backend/app/train.py

import json
import os
from transformers import (
    AutoTokenizer,
    AutoModelForSequenceClassification,
    TrainingArguments,
    Trainer,
    DataCollatorWithPadding,
)
import torch
from datasets import Dataset

# -------- Settings --------
MODEL_NAME = "distilbert-base-uncased"
DATA_PATH = "./backend/data/pregnancy_dataset.json"
SAVE_PATH = "./data/best_model"

os.makedirs(SAVE_PATH, exist_ok=True)


# -------- Load and Preprocess Dataset --------
def load_and_prepare_dataset():
    with open(DATA_PATH, "r") as f:
        data = json.load(f)

    # Map risk levels to integer labels
    label_map = {"low risk": 0, "medium risk": 1, "high risk": 2}

    def preprocess(example):
        prompt = (
            f"Age: {example['Age']}, SystolicBP: {example['SystolicBP']}, "
            f"DiastolicBP: {example['DiastolicBP']}, BS: {example['BS']}, "
            f"BodyTemp: {example['BodyTemp']}, HeartRate: {example['HeartRate']}. "
            f"Predict the Risk Level."
        )
        # Ensure consistent and safe label mapping
        label_str = str(example.get("RiskLevel", "")).lower()
        label = label_map.get(label_str, 0)
        return {"text": prompt, "label": label}

    dataset = Dataset.from_list(data)
    return dataset.map(preprocess)

# -------- Tokenization --------
def tokenize_function(example, tokenizer):
    tokens = tokenizer(
        example["text"],
        truncation=True,
        padding=True,
        max_length=64,
    )
    tokens["label"] = example["label"]
    return tokens

# -------- Main Training Function --------
def train():
    tokenizer = AutoTokenizer.from_pretrained(MODEL_NAME)
    model = AutoModelForSequenceClassification.from_pretrained(MODEL_NAME, num_labels=3)

    dataset = load_and_prepare_dataset()

    # Tokenize dataset
    tokenized_dataset = dataset.map(lambda x: tokenize_function(x, tokenizer), batched=False)

    # Remove any non-tensor-compatible fields
    tokenized_dataset = tokenized_dataset.remove_columns(
        [col for col in tokenized_dataset.column_names if col not in ["input_ids", "attention_mask", "label"]]
    )

    # Optional sanity check
    print("🔎 Sample tokenized example:", tokenized_dataset[0])

    training_args = TrainingArguments(
        output_dir=SAVE_PATH,
        num_train_epochs=3,
        per_device_train_batch_size=4,
        save_steps=50,
        logging_steps=10,
        save_total_limit=1,
        remove_unused_columns=False,
        report_to="none",
    )

    data_collator = DataCollatorWithPadding(tokenizer=tokenizer)

    trainer = Trainer(
        model=model,
        args=training_args,
        train_dataset=tokenized_dataset,
        tokenizer=tokenizer,
        data_collator=data_collator,
    )

    trainer.train()
    trainer.save_model(SAVE_PATH)
    tokenizer.save_pretrained(SAVE_PATH)
    print("✅ Fine-tuned model saved!")

# -------- Entry Point --------
if __name__ == "__main__":
    train()