app.py

import torch
import torch.nn as nn
import torch.nn.functional as F
import numpy as np
import math
import gradio as gr

# ===== DATASET =====
with open("dataset.txt", "r", encoding="utf-8") as f:
    text = f.read().lower()

chars = sorted(list(set(text)))
vocab_size = len(chars)
stoi = {ch:i for i,ch in enumerate(chars)}
itos = {i:ch for i,ch in enumerate(chars)}

def encode(s): return [stoi.get(c, 0) for c in s]
def decode(l): return "".join([itos[i] for i in l])

# ===== GPT-Style Transformer Decoder =====
class GPTBlock(nn.Module):
    def __init__(self, d_model, nhead, dim_feedforward, dropout):
        super().__init__()
        self.attn = nn.MultiheadAttention(d_model, nhead, dropout=dropout)
        self.ff = nn.Sequential(
            nn.Linear(d_model, dim_feedforward),
            nn.GELU(),
            nn.Linear(dim_feedforward, d_model),
            nn.Dropout(dropout),
        )
        self.ln1 = nn.LayerNorm(d_model)
        self.ln2 = nn.LayerNorm(d_model)

    def forward(self, x, mask=None):
        attn_out, _ = self.attn(x, x, x, attn_mask=mask)
        x = self.ln1(x + attn_out)
        ff_out = self.ff(x)
        x = self.ln2(x + ff_out)
        return x

class GPTModel(nn.Module):
    def __init__(self, vocab_size, d_model=128, nhead=8, num_layers=4, dim_feedforward=512, max_len=5000, dropout=0.1):
        super().__init__()
        self.token_emb = nn.Embedding(vocab_size, d_model)
        self.pos_emb = nn.Parameter(torch.zeros(1, max_len, d_model))
        self.blocks = nn.ModuleList([GPTBlock(d_model, nhead, dim_feedforward, dropout) for _ in range(num_layers)])
        self.ln_f = nn.LayerNorm(d_model)
        self.head = nn.Linear(d_model, vocab_size)

    def forward(self, x):
        seq_len = x.size(1)
        token_embeddings = self.token_emb(x)  # (batch, seq_len, d_model)
        pos_embeddings = self.pos_emb[:, :seq_len, :]  # (1, seq_len, d_model)
        x = token_embeddings + pos_embeddings
        x = x.transpose(0, 1)  # for MultiheadAttention: (seq_len, batch, d_model)

        # causal mask (upper triangular)
        mask = torch.triu(torch.ones(seq_len, seq_len) * float('-inf'), diagonal=1).to(x.device)

        for block in self.blocks:
            x = block(x, mask)

        x = x.transpose(0, 1)  # back to (batch, seq_len, d_model)
        x = self.ln_f(x)
        logits = self.head(x)  # (batch, seq_len, vocab_size)
        return logits

# ===== TRAINING =====
device = torch.device("cuda" if torch.cuda.is_available() else "cpu")
model = GPTModel(vocab_size).to(device)
optimizer = torch.optim.Adam(model.parameters(), lr=0.005)
criterion = nn.CrossEntropyLoss()

seq_len = 25
batch_size = 1
epochs = 300

data_tensor = torch.tensor(encode(text), dtype=torch.long)

for epoch in range(epochs):
    model.train()
    idx = np.random.randint(0, len(data_tensor) - seq_len - 1)
    chunk = data_tensor[idx:idx+seq_len+1].unsqueeze(0).to(device)  # (1, seq_len+1)
    input_seq = chunk[:, :-1]
    target_seq = chunk[:, 1:]

    optimizer.zero_grad()
    logits = model(input_seq)
    loss = criterion(logits.view(-1, vocab_size), target_seq.view(-1))
    loss.backward()
    optimizer.step()

    if epoch % 50 == 0:
        print(f"Epoch {epoch}, Loss: {loss.item():.4f}")

# ===== TEXT GENERATION =====
def generate_text(model, seed, max_len=100):
    model.eval()
    input_ids = torch.tensor(encode(seed), dtype=torch.long).unsqueeze(0).to(device)
    generated = seed

    with torch.no_grad():
        for _ in range(max_len):
            logits = model(input_ids)
            probs = F.softmax(logits[0, -1], dim=-1).cpu().numpy()
            next_id = np.random.choice(len(probs), p=probs)
            generated += itos[next_id]
            next_token = torch.tensor([[next_id]], device=device)
            input_ids = torch.cat([input_ids, next_token], dim=1)

    return generated

# ===== GRADIO CHAT =====
def chat_with_ai(inp):
    return generate_text(model, inp, max_len=100)[len(inp):]

import gradio as gr
iface = gr.Interface(fn=chat_with_ai,
                     inputs=gr.Textbox(lines=1, placeholder="Ketik chat kamu..."),
                     outputs="text",
                     title="Chat AI Transformer GPT Style",
                     description="Chat AI pake model Transformer GPT-style sederhana")

iface.launch()