app.py

import torch
import torch.nn as nn
import torch.nn.functional as F
import json
import os
import random
import numpy as np
from collections import deque
from fastapi import FastAPI
from pydantic import BaseModel
from transformers import AutoTokenizer, AutoModel
from datasets import load_dataset

ACTIONS = ["GITHUB", "MAIL", "CALENDAR"]
NUM_ACTIONS = len(ACTIONS)
HF_DATASET = "iteratehack/code19-dataset"

# Confidence threshold - below this returns NONE
CONFIDENCE_THRESHOLD = 0.6

# Distance threshold for outlier detection (cosine similarity)
DISTANCE_THRESHOLD = 0.93

app = FastAPI()

model_state = {
    "ready": False,
    "agent": None,
    "tokenizer": None,
    "encoder": None,
    "class_centroids": None,  # Mean embeddings per class
}


class MessageRequest(BaseModel):
    message: str


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


class PolicyNetwork(nn.Module):
    """Policy network that outputs action probabilities."""

    def __init__(self, state_dim, num_actions, hidden_dim=128):
        super().__init__()
        self.net = nn.Sequential(
            nn.Linear(state_dim, hidden_dim),
            nn.LayerNorm(hidden_dim),
            nn.ReLU(),
            nn.Dropout(0.1),
            nn.Linear(hidden_dim, hidden_dim),
            nn.LayerNorm(hidden_dim),
            nn.ReLU(),
            nn.Dropout(0.1),
            nn.Linear(hidden_dim, num_actions)
        )

        # Initialize last layer with small weights for balanced initial policy
        nn.init.xavier_uniform_(self.net[-1].weight, gain=0.01)
        nn.init.zeros_(self.net[-1].bias)

    def forward(self, state):
        return self.net(state)

    def get_action_probs(self, state):
        logits = self.forward(state)
        return F.softmax(logits, dim=-1)

    def get_action(self, state, deterministic=False, temperature=1.0):
        logits = self.forward(state)

        # Apply temperature for exploration control
        scaled_logits = logits / temperature
        probs = F.softmax(scaled_logits, dim=-1)

        if deterministic:
            action = torch.argmax(probs, dim=-1)
        else:
            dist = torch.distributions.Categorical(probs)
            action = dist.sample()

        return action, probs


class QNetwork(nn.Module):
    """Q-Network for action-value estimation."""

    def __init__(self, state_dim, num_actions, hidden_dim=128):
        super().__init__()
        self.net = nn.Sequential(
            nn.Linear(state_dim, hidden_dim),
            nn.LayerNorm(hidden_dim),
            nn.ReLU(),
            nn.Linear(hidden_dim, hidden_dim),
            nn.LayerNorm(hidden_dim),
            nn.ReLU(),
            nn.Linear(hidden_dim, num_actions)
        )

    def forward(self, state):
        return self.net(state)


class RLAgent:
    """
    RL Agent using Double DQN with proper exploration.
    """

    def __init__(self, state_dim, num_actions, lr=1e-3, gamma=0.95):
        self.state_dim = state_dim
        self.num_actions = num_actions
        self.gamma = gamma

        # Q-Networks (Double DQN)
        self.q_net = QNetwork(state_dim, num_actions)
        self.target_q_net = QNetwork(state_dim, num_actions)
        self.target_q_net.load_state_dict(self.q_net.state_dict())

        # Policy network
        self.policy_net = PolicyNetwork(state_dim, num_actions)

        self.q_optimizer = torch.optim.AdamW(self.q_net.parameters(), lr=lr, weight_decay=1e-4)
        self.policy_optimizer = torch.optim.AdamW(self.policy_net.parameters(), lr=lr, weight_decay=1e-4)

        # Exploration parameters
        self.epsilon = 1.0
        self.epsilon_min = 0.05
        self.epsilon_decay = 0.995
        self.temperature = 1.0

    def select_action(self, state, deterministic=True):
        """Select action given state."""
        with torch.no_grad():
            if deterministic:
                # Use policy network for inference
                action, probs = self.policy_net.get_action(state, deterministic=True)
                action_idx = action.item()

