from __future__ import annotations

"""MDGTv2 — DINOv2/ViT + TRAM + GNN full pipeline.

End-to-end fingerprint embedding without external minutiae extraction::

    Image (B, 1, 224, 224)
      ├─ DINOv2 backbone → P patch tokens + CLS token + 12 attn maps
      │                           │                  │
      │              TRAM selection → K tokens    cls_head → cls_logits
      │                           │
      │              Input projection → gnn_dim
      │                           │
      │              k-NN graph + GridRelationalPE (5→64-dim)
      │                           │
      │              L × GATLayerRPE (3-way RPE modulation)
      │                           │
      │              Multi-head attentive pooling
      │                           │
      └──────────── Projection → 256-D → L2-norm → embedding

Backbone options:
    ``"dinov2_vits14"``  — pretrained DINOv2 ViT-S/14 (384-D, default).
    ``"dinov2_vitb14"``  — pretrained DINOv2 ViT-B/14 (768-D).
    ``"tiny"`` / ``"small"`` / ``"base"`` — custom ViT from scratch.

Returns both ``embedding`` (for ArcFace + Triplet) and ``cls_logits``
(for auxiliary CLS classification loss).
"""

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

from .dinov2_backbone import DINOv2Backbone
from .vit import ViT
from .tram import TRAMSelector
from .gat_rpe import GATLayerRPE
from .grid_rpe import GridRelationalPE
from .pooling import MultiHeadPool, AttentivePool
from .dynamic_graph import knn


def _knn_to_mask(idx: torch.Tensor, K: int) -> torch.Tensor:
    """Convert k-NN indices ``(B, K, k)`` to adjacency mask ``(B, K, K)``."""
    B = idx.shape[0]
    k = idx.shape[2]
    mask = torch.zeros(B, K, K, dtype=torch.bool, device=idx.device)
    batch = torch.arange(B, device=idx.device)[:, None, None].expand_as(idx)
    nodes = torch.arange(K, device=idx.device)[None, :, None].expand_as(idx)
    mask[batch, nodes, idx] = True
    return mask


class MDGTv2(nn.Module):
    """MDGT v2: DINOv2/ViT + TRAM + GNN pipeline.

    Parameters
    ----------
    vit_variant : str
        Backbone selector.  DINOv2 pretrained names (``"dinov2_vits14"``,
        ``"dinov2_vitb14"``) load from torch.hub.  Custom ViT names
        (``"tiny"``, ``"small"``, ``"base"``) train from scratch.
    num_classes : int
        Number of training identities (for auxiliary CLS head).
    tram_k : int
        Number of tokens selected by TRAM.
    gnn_layers : int
        Number of GATLayerRPE layers.
    gnn_dim : int
        GNN hidden dimension. If 0, defaults to 256.
    gnn_heads : int
        Number of attention heads in GNN.
    gnn_k : int
        k-NN neighbor count for graph construction.
    pool_heads : int
        Number of seed vectors for multi-head attentive pooling.
    output_dim : int
        Final embedding dimension (L2-normalised).
    image_size : int
        Input image resolution (square).
    rpe_dim : int
        GridRelationalPE output dimension (fed into GNN 3-way RPE).
    drop_rate : float
        Dropout rate for embeddings and MLP.
    drop_path_rate : float
        Stochastic depth rate (custom ViT only; DINOv2 ignores this).
    patch_size : int
        ViT patch size (custom ViT only; DINOv2 uses its own).
    """

    DINOV2_MODELS = DINOv2Backbone.KNOWN_MODELS

    def __init__(
        self,
        vit_variant: str = "dinov2_vits14",
        num_classes: int = 100,
        tram_k: int = 30,
        gnn_layers: int = 4,
        gnn_dim: int = 0,
        gnn_heads: int = 4,
        gnn_k: int = 9,
        pool_heads: int = 4,
        output_dim: int = 256,
        image_size: int = 224,
        rpe_dim: int = 64,
        drop_rate: float = 0.0,
        drop_path_rate: float = 0.1,
        patch_size: int = 0,
    ):
        super().__init__()

        # ---- Backbone ----
        self._use_dinov2 = vit_variant in self.DINOV2_MODELS

        if self._use_dinov2:
            self.vit = DINOv2Backbone(
                model_name=vit_variant,
                image_size=image_size,
            )
        else:
            if patch_size <= 0:
                patch_size = 14 if vit_variant == "dinov2_vitb14_reg" else 16
            self.vit = ViT(
                variant=vit_variant,
                img_size=image_size,
                patch_size=patch_size,
                in_chans=1,
                drop_rate=drop_rate,
                drop_path_rate=drop_path_rate,
            )

        vit_dim = self.vit.embed_dim

        # GNN dim defaults to 256 for most variants
        if gnn_dim <= 0:
            gnn_dim = vit_dim if vit_variant == "tiny" else 256
        self._gnn_dim = gnn_dim

        # ---- TRAM (training-free, incoming sum) ----
        self.tram = TRAMSelector(
            num_tokens=tram_k,
            method="tram",
        )

        # ---- Input projection: vit_dim -> gnn_dim ----
        self.input_proj = nn.Sequential(
            nn.Linear(vit_dim, gnn_dim),
            nn.LayerNorm(gnn_dim),
            nn.GELU(),
        )

        # ---- Grid RPE: 5-dim raw features -> rpe_dim embeddings ----
        self.grid_rpe = GridRelationalPE(
            input_dim=5,
            hidden_dim=rpe_dim,
            output_dim=rpe_dim,
        )
        self._rpe_dim = rpe_dim

