"""Self-contained ymodel3 inference module.

Only depends on: torch, safetensors.
No dependency on kernel.*, model.ymodel3, transformers.
"""

from __future__ import annotations

import json
import math
from pathlib import Path
from typing import Optional, Union

import torch
import torch.nn as nn
import torch.nn.functional as F
from safetensors.torch import load_file as load_safetensors


# ── Config ──────────────────────────────────────────────────────────


class YConfig3:
    model_type = "ynet3"

    def __init__(self, **kwargs):
        self.dropout = kwargs.get("dropout", 0.0)
        self.bos_token_id = kwargs.get("bos_token_id", 151644)
        self.eos_token_id = kwargs.get("eos_token_id", 151645)
        self.pad_token_id = kwargs.get("pad_token_id", 151643)
        self.hidden_act = kwargs.get("hidden_act", "silu")
        self.hidden_size = kwargs.get("hidden_size", 768)
        self.num_hidden_layers = kwargs.get("num_hidden_layers", 8)
        self.max_position_embeddings = kwargs.get("max_position_embeddings", 8192)
        self.vocab_size = kwargs.get("vocab_size", 6400)
        self.rms_norm_eps = kwargs.get("rms_norm_eps", 1e-6)
        self.rope_theta = kwargs.get("rope_theta", 5e4)
        self.rope_scaling = kwargs.get("rope_scaling", None)
        self.dtype = kwargs.get("dtype", "float32")
        self.self_distill = kwargs.get("self_distill", True)
        self.intermediate_size = kwargs.get("intermediate_size", 1536)
        self.expert_intermediate_size = kwargs.get("expert_intermediate_size", None) or self.intermediate_size
        self.n_routed_experts = kwargs.get("n_routed_experts", 0)
        self.moe_topk = kwargs.get("moe_topk", 2)
        self.score_func = kwargs.get("score_func", "softmax")
        self.n_shared_experts = kwargs.get("n_shared_experts", 0)
        self.top_k_layer_dense = kwargs.get("top_k_layer_dense", 1)
        self.aux_loss_alpha = kwargs.get("aux_loss_alpha", 0.02)
        self.seq_aux = kwargs.get("seq_aux", False)
        self.norm_topk_prob = kwargs.get("norm_topk_prob", True)
        self.noisy_expert = kwargs.get("noisy_expert", 0.0)
        self.moe_backend = kwargs.get("moe_backend", "compact")
        self.router_bias_enabled = kwargs.get("router_bias_enabled", True)
        self.router_bias_update_rate = kwargs.get("router_bias_update_rate", 1e-3)
        self.router_bias_clamp = kwargs.get("router_bias_clamp", 5.0)
        self.num_heads = kwargs.get("num_heads", 12)
        self.mla_kv_lora_rank = kwargs.get("mla_kv_lora_rank", 64)
        self.mla_qk_nope_head_dim = kwargs.get("mla_qk_nope_head_dim", 64)
        self.mla_qk_rope_head_dim = kwargs.get("mla_qk_rope_head_dim", 32)
        self.mla_attn_impl = kwargs.get("mla_attn_impl", "absorb")
        self.qkv_lora = kwargs.get("qkv_lora", False)

    @property
    def head_dim(self) -> int:
        return self.mla_qk_nope_head_dim + self.mla_qk_rope_head_dim

