''' 
    Bootstrapped from https://github.com/NewKnowledge/imagenet and refined for D3M purposes
    Original implementation from Craig Corcoran
'''

import os
import math
import numpy as np
import tensorflow as tf
from tensorflow.keras.applications import inception_v3, mobilenet_v2, xception
from tensorflow.keras.models import Model
from tensorflow.keras.layers import Dense, GlobalAveragePooling2D, GlobalMaxPooling2D
from tensorflow.keras.utils import to_categorical, Sequence

import logging

logger = logging.getLogger(__name__)
#logger.setLevel(logging.INFO)

class ImagenetModel:

    ''' A class for featurizing images using pre-trained neural nets on ImageNet
        and finetuning those nets for downstream classification
    '''

    def __init__(self, 
        model='inception_v3', 
        weights = 'imagenet',
        include_top = False,
        pooling=None, 
        n_channels=None,  
        clf_head_dense_dim = 1024,
    ):
        ''' Creates ImageNet base model for featurization or classification and corresponding image
            preprocessing function
                :param model: options are xception, inception_v3, and mobilenet_v2
                :param weights: 'imagenet' or filepath
                :param include_top: whether to include original ImageNet classification head with 1000 classes
                :param pooling: 'avg', 'max', or None
                :param n_channels: number of channels to keep if performing featurization
                :param clf_head_dense_dim: dimension of dense layer before softmax classification (only applies
                    if `include_top` is false)
        '''

        self.include_top = include_top  # determines if used for classification or featurization
        self.n_channels = n_channels
        self.pooling = pooling
        self.clf_head_dense_dim = clf_head_dense_dim

        if model == 'xception':
            self.model = xception.Xception(weights=weights, include_top=include_top, pooling=pooling)
            self.preprocess = xception.preprocess_input
            self.target_size = (299, 299)
            if include_top:
                self.decode = xception.decode_predictions
            else:
                self.output_dim = (n_channels if n_channels else 2048) * (1 if pooling else 10**2)
        elif model == 'inception_v3':
            self.model = inception_v3.InceptionV3(weights=weights, include_top=include_top, pooling=pooling)
            self.preprocess = inception_v3.preprocess_input
            self.target_size = (299, 299)
            if include_top:
                self.decode = inception_v3.decode_predictions
            else:
                self.output_dim = (n_channels if n_channels else 2048) * (1 if pooling else 8**2)
        elif model == 'mobilenet_v2':
            self.model = mobilenetv2.MobileNetV2(weights=weights, include_top=include_top, pooling=pooling)
            self.preprocess = mobilenetv2.preprocess_input
            self.target_size = (244, 244)
            if include_top:
                self.decode = mobilenetv2.decode_predictions
            else:
                self.output_dim = (n_channels if n_channels else 1280) * (1 if pooling else 7**2)
        else:
            raise Exception('model option not implemented')
        
    def _load_finetune_model(
        self,
        nclasses = 2,
        weights_path = None,
    ):
        ''' Constructs finetuning model architecture and optionally loads weights
                :param nclasses: number of classes on which to softmax over
                :param weights_path: optional filepath from which to try to load weights
        '''
        
        out = self.model.output
        if self.pooling is None:
            out = GlobalAveragePooling2D()(out)# if self.pooling == 'avg' else GlobalMaxPooling2D()(out)
        dense = Dense(self.clf_head_dense_dim, activation='relu')(out)
        preds = Dense(nclasses, activation='softmax')(dense)
        finetune_model = Model(inputs = self.model.input, outputs = preds)

        # try to load weights
        if weights_path is not None:
            if os.path.isfile(weights_path):
                finetune_model.load_weights(weights_path)
        
        return finetune_model

    def get_features(self, images_array):
        ''' takes a batch of images as a 4-d array and returns the (flattened) imagenet features for those images as a 2-d array '''
        if self.include_top:
            raise Exception('getting features from a classification model with include_top=True is currently not supported')

        if images_array.ndim != 4:
            raise Exception('invalid input shape for images_array, expects a 4d array')

        # preprocess and compute image features
        logger.debug(f'preprocessing {images_array.shape[0]} images')
        images_array = self.preprocess(images_array)
        logger.debug(f'computing image features')
        image_features = self.model.predict(images_array)

        # if n_channels is specified, only keep that number of channels
        if self.n_channels:
            logger.debug(f'truncating to first {self.n_channels} channels')
            image_features = image_features.T[: self.n_channels].T

