"""
GLADIUS v2.0 — Warm Memory: Share + EBLoRA + Locas Synthesis

The dragon. Three papers forged into one mechanism:
  - Locas (2602.05085): GLU-FFN structure, principled initialization, merge capability
  - Share (2602.06043): Evolving shared subspace, incremental integration
  - EBLoRA (2602.00722): Spectral balancing, Stiefel manifold constraint

This replaces the stub WarmMemory in memory.py.
"""

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


class LocasAdapter(nn.Module):
    """
    Locas-style GLU-FFN adapter.

    Same structure as base model's SwiGLU layers, but low-rank.
    Can be merged INTO base model weights (permanentize).
    Initialized from base model parameters for fast convergence.
    """

    def __init__(self, hidden_dim: int, rank: int):
        super().__init__()
        self.hidden_dim = hidden_dim
        self.rank = rank

        # Low-rank GLU-FFN: hidden_dim → rank → hidden_dim
        self.gate_proj = nn.Linear(hidden_dim, rank, bias=False)
        self.up_proj = nn.Linear(hidden_dim, rank, bias=False)
        self.down_proj = nn.Linear(rank, hidden_dim, bias=False)

        # Scale (starts small, grows as adapter learns)
        self.scale = nn.Parameter(torch.tensor(0.01))

        self._init_weights()

    def _init_weights(self):
        # Small random init (Locas principled init happens externally
        # when base model layers are available)
        nn.init.normal_(self.gate_proj.weight, std=0.01)
        nn.init.normal_(self.up_proj.weight, std=0.01)
        nn.init.zeros_(self.down_proj.weight)  # Zero init → starts as identity

    def init_from_base(self, base_gate: nn.Linear, base_up: nn.Linear):
        """
        Locas principled initialization: extract top-k singular vectors
        from base model's FFN projections.
        """
        with torch.no_grad():
            # Gate: top-rank directions of base gate projection
            try:
                U, S, V = torch.linalg.svd(base_gate.weight, full_matrices=False)
                self.gate_proj.weight.data = V[:self.rank, :]
            except torch._C._LinAlgError:
                pass  # Keep random init

            # Up: top-rank directions of base up projection
            try:
                U, S, V = torch.linalg.svd(base_up.weight, full_matrices=False)
                self.up_proj.weight.data = V[:self.rank, :]
            except torch._C._LinAlgError:
                pass  # Keep random init

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        """GLU-FFN forward. Returns residual to add to hidden state."""
        gate = F.silu(self.gate_proj(x))
        up = self.up_proj(x)
        return self.down_proj(gate * up) * self.scale

    def get_weight_matrix(self) -> torch.Tensor:
        """
        Reconstruct the effective weight matrix for spectral analysis.
        Returns the linearized adapter: W_eff ≈ down @ (gate ⊙ up) [simplified]
        For spectral analysis, we use the dominant path: down @ up
        """
        return self.down_proj.weight @ self.up_proj.weight  # (hidden, hidden)


class SpectralBalancer:
    """
    EBLoRA-inspired spectral balancing.

    Monitors the condition number of the adapter and rebalances
    when singular values become too skewed (which causes forgetting).
    """

    def __init__(self, condition_threshold: float = 10.0):
        self.condition_threshold = condition_threshold
        self.history = []

    def condition_number(self, adapter: LocasAdapter) -> float:
        """Compute σ_max / σ_min of the effective weight matrix."""
        with torch.no_grad():
            W = adapter.get_weight_matrix()
            try:
                S = torch.linalg.svdvals(W)
            except torch._C._LinAlgError:
                return 1.0  # Can't compute — assume healthy
            S_nonzero = S[S > 1e-8]
            if len(S_nonzero) < 2:
                return 1.0
            return (S_nonzero[0] / S_nonzero[-1]).item()

    def needs_rebalance(self, adapter: LocasAdapter) -> bool:
        cn = self.condition_number(adapter)
        self.history.append(cn)
        return cn > self.condition_threshold

    def rebalance(self, adapter: LocasAdapter):
        """
        Force spectral balance by normalizing singular values.