    def scale_lvl(self, lvl: int = 0):
        if lvl == 0:
            self.hidden_size = 1024
            self.num_hidden_layers = 8
            self.num_heads = 8
            self.mla_kv_lora_rank = 256
            self.mla_qk_nope_head_dim = 192
            self.mla_qk_rope_head_dim = 64
            self.intermediate_size = 2048
            self.expert_intermediate_size = 512
            self.n_routed_experts = 16
            self.moe_topk = 1
            self.n_shared_experts = 0
            self.top_k_layer_dense = 1
            self.router_bias_update_rate = 1e-3
        elif lvl == -1:
            self.hidden_size = 768
            self.num_hidden_layers = 8
            self.num_heads = 6
            self.mla_kv_lora_rank = 128
            self.mla_qk_nope_head_dim = 64
            self.mla_qk_rope_head_dim = 64
            self.intermediate_size = 1536
            self.expert_intermediate_size = 768
            self.n_routed_experts = 0
            self.moe_topk = 2
            self.n_shared_experts = 0
            self.top_k_layer_dense = 8
        elif lvl == -2:
            self.hidden_size = 512
            self.num_hidden_layers = 4
            self.num_heads = 4
            self.mla_kv_lora_rank = 128
            self.mla_qk_nope_head_dim = 64
            self.mla_qk_rope_head_dim = 32
            self.intermediate_size = 1024
            self.expert_intermediate_size = 512
            self.n_routed_experts = 0
            self.moe_topk = 2
            self.n_shared_experts = 0
            self.top_k_layer_dense = 4
        else:
            raise ValueError(f"invalid ymodel3 scale level: {lvl}")
        return self

    @classmethod
    def from_json_file(cls, path: str) -> "YConfig3":
        with open(path, "r", encoding="utf-8") as f:
            data = json.load(f)
        return cls(**data)

    @classmethod
    def from_dict(cls, data: dict) -> "YConfig3":
        return cls(**data)


# ── Basic modules ──────────────────────────────────────────────────


class RMSNorm(nn.Module):
    def __init__(self, dim: int, eps: float = 1e-6):
        super().__init__()
        self.eps = eps
        self.weight = nn.Parameter(torch.ones(dim, dtype=torch.float32))

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        out = x.float() * torch.rsqrt(x.float().pow(2).mean(-1, keepdim=True) + self.eps)
        return (out * self.weight.float()).to(x.dtype)


class SEBlock(nn.Module):
    def __init__(self, dim: int, reduction: int = 16, act: Optional[nn.Module] = None):
        super().__init__()
        reduction = max(reduction, dim // reduction)
        self.se = nn.Sequential(
            nn.Linear(dim, reduction, bias=False),
            act or nn.SiLU(),
            nn.Linear(reduction, dim, bias=False),
            nn.Sigmoid(),
        )

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        return x * self.se(x)


# ── RoPE helpers ──────────────────────────────────────────────────


def _yarn_linear_ramp(low: float, high: float, dim: int) -> torch.Tensor:
    if low == high:
        high += 0.001
    linear = (torch.arange(dim, dtype=torch.float32) - low) / (high - low)
    return torch.clamp(linear, 0.0, 1.0)


def _yarn_correction_dim(num_rotations: float, dim: int, theta: float, max_position_embeddings: int) -> float:
    return dim * math.log(max_position_embeddings / (num_rotations * 2 * math.pi)) / (2 * math.log(theta))


def precompute_freqs_cis(
    dim: int,
    end: int,
    theta: float,
    rope_scaling: Optional[dict] = None,
) -> tuple[torch.Tensor, torch.Tensor]:
    freqs = 1.0 / (theta ** (torch.arange(0, dim, 2).float() / dim))
    attention_factor = 1.0
    if rope_scaling and str(rope_scaling.get("type", "yarn")).lower() == "yarn":
        factor = float(rope_scaling.get("factor", 1.0))
        if factor > 1.0:
            original = int(rope_scaling.get("original_max_position_embeddings", end))
            beta_fast = float(rope_scaling.get("beta_fast", 32.0))
            beta_slow = float(rope_scaling.get("beta_slow", 1.0))
            low = math.floor(_yarn_correction_dim(beta_fast, dim, theta, original))
            high = math.ceil(_yarn_correction_dim(beta_slow, dim, theta, original))
            ramp = _yarn_linear_ramp(low, high, dim // 2)
            freqs = freqs / factor * (1.0 - ramp) + freqs * ramp
            attention_factor = float(rope_scaling.get("attention_factor", 1.0))
    t = torch.arange(end)
    freqs = torch.outer(t, freqs).float()
    freqs_cos = torch.cat([torch.cos(freqs), torch.cos(freqs)], dim=-1) * attention_factor
    freqs_sin = torch.cat([torch.sin(freqs), torch.sin(freqs)], dim=-1) * attention_factor
    return freqs_cos, freqs_sin


