'''
Code here is mostly based on the code from the torchsample and Keras packages

CREDIT TO THE TORCHSAMPLE AND KERAS TEAMS
'''
import numpy as np
import os
import time
import shutil
import datetime
import warnings
import torch

from torch import nn
from tqdm import tqdm
from copy import deepcopy
from .wdtypes import *


def _get_current_time():
    return datetime.datetime.now().strftime("%B %d, %Y - %I:%M%p")


class CallbackContainer(object):
    """
    Container holding a list of callbacks.
    """
    def __init__(self, callbacks:Optional[List]=None, queue_length:int=10):
        instantiated_callbacks = []
        if callbacks is not None:
            for callback in callbacks:
                if isinstance(callback, type): instantiated_callbacks.append(callback())
                else: instantiated_callbacks.append(callback)
        self.callbacks = [c for c in instantiated_callbacks]
        self.queue_length = queue_length

    def set_params(self, params):
        for callback in self.callbacks:
            callback.set_params(params)

    def set_model(self, model:nn.Module):
        self.model = model
        for callback in self.callbacks:
            callback.set_model(model)

    def on_epoch_begin(self, epoch:int, logs:Optional[Dict]=None):
        logs = logs or {}
        for callback in self.callbacks:
            callback.on_epoch_begin(epoch, logs)

    def on_epoch_end(self, epoch:int, logs:Optional[Dict]=None):
        logs = logs or {}
        for callback in self.callbacks:
            callback.on_epoch_end(epoch, logs)

    def on_batch_begin(self, batch:int, logs:Optional[Dict]=None):
        logs = logs or {}
        for callback in self.callbacks:
            callback.on_batch_begin(batch, logs)

    def on_batch_end(self, batch:int, logs:Optional[Dict]=None):
        logs = logs or {}
        for callback in self.callbacks:
            callback.on_batch_end(batch, logs)

    def on_train_begin(self, logs:Optional[Dict]=None):
        logs = logs or {}
        logs['start_time'] = _get_current_time()
        for callback in self.callbacks:
            callback.on_train_begin(logs)

    def on_train_end(self, logs:Optional[Dict]=None):
        logs = logs or {}
        # logs['final_loss'] = self.model.history.epoch_losses[-1],
        # logs['best_loss'] = min(self.model.history.epoch_losses),
        # logs['stop_time'] = _get_current_time()
        for callback in self.callbacks:
            callback.on_train_end(logs)


class Callback(object):
    """
    Abstract base class used to build new callbacks.
    """

    def __init__(self):
        pass

    def set_params(self, params):
        self.params = params

    def set_model(self, model:nn.Module):
        self.model = model

    def on_epoch_begin(self, epoch:int, logs:Optional[Dict]=None):
        pass

    def on_epoch_end(self, epoch:int, logs:Optional[Dict]=None):
        pass

    def on_batch_begin(self, batch:int, logs:Optional[Dict]=None):
        pass

    def on_batch_end(self, batch:int, logs:Optional[Dict]=None):
        pass

    def on_train_begin(self, logs:Optional[Dict]=None):
        pass

    def on_train_end(self, logs:Optional[Dict]=None):
        pass


class History(Callback):
    """
    Callback that records events into a `History` object.
    """

    def on_train_begin(self, logs:Optional[Dict]=None):
        self.epoch = []
        self._history = {}

    def on_epoch_begin(self, epoch:int, logs:Optional[Dict]=None):
        # avoid mutation during epoch run
        logs = deepcopy(logs) or {}
        for k, v in logs.items():
            self._history.setdefault(k, []).append(v)

    def on_epoch_end(self, epoch:int, logs:Optional[Dict]=None):
        logs = logs or {}
        self.epoch.append(epoch)
        for k, v in logs.items():
            self._history.setdefault(k, []).append(v)


