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"""
Text Classification with TorchText
==================================

This tutorial shows how to use the text classification datasets
in ``torchtext``, including

::

   - AG_NEWS,
   - SogouNews,
   - DBpedia,
   - YelpReviewPolarity,
   - YelpReviewFull,
   - YahooAnswers,
   - AmazonReviewPolarity,
   - AmazonReviewFull

This example shows how to train a supervised learning algorithm for
classification using one of these ``TextClassification`` datasets.

Load data with ngrams
---------------------

A bag of ngrams feature is applied to capture some partial information
about the local word order. In practice, bi-gram or tri-gram are applied
to provide more benefits as word groups than only one word. An example:

::

   "load data with ngrams"
   Bi-grams results: "load data", "data with", "with ngrams"
   Tri-grams results: "load data with", "data with ngrams"

``TextClassification`` Dataset supports the ngrams method. By setting
ngrams to 2, the example text in the dataset will be a list of single
words plus bi-grams string.

"""

import torch
import torchtext
from torchtext.datasets import text_classification
NGRAMS = 2
import os
if not os.path.isdir('./.data'):
	os.mkdir('./.data')
train_dataset, test_dataset = text_classification.DATASETS['AG_NEWS'](
    root='./.data', ngrams=NGRAMS, vocab=None)
BATCH_SIZE = 16
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")


######################################################################
# Define the model
# ----------------
#
# The model is composed of the
# `EmbeddingBag <https://pytorch.org/docs/stable/nn.html?highlight=embeddingbag#torch.nn.EmbeddingBag>`__
# layer and the linear layer (see the figure below). ``nn.EmbeddingBag``
# computes the mean value of a “bag” of embeddings. The text entries here
# have different lengths. ``nn.EmbeddingBag`` requires no padding here
# since the text lengths are saved in offsets.
#
# Additionally, since ``nn.EmbeddingBag`` accumulates the average across
# the embeddings on the fly, ``nn.EmbeddingBag`` can enhance the
# performance and memory efficiency to process a sequence of tensors.
#
# .. image:: ../_static/img/text_sentiment_ngrams_model.png
#

import torch.nn as nn
import torch.nn.functional as F
class TextSentiment(nn.Module):
    def __init__(self, vocab_size, embed_dim, num_class):
        super().__init__()
        self.embedding = nn.EmbeddingBag(vocab_size, embed_dim, sparse=True)
        self.fc = nn.Linear(embed_dim, num_class)
        self.init_weights()

    def init_weights(self):
        initrange = 0.5
        self.embedding.weight.data.uniform_(-initrange, initrange)
        self.fc.weight.data.uniform_(-initrange, initrange)
        self.fc.bias.data.zero_()

    def forward(self, text, offsets):
        embedded = self.embedding(text, offsets)
        return self.fc(embedded)


######################################################################
# Initiate an instance
# --------------------
#
# The AG_NEWS dataset has four labels and therefore the number of classes
# is four.
#
# ::
#
#    1 : World
#    2 : Sports
#    3 : Business
#    4 : Sci/Tec
#
# The vocab size is equal to the length of vocab (including single word
# and ngrams). The number of classes is equal to the number of labels,
# which is four in AG_NEWS case.
#

VOCAB_SIZE = len(train_dataset.get_vocab())
EMBED_DIM = 32
NUN_CLASS = len(train_dataset.get_labels())
model = TextSentiment(VOCAB_SIZE, EMBED_DIM, NUN_CLASS).to(device)


######################################################################
# Functions used to generate batch
# --------------------------------
#


######################################################################
# Since the text entries have different lengths, a custom function
# generate_batch() is used to generate data batches and offsets. The
# function is passed to ``collate_fn`` in ``torch.utils.data.DataLoader``.
# The input to ``collate_fn`` is a list of tensors with the size of
# batch_size, and the ``collate_fn`` function packs them into a
# mini-batch. Pay attention here and make sure that ``collate_fn`` is
# declared as a top level def. This ensures that the function is available
# in each worker.
#
# The text entries in the original data batch input are packed into a list
# and concatenated as a single tensor as the input of ``nn.EmbeddingBag``.
# The offsets is a tensor of delimiters to represent the beginning index
# of the individual sequence in the text tensor. Label is a tensor saving
# the labels of individual text entries.
#