                # Use entropy-based confidence: high entropy = low confidence
                entropy = -(probs * torch.log(probs + 1e-8)).sum(dim=-1).item()
                max_entropy = np.log(self.num_actions)  # Maximum possible entropy

                # Confidence based on how certain the distribution is
                # Low entropy = high confidence, high entropy = low confidence
                confidence = 1.0 - (entropy / max_entropy)

                # Also factor in the raw probability
                raw_prob = probs[0, action_idx].item()
                confidence = confidence * raw_prob
            else:
                # Epsilon-greedy for training
                if random.random() < self.epsilon:
                    action_idx = random.randint(0, self.num_actions - 1)
                    confidence = 1.0 / self.num_actions
                else:
                    action, probs = self.policy_net.get_action(state, deterministic=False, temperature=self.temperature)
                    action_idx = action.item()
                    confidence = probs[0, action_idx].item()

        return action_idx, confidence

    def update_q(self, states, actions, rewards, next_states, dones):
        """Update Q-network using TD learning."""
        # Current Q values
        q_values = self.q_net(states)
        q_values = q_values.gather(1, actions.unsqueeze(1)).squeeze(1)

        # Target Q values (Double DQN)
        with torch.no_grad():
            # Select best action using online network
            next_q_online = self.q_net(next_states)
            best_actions = next_q_online.argmax(dim=1)

            # Evaluate using target network
            next_q_target = self.target_q_net(next_states)
            next_q_values = next_q_target.gather(1, best_actions.unsqueeze(1)).squeeze(1)

            target_q_values = rewards + self.gamma * next_q_values * (1 - dones)

        # Q-network loss
        q_loss = F.smooth_l1_loss(q_values, target_q_values)

        self.q_optimizer.zero_grad()
        q_loss.backward()
        torch.nn.utils.clip_grad_norm_(self.q_net.parameters(), 1.0)
        self.q_optimizer.step()

        return q_loss.item()

    def update_policy(self, states, actions):
        """Update policy network to match Q-values (actor-critic style)."""
        # Get Q-values for actions
        with torch.no_grad():
            q_values = self.q_net(states)
            # Advantage = Q(s,a) - V(s), where V(s) = E[Q(s,a)]
            v_values = q_values.mean(dim=1, keepdim=True)
            advantages = q_values - v_values

        # Policy logits
        logits = self.policy_net(states)
        log_probs = F.log_softmax(logits, dim=-1)

        # Policy loss: maximize advantage-weighted log probability
        action_log_probs = log_probs.gather(1, actions.unsqueeze(1)).squeeze(1)
        action_advantages = advantages.gather(1, actions.unsqueeze(1)).squeeze(1)

        # Add entropy bonus for exploration
        probs = F.softmax(logits, dim=-1)
        entropy = -(probs * log_probs).sum(dim=-1).mean()

        policy_loss = -(action_log_probs * action_advantages.detach()).mean() - 0.05 * entropy

        self.policy_optimizer.zero_grad()
        policy_loss.backward()
        torch.nn.utils.clip_grad_norm_(self.policy_net.parameters(), 1.0)
        self.policy_optimizer.step()

        return policy_loss.item()

    def update_target_network(self, tau=0.005):
        """Soft update target network."""
        for target_param, param in zip(self.target_q_net.parameters(), self.q_net.parameters()):
            target_param.data.copy_(tau * param.data + (1 - tau) * target_param.data)

    def decay_exploration(self):
        """Decay exploration parameters."""
        self.epsilon = max(self.epsilon_min, self.epsilon * self.epsilon_decay)


def load_hf_dataset():
    dataset = load_dataset(HF_DATASET, split="train")
    data = []
    for item in dataset:
        user_msg = item["messages"][1]["content"]
        label = item["messages"][2]["content"]
        if label in ACTIONS:
            data.append((user_msg, ACTIONS.index(label)))

    random.shuffle(data)
    return data


def encode_texts(texts, tokenizer, encoder):
    """Batch encode texts to state representations."""
    inputs = tokenizer(texts, return_tensors="pt", truncation=True, max_length=64, padding=True)
    with torch.no_grad():
        hidden = encoder(**inputs).last_hidden_state[:, 0, :]
    return hidden


def train_rl_agent(tokenizer, encoder, data, num_epochs=50, batch_size=64):
    """
    Train RL agent using offline RL on dataset.

