"""
GLADIUS v2.0 — MoDA: Multi-Head Depth Attention

The insight: Standard transformers compute Q, K, V from the CURRENT layer's hidden
state only. But every previous layer already computed useful representations that get
discarded. MoDA adds a second set of K, V projections that attend over a "depth cache"
— the hidden states from ALL previous layers at each position.

This is NOT cross-attention (fixed external memory). This is SELF-attention through
depth — the model attending to its own computation history.

Architecture per layer l:
    Sequence path (standard):
        Q_seq = W_q @ x_l          (query from current layer)
        K_seq = W_k @ x_l          (key from current layer)  
        V_seq = W_v @ x_l          (value from current layer)
        O_seq = softmax(Q_seq @ K_seq^T / sqrt(d)) @ V_seq

    Depth path (NEW):
        K_depth = W_k_depth @ stack(x_0, x_1, ..., x_{l-1})
        V_depth = W_v_depth @ stack(x_0, x_1, ..., x_{l-1})
        O_depth = softmax(Q_seq @ K_depth^T / sqrt(d)) @ V_depth

    Combined:
        O = gate * O_seq + (1 - gate) * O_depth

The depth KV projections are TINY (hidden_dim → head_dim per group), and the depth
cache grows linearly with layers (not sequence length), so the cost is negligible.

For GLADIUS Wyrm (640d, 14L, 20H):
    Depth cache at layer 13: 13 × seq_len depth tokens per position
    Extra params per layer: 2 × hidden_dim × (hidden_dim / num_groups) ≈ 40K
    Total extra: 14 × 40K ≈ 560K params (0.5% of 104.9M)

Reference: MoDA paper (Multi-Head Depth Attention) + Ali's SLA2 hybrid architecture.
"""

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

from .config import KernelConfig
from .attention import RoPE, RMSNorm, SwiGLU


class DepthKVProjection(nn.Module):
    """
    Projects depth cache hidden states into K, V for depth attention.
    
    Uses Grouped Query Attention (GQA) style — fewer KV heads than Q heads
    to keep the depth path lightweight.
    
    For Wyrm: 20 Q heads, 4 KV groups → 5 Q heads per KV group.
    """
    
    def __init__(self, hidden_dim: int, num_kv_heads: int, head_dim: int):
        super().__init__()
        self.num_kv_heads = num_kv_heads
        self.head_dim = head_dim
        self.kv_dim = num_kv_heads * head_dim
        
        self.k_proj = nn.Linear(hidden_dim, self.kv_dim, bias=False)
        self.v_proj = nn.Linear(hidden_dim, self.kv_dim, bias=False)
        
        self._init_weights()
    
    def _init_weights(self):
        # Initialize from small noise — depth path starts quiet
        nn.init.normal_(self.k_proj.weight, std=0.005)
        nn.init.normal_(self.v_proj.weight, std=0.005)
    
    def forward(self, depth_cache: torch.Tensor):
        """
        Args:
            depth_cache: (batch, depth_len, hidden_dim) — stacked hidden states from previous layers
        Returns:
            K_depth: (batch, num_kv_heads, depth_len, head_dim)
            V_depth: (batch, num_kv_heads, depth_len, head_dim)
        """
        B, D_len, _ = depth_cache.shape
        K = self.k_proj(depth_cache).view(B, D_len, self.num_kv_heads, self.head_dim).transpose(1, 2)
        V = self.v_proj(depth_cache).view(B, D_len, self.num_kv_heads, self.head_dim).transpose(1, 2)
        return K, V


class MoDAAttention(nn.Module):
    """
    Multi-Head Depth Attention — the core MoDA mechanism.
    
    Combines standard sequence attention (SLA2 hybrid: softmax + linear blend)
    with depth attention over previous layers' hidden states.
    