def rotate_half(x: torch.Tensor) -> torch.Tensor:
    return torch.cat((-x[..., x.shape[-1] // 2 :], x[..., : x.shape[-1] // 2]), dim=-1)


def apply_rope_to_single(x: torch.Tensor, cos: torch.Tensor, sin: torch.Tensor) -> torch.Tensor:
    if cos.dim() == 2:
        cos = cos.unsqueeze(0).unsqueeze(0)
        sin = sin.unsqueeze(0).unsqueeze(0)
    elif cos.dim() == 3:
        cos = cos.unsqueeze(1)
        sin = sin.unsqueeze(1)
    return (x * cos) + (rotate_half(x) * sin)


# ── Attention ──────────────────────────────────────────────────────


class MLGA(nn.Module):
    """Multihead Latent Gated Attention"""

    def __init__(self, config: YConfig3, layer_id: int):
        super().__init__()
        self.layer_id = layer_id
        self.hidden_size = config.hidden_size
        self.num_heads = config.num_heads
        self.dropout = config.dropout
        self.kv_lora_rank = config.mla_kv_lora_rank
        self.qk_nope_head_dim = config.mla_qk_nope_head_dim
        self.qk_rope_head_dim = config.mla_qk_rope_head_dim
        self.qk_head_dim = self.qk_nope_head_dim + self.qk_rope_head_dim
        self.attn_impl = config.mla_attn_impl
        self.softmax_scale = self.qk_head_dim ** -0.5
        self.out_dim = self.num_heads * self.kv_lora_rank

        self.wq = nn.Linear(self.hidden_size, self.num_heads * self.qk_head_dim, bias=False)
        self.wkv_a = nn.Linear(self.hidden_size, self.kv_lora_rank + self.qk_rope_head_dim, bias=False)
        self.kv_norm = RMSNorm(self.kv_lora_rank, config.rms_norm_eps)
        self.wkv_b = nn.Linear(self.kv_lora_rank, self.num_heads * self.qk_nope_head_dim, bias=False)
        self.z_proj = nn.Linear(self.hidden_size, self.out_dim, bias=False)
        self.o_proj = nn.Linear(self.out_dim, self.hidden_size, bias=False)

    def _project_q(self, x: torch.Tensor) -> tuple[torch.Tensor, torch.Tensor]:
        bsz, seq_len, _ = x.shape
        q = self.wq(x)
        q = q.reshape(bsz, seq_len, self.num_heads, self.qk_head_dim)
        return q.split([self.qk_nope_head_dim, self.qk_rope_head_dim], dim=-1)

    def _project_kv(self, x: torch.Tensor, cos: torch.Tensor, sin: torch.Tensor) -> tuple[torch.Tensor, torch.Tensor]:
        raw = self.wkv_a(x)
        c_kv, k_pe = raw.split([self.kv_lora_rank, self.qk_rope_head_dim], dim=-1)
        c_kv = self.kv_norm(c_kv)
        k_pe = apply_rope_to_single(k_pe.unsqueeze(1), cos, sin).permute(0, 2, 1, 3)
        return c_kv, k_pe

    def _explicit_kv(self, c_kv: torch.Tensor, k_pe: torch.Tensor) -> tuple[torch.Tensor, torch.Tensor]:
        bsz, seq_len, _ = c_kv.shape
        k_nope = self.wkv_b(c_kv).reshape(bsz, seq_len, self.num_heads, self.qk_nope_head_dim)
        k = torch.cat([k_nope, k_pe.expand(-1, -1, self.num_heads, -1)], dim=-1)
        v = c_kv.unsqueeze(2).expand(-1, -1, self.num_heads, -1)
        return k, v

    def _attention_mask(self, attention_mask: Optional[torch.Tensor], bsz: int, seq_len: int, total_len: int):
        if attention_mask is None:
            return None
        if attention_mask.shape[-1] != total_len:
            attention_mask = attention_mask[..., -total_len:]
        mask = attention_mask.reshape(bsz, 1, 1, total_len).bool()
        return mask.expand(bsz, self.num_heads, seq_len, total_len)