        Decouples magnitude from direction (EBLoRA core principle):
        1. SVD the effective weight
        2. Soft-clamp singular values toward the mean
        3. Reconstruct
        """
        with torch.no_grad():
            # Work on down @ up (the dominant linear path)
            W = adapter.down_proj.weight @ adapter.up_proj.weight  # (H, H)

            # Diagonal epsilon — regularize ill-conditioned matrices
            # Prevents SVD convergence failure from degenerate/repeated singular values
            eps = 1e-6 * torch.eye(W.shape[0], W.shape[1], device=W.device, dtype=W.dtype)
            W = W + eps

            try:
                U, S, Vh = torch.linalg.svd(W, full_matrices=False)
            except torch._C._LinAlgError:
                # Matrix still too sick — skip this rebalance cycle
                return

            # Filter near-zero singular values
            mask = S > 1e-6
            if mask.sum() < 2:
                return  # Nothing meaningful to balance

            S_active = S[mask]

            # Soft-clamp: move singular values toward geometric mean
            log_S = torch.log(S_active)
            log_mean = log_S.mean()
            # Shrink toward mean by 50%
            balanced_log_S = log_mean + 0.5 * (log_S - log_mean)
            S_balanced = S.clone()
            S_balanced[mask] = torch.exp(balanced_log_S)

            # Reconstruct balanced weight
            rank = adapter.rank
            # Safe reconstruction: use min of available dims
            k = min(rank, S_balanced.shape[0], U.shape[1], Vh.shape[0])
            sqrt_S = torch.sqrt(S_balanced[:k].clamp(min=1e-8))

            new_down_full = U[:, :k] @ torch.diag(sqrt_S)    # (H, k)
            new_up_full = torch.diag(sqrt_S) @ Vh[:k, :]     # (k, H)

            # Write back (truncate to adapter rank)
            r = min(rank, k)
            adapter.down_proj.weight.data[:, :r] = new_down_full[:, :r]
            adapter.up_proj.weight.data[:r, :] = new_up_full[:r, :]


class SubspaceTracker:
    """
    Share-inspired evolving subspace tracker.

    Maintains a compact representation of what the warm memory "knows."
    New knowledge is checked against this subspace:
    - If it projects well → already known → small update
    - If large residual → novel knowledge → evolve subspace
    """

    def __init__(self, hidden_dim: int, rank: int, novelty_threshold: float = 0.1):
        self.hidden_dim = hidden_dim
        self.rank = rank
        self.novelty_threshold = novelty_threshold

        # The subspace basis (orthonormal)
        self.basis = torch.zeros(rank, hidden_dim)
        # Importance of each basis direction
        self.importance = torch.zeros(rank)
        self.initialized = False

    def initialize_from_adapter(self, adapter: LocasAdapter):
        """Extract subspace from current adapter state."""
        with torch.no_grad():
            W = adapter.get_weight_matrix()
            U, S, Vh = torch.linalg.svd(W, full_matrices=False)
            k = min(self.rank, len(S))
            self.basis[:k] = Vh[:k]
            self.importance[:k] = S[:k]
            self.initialized = True

    def compute_novelty(self, gradient: torch.Tensor) -> tuple[float, torch.Tensor]:
        """
        Measure how much of the gradient is NOT captured by current subspace.
        """
        if not self.initialized:
            return float('inf'), gradient

        # Flatten gradient and basis to same dimensionality
        g_flat = gradient.flatten()
        basis_flat = self.basis.reshape(self.rank, -1).to(g_flat.device)

        # Ensure compatible dimensions: truncate/pad basis if needed
        g_dim = g_flat.shape[0]
        b_dim = basis_flat.shape[1]

        if g_dim != b_dim:
            # Project gradient down to basis dimensionality
            g_proj = g_flat[:b_dim] if g_dim > b_dim else F.pad(g_flat, (0, b_dim - g_dim))
        else:
            g_proj = g_flat

        projection = basis_flat @ g_proj  # (rank,)
        reconstructed = projection @ basis_flat  # (b_dim,)
        residual = g_proj - reconstructed
        novelty = residual.norm().item()

        return novelty, residual.reshape(self.hidden_dim)

    def evolve(self, new_direction: torch.Tensor, importance: float):
        """
        Integrate a new direction into the subspace.
        Replaces the least important existing direction.
        """
        # Normalize
        new_dir_flat = new_direction.flatten()
        new_dir_flat = new_dir_flat / (new_dir_flat.norm() + 1e-8)

        # Replace least important direction
        least_idx = self.importance.argmin().item()
        self.basis[least_idx] = new_dir_flat[:self.hidden_dim]  # Truncate if needed
        self.importance[least_idx] = importance

        # Decay all importance values slightly (recency bias)
        self.importance *= 0.99


class RealWarmMemory(nn.Module):
    """
    Full warm memory implementation: Locas + Share + EBLoRA.