    The depth path uses GQA with fewer KV heads for efficiency.
    A learned gate controls the blend between sequence and depth paths.
    """
    
    def __init__(self, config: KernelConfig, layer_idx: int = 0,
                 num_depth_kv_heads: int = 4):
        super().__init__()
        self.config = config
        self.layer_idx = layer_idx
        self.num_heads = config.num_heads
        self.head_dim = config.head_dim
        self.hidden_dim = config.hidden_dim
        self.num_depth_kv_heads = num_depth_kv_heads
        
        # How many Q heads share each depth KV head
        assert config.num_heads % num_depth_kv_heads == 0, \
            f"num_heads ({config.num_heads}) must be divisible by num_depth_kv_heads ({num_depth_kv_heads})"
        self.q_per_kv = config.num_heads // num_depth_kv_heads
        
        # === Sequence path (standard projections) ===
        self.q_proj = nn.Linear(config.hidden_dim, config.hidden_dim, bias=False)
        self.k_proj = nn.Linear(config.hidden_dim, config.hidden_dim, bias=False)
        self.v_proj = nn.Linear(config.hidden_dim, config.hidden_dim, bias=False)
        self.o_proj = nn.Linear(config.hidden_dim, config.hidden_dim, bias=False)
        
        # === Depth path (new KV projections over depth cache) ===
        self.depth_kv = DepthKVProjection(config.hidden_dim, num_depth_kv_heads, config.head_dim)
        
        # === Depth gate: per-head learned blend between seq and depth ===
        # Input: current hidden state → per-head gate in [0, 1]
        # 0 = pure sequence attention, 1 = pure depth attention
        self.depth_gate = nn.Sequential(
            nn.Linear(config.hidden_dim, config.num_heads),
            nn.Sigmoid()
        )
        
        # === SLA2 alpha: blend between softmax and linear (sequence path only) ===
        self.alpha_router = nn.Sequential(
            nn.Linear(config.hidden_dim, config.num_heads),
            nn.Sigmoid()
        )
        
        # === RoPE (sequence positions only — depth has no position) ===
        self.rope = RoPE(config.head_dim, config.max_seq_len)
        
        # QK-Clip for stability
        self.qk_softcap = getattr(config, 'qk_softcap', None)
        
        self._init_weights()
    
    def _init_weights(self):
        for proj in [self.q_proj, self.k_proj, self.v_proj, self.o_proj]:
            nn.init.normal_(proj.weight, std=0.02)
        # Initialize depth gate bias negative → start with mostly sequence attention
        # sigmoid(-2) ≈ 0.12, so depth starts at ~12% influence
        nn.init.constant_(self.depth_gate[0].bias, -2.0)
        nn.init.zeros_(self.alpha_router[0].bias)
    
    def _expand_kv_heads(self, kv: torch.Tensor) -> torch.Tensor:
        """
        Expand GQA KV heads to match Q heads.
        (B, num_kv_heads, L, D) → (B, num_heads, L, D)
        """
        B, H_kv, L, D = kv.shape
        # Repeat each KV head for q_per_kv Q heads
        return kv.unsqueeze(2).expand(B, H_kv, self.q_per_kv, L, D).reshape(B, self.num_heads, L, D)
    
    def forward(
        self,
        x: torch.Tensor,
        mask: torch.Tensor | None = None,
        depth_cache: torch.Tensor | None = None,
    ) -> torch.Tensor:
        """
        Args:
            x: (batch, seq_len, hidden_dim) — current layer input
            mask: (batch, 1, seq_len, seq_len) — causal mask
            depth_cache: (batch, num_prev_layers * seq_len, hidden_dim) — stacked previous layers
                         OR None for layer 0 (no depth history yet)
        Returns:
            (batch, seq_len, hidden_dim)
        """
        B, S, D = x.shape
        
        # === Sequence projections ===
        Q = self.q_proj(x).view(B, S, self.num_heads, self.head_dim).transpose(1, 2)  # (B, H, S, D_h)
        K = self.k_proj(x).view(B, S, self.num_heads, self.head_dim).transpose(1, 2)
        V = self.v_proj(x).view(B, S, self.num_heads, self.head_dim).transpose(1, 2)
        
        # Apply RoPE to sequence Q, K
        Q_rope = self.rope(Q, S)
        K_rope = self.rope(K, S)
        
        # === SLA2 Hybrid Sequence Attention ===
        # Linear path
        Q_lin = F.elu(Q_rope) + 1
        K_lin = F.elu(K_rope) + 1
        KV_lin = torch.matmul(K_lin.transpose(-2, -1), V)
        Z_lin = K_lin.transpose(-2, -1).sum(dim=-1, keepdim=True)
        O_linear = torch.matmul(Q_lin, KV_lin) / (torch.matmul(Q_lin, Z_lin) + 1e-6)
        
