src/final_flow_model.py

import torch
import torch.nn as nn
import torch.nn.functional as F
import math

class SinusoidalTimeEmbedding(nn.Module):
    """Sinusoidal time embedding as used in ProtFlow paper."""
    
    def __init__(self, dim):
        super().__init__()
        self.dim = dim
        
    def forward(self, time):
        device = time.device
        half_dim = self.dim // 2
        embeddings = math.log(10000) / (half_dim - 1)
        embeddings = torch.exp(torch.arange(half_dim, device=device) * -embeddings)
        # Ensure time is 2D: [B, 1] and embeddings is 1D: [half_dim]
        if time.dim() > 2:
            time = time.squeeze()  # Remove extra dimensions
        embeddings = time.unsqueeze(-1) * embeddings.unsqueeze(0)  # [B, half_dim]
        embeddings = torch.cat((embeddings.sin(), embeddings.cos()), dim=-1)  # [B, dim]
        # Ensure output is exactly 2D
        if embeddings.dim() > 2:
            embeddings = embeddings.squeeze()
        return embeddings

class LabelMLP(nn.Module):
    """
    MLP for processing class labels into embeddings.
    This approach processes labels separately from time embeddings.
    """
    def __init__(self, num_classes=3, hidden_dim=480, mlp_dim=256):
        super().__init__()
        self.num_classes = num_classes
        
        # MLP to process labels
        self.label_mlp = nn.Sequential(
            nn.Embedding(num_classes, mlp_dim),
            nn.Linear(mlp_dim, mlp_dim),
            nn.GELU(),
            nn.Linear(mlp_dim, hidden_dim),
            nn.GELU(),
            nn.Linear(hidden_dim, hidden_dim)
        )
        
        # Initialize embeddings
        nn.init.normal_(self.label_mlp[0].weight, std=0.02)
    
    def forward(self, labels):
        """
        Args:
            labels: (B,) tensor of class labels
                   - 0: AMP (MIC < 100)
                   - 1: Non-AMP (MIC >= 100)
                   - 2: Mask (Unknown MIC)
        Returns:
            embeddings: (B, hidden_dim) tensor of processed label embeddings
        """
        return self.label_mlp(labels)

class AMPFlowMatcherCFGConcat(nn.Module):
    """
    Flow Matching model with Classifier-Free Guidance using concatenation approach.
    - 12-layer transformer with long skip connections
    - Time embedding + MLP-processed label embedding (concatenated then projected)
    - Optimized for peptide sequences (max length 50)
    """
    
    def __init__(self, hidden_dim=480, compressed_dim=30, n_layers=12, n_heads=16, 
                 dim_ff=3072, dropout=0.1, max_seq_len=25, use_cfg=True):
        super().__init__()
        self.hidden_dim = hidden_dim
        self.compressed_dim = compressed_dim
        self.n_layers = n_layers
        self.max_seq_len = max_seq_len
        self.use_cfg = use_cfg
        
        # Time embedding
        self.time_embed = nn.Sequential(
            SinusoidalTimeEmbedding(hidden_dim),
            nn.Linear(hidden_dim, hidden_dim),
            nn.GELU(),
            nn.Linear(hidden_dim, hidden_dim)
        )
        
        # CFG components using concatenation approach
        if use_cfg:
            self.label_mlp = LabelMLP(num_classes=3, hidden_dim=hidden_dim)
            
            # Projection layer for concatenated time + label embeddings
            self.condition_proj = nn.Sequential(
                nn.Linear(hidden_dim * 2, hidden_dim),  # 2 for time + label
                nn.GELU(),
                nn.Linear(hidden_dim, hidden_dim)
            )
        
        # Projection layers for compressed space
        self.compress_proj = nn.Linear(compressed_dim, hidden_dim)
        self.decompress_proj = nn.Linear(hidden_dim, compressed_dim)
        
        # Positional encoding for peptide sequences
        self.pos_embed = nn.Parameter(torch.randn(1, max_seq_len, hidden_dim))
        
        # Transformer layers with long skip connections
        self.layers = nn.ModuleList([
            nn.TransformerEncoderLayer(
                d_model=hidden_dim,
                nhead=n_heads,
                dim_feedforward=dim_ff,
                dropout=dropout,
                activation='gelu',
                batch_first=True
            ) for _ in range(n_layers)
        ])
        
        # Long skip connections (U-ViT style)
        self.skip_projections = nn.ModuleList([
            nn.Linear(hidden_dim, hidden_dim) for _ in range(n_layers - 1)
        ])
        
        # Output projection
        self.output_proj = nn.Linear(hidden_dim, compressed_dim)
        
    def forward(self, x, t, labels=None, mask=None):
        """
        Args:
            x: compressed latent (B, L, compressed_dim) - AMP embeddings
            t: time scalar (B,) or (B, 1)
            labels: class labels (B,) for CFG - 0=AMP, 1=Non-AMP, 2=Mask
            mask: attention mask (B, L) if needed
        """
        B, L, D = x.shape
        
        # Project to hidden dimension
        x = self.compress_proj(x)  # (B, L, hidden_dim)
        
        # Add positional encoding
        if L <= self.max_seq_len:
            x = x + self.pos_embed[:, :L, :]
        
        # Time embedding - ensure t is 2D (B, 1)
        if t.dim() == 1:
            t = t.unsqueeze(-1)  # (B, 1)
        elif t.dim() > 2:
            t = t.squeeze()  # Remove extra dimensions
            if t.dim() == 1:
                t = t.unsqueeze(-1)  # (B, 1)
        
        t_emb = self.time_embed(t)  # (B, hidden_dim)
        # Ensure t_emb is 2D before expanding
        if t_emb.dim() > 2:
            t_emb = t_emb.squeeze()  # Remove extra dimensions
        t_emb = t_emb.unsqueeze(1).expand(-1, L, -1)  # (B, L, hidden_dim)
        