class LRHistory(Callback):
    r"""
    Save the learning rates during training. Given the fact that non-cyclic
    learning rates and cyclic learning rates are called at different stages
    during training, the saving procedure is a bit convoluted.
    """
    def __init__(self, n_epochs):
        super(LRHistory, self).__init__()
        self.n_epochs = n_epochs

    def on_epoch_begin(self, epoch:int, logs:Optional[Dict]=None):
        if epoch==0 and self.model.lr_scheduler:
            # If is the first epoch and we use a scheduler, define the
            # lr_history Dict and save
            self.model.lr_history = {}
            if self.model.lr_scheduler.__class__.__name__ == 'MultipleLRScheduler':
                # if we use multiple schedulers, we save the learning rate for
                # each param_group of the optimizer.
                for model_name, opt in self.model.optimizer._optimizers.items():
                    if model_name in self.model.lr_scheduler._schedulers:
                        for group_idx, group in enumerate(opt.param_groups):
                            self.model.lr_history.setdefault(
                                ("_").join(['lr', model_name, str(group_idx)]),[]
                                ).append(group['lr'])
            elif not self.model.cyclic:
                # if we use one lr_scheduler and is not cyclic, save the
                # learning rate for each param_group of the optimizer.
                for group_idx, group in enumerate(self.model.optimizer.param_groups):
                    self.model.lr_history.setdefault(
                        ("_").join(['lr', str(group_idx)]),[]).append(group['lr'])

    def on_batch_end(self, batch:int, logs:Optional[Dict]=None):
        if self.model.lr_scheduler:
            if self.model.lr_scheduler.__class__.__name__ == 'MultipleLRScheduler':
                # if we use multiple schedulers, we save the learning rate for
                # each param_group of the optimizer IF IS CYCLIC
                for model_name, opt in self.model.optimizer._optimizers.items():
                    if model_name in self.model.lr_scheduler._schedulers:
                        if 'cycl' in self.model.lr_scheduler._schedulers[model_name].__class__.__name__.lower():
                            for group_idx, group in enumerate(opt.param_groups):
                                self.model.lr_history.setdefault(
                                    ("_").join(['lr', model_name, str(group_idx)]),[]
                                    ).append(group['lr'])
            elif self.model.cyclic:
                # if we use one lr_scheduler and IS CYCLIC, save the
                # learning rate for each param_group of the optimizer.
                for group_idx, group in enumerate(self.model.optimizer.param_groups):
                    self.model.lr_history.setdefault(
                        ("_").join(['lr', str(group_idx)]),[]).append(group['lr'])

    def on_epoch_end(self, epoch:int, logs:Optional[Dict]=None):
        if epoch != (self.n_epochs-1) and self.model.lr_scheduler:
            if self.model.lr_scheduler.__class__.__name__ == 'MultipleLRScheduler':
                # if we use multiple schedulers, we save the learning rate for
                # each param_group of the optimizer IF IS NOT CYCLIC
                for model_name, opt in self.model.optimizer._optimizers.items():
                    if model_name in self.model.lr_scheduler._schedulers:
                        if 'cycl' not in self.model.lr_scheduler._schedulers[model_name].__class__.__name__.lower():
                            for group_idx, group in enumerate(opt.param_groups):
                                self.model.lr_history.setdefault(
                                    ("_").join(['lr', model_name, str(group_idx)]),
                                    []).append(group['lr'])
            elif not self.model.cyclic:
                # if we use one lr_scheduler and IS NOT CYCLIC, save the
                # learning rate for each param_group of the optimizer.
                for group_idx, group in enumerate(self.model.optimizer.param_groups):
                    self.model.lr_history.setdefault(
                        ("_").join(['lr', str(group_idx)]),[]).append(group['lr'])


class ModelCheckpoint(Callback):
    r"""
    Save the model after every epoch. This class is almost identical to the
    corresponding keras class. Therefore, credit to the Keras Team.