        # Softmax path
        scores = torch.matmul(Q_rope, K_rope.transpose(-2, -1)) / math.sqrt(self.head_dim)
        if self.qk_softcap is not None and self.qk_softcap > 0:
            scores = self.qk_softcap * torch.tanh(scores / self.qk_softcap)
        if mask is not None:
            scores = scores.masked_fill(mask == 0, float('-inf'))
        attn_weights = F.softmax(scores, dim=-1)
        O_softmax = torch.matmul(attn_weights, V)
        
        # SLA2 blend
        alpha = self.alpha_router(x).permute(0, 2, 1).unsqueeze(-1)  # (B, H, S, 1)
        O_seq = alpha * O_softmax + (1 - alpha) * O_linear
        
        # === Depth Attention (if we have depth history) ===
        if depth_cache is not None and depth_cache.shape[1] > 0:
            # Project depth cache to K, V
            K_depth, V_depth = self.depth_kv(depth_cache)  # (B, H_kv, D_len, D_h)
            
            # Expand GQA to match Q heads
            K_depth = self._expand_kv_heads(K_depth)  # (B, H, D_len, D_h)
            V_depth = self._expand_kv_heads(V_depth)
            
            # Depth attention scores — Q from current layer, K from depth cache
            # No RoPE on depth (depth positions are layer indices, not sequence positions)
            # Use un-rotated Q for depth to keep the paths independent
            depth_scores = torch.matmul(Q, K_depth.transpose(-2, -1)) / math.sqrt(self.head_dim)
            
            if self.qk_softcap is not None and self.qk_softcap > 0:
                depth_scores = self.qk_softcap * torch.tanh(depth_scores / self.qk_softcap)
            
            # No causal mask needed for depth — all previous layers are always available
            depth_attn = F.softmax(depth_scores, dim=-1)
            O_depth = torch.matmul(depth_attn, V_depth)  # (B, H, S, D_h)
            
            # Depth gate: how much to blend in depth attention
            gate = self.depth_gate(x).permute(0, 2, 1).unsqueeze(-1)  # (B, H, S, 1)
            O = (1 - gate) * O_seq + gate * O_depth
        else:
            # Layer 0: no depth history, pure sequence attention
            O = O_seq
        
        # Reshape and project output
        O = O.transpose(1, 2).contiguous().view(B, S, D)
        return self.o_proj(O)


class MoDATransformerLayer(nn.Module):
    """
    Transformer layer with MoDA attention.
    
    Drop-in replacement for TransformerLayer, but forward() now accepts
    and returns depth_cache for the depth attention mechanism.
    """
    
    def __init__(self, config: KernelConfig, layer_idx: int = 0,
                 num_depth_kv_heads: int = 4):
        super().__init__()
        self.layer_idx = layer_idx
        self.attention = MoDAAttention(config, layer_idx, num_depth_kv_heads)
        self.ffn = SwiGLU(config)
        self.attn_norm = RMSNorm(config.hidden_dim)
        self.ffn_norm = RMSNorm(config.hidden_dim)
    
    def forward(
        self,
        x: torch.Tensor,
        mask: torch.Tensor | None = None,
        depth_cache: torch.Tensor | None = None,
    ) -> torch.Tensor:
        """
        Args:
            x: (batch, seq_len, hidden_dim)
            mask: causal mask
            depth_cache: stacked previous layer outputs (batch, prev_layers * seq_len, hidden_dim)
        Returns:
            x: (batch, seq_len, hidden_dim) — output of this layer
        """
        x = x + self.attention(self.attn_norm(x), mask=mask, depth_cache=depth_cache)
        x = x + self.ffn(self.ffn_norm(x))
        return x


def upgrade_kernel_to_moda(kernel, num_depth_kv_heads: int = 4, 
                            init_from_sequence: bool = True):
    """
    Surgical upgrade: replace HybridAttention layers with MoDA layers.
    
    Preserves ALL existing weights (Q, K, V, O projections, FFN, norms).
    Only adds new depth_kv projections and depth_gate.
    