    def _forward_sdpa(
        self,
        q_nope: torch.Tensor,
        q_pe: torch.Tensor,
        c_kv: torch.Tensor,
        k_pe: torch.Tensor,
        z: torch.Tensor,
        attention_mask: Optional[torch.Tensor],
    ) -> torch.Tensor:
        bsz, seq_len, _, _ = q_nope.shape
        total_len = c_kv.shape[1]
        k, v = self._explicit_kv(c_kv, k_pe)
        q = torch.cat([q_nope, q_pe], dim=-1).permute(0, 2, 1, 3)
        k = k.permute(0, 2, 1, 3)
        v = v.permute(0, 2, 1, 3)
        attn_mask = self._attention_mask(attention_mask, bsz, seq_len, total_len)
        is_causal = attention_mask is None and seq_len == total_len
        out = F.scaled_dot_product_attention(
            q, k, v,
            attn_mask=attn_mask,
            dropout_p=self.dropout if self.training else 0.0,
            is_causal=is_causal,
            scale=self.softmax_scale,
        )
        out = out.permute(0, 2, 1, 3).reshape(bsz, seq_len, self.out_dim)
        out = out * torch.sigmoid(z)
        return self.o_proj(out)

    def _forward_absorb(
        self,
        q_nope: torch.Tensor,
        q_pe: torch.Tensor,
        c_kv: torch.Tensor,
        k_pe: torch.Tensor,
        z: torch.Tensor,
        attention_mask: Optional[torch.Tensor],
    ) -> torch.Tensor:
        bsz, seq_len, _, _ = q_nope.shape
        total_len = c_kv.shape[1]
        w = self.wkv_b.weight.reshape(self.num_heads, self.qk_nope_head_dim, self.kv_lora_rank)
        q_nope_c = torch.einsum("bshd,hdc->bshc", q_nope, w)
        scores = torch.einsum("bshc,btc->bsht", q_nope_c, c_kv)
        scores = scores + torch.einsum("bshr,btr->bsht", q_pe, k_pe.squeeze(2))
        scores = scores * self.softmax_scale

        causal = torch.full((seq_len, seq_len), float("-inf"), device=scores.device, dtype=scores.dtype)
        causal = torch.triu(causal, diagonal=1).reshape(1, seq_len, 1, seq_len)
        scores = scores + F.pad(causal, (total_len - seq_len, 0), value=0.0)
        if attention_mask is not None:
            if attention_mask.shape[-1] != total_len:
                attention_mask = attention_mask[..., -total_len:]
            scores = scores + (1.0 - attention_mask.reshape(bsz, 1, 1, total_len).float()) * -1e9
        probs = torch.softmax(scores.float(), dim=-1).to(q_nope.dtype)
        out = torch.einsum("bsht,btc->bshc", probs, c_kv).reshape(bsz, seq_len, self.out_dim)
        out = out * torch.sigmoid(z)
        return self.o_proj(out)

    def forward(
        self,
        x: torch.Tensor,
        position_embeddings: tuple[torch.Tensor, torch.Tensor],
        past_key_values: Optional[tuple[torch.Tensor, torch.Tensor]] = None,
        attention_mask: Optional[torch.Tensor] = None,
        use_cache: bool = False,
        **kwargs,
    ) -> tuple[torch.Tensor, Optional[tuple[torch.Tensor, torch.Tensor]]]:
        bsz, seq_len, _ = x.shape
        cos, sin = position_embeddings
        if cos.dim() == 2:
            cos = cos[:seq_len, : self.qk_rope_head_dim]
            sin = sin[:seq_len, : self.qk_rope_head_dim]
        else:
            cos = cos[:, :seq_len, : self.qk_rope_head_dim]
            sin = sin[:, :seq_len, : self.qk_rope_head_dim]
        q_nope, q_pe = self._project_q(x)
        q_pe = apply_rope_to_single(q_pe.permute(0, 2, 1, 3), cos, sin).permute(0, 2, 1, 3)
        c_kv, k_pe = self._project_kv(x, cos, sin)
        z = self.z_proj(x)

        if past_key_values is not None:
            past_c, past_pe = past_key_values
            c_kv = torch.cat([past_c, c_kv], dim=1)
            k_pe = torch.cat([past_pe, k_pe], dim=1)
        new_past = (c_kv, k_pe) if use_cache else None

        if self.attn_impl == "naive":
            out = self._forward_sdpa(q_nope, q_pe, c_kv, k_pe, z, attention_mask)
        else:
            out = self._forward_absorb(q_nope, q_pe, c_kv, k_pe, z, attention_mask)
        out = F.dropout(out, p=self.dropout, training=self.training)
        return out, new_past


