app.py

import torch
import torch.nn as nn
import json
import os
from fastapi import FastAPI
from pydantic import BaseModel
from transformers import AutoTokenizer, AutoModel

# Simple RL Classifier using Transformer
ACTIONS = ["TRIP", "NONE", "GITHUB", "MAIL"]
DATASET_PATH = os.path.join(os.path.dirname(__file__), "dataset.jsonl")

app = FastAPI()

# Global model state - loaded lazily
model_state = {"ready": False, "tokenizer": None, "encoder": None, "policy_head": None}


class MessageRequest(BaseModel):
    message: str


class ActionResponse(BaseModel):
    action: str
    score: float


@app.get("/health")
def health():
    return {"status": "ok", "model_ready": model_state["ready"]}


def load_model():
    tokenizer = AutoTokenizer.from_pretrained("distilbert-base-uncased")
    encoder = AutoModel.from_pretrained("distilbert-base-uncased")

    # Simple policy head
    policy_head = nn.Linear(768, len(ACTIONS))

    # Load dataset for training
    data = []
    with open(DATASET_PATH, "r") as f:
        for line in f:
            item = json.loads(line)
            user_msg = item["messages"][1]["content"]
            label = item["messages"][2]["content"]
            data.append((user_msg, ACTIONS.index(label)))

    # Quick RL-style training (policy gradient simplified)
    optimizer = torch.optim.Adam(policy_head.parameters(), lr=1e-3)
    encoder.eval()

    for epoch in range(3):
        total_reward = 0
        for text, label in data[:100]:  # use subset for speed
            inputs = tokenizer(text, return_tensors="pt", truncation=True, max_length=64)
            with torch.no_grad():
                hidden = encoder(**inputs).last_hidden_state[:, 0, :]

            logits = policy_head(hidden)
            probs = torch.softmax(logits, dim=-1)

            # Sample action (RL style)
            action = torch.multinomial(probs, 1).item()

            # Reward: +1 if correct, -1 if wrong
            reward = 1.0 if action == label else -1.0
            total_reward += reward

            # Policy gradient update
            log_prob = torch.log(probs[0, action])
            loss = -log_prob * reward

            optimizer.zero_grad()
            loss.backward()
            optimizer.step()

    return tokenizer, encoder, policy_head


def predict(text, tokenizer, encoder, policy_head):
    inputs = tokenizer(text, return_tensors="pt", truncation=True, max_length=64)
    with torch.no_grad():
        hidden = encoder(**inputs).last_hidden_state[:, 0, :]
        logits = policy_head(hidden)
        probs = torch.softmax(logits, dim=-1)
        action_idx = torch.argmax(probs, dim=-1).item()
        score = probs[0, action_idx].item()

    return ACTIONS[action_idx], score


@app.on_event("startup")
async def startup_event():
    import threading

    def load_in_background():
        tokenizer, encoder, policy_head = load_model()
        model_state["tokenizer"] = tokenizer
        model_state["encoder"] = encoder
        model_state["policy_head"] = policy_head
        model_state["ready"] = True
        print("Model loaded and ready!")

    # Load model in background thread so server can respond immediately
    thread = threading.Thread(target=load_in_background)
    thread.start()


@app.post("/action", response_model=ActionResponse)
def action(request: MessageRequest):
    if not model_state["ready"]:
        from fastapi import HTTPException
        raise HTTPException(status_code=503, detail="Model is still loading, please wait")

    action_name, score = predict(
        request.message,
        model_state["tokenizer"],
        model_state["encoder"],
        model_state["policy_head"]
    )
    return ActionResponse(action=action_name, score=round(score, 4))