    Args:
        kernel: GladiusKernel instance with existing trained weights
        num_depth_kv_heads: number of KV heads for depth attention (GQA)
        init_from_sequence: if True, initialize depth KV from sequence KV weights
    
    Returns:
        Modified kernel with MoDA layers (in-place)
    """
    config = kernel.config
    device = next(kernel.parameters()).device
    dtype = next(kernel.parameters()).dtype
    
    new_layers = nn.ModuleList()
    
    for i, old_layer in enumerate(kernel.layers):
        # Create new MoDA layer
        moda_layer = MoDATransformerLayer(config, layer_idx=i, 
                                           num_depth_kv_heads=num_depth_kv_heads)
        
        # === Transfer existing weights ===
        # Sequence Q, K, V, O projections
        moda_layer.attention.q_proj.weight.data.copy_(old_layer.attention.q_proj.weight.data)
        moda_layer.attention.k_proj.weight.data.copy_(old_layer.attention.k_proj.weight.data)
        moda_layer.attention.v_proj.weight.data.copy_(old_layer.attention.v_proj.weight.data)
        moda_layer.attention.o_proj.weight.data.copy_(old_layer.attention.o_proj.weight.data)
        
        # SLA2 alpha router
        moda_layer.attention.alpha_router[0].weight.data.copy_(old_layer.attention.alpha_router[0].weight.data)
        moda_layer.attention.alpha_router[0].bias.data.copy_(old_layer.attention.alpha_router[0].bias.data)
        
        # RoPE buffers
        moda_layer.attention.rope.inv_freq.data.copy_(old_layer.attention.rope.inv_freq.data)
        moda_layer.attention.rope.cos_cached.data.copy_(old_layer.attention.rope.cos_cached.data)
        moda_layer.attention.rope.sin_cached.data.copy_(old_layer.attention.rope.sin_cached.data)
        
        # FFN (SwiGLU)
        moda_layer.ffn.gate_proj.weight.data.copy_(old_layer.ffn.gate_proj.weight.data)
        moda_layer.ffn.up_proj.weight.data.copy_(old_layer.ffn.up_proj.weight.data)
        moda_layer.ffn.down_proj.weight.data.copy_(old_layer.ffn.down_proj.weight.data)
        
        # Norms
        moda_layer.attn_norm.weight.data.copy_(old_layer.attn_norm.weight.data)
        moda_layer.ffn_norm.weight.data.copy_(old_layer.ffn_norm.weight.data)
        
        # === Initialize depth KV from sequence KV (warm start) ===
        if init_from_sequence:
            # Take a subset of the sequence K, V weights for depth initialization
            # Map from full hidden_dim projection to GQA-sized projection
            seq_k_weight = old_layer.attention.k_proj.weight.data  # (hidden_dim, hidden_dim)
            seq_v_weight = old_layer.attention.v_proj.weight.data
            
            # Select every q_per_kv-th head's K,V weights for the depth KV heads
            head_dim = config.head_dim
            q_per_kv = config.num_heads // num_depth_kv_heads
            kv_dim = num_depth_kv_heads * head_dim
            
            # Extract weights for the GQA KV heads (take every q_per_kv-th head)
            depth_k_weight = torch.zeros(kv_dim, config.hidden_dim, device=device, dtype=dtype)
            depth_v_weight = torch.zeros(kv_dim, config.hidden_dim, device=device, dtype=dtype)
            
            for g in range(num_depth_kv_heads):
                src_head = g * q_per_kv  # Take the first Q head from each group
                src_start = src_head * head_dim
                src_end = src_start + head_dim
                dst_start = g * head_dim
                dst_end = dst_start + head_dim
                
                depth_k_weight[dst_start:dst_end] = seq_k_weight[src_start:src_end]
                depth_v_weight[dst_start:dst_end] = seq_v_weight[src_start:src_end]
            
            # Scale down to let depth path start gentle
            moda_layer.attention.depth_kv.k_proj.weight.data.copy_(depth_k_weight * 0.1)
            moda_layer.attention.depth_kv.v_proj.weight.data.copy_(depth_v_weight * 0.1)
        
        new_layers.append(moda_layer)
    
    # Replace layers in kernel
    kernel.layers = new_layers.to(device)
    
    # We need to patch the forward to pass depth_cache through layers
    # Store reference to original forward
    kernel._moda_enabled = True
    kernel._num_depth_kv_heads = num_depth_kv_heads
    
    # Report new param count
    total = sum(p.numel() for p in kernel.parameters())
    trainable = sum(p.numel() for p in kernel.parameters() if p.requires_grad)
    depth_params = sum(
        sum(p.numel() for p in layer.attention.depth_kv.parameters()) +
        sum(p.numel() for p in layer.attention.depth_gate.parameters())
        for layer in kernel.layers
    )
    
    print(f"\n=== MoDA Upgrade Complete ===")
    print(f"  Total params: {total:,} (+{depth_params:,} depth params)")
    print(f"  Trainable: {trainable:,}")
    print(f"  Depth overhead: {depth_params/total*100:.2f}%")
    print(f"  Depth KV heads: {num_depth_kv_heads} (GQA ratio: {config.num_heads // num_depth_kv_heads}:1)")
    print(f"  Memory: {total * 2 / 1024 / 1024:.1f} MB (bfloat16)")
    
    return kernel


class MoDAKernelMixin:
    """
    Mixin to patch GladiusKernel.forward() for depth cache propagation.
    