# ── FFN / MoE ──────────────────────────────────────────────────────


_ACT_FNS = {
    "silu": F.silu,
    "swish": F.silu,
    "relu": F.relu,
    "gelu": lambda x: F.gelu(x, approximate="tanh"),
    "sigmoid": torch.sigmoid,
}

_ACT_MODULES = {
    "silu": nn.SiLU,
    "swish": nn.SiLU,
    "relu": nn.ReLU,
    "gelu": lambda: nn.GELU(approximate="tanh"),
    "sigmoid": nn.Sigmoid,
}


class DenseFFN(nn.Module):
    def __init__(self, config: YConfig3, intermediate_size: Optional[int] = None):
        super().__init__()
        inter = intermediate_size or config.intermediate_size
        self.up_proj = nn.Linear(config.hidden_size, inter, bias=False)
        self.gate_proj = nn.Linear(config.hidden_size, inter, bias=False)
        self.down_proj = nn.Linear(inter, config.hidden_size, bias=False)
        self.hidden_act = config.hidden_act
        self.act = _ACT_FNS.get(config.hidden_act, F.silu)
        self.dropout = config.dropout

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        up, gate = self.up_proj(x), self.gate_proj(x)
        up = self.act(gate) * up
        up = F.dropout(up, p=self.dropout, training=self.training)
        return self.down_proj(up)


class MoEGate(nn.Module):
    def __init__(self, config: YConfig3):
        super().__init__()
        self.n_routed_experts = config.n_routed_experts
        self.topk = min(config.moe_topk, max(1, config.n_routed_experts))
        self.score_func = config.score_func
        self.norm_topk_prob = config.norm_topk_prob
        self.aux_loss_alpha = config.aux_loss_alpha
        self.seq_aux = config.seq_aux
        self.router_bias_enabled = config.router_bias_enabled
        self.router_bias_update_rate = config.router_bias_update_rate
        self.router_bias_clamp = config.router_bias_clamp
        self.weight = nn.Linear(int(config.hidden_size), int(self.n_routed_experts), bias=False)
        if self.router_bias_enabled:
            self.register_buffer("router_bias", torch.zeros(self.n_routed_experts), persistent=True)
        else:
            self.register_buffer("router_bias", None, persistent=False)

    def forward(self, x: torch.Tensor, aux_mask: Optional[torch.Tensor] = None):
        bsz, seq_len, hidden = x.shape
        flat = x.reshape(-1, hidden)
        route_logits = self.weight(flat)
        if self.score_func == "softmax":
            route_scores = torch.softmax(route_logits.float(), dim=-1).to(x.dtype)
        elif self.score_func == "sigmoid":
            route_scores = torch.sigmoid(route_logits.float()).to(x.dtype)
        else:
            raise ValueError(f"unsupported MoE score_func: {self.score_func}")

        choice_scores = route_scores
        if self.router_bias is not None:
            choice_scores = choice_scores + self.router_bias.to(dtype=choice_scores.dtype).unsqueeze(0)

        topk_idx = torch.topk(choice_scores, k=self.topk, dim=-1, sorted=False).indices
        topk_weight = route_scores.gather(1, topk_idx)
        if self.topk > 1 and self.norm_topk_prob:
            denom = topk_weight.float().sum(dim=-1, keepdim=True) + 1e-20
            topk_weight = (topk_weight.float() / denom).to(x.dtype)

        aux_loss = x.new_zeros((), dtype=x.dtype)
        return (
            topk_idx.reshape(bsz, seq_len, self.topk),
            topk_weight.reshape(bsz, seq_len, self.topk),
            aux_loss,
        )


