import torch
import torch.nn as nn
import torch.optim as optim
import pandas as pd
from TorchCRF import CRF
from sklearn.model_selection import train_test_split
from torch.nn.utils.rnn import pad_sequence
from torch.utils.data import Dataset, DataLoader
from torch.cuda.amp import autocast, GradScaler

# Set device
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
print(f"Using device: {device}")


# Define the BiLSTM-CRF model with Layer Normalization
class BiLSTMCRFModel(nn.Module):
    def __init__(self, vocab_size, embedding_dim, hidden_dim, num_labels):
        super(BiLSTMCRFModel, self).__init__()
        self.embedding = nn.Embedding(vocab_size, embedding_dim)
        self.lstm = nn.LSTM(embedding_dim, hidden_dim, bidirectional=True, batch_first=True)
        self.layer_norm = nn.LayerNorm(hidden_dim * 2)  # Layer Normalization
        self.fc = nn.Linear(hidden_dim * 2, num_labels)
        self.crf = CRF(num_labels)

    def forward(self, words, attention_mask, labels=None):
        embedded = self.embedding(words)
        lstm_out, _ = self.lstm(embedded)
        lstm_out = self.layer_norm(lstm_out)  # Stabilize outputs
        emissions = self.fc(lstm_out)

        if labels is not None:
            loss = -self.crf(emissions, labels, mask=attention_mask.bool())
            return loss
        else:
            return self.crf.viterbi_decode(emissions, mask=attention_mask.bool())


# Dataset class
class NERDataset(Dataset):
    def __init__(self, words, tags):
        self.words = words
        self.tags = tags

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

    def __getitem__(self, idx):
        return torch.tensor(self.words[idx]), torch.tensor(self.tags[idx])


# Proper collate function for DataLoader
def collate_fn(batch):
    words, tags = zip(*batch)  # Unpack batch into separate lists
    words_padded = pad_sequence(words, batch_first=True, padding_value=0)
    tags_padded = pad_sequence(tags, batch_first=True, padding_value=0)
    return words_padded, tags_padded


# Load and preprocess data
def prepare_data(df):
    df['Tag'] = df['Tag'].fillna('O').astype(str).apply(lambda x: x.strip().upper())

    word_to_id = {word: idx for idx, word in enumerate(set(df['Word']))}
    word_to_id['<UNK>'] = len(word_to_id)

    tag_to_id = {tag: idx for idx, tag in enumerate(set(df['Tag']))}
    id_to_tag = {idx: tag for tag, idx in tag_to_id.items()}

    words, tags = [], []
    for _, group in df.groupby('Sentence'):
        words.append([word_to_id.get(w, word_to_id['<UNK>']) for w in group['Word']])
        tags.append([tag_to_id[t] for t in group['Tag']])

    return words, tags, word_to_id, tag_to_id, id_to_tag


# Load dataset
df = pd.read_excel('Augmented_Dataset.xlsx', engine='openpyxl')

# Shuffle the dataset before splitting
df = df.sample(frac=1, random_state=42).reset_index(drop=True)  # Shuffling the dataset

words, tags, word_to_id, tag_to_id, id_to_tag = prepare_data(df)

# Split into train and test
train_words, test_words, train_tags, test_tags = train_test_split(words, tags, test_size=0.2, random_state=42,
                                                                  shuffle=True)

# Create PyTorch DataLoaders
train_dataset = NERDataset(train_words, train_tags)
test_dataset = NERDataset(test_words, test_tags)

train_loader = DataLoader(train_dataset, batch_size=256, shuffle=True, collate_fn=collate_fn)
test_loader = DataLoader(test_dataset, batch_size=256, shuffle=False, collate_fn=collate_fn)

# Model initialization
vocab_size = len(word_to_id)
embedding_dim = 100
hidden_dim = 128
num_labels = len(tag_to_id)

model = BiLSTMCRFModel(vocab_size, embedding_dim, hidden_dim, num_labels).to(device)
optimizer = optim.AdamW(model.parameters(), lr=0.001, weight_decay=1e-5)
scheduler = optim.lr_scheduler.ReduceLROnPlateau(optimizer, mode='min', factor=0.5, patience=2)
scaler = GradScaler()  # Mixed precision training

# Training loop with optimizations
num_epochs = 10
accumulation_steps = 4
best_loss = float('inf')

print("Starting Training...")
for epoch in range(num_epochs):
    model.train()
    total_loss = 0
    optimizer.zero_grad()

    for i, (batch_words, batch_tags) in enumerate(train_loader):
        batch_words, batch_tags = batch_words.to(device), batch_tags.to(device)
        attention_mask = (batch_words != 0).to(device)

        with autocast():  # Mixed precision training
            loss = model(batch_words, attention_mask, batch_tags)
            loss = loss.mean() / accumulation_steps  # Scale loss

        scaler.scale(loss).backward()  # Scale gradients

        if (i + 1) % accumulation_steps == 0:
            scaler.step(optimizer)
            scaler.update()
            optimizer.zero_grad()

        total_loss += loss.item()

    avg_loss = total_loss / len(train_loader)
    scheduler.step(avg_loss)

    print(f"Epoch {epoch + 1}, Loss: {avg_loss:.4f}, LR: {optimizer.param_groups[0]['lr']}")

    if avg_loss < best_loss:
        best_loss = avg_loss
        torch.save(model.state_dict(), "best_model.pth")
        print(f"New best model saved with loss: {best_loss:.4f}")

    torch.cuda.empty_cache()  # Free GPU memory

print("Training Complete!")

# Evaluate model
def evaluate_model(model, test_loader, id_to_tag):
    model.eval()
    true_labels, pred_labels = [], []

    with torch.no_grad():
        for batch_words, batch_tags in test_loader:
            batch_words, batch_tags = batch_words.to(device), batch_tags.to(device)
            attention_mask = (batch_words != 0).to(device)  # Masking out padding tokens

            pred_tags = model(batch_words, attention_mask)

            for i in range(batch_words.shape[0]):  # Iterate over batch
                true_seq = batch_tags[i].tolist()
                pred_seq = pred_tags[i]

                # Remove padding (ignore 0-padded labels)
                true_seq_filtered = [id_to_tag[t] for t in true_seq if t in id_to_tag]
                pred_seq_filtered = [id_to_tag[p] for p in pred_seq if p in id_to_tag]

                # Ensure equal lengths (trim longer list)
                min_len = min(len(true_seq_filtered), len(pred_seq_filtered))
                true_labels.extend(true_seq_filtered[:min_len])
                pred_labels.extend(pred_seq_filtered[:min_len])

    # Check if lengths are now consistent
    assert len(true_labels) == len(pred_labels), "Mismatch in true and predicted label counts!"

    from sklearn.metrics import classification_report, confusion_matrix
    import seaborn as sns
    import matplotlib.pyplot as plt

    print("Classification Report:")
    print(classification_report(true_labels, pred_labels))

    cm = confusion_matrix(true_labels, pred_labels, labels=list(id_to_tag.values()))
    plt.figure(figsize=(10, 8))
    sns.heatmap(cm, annot=True, fmt='d', cmap='Blues', xticklabels=list(id_to_tag.values()), yticklabels=list(id_to_tag.values()))
    plt.xlabel('Predicted')
    plt.ylabel('True')
    plt.title('Confusion Matrix')
    plt.show()



# Evaluate
print("\nFinal Evaluation:")
evaluate_model(model, test_loader, id_to_tag)