""" 
Simple GAN using fully connected layers

Programmed by Aladdin Persson <aladdin.persson at hotmail dot com>
* 2020-11-01: Initial coding
* 2022-12-20: Small revision of code, checked that it works with latest PyTorch version
"""


import torch
import torch.nn as nn
import torch.optim as optim
import torchvision
import torchvision.datasets as datasets
from torch.utils.data import DataLoader
import torchvision.transforms as transforms
from torch.utils.tensorboard import SummaryWriter  # to print to tensorboard


class Discriminator(nn.Module):
    def __init__(self, in_features):
        super().__init__()
        self.disc = nn.Sequential(
            nn.Linear(in_features, 128),
            nn.LeakyReLU(0.01),
            nn.Linear(128, 1),
            nn.Sigmoid(),
        )

    def forward(self, x):
        return self.disc(x)


class Generator(nn.Module):
    def __init__(self, z_dim, img_dim):
        super().__init__()
        self.gen = nn.Sequential(
            nn.Linear(z_dim, 256),
            nn.LeakyReLU(0.01),
            nn.Linear(256, img_dim),
            nn.Tanh(),  # normalize inputs to [-1, 1] so make outputs [-1, 1]
        )

    def forward(self, x):
        return self.gen(x)


# Hyperparameters etc.
device = "cuda" if torch.cuda.is_available() else "cpu"
lr = 3e-4
z_dim = 64
image_dim = 28 * 28 * 1  # 784
batch_size = 32
num_epochs = 50

disc = Discriminator(image_dim).to(device)
gen = Generator(z_dim, image_dim).to(device)
fixed_noise = torch.randn((batch_size, z_dim)).to(device)
transforms = transforms.Compose(
    [
        transforms.ToTensor(),
        transforms.Normalize((0.5,), (0.5,)),
    ]
)

dataset = datasets.MNIST(root="dataset/", transform=transforms, download=True)
loader = DataLoader(dataset, batch_size=batch_size, shuffle=True)
opt_disc = optim.Adam(disc.parameters(), lr=lr)
opt_gen = optim.Adam(gen.parameters(), lr=lr)
criterion = nn.BCELoss()
writer_fake = SummaryWriter(f"logs/fake")
writer_real = SummaryWriter(f"logs/real")
step = 0

for epoch in range(num_epochs):
    for batch_idx, (real, _) in enumerate(loader):
        real = real.view(-1, 784).to(device)
        batch_size = real.shape[0]

        ### Train Discriminator: max log(D(x)) + log(1 - D(G(z)))
        noise = torch.randn(batch_size, z_dim).to(device)
        fake = gen(noise)
        disc_real = disc(real).view(-1)
        lossD_real = criterion(disc_real, torch.ones_like(disc_real))
        disc_fake = disc(fake).view(-1)
        lossD_fake = criterion(disc_fake, torch.zeros_like(disc_fake))
        lossD = (lossD_real + lossD_fake) / 2
        disc.zero_grad()
        lossD.backward(retain_graph=True)
        opt_disc.step()

        ### Train Generator: min log(1 - D(G(z))) <-> max log(D(G(z))
        # where the second option of maximizing doesn't suffer from
        # saturating gradients
        output = disc(fake).view(-1)
        lossG = criterion(output, torch.ones_like(output))
        gen.zero_grad()
        lossG.backward()
        opt_gen.step()

        if batch_idx == 0:
            print(
                f"Epoch [{epoch}/{num_epochs}] Batch {batch_idx}/{len(loader)} \
                      Loss D: {lossD:.4f}, loss G: {lossG:.4f}"
            )

            with torch.no_grad():
                fake = gen(fixed_noise).reshape(-1, 1, 28, 28)
                data = real.reshape(-1, 1, 28, 28)
                img_grid_fake = torchvision.utils.make_grid(fake, normalize=True)
                img_grid_real = torchvision.utils.make_grid(data, normalize=True)

                writer_fake.add_image(
                    "Mnist Fake Images", img_grid_fake, global_step=step
                )
                writer_real.add_image(
                    "Mnist Real Images", img_grid_real, global_step=step
                )
                step += 1