    Uses the dataset as demonstration data:
    - States: encoded text messages
    - Actions: correct labels from dataset (expert demonstrations)
    - Rewards: +1 for correct, -1 for incorrect
    """
    state_dim = 768  # DistilBERT hidden size
    agent = RLAgent(state_dim, NUM_ACTIONS, lr=3e-4)

    print("Encoding all dataset examples...")

    # Pre-encode all texts for efficiency
    all_texts = [text for text, _ in data]
    all_labels = [label for _, label in data]

    # Encode in batches
    all_states = []
    for i in range(0, len(all_texts), batch_size):
        batch_texts = all_texts[i:i+batch_size]
        batch_states = encode_texts(batch_texts, tokenizer, encoder)
        all_states.append(batch_states)

    all_states = torch.cat(all_states, dim=0)
    all_labels = torch.tensor(all_labels, dtype=torch.long)

    print(f"Encoded {len(all_states)} examples")

    # Print class distribution
    for i, action_name in enumerate(ACTIONS):
        count = (all_labels == i).sum().item()
        print(f"  {action_name}: {count} examples")

    # Create next states (shifted by 1, with wraparound)
    indices = torch.randperm(len(all_states))
    next_states = all_states[indices]

    print("Starting RL training...")

    for epoch in range(num_epochs):
        # Shuffle data each epoch
        perm = torch.randperm(len(all_states))
        states_shuffled = all_states[perm]
        labels_shuffled = all_labels[perm]
        next_states_shuffled = next_states[perm]

        epoch_q_loss = 0
        epoch_policy_loss = 0
        num_batches = 0

        for i in range(0, len(states_shuffled), batch_size):
            batch_states = states_shuffled[i:i+batch_size]
            batch_labels = labels_shuffled[i:i+batch_size]
            batch_next_states = next_states_shuffled[i:i+batch_size]

            # Simple rewards: +1 for correct, -1 for wrong
            batch_rewards = torch.ones(len(batch_labels), dtype=torch.float32)
            batch_dones = torch.zeros(len(batch_labels), dtype=torch.float32)

            # Add negative examples (wrong actions with negative reward)
            wrong_actions_list = []
            for label in batch_labels:
                wrong = (label.item() + random.randint(1, NUM_ACTIONS - 1)) % NUM_ACTIONS
                wrong_actions_list.append(wrong)
            wrong_actions = torch.tensor(wrong_actions_list, dtype=torch.long)
            wrong_rewards = -torch.ones(len(batch_labels), dtype=torch.float32)

            # Combine correct and incorrect transitions
            combined_states = torch.cat([batch_states, batch_states], dim=0)
            combined_actions = torch.cat([batch_labels, wrong_actions], dim=0)
            combined_rewards = torch.cat([batch_rewards, wrong_rewards], dim=0)
            combined_next_states = torch.cat([batch_next_states, batch_next_states], dim=0)
            combined_dones = torch.cat([batch_dones, batch_dones], dim=0)

            # Update Q-network
            q_loss = agent.update_q(
                combined_states, combined_actions, combined_rewards,
                combined_next_states, combined_dones
            )

            # Update policy (only on correct examples)
            policy_loss = agent.update_policy(batch_states, batch_labels)

            # Soft update target
            agent.update_target_network(tau=0.005)

            epoch_q_loss += q_loss
            epoch_policy_loss += policy_loss
            num_batches += 1

        agent.decay_exploration()

        if (epoch + 1) % 10 == 0:
            # Evaluate
            with torch.no_grad():
                _, probs = agent.policy_net.get_action(all_states, deterministic=True)
                predictions = probs.argmax(dim=-1)
                accuracy = (predictions == all_labels).float().mean().item() * 100

