app.py

import gradio as gr
import torch
import numpy as np
import json
import time
from transformers import AutoTokenizer
from llama_diffusion_model import CustomTransformerModel, CustomTransformerConfig, disable_dropout
import os

hf_token = os.getenv("HF_TOKEN")


# --- Load tokenizer ---
tokenizer = AutoTokenizer.from_pretrained("meta-llama/Llama-3.2-3B", use_fast=True, token=hf_token)
vocab_size = len(tokenizer)
pad_token = tokenizer.pad_token_id or tokenizer.eos_token_id
eot_token_id = tokenizer.eos_token_id
assistant_marker_ids = tokenizer.encode("Assistant:", add_special_tokens=False)

# --- Load token probabilities ---
with open("token_probabilities.json") as f:
    token_probs_dict = json.load(f)
token_probabilities = np.array([token_probs_dict[str(i)] for i in range(len(token_probs_dict))], dtype=np.float32)


def load_model():
    config = CustomTransformerConfig(vocab_size=vocab_size)
    model = CustomTransformerModel(config)
    model.load_state_dict(torch.hub.load_state_dict_from_url(
        "https://huggingface.co/Ruurd/tini_model/resolve/main/diffusion-model.pth",
        map_location="cuda",
        headers={"Authorization": f"Bearer {hf_token}"}
    ))
    model = disable_dropout(model)
    model.to("cuda")
    model.eval()
    return model

rng = np.random.default_rng()

# --- Utility Functions ---
def decode_tokens_safe(token_ids):
    return tokenizer.decode(token_ids, skip_special_tokens=True).replace("\n", " ")

def find_answer_start(input_ids, marker_ids):
    for i in range(len(input_ids) - len(marker_ids) + 1):
        if input_ids[i:i + len(marker_ids)] == marker_ids:
            return i + len(marker_ids)
    return None

def get_noising_schedule(i, max_it, sharpness=5.0):
    x = i / max_it
    return (np.exp(-sharpness * x) - np.exp(-sharpness)) / (1 - np.exp(-sharpness))

def noisify_answer(input_ids, answer_start, threshold=1.0, eot_weight=1.0):
    noised = input_ids.copy()
    answer_len = len(input_ids) - answer_start
    num_to_noise = int(threshold * answer_len)
    if num_to_noise > 0:
        indices = rng.choice(np.arange(answer_start, len(input_ids)), size=num_to_noise, replace=False)

        mixed_probs = token_probabilities.copy()
        mixed_probs[eot_token_id] *= eot_weight
        mixed_probs /= mixed_probs.sum()

        noise = rng.choice(np.arange(vocab_size), size=num_to_noise, p=mixed_probs)
        for idx, val in zip(indices, noise):
            noised[idx] = val
    return noised

def generate_diffusion_text(model, input_ids, answer_start):
    with torch.no_grad():
        input_tensor = torch.tensor([input_ids], dtype=torch.long).to(model.device)
        logits = model(input_ids=input_tensor)["logits"]
        probs = torch.nn.functional.softmax(logits, dim=-1).squeeze()
        probs = torch.clamp(probs, min=1e-8, max=1.0)
        sampled = torch.multinomial(probs, num_samples=1).squeeze().tolist()
    return input_ids[:answer_start] + sampled[answer_start:]

# --- Inference Wrapper ---
def diffusion_chat(question, eot_weight, max_it, sharpness, model):
    placeholder = "What do you know about the city of New York?"
    if question.strip() == "":
        question = placeholder

    prompt = f"User: {question}\nAssistant:"
    input_ids = tokenizer.encode(prompt, add_special_tokens=False)
    answer_start = find_answer_start(input_ids, assistant_marker_ids)
    if answer_start is None:
        yield "Error: Could not find Assistant marker in input."
        return

    if len(input_ids) < 256:
        input_ids += [pad_token] * (256 - len(input_ids))
    else:
        input_ids = input_ids[:256]

    ori_input_tokens = input_ids
    current_tokens = noisify_answer(ori_input_tokens, answer_start, threshold=1.0, eot_weight=eot_weight)
    prev_decoded_tokens = []
    last_tokens = []

    for i in range(max_it):
        generated_tokens = generate_diffusion_text(model, current_tokens, answer_start)
        current_tokens = generated_tokens

        decoded_ids = current_tokens[answer_start:]
        decoded_tokens = tokenizer.convert_ids_to_tokens(decoded_ids)
        filtered_tokens = [tok for tok in decoded_tokens if tokenizer.convert_tokens_to_ids(tok) != eot_token_id]
        filtered_prev_tokens = [tok for tok in prev_decoded_tokens if tokenizer.convert_tokens_to_ids(tok) != eot_token_id] if prev_decoded_tokens else []

        if filtered_prev_tokens:
            highlighted = []
            for tok_new, tok_old in zip(filtered_tokens, filtered_prev_tokens):
                if tok_new != tok_old:
                    highlighted.append(f'<span style="color:green">{tokenizer.convert_tokens_to_string([tok_new])}</span>')
                else:
                    highlighted.append(tokenizer.convert_tokens_to_string([tok_new]))
        else:
            highlighted = [tokenizer.convert_tokens_to_string([tok]) for tok in filtered_tokens]

        prev_decoded_tokens = decoded_tokens
        yield f"<b>Iteration {i+1}/{max_it} (running):</b><br>" + "".join(highlighted)

        last_tokens.append(generated_tokens)
        if len(last_tokens) > 3:
            last_tokens.pop(0)
        if len(last_tokens) == 3 and last_tokens[0] == last_tokens[1] == last_tokens[2]:
            yield f"<b>Stopped early after {i+1} iterations.</b>"
            break

        threshold = get_noising_schedule(i, max_it, sharpness=sharpness)
        current_tokens = noisify_answer(generated_tokens, answer_start, threshold=threshold, eot_weight=eot_weight)
        time.sleep(0.01)

    final_tokens = tokenizer.convert_ids_to_tokens(current_tokens[answer_start:])
    final_tokens = [tok for tok in final_tokens if tokenizer.convert_tokens_to_ids(tok) != eot_token_id]
    final_output = tokenizer.convert_tokens_to_string(final_tokens)
    yield f"<b>Final Output (after {i+1} iterations):</b><br>" + final_output

# --- Gradio Interface ---
model_state = gr.State(load_model())

demo = gr.Interface(
    fn=diffusion_chat,
    inputs=[
        gr.Textbox(label="User Question", lines=2, placeholder="What do you know about the city of New York?"),
        gr.Slider(0, 1, value=0.4, step=0.05, label="↓ = longer answers (EOT weight)"),
        gr.Slider(1, 512, value=64, step=1, label="↑ = more iterations"),
        gr.Slider(1.0, 20.0, value=5.0, step=0.5, label="↓ = more noising (sharpness)"),
        model_state
    ],
    outputs=gr.HTML(label="Diffusion Output"),
    title="Diffusion Language Model Chat",
    description="This interface runs a diffusion-based language model to generate answers progressively."
)

demo.launch()