def _torch_moe_swiglu(
    x: torch.Tensor,
    topk_idx: torch.Tensor,
    topk_weight: torch.Tensor,
    w_up: torch.Tensor,
    w_down: torch.Tensor,
    activation: str = "silu",
) -> torch.Tensor:
    """Pure PyTorch MoE SwiGLU forward (inference only, no noisy_expert)."""
    original_shape = x.shape
    x_flat = x.reshape(-1, x.shape[-1])
    idx = topk_idx.reshape(x_flat.shape[0], -1)
    weight = topk_weight.reshape(x_flat.shape[0], -1)
    y = torch.zeros_like(x_flat)
    n_experts = w_up.shape[0]
    inter = w_down.shape[-1]
    act_fn = _ACT_FNS.get(activation, F.silu)
    for expert_id in range(n_experts):
        token_pos, choice_pos = torch.where(idx == expert_id)
        if token_pos.numel() == 0:
            continue
        inp = x_flat[token_pos]
        uv = F.linear(inp, w_up[expert_id])
        up, gate = uv.split(inter, dim=-1)
        hidden = act_fn(gate) * up
        out = F.linear(hidden, w_down[expert_id])
        route_w = weight[token_pos, choice_pos].unsqueeze(-1)
        y.index_add_(0, token_pos, out * route_w)
    return y.reshape(original_shape)


class YMoE(nn.Module):
    """Pure PyTorch eval MoE (no Triton dependency)."""

    def __init__(self, config: YConfig3, layer_id: int):
        super().__init__()
        self.layer_id = layer_id
        self.hidden_size = config.hidden_size
        self.expert_intermediate_size = config.expert_intermediate_size
        self.intermediate_size = self.expert_intermediate_size
        self.n_routed_experts = config.n_routed_experts
        self.use_moe = self.n_routed_experts > 0 and layer_id >= config.top_k_layer_dense
        self.noisy_expert = config.noisy_expert
        if not self.use_moe:
            self.dense = DenseFFN(config)
            self.gate = None
            self.w_up = None
            self.w_down = None
            return
        self.dense = None
        self.gate = MoEGate(config)
        self.w_up = nn.Parameter(torch.empty(self.n_routed_experts, 2 * self.expert_intermediate_size, self.hidden_size))
        self.w_down = nn.Parameter(torch.empty(self.n_routed_experts, self.hidden_size, self.expert_intermediate_size))
        nn.init.kaiming_uniform_(self.w_up, a=math.sqrt(5))
        nn.init.kaiming_uniform_(self.w_down, a=math.sqrt(5))

    def forward(self, x: torch.Tensor, aux_mask: Optional[torch.Tensor] = None):
        if not self.use_moe:
            return self.dense(x), None
        topk_idx, topk_weight, aux_loss = self.gate(x, aux_mask)
        y = _torch_moe_swiglu(x, topk_idx, topk_weight, self.w_up, self.w_down, activation="silu")
        return y, aux_loss


# ── Transformer block ──────────────────────────────────────────────


class YBlock3(nn.Module):
    def __init__(self, config: YConfig3, layer_id: int):
        super().__init__()
        self.input_layernorm = RMSNorm(config.hidden_size, config.rms_norm_eps)
        self.post_attention_layernorm = RMSNorm(config.hidden_size, config.rms_norm_eps)
        self.attn = MLGA(config, layer_id)
        self.ffn = YMoE(config, layer_id)
        act_module = _ACT_MODULES.get(config.hidden_act, nn.SiLU)
        self.se1 = SEBlock(config.hidden_size, act=act_module() if isinstance(act_module, type) else act_module())
        self.se2 = SEBlock(config.hidden_size, act=nn.SiLU())

    def forward(
        self,
        x: torch.Tensor,
        position_embeddings: tuple[torch.Tensor, torch.Tensor],
        past_key_values=None,
        use_cache: bool = False,
        attention_mask: Optional[torch.Tensor] = None,
        aux_mask: Optional[torch.Tensor] = None,
        **kwargs,
    ):
        x0 = self.se1(self.input_layernorm(x))
        attn_out, past = self.attn(
            x0,
            position_embeddings,
            past_key_values=past_key_values,
            attention_mask=attention_mask,
            use_cache=use_cache,
        )
        x = x + attn_out
        x0 = self.se2(self.post_attention_layernorm(x))
        ffn_out, aux_loss = self.ffn(x0, aux_mask)
        x = x + ffn_out
        return x, past, aux_loss


