"""Two-block feature Predictor for Teacher-layer pair experiments."""

from __future__ import annotations

import copy

import torch
from torch import nn
from torch.utils.checkpoint import checkpoint

from predictor_training.single_block import TripleFeatureFusion
from wan.modules.causal_model import CausalWanAttentionBlock


class TwoBlockPredictor(nn.Module):
    """Fuse three inputs, run two causal Wan blocks, and predict an anchor residual."""

    def __init__(
        self,
        teacher_blocks: list[CausalWanAttentionBlock],
        dim: int = 1536,
        gradient_checkpointing: bool = True,
    ) -> None:
        super().__init__()
        if len(teacher_blocks) != 2:
            raise ValueError(f"Expected exactly two blocks, got {len(teacher_blocks)}")
        self.fusion = TripleFeatureFusion(dim)
        self.blocks = nn.ModuleList(
            [copy.deepcopy(block).float() for block in teacher_blocks]
        )
        self.residual_out = nn.Linear(dim, dim)
        nn.init.zeros_(self.residual_out.weight)
        nn.init.zeros_(self.residual_out.bias)
        self.gradient_checkpointing = gradient_checkpointing

    def fusion_parameters(self) -> list[nn.Parameter]:
        return list(self.fusion.parameters()) + list(self.residual_out.parameters())

    def block_parameters(self) -> list[nn.Parameter]:
        return list(self.blocks.parameters())

    def set_blocks_trainable(self, enabled: bool) -> None:
        self.blocks.requires_grad_(enabled)

    @staticmethod
    def _block_closure(
        *,
        block: CausalWanAttentionBlock,
        sequence: int,
        timestep_modulation: torch.Tensor,
        grid_sizes: torch.Tensor,
        freqs: torch.Tensor,
        history_k: torch.Tensor,
        history_v: torch.Tensor,
        cross_k: torch.Tensor,
        cross_v: torch.Tensor,
        current_start: int,
    ):
        batch = history_k.shape[0]
        dim = block.dim
        seq_lens = torch.full(
            (batch,), sequence, dtype=torch.long, device="cpu"
        )

        def run(value: torch.Tensor) -> torch.Tensor:
            heads = history_k.shape[2]
            head_dim = history_k.shape[3]
            current_k = history_k.new_empty(batch, sequence, heads, head_dim)
            current_v = history_v.new_empty(batch, sequence, heads, head_dim)
            kv_cache = {
                "k": torch.cat([history_k, current_k], dim=1),
                "v": torch.cat([history_v, current_v], dim=1),
                "global_end_index": torch.tensor(
                    [current_start], device=value.device, dtype=torch.long
                ),
                "local_end_index": torch.tensor(
                    [current_start], device=value.device, dtype=torch.long
                ),
            }
            crossattn_cache = {
                "k": cross_k,
                "v": cross_v,
                "is_init": True,
            }
            context = value.new_zeros(batch, 1, dim)
            return block(
                value,
                e=timestep_modulation,
                seq_lens=seq_lens,
                grid_sizes=grid_sizes,
                freqs=freqs,
                context=context,
                context_lens=None,
                block_mask=None,
                kv_cache=kv_cache,
                crossattn_cache=crossattn_cache,
                current_start=current_start,
                cache_start=None,
            )

        return run

    def forward(
        self,
        *,
        current_tokens: torch.Tensor,
        anchor_hidden: torch.Tensor,
        previous_hidden: torch.Tensor,
        timestep_modulation: torch.Tensor,
        grid_sizes: torch.Tensor,
        freqs: torch.Tensor,
        history_ks: list[torch.Tensor],
        history_vs: list[torch.Tensor],
        cross_ks: list[torch.Tensor],
        cross_vs: list[torch.Tensor],
        current_start: int,
    ) -> torch.Tensor:
        cache_lists = (history_ks, history_vs, cross_ks, cross_vs)
        if any(len(values) != 2 for values in cache_lists):
            raise ValueError("Two cache sets are required")
        transformed = self.fusion(current_tokens, anchor_hidden, previous_hidden)
        batch, sequence, _ = transformed.shape

        for position, block in enumerate(self.blocks):
            history_k = history_ks[position]
            history_v = history_vs[position]
            if history_k.shape[:2] != (batch, current_start):
                raise ValueError(
                    f"history_k[{position}] {history_k.shape} incompatible with "
                    f"batch={batch}, current_start={current_start}"
                )
            if history_v.shape != history_k.shape:
                raise ValueError(f"History K/V shapes differ at block {position}")
            run_block = self._block_closure(
                block=block,
                sequence=sequence,
                timestep_modulation=timestep_modulation,
                grid_sizes=grid_sizes,
                freqs=freqs,
                history_k=history_k,
                history_v=history_v,
                cross_k=cross_ks[position],
                cross_v=cross_vs[position],
                current_start=current_start,
            )
            if self.training and self.gradient_checkpointing:
                transformed = checkpoint(
                    run_block, transformed, use_reentrant=False
                )
            else:
                transformed = run_block(transformed)
        return anchor_hidden + self.residual_out(transformed)