        # reshape output array by flattening each image into a vector of features
        shape = image_features.shape
        return image_features.reshape(shape[0], np.prod(shape[1:]))

    def predict(self, images_array):
        ''' alias for get_features to more closely match scikit-learn interface '''
        return self.get_features(images_array)

    def finetune(self, 
                train_dataset, 
                val_dataset = None, 
                nclasses = 2,
                top_layer_epochs = 1,
                unfreeze_proportions = [0.5],
                all_layer_epochs = 5, 
                class_weight = None,
                optimizer_top = 'rmsprop',
                optimizer_full = 'sgd',
                callbacks = None, 
                num_workers = 8,
                load_weights_path = None,
                save_weights_path = None,
        ):
        ''' Finetunes the Imagenet model iteratively on a smaller set of images with (potentially) a smaller set of classes.
            First finetunes last layer then freezes bottom N layers and retrains the rest
                :param train_dataset: (X, y) pair of tf.constant tensors for training 
                :param val_dataset: (X, y) pair of tf.constant tensors for validation, optional 
                :param nclasses: number of classes 
                :param top_layer_epochs: how many epochs for which to finetune classification head (happens first)
                :param unfreeze_proportions: list of proportions representing how much of the base ImageNet model one wants to
                    unfreeze (later layers unfrozen) for another round of finetuning
                :param all_layer_epochs: how many epochs for which to finetune entire model (happens second)
                :param class_weight: class weights (used for both training steps)
                :param optimizer_top: optimizer to use for training of classification head
                :param optimizer_full: optimizer to use for training full classification model
                    * suggest to use lower learning rate / more conservative optimizer for this step to 
                      prevent catastrophic forgetting 
                :param callbacks: optional list of callbacks to use for each round of finetuning
                :param num_workers: number of workers to use for multiprocess data loading
                :param load_weights_path: optional filepath from which to try to load weights
                :param save_weights_path: optional filepath to which to store weights
        '''
        
        finetune_model = self._load_finetune_model(
            nclasses = nclasses,
            weights_path=load_weights_path
        )

        fitting_histories = []

        # freeze all convolutional InceptionV3 layers, retrain top layer
        for layer in self.model.layers:
            layer.trainable = False
        finetune_model.compile(
            optimizer=optimizer_top, 
            loss='categorical_crossentropy')

        fitting_histories.append(
            finetune_model.fit(
                train_dataset, 
                validation_data = val_dataset,
                epochs = top_layer_epochs,
                class_weight = class_weight, 
                shuffle = True, 
                use_multiprocessing = True, 
                workers = num_workers, 
                callbacks = callbacks
            )
        )

        # iteratively unfreeze specified proportion of later ImageNet base layers and finetune
        finetune_model.compile(
            # SGD(lr=0.0001, momentum=0.9)
            optimizer=optimizer_full, 
            loss='categorical_crossentropy')
        for p in unfreeze_proportions:
            freeze_count = int(len(self.model.layers) * p)
            for layer in finetune_model.layers[:freeze_count]:
                layer.trainable = False
            for layer in finetune_model.layers[freeze_count:]:
                layer.trainable = True

            fitting_histories.append(
                finetune_model.fit(
                    train_dataset, 
                    validation_data = val_dataset,
                    epochs = all_layer_epochs,
                    class_weight = class_weight, 
                    shuffle = True, 
                    use_multiprocessing = True, 
                    workers = num_workers, 
                    callbacks = callbacks
                )
            )
        
        # save weights
        if save_weights_path is not None:
            finetune_model.save_weights(save_weights_path)
        
        return fitting_histories

    def finetune_classify(self, 
        test_dataset, 
        nclasses = 2,
        num_workers = 8,
        load_weights_path = None,
    ):

        ''' Uses the finetuned model to predict on a test dataset. 
                :param test_dataset: X, tf.constant tensor for inference
                :param nclasses: number of classes 
                :param num_workers: number of workers to use for multiprocess data loading
                :return: array of softmaxed prediction probabilities
                :param load_weights_path: optional filepath from which to try to load weights
        '''    

        finetune_model = self._load_finetune_model(
            nclasses = nclasses,
            weights_path = load_weights_path
        )

        return finetune_model.predict_generator(test_dataset, 
            use_multiprocessing = True, 
            workers = num_workers
        )

class ImageNetGen(Sequence):
    """ Tf.Keras Sequence for ImageNet input data """

    def __init__(self, X, y = None, batch_size = 32):
        self.X = X
        self.y = y
        self.batch_size = batch_size

    def __len__(self):
        return math.ceil(self.X.shape[0] / self.batch_size)

    def __getitem__(self, idx):
        batch_x = self.X[idx * self.batch_size:(idx + 1) * self.batch_size]
        if self.y is None:
            return tf.constant(batch_x)
        else:
            batch_y = self.y[idx * self.batch_size:(idx + 1) * self.batch_size]
            return tf.constant(batch_x), tf.constant(batch_y)
            
tensorflow.constant tensorflow.keras.layers.GlobalAveragePooling2D tensorflow.keras.applications.xception.Xception tensorflow.keras.models.Model tensorflow.keras.layers.Dense numpy.prod tensorflow.keras.applications.inception_v3.InceptionV3
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