    Parameters
    ----------
    filepath: Str,
        Full path to save the output weights. It must contain only the root of
        the filenames. Epoch number and '.pt' extension (for pytorch) will be
        added.
        e.g. filepath="path/to/output_weights/weights_out"
        And the saved files in that directory will be named
        weights_out_1.pt
        weights_out_2.pt
        ...
    monitor: Str, default='val_loss'
        quantity to monitor
    verbose:Int, default=0,
    save_best_only: Boolean, default=False,
        the latest best model according to the quantity monitored will not be
        overwritten.
    mode: Str, default='auto',
        If 'save_best_only=True', the decision to overwrite the current save
        file is made based on either the maximization or the minimization of
        the monitored quantity. For 'val_acc', this should be 'max', for
        'val_loss' this should be 'min', etc. In 'auto' mode, the direction is
        automatically inferred from the name of the monitored quantity.
    period: Int, default=1,
        Interval (number of epochs) between checkpoints.
    max_save:Int, default=-1
        Max number of outputs to save. If -1 will save all outputs
    """
    def __init__(self, filepath:str, monitor:str='val_loss', verbose:int=0,
                 save_best_only:bool=False, mode:str='auto', period:int=1,
                 max_save:int=-1):
        super(ModelCheckpoint, self).__init__()
        self.monitor = monitor
        self.verbose = verbose
        self.filepath = filepath
        self.save_best_only = save_best_only
        self.period = period
        self.epochs_since_last_save = 0
        self.max_save = max_save

        root_dir = ('/').join(filepath.split("/")[:-1])
        if not os.path.exists(root_dir):
            os.makedirs(root_dir)

        if self.max_save > 0:
            self.old_files = []

        if mode not in ['auto', 'min', 'max']:
            warnings.warn('ModelCheckpoint mode %s is unknown, '
                          'fallback to auto mode.' % (mode),
                          RuntimeWarning)
            mode = 'auto'
        if mode == 'min':
            self.monitor_op = np.less
            self.best = np.Inf
        elif mode == 'max':
            self.monitor_op = np.greater
            self.best = -np.Inf
        else:
            if 'acc' in self.monitor or self.monitor.startswith('fmeasure'):
                self.monitor_op = np.greater
                self.best = -np.Inf
            else:
                self.monitor_op = np.less
                self.best = np.Inf

    def on_epoch_end(self, epoch:int, logs:Optional[Dict]=None):
        logs = logs or {}
        self.epochs_since_last_save += 1
        if self.epochs_since_last_save >= self.period:
            self.epochs_since_last_save = 0
            filepath = '{}_{}.p'.format(self.filepath, epoch+1)
            if self.save_best_only:
                current = logs.get(self.monitor)
                if current is None:
                    warnings.warn('Can save best model only with %s available, '
                                  'skipping.' % (self.monitor), RuntimeWarning)
                else:
                    if self.monitor_op(current, self.best):
                        if self.verbose > 0:
                            print('\nEpoch %05d: %s improved from %0.5f to %0.5f,'
                                  ' saving model to %s'
                                  % (epoch + 1, self.monitor, self.best,
                                     current, filepath))
                        self.best = current
                        torch.save(self.model.state_dict(), filepath)
                        if self.max_save > 0:
                            if len(self.old_files) == self.max_save:
                                try:
                                    os.remove(self.old_files[0])
                                except:
                                    pass
                                self.old_files = self.old_files[1:]
                            self.old_files.append(filepath)
                    else:
                        if self.verbose > 0:
                            print('\nEpoch %05d: %s did not improve from %0.5f' %
                                  (epoch + 1, self.monitor, self.best))
            else:
                if self.verbose > 0:
                    print('\nEpoch %05d: saving model to %s' % (epoch + 1, filepath))
                torch.save(self.model.state_dict(), filepath)
                if self.max_save > 0:
                    if len(self.old_files) == self.max_save:
                        try:
                            os.remove(self.old_files[0])
                        except:
                            pass
                        self.old_files = self.old_files[1:]
                    self.old_files.append(filepath)


class EarlyStopping(Callback):
    r"""
    Stop training when a monitored quantity has stopped improving. This class
    is almost identical to the corresponding keras class. Therefore, credit to
    the Keras Team.