        # ---- GNN layers (3-way RPE modulation) ----
        self._gnn_k = gnn_k
        self.gnn_layers = nn.ModuleList([
            GATLayerRPE(
                dim=gnn_dim,
                num_heads=gnn_heads,
                rpe_dim=rpe_dim,
                dropout=drop_rate,
            )
            for _ in range(gnn_layers)
        ])

        # ---- Pooling ----
        self.pool = MultiHeadPool(
            gnn_dim, num_heads=pool_heads, hidden_dim=gnn_dim,
        )

        # ---- CLS token projection (skip connection from backbone CLS) ----
        self.cls_proj = nn.Sequential(
            nn.Linear(vit_dim, gnn_dim),
            nn.LayerNorm(gnn_dim),
            nn.GELU(),
        )

        # ---- Projection head -> output_dim ----
        # Takes concatenation of GNN-pooled (gnn_dim) + CLS-proj (gnn_dim)
        self.head = nn.Sequential(
            nn.Linear(gnn_dim * 2, gnn_dim),
            nn.BatchNorm1d(gnn_dim),
            nn.GELU(),
            nn.Linear(gnn_dim, output_dim),
            nn.BatchNorm1d(output_dim),
        )

        # ---- Auxiliary CLS classification head ----
        # Operates on pre-normalization embeddings so CE gradients flow
        # without L2-norm bottleneck.  Trains the full GNN pipeline.
        self.cls_head = nn.Linear(output_dim, num_classes)

        # Training-only bootstrap: bypass TRAM/GNN until ViT attention stabilises.
        self._warmup_mode = False

        # ---- Init non-ViT modules ----
        for module in [self.input_proj, self.cls_proj, self.gnn_layers,
                       self.pool, self.head, self.grid_rpe]:
            module.apply(self._init_weights)
        nn.init.trunc_normal_(self.cls_head.weight, std=0.02)
        nn.init.zeros_(self.cls_head.bias)

    # ------------------------------------------------------------------
    @staticmethod
    def _init_weights(m: nn.Module):
        if isinstance(m, nn.Linear):
            nn.init.xavier_uniform_(m.weight)
            if m.bias is not None:
                nn.init.zeros_(m.bias)

    # ------------------------------------------------------------------
    def forward(
        self, images: torch.Tensor
    ) -> tuple[torch.Tensor, torch.Tensor]:
        """
        Args:
            images: ``(B, 1, 224, 224)`` grayscale fingerprint.

        Returns:
            emb:        ``(B, output_dim)`` L2-normalised embedding.
            cls_logits: ``(B, num_classes)`` CLS-token classification logits.
        """
        # 1. Backbone -> patch tokens + CLS token + attention maps
        patch_tokens, cls_token, attn_maps = self.vit(images)

        # CLS skip connection: project CLS token -> gnn_dim
        cls_emb = self.cls_proj(cls_token)              # (B, gnn_dim)

        # Phase-0 bootstrap: let ViT/CLS learn before sparse token selection.
        if self._warmup_mode:
            x = self.input_proj(patch_tokens)          # (B, P, gnn_dim)
            gnn_emb = self.pool(x, mask=None)
            pre_norm = self.head(torch.cat([gnn_emb, cls_emb], dim=-1))
            cls_logits = self.cls_head(pre_norm)
            emb = F.normalize(pre_norm, p=2, dim=-1)
            return emb, cls_logits

        # 2. TRAM -> K sparse tokens
        num_prefix = getattr(self.vit, "num_prefix_tokens", 1)
        selected_tokens, selected_indices, _ = self.tram(
            patch_tokens, attn_maps, num_prefix_tokens=num_prefix,
        )

        # 3. Input projection
        x = self.input_proj(selected_tokens)          # (B, K, gnn_dim)
        K = x.shape[1]

        # 4. Graph construction: k-NN + RPE
        graph_k = min(self._gnn_k, K)
        idx = knn(x, graph_k, metric="euclidean")     # (B, K, k)
        edge_mask = _knn_to_mask(idx, K)               # (B, K, K)

        # Grid RPE: indices -> (B, K, K, rpe_dim)
        rpe = self.grid_rpe(selected_indices, self.vit.grid_size)

        # 5. GNN message passing
        for layer in self.gnn_layers:
            x = layer(x, rpe, edge_mask)

        # 6. Pool + CLS skip -> embedding
        gnn_emb = self.pool(x, mask=None)              # (B, gnn_dim)
        pre_norm = self.head(torch.cat([gnn_emb, cls_emb], dim=-1))  # (B, output_dim)

        # 7. CLS classification on pre-norm features (stable CE gradient flow)
        cls_logits = self.cls_head(pre_norm)            # (B, num_classes)
        emb = F.normalize(pre_norm, p=2, dim=-1)

        return emb, cls_logits

    # ------------------------------------------------------------------
    def set_warmup_mode(self, enabled: bool):
        self._warmup_mode = bool(enabled)

    # ------------------------------------------------------------------
    def freeze_vit(self):
        """Freeze only the backbone (ViT or DINOv2).

        The auxiliary ``cls_head`` stays trainable so phase-2 runs can still
        use a learnable softmax head on top of frozen CLS features.
        """
        if self._use_dinov2:
            self.vit.freeze()
        else:
            for p in self.vit.parameters():
                p.requires_grad = False

    def unfreeze_vit(self):
        """Unfreeze backbone."""
        if self._use_dinov2:
            self.vit.unfreeze()
        else:
            for p in self.vit.parameters():
                p.requires_grad = True