stats(self, i, loader, batch_size):
        self.num_frames += batch_size
        current_time = time.time()
        average_fps = self.num_frames / (current_time - self.start_time)
        prev_frame_time_backup = self.prev_time
        self.prev_time = current_time

        self.avg_date_time += (self.data_read_done_time - prev_frame_time_backup)
        self.avg_gpu_trans_time += (self.data_to_gpu_time - self.data_read_done_time)
        self.avg_forward_time += current_time - self.data_to_gpu_time

        if self.settings.local_rank in [-1, 0] and i == loader.__len__():
            print_str = '[%d: %d]' % (self.epoch, loader.__len__())
            print_str += 'FPS: %.1f, ' % (average_fps)
            for name, val in self.stats[loader.name].items():
                if (self.settings.print_stats is None or name in self.settings.print_stats):
                    if hasattr(val, 'avg'):
                        print_str += '%s: %.3f, ' % (name, val.avg)

            print(print_str[:-2])
            log_str = print_str[:-2] + '\n'
            with open(self.settings.log_file, 'a') as f:
                f.write(log_str)

    def _stats_new_epoch(self):
        # Record learning rate
        for loader in self.loaders:
            if loader.training:
                try:
                    lr_list = self.lr_scheduler.get_last_lr()
                except:
                    lr_list = self.lr_scheduler._get_lr(self.epoch)
                for i, lr in enumerate(lr_list):
                    var_name = 'LearningRate/group{}'.format(i)
                    if var_name not in self.stats[loader.name].keys():
                        self.stats[loader.name][var_name] = StatValue()
                    self.stats[loader.name][var_name].update(lr)

        for loader_stats in self.stats.values():
            if loader_stats is None:
                continue
            for stat_value in loader_stats.values():
                if hasattr(stat_value, 'new_epoch'):
                    stat_value.new_epoch()

    def _write_tensorboard(self):
        if self.epoch == 1:
            self.tensorboard_writer.write_info(self.settings.script_name, self.settings.description)

        self.tensorboard_writer.write_epoch(self.stats, self.epoch)