# ── Full model ────────────────────────────────────────────────────


class YModel3(nn.Module):
    def __init__(self, config: YConfig3):
        super().__init__()
        self.config = config
        self.vocab_size = config.vocab_size
        self.num_layers = config.num_hidden_layers
        self.embed_tokens = nn.Embedding(config.vocab_size, config.hidden_size)
        self.dropout = config.dropout
        self.use_self_distill = config.self_distill
        self.layers = nn.ModuleList([YBlock3(config, i) for i in range(config.num_hidden_layers)])
        self.norm = RMSNorm(config.hidden_size, config.rms_norm_eps)
        freqs_cos, freqs_sin = precompute_freqs_cis(
            dim=config.mla_qk_rope_head_dim,
            end=config.max_position_embeddings,
            theta=config.rope_theta,
            rope_scaling=config.rope_scaling,
        )
        self.register_buffer("freqs_cos", freqs_cos, persistent=False)
        self.register_buffer("freqs_sin", freqs_sin, persistent=False)

    def forward(
        self,
        input_ids: Optional[torch.Tensor] = None,
        attention_mask: Optional[torch.Tensor] = None,
        past_key_values: Optional[list] = None,
        use_cache: bool = False,
        cache_position: Optional[torch.LongTensor] = None,
        position_ids: Optional[torch.LongTensor] = None,
        **kwargs,
    ):
        bsz, seq_len = input_ids.shape
        if use_cache and past_key_values is None:
            past_key_values = [None] * self.num_layers
        if cache_position is None:
            if past_key_values is not None and past_key_values[0] is not None:
                past_seen = past_key_values[0][0].shape[1]
            else:
                past_seen = 0
            cache_position = torch.arange(past_seen, past_seen + seq_len, device=input_ids.device)

        x = F.dropout(self.embed_tokens(input_ids), p=self.dropout, training=self.training)
        if position_ids is None:
            position_ids = cache_position
        position_embeddings = (self.freqs_cos[position_ids].to(x.device), self.freqs_sin[position_ids].to(x.device))
        aux_mask = None
        new_past = [] if use_cache else None
        aux_loss = None

        for i, layer in enumerate(self.layers):
            past = past_key_values[i] if past_key_values is not None else None
            x, layer_past, layer_aux = layer(
                x,
                position_embeddings=position_embeddings,
                past_key_values=past,
                attention_mask=attention_mask,
                use_cache=use_cache,
                aux_mask=aux_mask,
            )
            if use_cache:
                new_past.append(layer_past)
            if self.training and layer_aux is not None:
                aux_loss = layer_aux if aux_loss is None else aux_loss + layer_aux

        return self.norm(x), new_past, None, aux_loss


class _InferenceOutput:
    """Simple container for model outputs (replaces transformers CausalLMOutputWithPast)."""

    __slots__ = ("last_hidden_state", "logits", "past_key_values", "dist_loss", "aux_loss")

    def __init__(self):
        self.last_hidden_state = None
        self.logits = None
        self.past_key_values = None
        self.dist_loss = None
        self.aux_loss = None

    def __setitem__(self, key, value):
        setattr(self, key, value)


class YForCausalLM3(nn.Module):
    """Pure PyTorch CausalLM wrapper for ymodel3 inference (no transformers dependency)."""