    # Arguments
        monitor: Str, default='val_loss'.
            Quantity to be monitored.
        min_delta: Float, default=0.
            minimum change in the monitored quantity to qualify as an
            improvement, i.e. an absolute change of less than min_delta, will
            count as no improvement.
        patience: Int, default=10.
            Number of epochs that produced the monitored quantity with no
            improvement after which training will be stopped.
        verbose: Int.
            verbosity mode.
        mode: Str, default='auto'
            one of {auto, min, max}. In `min` mode, training will stop when
            the quantity monitored has stopped decreasing; in `max` mode it
            will stop when the quantity monitored has stopped increasing; in
            `auto` mode, the direction is automatically inferred from the name
            of the monitored quantity.
        baseline: Float, Optional. default=None.
            Baseline value for the monitored quantity to reach. Training will
            stop if the model doesn't show improvement over the baseline.
        restore_best_weights: Boolean, default=None
            Whether to restore model weights from the epoch with the best
            value of the monitored quantity. If False, the model weights
            obtained at the last step of training are used.
    """
    def __init__(self, monitor:str='val_loss', min_delta:float=0., patience:int=10,
        verbose:int=0,mode:str='auto', baseline:Optional[float]=None,
        restore_best_weights:bool=False):

        super(EarlyStopping,self).__init__()

        self.monitor = monitor
        self.baseline = baseline
        self.patience = patience
        self.verbose = verbose
        self.min_delta = min_delta
        self.wait = 0
        self.stopped_epoch = 0
        self.restore_best_weights = restore_best_weights
        self.state_dict = None

        if mode not in ['auto', 'min', 'max']:
            warnings.warn('EarlyStopping mode %s is unknown, '
                          'fallback to auto mode.' % mode,
                          RuntimeWarning)
            mode = 'auto'

        if mode == 'min':
            self.monitor_op = np.less
        elif mode == 'max':
            self.monitor_op = np.greater
        else:
            if 'acc' in self.monitor:
                self.monitor_op = np.greater
            else:
                self.monitor_op = np.less

        if self.monitor_op == np.greater:
            self.min_delta *= 1
        else:
            self.min_delta *= -1

    def on_train_begin(self, logs:Optional[Dict]=None):
        # Allow instances to be re-used
        self.wait = 0
        self.stopped_epoch = 0
        if self.baseline is not None:
            self.best = self.baseline
        else:
            self.best = np.Inf if self.monitor_op == np.less else -np.Inf

    def on_epoch_end(self, epoch:int, logs:Optional[Dict]=None):
        current = self.get_monitor_value(logs)
        if current is None:
            return

        if self.monitor_op(current - self.min_delta, self.best):
            self.best = current
            self.wait = 0
            if self.restore_best_weights:
                self.state_dict = self.model.state_dict()
        else:
            self.wait += 1
            if self.wait >= self.patience:
                self.stopped_epoch = epoch
                self.model.early_stop = True
                if self.restore_best_weights:
                    if self.verbose > 0:
                        print('Restoring model weights from the end of '
                              'the best epoch')
                    self.model.load_state_dict(self.state_dict)

    def on_train_end(self, logs:Optional[Dict]=None):
        if self.stopped_epoch > 0 and self.verbose > 0:
            print('Epoch %05d: early stopping' % (self.stopped_epoch + 1))

    def get_monitor_value(self, logs):
        monitor_value = logs.get(self.monitor)
        if monitor_value is None:
            warnings.warn('Early stopping conditioned on metric `%s` '
                'which is not available. Available metrics are: %s' %
                (self.monitor, ','.join(list(logs.keys()))), RuntimeWarning
            )
        return monitor_value