    Usage:
        kernel = GladiusKernel.load_checkpoint(path)
        kernel = upgrade_kernel_to_moda(kernel)
        patch_kernel_forward_for_moda(kernel)
    """
    pass


def patch_kernel_forward_for_moda(kernel):
    """
    Monkey-patch the kernel's forward to thread depth cache through layers.
    
    The original forward just does:
        for layer in self.layers:
            x = layer(x, mask=mask)
    
    MoDA needs:
        depth_cache = []
        for layer in self.layers:
            x = layer(x, mask=mask, depth_cache=stack(depth_cache))
            depth_cache.append(x)
    """
    import types
    
    _original_forward = kernel.forward
    
    def moda_forward(self, input_ids=None, timestamp=None, images=None, audio=None):
        """MoDA-patched forward: threads depth cache through transformer layers."""
        # Replicate pre-transformer logic from original forward
        text_embeds = None
        if input_ids is not None:
            B, S = input_ids.shape
            text_embeds = self.embeddings.embed(input_ids)
        
        modality_mask = None
        if self.has_senses and (images is not None or audio is not None):
            x, modality_mask = self.senses(text_embeds=text_embeds, images=images, audio=audio)
            B, S = x.shape[0], x.shape[1]
        elif text_embeds is not None:
            x = text_embeds
            B, S = x.shape[0], x.shape[1]
        else:
            raise ValueError("Must provide input_ids, images, or audio")
        
        # Memory read
        x = self.memory.read(x)
        
        # Temporal encoding
        time_embed = None
        if timestamp is not None:
            if isinstance(timestamp, (int, float)):
                timestamp = torch.tensor([timestamp] * B, dtype=torch.float32, device=x.device)
            time_embed = self.time_engine(timestamp)
            x = x + time_embed.unsqueeze(1)
        
        # === MoDA Transformer layers with depth cache ===
        if S <= self.config.max_seq_len:
            mask = self.causal_mask[:, :, :S, :S]
        else:
            mask = torch.tril(torch.ones(1, 1, S, S, device=x.device))
        
        depth_states = []  # Collect hidden states for depth attention
        for layer in self.layers:
            # Build depth cache from all previous layers
            if len(depth_states) > 0:
                # Stack previous layer summaries: (B, num_prev_layers, D)
                # Each layer contributes ONE summary vector per position, not S vectors
                # This keeps depth cache at O(L) not O(L*S) — critical for VRAM
                depth_cache = torch.stack(depth_states, dim=1)  # (B, num_prev, D)
            else:
                depth_cache = None
            
            x = layer(x, mask=mask, depth_cache=depth_cache)
            # Store mean-pooled representation of this layer (detached)
            depth_states.append(x.mean(dim=1).detach())  # (B, D)
            # NOTE: detach() means depth cache doesn't backprop through previous layers.
            # This is intentional — depth attention learns to READ from previous layers,
            # not to CHANGE them. Keeps memory O(L*S*D) instead of O(L^2*S*D).
        
        # Final norm
        x = self.final_norm(x)
        
        # Tool check
        tool_result = self.tool_cortex.check_activation(x)
        if tool_result is not None:
            x = x + tool_result
        
        # Modulate
        logits, silence, pixel_output = self.modulator(x, self.embeddings.output_head, temporal_embedding=time_embed)
        
        # Memory write
        importance = self.memory.write(x)
        
        # Cognition heartbeat
        mode, cognitive_state, mode_probs = self.cognition.heartbeat(x)
        
        if self.cognition.should_consolidate():
            self.memory.consolidate()
        
        self.time_engine.record_event()
        
        return {
            'logits': logits,
            'silence': silence,
            'pixel_output': pixel_output,
            'mode': mode,
            'importance': importance,
            'modality_mask': modality_mask,
            'cognitive_state': cognitive_state,
            'mode_probs': mode_probs,
        }
    
    kernel.forward = types.MethodType(moda_forward, kernel)
    print("  Forward pass patched for MoDA depth cache propagation ✅")
    return kernel