                # Check policy entropy (diversity)
                avg_entropy = -(probs * torch.log(probs + 1e-8)).sum(dim=-1).mean().item()

            print(f"Epoch {epoch + 1}/{num_epochs} | "
                  f"Q-Loss: {epoch_q_loss/num_batches:.4f} | "
                  f"Policy-Loss: {epoch_policy_loss/num_batches:.4f} | "
                  f"Accuracy: {accuracy:.1f}% | "
                  f"Entropy: {avg_entropy:.3f} | "
                  f"Epsilon: {agent.epsilon:.3f}")

    # Set networks to eval mode (disables dropout for deterministic inference)
    agent.policy_net.eval()
    agent.q_net.eval()

    # Final evaluation
    print("\nFinal Evaluation:")
    with torch.no_grad():
        _, probs = agent.policy_net.get_action(all_states, deterministic=True)
        predictions = probs.argmax(dim=-1)

        for i, action_name in enumerate(ACTIONS):
            mask = all_labels == i
            if mask.sum() > 0:
                action_acc = (predictions[mask] == i).float().mean().item() * 100
                print(f"  {action_name}: {action_acc:.1f}% ({mask.sum().item()} samples)")

        overall_acc = (predictions == all_labels).float().mean().item() * 100
        print(f"  Overall: {overall_acc:.1f}%")

    # Compute class centroids for outlier detection
    print("\nComputing class centroids...")
    centroids = []
    for i in range(NUM_ACTIONS):
        mask = all_labels == i
        class_states = all_states[mask]
        centroid = class_states.mean(dim=0)
        centroids.append(centroid)
    class_centroids = torch.stack(centroids)

    return agent, class_centroids


def load_model():
    """Load encoder and train RL agent."""
    print("Loading tokenizer and encoder...")
    tokenizer = AutoTokenizer.from_pretrained("distilbert-base-uncased")
    encoder = AutoModel.from_pretrained("distilbert-base-uncased")
    encoder.eval()

    print("Loading dataset...")
    data = load_hf_dataset()
    print(f"Dataset size: {len(data)} examples")

    print("Training RL agent...")
    agent, class_centroids = train_rl_agent(tokenizer, encoder, data)

    return tokenizer, encoder, agent, class_centroids


def predict(text, tokenizer, encoder, agent, class_centroids):
    """Use trained RL agent to predict action for given text."""
    inputs = tokenizer(text, return_tensors="pt", truncation=True, max_length=64)
    with torch.no_grad():
        hidden = encoder(**inputs).last_hidden_state[:, 0, :]
        action_idx, confidence = agent.select_action(hidden, deterministic=True)

        # Compute cosine similarity to closest class centroid
        hidden_norm = hidden / hidden.norm(dim=-1, keepdim=True)
        centroids_norm = class_centroids / class_centroids.norm(dim=-1, keepdim=True)
        similarities = torch.mm(hidden_norm, centroids_norm.t()).squeeze(0)
        max_similarity = similarities.max().item()

    # Return NONE if similarity is too low OR confidence is too low
    if max_similarity < DISTANCE_THRESHOLD or confidence < CONFIDENCE_THRESHOLD:
        return "NONE", confidence

    return ACTIONS[action_idx], confidence


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


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

    def load_in_background():
        tokenizer, encoder, agent, class_centroids = load_model()
        model_state["tokenizer"] = tokenizer
        model_state["encoder"] = encoder
        model_state["agent"] = agent
        model_state["class_centroids"] = class_centroids
        model_state["ready"] = True
        print("RL Agent loaded and ready!")

    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["agent"],
        model_state["class_centroids"]
    )
    return ActionResponse(action=action_name, score=round(score, 4))