    Architecture: Locas GLU-FFN adapter (per transformer layer)
    Evolution: Share subspace tracking for novelty detection
    Stability: EBLoRA spectral balancing

    This is the dragon, tamed.
    """

    def __init__(self, config, num_layers: int | None = None):
        super().__init__()
        from .config import KernelConfig
        self.config = config
        self.hidden_dim = config.hidden_dim
        self.rank = config.warm_rank
        num_layers = num_layers or config.num_layers

        # Per-layer Locas adapters
        self.adapters = nn.ModuleList([
            LocasAdapter(config.hidden_dim, config.warm_rank)
            for _ in range(num_layers)
        ])

        # Shared spectral balancer
        self.balancer = SpectralBalancer(config.warm_condition_threshold)

        # Per-layer subspace trackers (not nn.Module — just tracking)
        self.trackers = [
            SubspaceTracker(config.hidden_dim, config.warm_rank, config.warm_novelty_threshold)
            for _ in range(num_layers)
        ]

        # Update counter
        self.register_buffer('update_count', torch.tensor(0, dtype=torch.long))

    def forward(self, x: torch.Tensor, layer_idx: int = 0) -> torch.Tensor:
        """Apply warm memory adapter for a specific layer."""
        if layer_idx < len(self.adapters):
            return x + self.adapters[layer_idx](x)
        return x

    def forward_all(self, x: torch.Tensor) -> torch.Tensor:
        """Apply all adapters sequentially (for simple use)."""
        for adapter in self.adapters:
            x = x + adapter(x)
        return x

    @torch.no_grad()
    def consolidate(self, hot_keys: torch.Tensor, hot_values: torch.Tensor,
                    importance_scores: torch.Tensor):
        """
        Real consolidation: hot memory → warm adapters.

        1. Filter by importance
        2. Check novelty against subspace
        3. Update adapters with spectral balancing
        """
        self.update_count += 1

        # Average hot memory signal
        signal = hot_values.mean(dim=0)
        if signal.norm() < 1e-6:
            return  # Nothing meaningful in hot memory

        for i, (adapter, tracker) in enumerate(zip(self.adapters, self.trackers)):
            # Initialize tracker if needed
            if not tracker.initialized:
                tracker.initialize_from_adapter(adapter)

            # Compute pseudo-gradient from hot memory content
            W_grad = torch.outer(signal, signal)  # Rank-1 outer product

            # Check novelty
            novelty, residual = tracker.compute_novelty(W_grad)

            if novelty > tracker.novelty_threshold:
                # Novel knowledge → evolve subspace
                tracker.evolve(residual, novelty)

                # Small update to adapter (learning rate controlled)
                lr = 0.001
                r = min(adapter.rank, residual.shape[0])
                h = min(self.hidden_dim, adapter.up_proj.weight.shape[1])
                adapter.up_proj.weight.data[:r, :h] += lr * residual[:r].unsqueeze(1).expand(r, h) * 0.01

                # UPDATE DOWN_PROJ — the missing link!
                # Without this, warm memory tracks knowledge but can't express it.
                # down_proj maps rank-space → hidden-space (the output pathway)
                # CRITICAL: once down_proj is non-zero, backprop gradients flow through
                # the adapter during training, enabling the optimizer to refine warm memory.
                signal_norm = signal / (signal.norm() + 1e-8)
                r_down = min(adapter.rank, adapter.down_proj.weight.shape[1])
                h_down = min(self.hidden_dim, adapter.down_proj.weight.shape[0])
                down_update = signal_norm[:h_down].unsqueeze(1) * residual[:r_down].unsqueeze(0)
                # Use 10x the up_proj rate to bootstrap the output pathway
                adapter.down_proj.weight.data[:h_down, :r_down] += lr * down_update * 0.1

                # Ramp scale toward 0.3 (from init 0.01) so adapter output is meaningful
                target_scale = 0.3
                adapter.scale.data += lr * 0.1 * (target_scale - adapter.scale.data)

        # Periodic spectral rebalancing (ALWAYS check, not just on consolidation)
            if self.update_count % max(1, self.config.warm_balance_frequency // 10) == 0:
                cn = self.balancer.condition_number(adapter)
                if cn > self.config.warm_condition_threshold:
                    self.balancer.rebalance(adapter)

    def condition_number(self) -> float:
        """Average condition number across all adapter layers."""
        cns = [self.balancer.condition_number(a) for a in self.adapters]
        return sum(cns) / len(cns)

    def checkpoint(self, path: str):
        """Save warm memory state."""
        state = {
            'adapters': self.state_dict(),
            'update_count': self.update_count.item(),
            'subspace_states': [
                {'basis': t.basis.clone(), 'importance': t.importance.clone()}
                for t in self.trackers
            ],
            'spectral_history': self.balancer.history[-100:],  # Last 100
        }
        torch.save(state, path)

    def restore(self, path: str):
        """Load warm memory state."""
        state = torch.load(path, weights_only=False)
        self.load_state_dict(state['adapters'], strict=False)
        self.update_count.fill_(state['update_count'])
        for tracker, ss in zip(self.trackers, state.get('subspace_states', [])):
            tracker.basis = ss['basis']
            tracker.importance = ss['importance']
            tracker.initialized = True
        self.balancer.history = state.get('spectral_history', [])