def generate_batch(batch):
    label = torch.tensor([entry[0] for entry in batch])
    text = [entry[1] for entry in batch]
    offsets = [0] + [len(entry) for entry in text]
    # torch.Tensor.cumsum returns the cumulative sum
    # of elements in the dimension dim.
    # torch.Tensor([1.0, 2.0, 3.0]).cumsum(dim=0)

    offsets = torch.tensor(offsets[:-1]).cumsum(dim=0)
    text = torch.cat(text)
    return text, offsets, label


######################################################################
# Define functions to train the model and evaluate results.
# ---------------------------------------------------------
#


######################################################################
# `torch.utils.data.DataLoader <https://pytorch.org/docs/stable/data.html?highlight=dataloader#torch.utils.data.DataLoader>`__
# is recommended for PyTorch users, and it makes data loading in parallel
# easily (a tutorial is
# `here <https://pytorch.org/tutorials/beginner/data_loading_tutorial.html>`__).
# We use ``DataLoader`` here to load AG_NEWS datasets and send it to the
# model for training/validation.
#

from torch.utils.data import DataLoader

def train_func(sub_train_):

    # Train the model
    train_loss = 0
    train_acc = 0
    data = DataLoader(sub_train_, batch_size=BATCH_SIZE, shuffle=True,
                      collate_fn=generate_batch)
    for i, (text, offsets, cls) in enumerate(data):
        optimizer.zero_grad()
        text, offsets, cls = text.to(device), offsets.to(device), cls.to(device)
        output = model(text, offsets)
        loss = criterion(output, cls)
        train_loss += loss.item()
        loss.backward()
        optimizer.step()
        train_acc += (output.argmax(1) == cls).sum().item()

    # Adjust the learning rate
    scheduler.step()

    return train_loss / len(sub_train_), train_acc / len(sub_train_)

def test(data_):
    loss = 0
    acc = 0
    data = DataLoader(data_, batch_size=BATCH_SIZE, collate_fn=generate_batch)
    for text, offsets, cls in data:
        text, offsets, cls = text.to(device), offsets.to(device), cls.to(device)
        with torch.no_grad():
            output = model(text, offsets)
            loss = criterion(output, cls)
            loss += loss.item()
            acc += (output.argmax(1) == cls).sum().item()

    return loss / len(data_), acc / len(data_)


######################################################################
# Split the dataset and run the model
# -----------------------------------
#
# Since the original AG_NEWS has no valid dataset, we split the training
# dataset into train/valid sets with a split ratio of 0.95 (train) and
# 0.05 (valid). Here we use
# `torch.utils.data.dataset.random_split <https://pytorch.org/docs/stable/data.html?highlight=random_split#torch.utils.data.random_split>`__
# function in PyTorch core library.
#
# `CrossEntropyLoss <https://pytorch.org/docs/stable/nn.html?highlight=crossentropyloss#torch.nn.CrossEntropyLoss>`__
# criterion combines nn.LogSoftmax() and nn.NLLLoss() in a single class.
# It is useful when training a classification problem with C classes.
# `SGD <https://pytorch.org/docs/stable/_modules/torch/optim/sgd.html>`__
# implements stochastic gradient descent method as optimizer. The initial
# learning rate is set to 4.0.
# `StepLR <https://pytorch.org/docs/master/_modules/torch/optim/lr_scheduler.html#StepLR>`__
# is used here to adjust the learning rate through epochs.
#

import time
from torch.utils.data.dataset import random_split
N_EPOCHS = 5
min_valid_loss = float('inf')

criterion = torch.nn.CrossEntropyLoss().to(device)
optimizer = torch.optim.SGD(model.parameters(), lr=4.0)
scheduler = torch.optim.lr_scheduler.StepLR(optimizer, 1, gamma=0.9)

train_len = int(len(train_dataset) * 0.95)
sub_train_, sub_valid_ = \
    random_split(train_dataset, [train_len, len(train_dataset) - train_len])

for epoch in range(N_EPOCHS):

    start_time = time.time()
    train_loss, train_acc = train_func(sub_train_)
    valid_loss, valid_acc = test(sub_valid_)

    secs = int(time.time() - start_time)
    mins = secs / 60
    secs = secs % 60

    print('Epoch: %d' %(epoch + 1), " | time in %d minutes, %d seconds" %(mins, secs))
    print(f'\tLoss: {train_loss:.4f}(train)\t|\tAcc: {train_acc * 100:.1f}%(train)')
    print(f'\tLoss: {valid_loss:.4f}(valid)\t|\tAcc: {valid_acc * 100:.1f}%(valid)')