        # CFG: Process label embedding if enabled
        if self.use_cfg and labels is not None:
            # Process labels through MLP
            label_emb = self.label_mlp(labels)  # (B, hidden_dim)
            label_emb = label_emb.unsqueeze(1).expand(-1, L, -1)  # (B, L, hidden_dim)
            
            # Professor's approach: Concatenate time and label embeddings
            combined_emb = torch.cat([t_emb, label_emb], dim=-1)  # (B, L, hidden_dim*2)
            projected_emb = self.condition_proj(combined_emb)  # (B, L, hidden_dim)
        else:
            projected_emb = t_emb  # Just use time embedding if no CFG
        
        # Store intermediate representations for skip connections
        skip_features = []
        
        # Pass through transformer layers with skip connections
        for i, layer in enumerate(self.layers):
            # Add skip connection from earlier layers
            if i > 0 and i < len(self.layers) - 1:
                skip_feat = skip_features[i-1]
                skip_feat = self.skip_projections[i-1](skip_feat)
                x = x + skip_feat
            
            # Store current features for future skip connections
            if i < len(self.layers) - 1:
                skip_features.append(x.clone())
            
            # Add projected condition embedding to EACH layer
            x = x + projected_emb
            
            # Apply transformer layer
            x = layer(x, src_key_padding_mask=mask)
        
        # Project back to compressed dimension
        x = self.output_proj(x)  # (B, L, compressed_dim)
        
        return x

class AMPProtFlowPipelineCFG:
    """
    Complete ProtFlow pipeline for AMP generation with CFG.
    """
    
    def __init__(self, compressor, decompressor, flow_model, device='cuda'):
        self.compressor = compressor
        self.decompressor = decompressor
        self.flow_model = flow_model
        self.device = device
        
        # Load normalization stats
        self.stats = torch.load('normalization_stats.pt', map_location=device)
        
    def generate_amps_cfg(self, num_samples=100, num_steps=25, cfg_scale=7.5, 
                         condition_label=0):
        """
        Generate AMP samples using CFG.
        
        Args:
            num_samples: Number of samples to generate
            num_steps: Number of ODE solving steps
            cfg_scale: CFG guidance scale (higher = stronger conditioning)
            condition_label: 0=AMP, 1=Non-AMP, 2=Mask
        """
        print(f"Generating {num_samples} samples with CFG (label={condition_label}, scale={cfg_scale})...")
        
        # Sample random noise
        batch_size = min(num_samples, 32)  # Process in batches
        all_samples = []
        
        for i in range(0, num_samples, batch_size):
            current_batch = min(batch_size, num_samples - i)
            
            # Initialize with noise
            eps = torch.randn(current_batch, self.flow_model.max_seq_len, 
                            self.flow_model.compressed_dim, device=self.device)
            
            # ODE solving steps with CFG
            xt = eps.clone()
            for step in range(num_steps):
                t = torch.ones(current_batch, device=self.device) * (1.0 - step/num_steps)
                
                # CFG: Generate with condition and without condition
                if cfg_scale > 0:
                    # With condition
                    vt_cond = self.flow_model(xt, t, 
                                            labels=torch.full((current_batch,), condition_label, 
                                                            device=self.device))
                    
                    # Without condition (mask)
                    vt_uncond = self.flow_model(xt, t, 
                                              labels=torch.full((current_batch,), 2, 
                                                              device=self.device))
                    
                    # CFG interpolation
                    vt = vt_uncond + cfg_scale * (vt_cond - vt_uncond)
                else:
                    # No CFG, use mask label
                    vt = self.flow_model(xt, t, 
                                       labels=torch.full((current_batch,), 2, 
                                                       device=self.device))
                
                # Euler step for backward integration (t: 1 -> 0)
                # Use negative dt to integrate backward from noise to data
                dt = -1.0 / num_steps
                xt = xt + vt * dt
            
            all_samples.append(xt)
        
        # Concatenate all batches
        generated = torch.cat(all_samples, dim=0)
        
        # Decompress and decode
        with torch.no_grad():
            # Decompress
            decompressed = self.decompressor(generated)
            
            # Apply reverse normalization
            m, s, mn, mx = self.stats['mean'], self.stats['std'], self.stats['min'], self.stats['max']
            decompressed = decompressed * (mx - mn + 1e-8) + mn
            decompressed = decompressed * s + m
            
        return generated, decompressed

# Example usage
if __name__ == "__main__":
    # Initialize FINAL AMP flow model with CFG using concatenation approach
    flow_model = AMPFlowMatcherCFGConcat(
        hidden_dim=480,
        compressed_dim=30,  # 16x compression of 480
        n_layers=12,
        n_heads=16,
        dim_ff=3072,
        max_seq_len=25,  # For AMP sequences (max 50, halved by pooling)
        use_cfg=True
    )
    
    print(f"FINAL AMP Flow Model with CFG (Concat+Proj) parameters: {sum(p.numel() for p in flow_model.parameters()):,}")
    
    # Test forward pass
    batch_size = 4
    seq_len = 20
    compressed_dim = 30
    
    x = torch.randn(batch_size, seq_len, compressed_dim)
    t = torch.rand(batch_size)
    labels = torch.randint(0, 3, (batch_size,))  # Random labels
    
    with torch.no_grad():
        output = flow_model(x, t, labels=labels)
        print(f"Input shape: {x.shape}")
        print(f"Output shape: {output.shape}")
        print(f"Time embedding shape: {t.shape}")
        print(f"Labels: {labels}")
    
    print("🎯 FINAL AMP Flow Model with CFG (Concat+Proj) ready for training!")