######################################################################
# Running the model on GPU with the following information:
#
# Epoch: 1 \| time in 0 minutes, 11 seconds
#
# ::
#
#        Loss: 0.0263(train)     |       Acc: 84.5%(train)
#        Loss: 0.0001(valid)     |       Acc: 89.0%(valid)
#
#
# Epoch: 2 \| time in 0 minutes, 10 seconds
#
# ::
#
#        Loss: 0.0119(train)     |       Acc: 93.6%(train)
#        Loss: 0.0000(valid)     |       Acc: 89.6%(valid)
#
#
# Epoch: 3 \| time in 0 minutes, 9 seconds
#
# ::
#
#        Loss: 0.0069(train)     |       Acc: 96.4%(train)
#        Loss: 0.0000(valid)     |       Acc: 90.5%(valid)
#
#
# Epoch: 4 \| time in 0 minutes, 11 seconds
#
# ::
#
#        Loss: 0.0038(train)     |       Acc: 98.2%(train)
#        Loss: 0.0000(valid)     |       Acc: 90.4%(valid)
#
#
# Epoch: 5 \| time in 0 minutes, 11 seconds
#
# ::
#
#        Loss: 0.0022(train)     |       Acc: 99.0%(train)
#        Loss: 0.0000(valid)     |       Acc: 91.0%(valid)
#


######################################################################
# Evaluate the model with test dataset
# ------------------------------------
#

print('Checking the results of test dataset...')
test_loss, test_acc = test(test_dataset)
print(f'\tLoss: {test_loss:.4f}(test)\t|\tAcc: {test_acc * 100:.1f}%(test)')


######################################################################
# Checking the results of test dataset…
#
# ::
#
#        Loss: 0.0237(test)      |       Acc: 90.5%(test)
#


######################################################################
# Test on a random news
# ---------------------
#
# Use the best model so far and test a golf news. The label information is
# available
# `here <https://pytorch.org/text/datasets.html?highlight=ag_news#torchtext.datasets.AG_NEWS>`__.
#

import re
from torchtext.data.utils import ngrams_iterator
from torchtext.data.utils import get_tokenizer

ag_news_label = {1 : "World",
                 2 : "Sports",
                 3 : "Business",
                 4 : "Sci/Tec"}

def predict(text, model, vocab, ngrams):
    tokenizer = get_tokenizer("basic_english")
    with torch.no_grad():
        text = torch.tensor([vocab[token]
                            for token in ngrams_iterator(tokenizer(text), ngrams)])
        output = model(text, torch.tensor([0]))
        return output.argmax(1).item() + 1

ex_text_str = "MEMPHIS, Tenn. – Four days ago, Jon Rahm was \
    enduring the season’s worst weather conditions on Sunday at The \
    Open on his way to a closing 75 at Royal Portrush, which \
    considering the wind and the rain was a respectable showing. \
    Thursday’s first round at the WGC-FedEx St. Jude Invitational \
    was another story. With temperatures in the mid-80s and hardly any \
    wind, the Spaniard was 13 strokes better in a flawless round. \
    Thanks to his best putting performance on the PGA Tour, Rahm \
    finished with an 8-under 62 for a three-stroke lead, which \
    was even more impressive considering he’d never played the \
    front nine at TPC Southwind."

vocab = train_dataset.get_vocab()
model = model.to("cpu")

print("This is a %s news" %ag_news_label[predict(ex_text_str, model, vocab, 2)])

######################################################################
# This is a Sports news
#


######################################################################
# You can find the code examples displayed in this note
# `here <https://github.com/pytorch/text/tree/master/examples/text_classification>`__.
#