    config_class = YConfig3

    def __init__(self, config: Optional[YConfig3] = None):
        super().__init__()
        self.config = config or YConfig3()
        self.model = YModel3(self.config)
        self.lm_head = nn.Linear(self.config.hidden_size, self.config.vocab_size, bias=False)
        self.model.embed_tokens.weight = self.lm_head.weight
        self.OUT = _InferenceOutput()
        dtype = {"float16": torch.float16, "bfloat16": torch.bfloat16, "float32": torch.float32}.get(self.config.dtype)
        if dtype is not None:
            self.to(dtype)

    def forward(
        self,
        input_ids: Optional[torch.Tensor] = None,
        attention_mask: Optional[torch.Tensor] = None,
        past_key_values: Optional[list] = None,
        use_cache: bool = False,
        logits_to_keep: Union[int, torch.Tensor] = 0,
        cache_position: Optional[torch.LongTensor] = None,
        **kwargs,
    ):
        h, past_kvs, dist_loss, aux_loss = self.model(
            input_ids=input_ids,
            attention_mask=attention_mask,
            past_key_values=past_key_values,
            use_cache=use_cache,
            cache_position=cache_position,
            position_ids=kwargs.get("position_ids", None),
        )
        slice_indices = slice(-logits_to_keep, None) if isinstance(logits_to_keep, int) else logits_to_keep
        logits = self.lm_head(h[:, slice_indices, :])
        self.OUT.__setitem__("last_hidden_state", h)
        self.OUT.__setitem__("logits", logits)
        self.OUT.__setitem__("past_key_values", past_kvs)
        self.OUT.__setitem__("dist_loss", dist_loss)
        self.OUT.__setitem__("aux_loss", aux_loss)
        return self.OUT

    def generate(
        self,
        inputs,
        attention_mask=None,
        max_new_tokens=8192,
        temperature=0.85,
        top_p=0.85,
        top_k=50,
        eos_token_id=None,
        streamer=None,
        use_cache=True,
        num_return_sequences=1,
        do_sample=True,
        repetition_penalty=1.0,
        **kwargs,
    ):
        input_ids = kwargs.get("input_ids", inputs).repeat(num_return_sequences, 1)
        attention_mask = attention_mask.repeat(num_return_sequences, 1) if attention_mask is not None else None
        past_key_values = None
        if streamer:
            streamer.put(input_ids.cpu())
        with torch.no_grad():
            for _ in range(max_new_tokens):
                if use_cache and past_key_values is not None:
                    outputs = self.forward(input_ids[:, -1:], None, past_key_values, use_cache=use_cache)
                else:
                    outputs = self.forward(input_ids, attention_mask, past_key_values, use_cache=use_cache)
                logits = outputs.logits[:, -1, :] / temperature
                if repetition_penalty != 1.0:
                    for i in range(input_ids.shape[0]):
                        logits[i, torch.unique(input_ids[i])] /= repetition_penalty
                if top_k > 0:
                    logits[logits < torch.topk(logits, top_k)[0][..., -1, None]] = -float("inf")
                if top_p < 1.0:
                    sorted_logits, sorted_indices = torch.sort(logits, descending=True)
                    mask = torch.cumsum(torch.softmax(sorted_logits, dim=-1), dim=-1) > top_p
                    mask[..., 1:], mask[..., 0] = mask[..., :-1].clone(), 0
                    logits[mask.scatter(1, sorted_indices, mask)] = -float("inf")
                next_token = torch.multinomial(torch.softmax(logits, dim=-1), 1) if do_sample else torch.argmax(logits, dim=-1, keepdim=True)
                input_ids = torch.cat([input_ids, next_token], dim=-1)
                past_key_values = outputs.past_key_values if use_cache else None
                if streamer:
                    streamer.put(next_token.cpu())
                if eos_token_id and (next_token == eos_token_id).any():
                    break
        if streamer:
            streamer.end()
        return input_ids


# ── Loading utilities ──────────────────────────────────────────────


def _load_state_dict(path: Union[str, Path]) -> dict[str, torch.Tensor]:
    path = Path(path)
    if path.is_dir():
        safetensors_path = path / "model.safetensors"
        bin_path = path / "pytorch_model.bin"
        if safetensors_path.exists():
            path = safetensors_path
        elif bin_path.exists():
            path = bin_path
        else:
            raise FileNotFoundError(f"no model.safetensors or pytorch_model.bin found in {path}")
    if path.suffix == ".safetensors":
        return load_safetensors(str(path), device="cpu")
    return torch.load(path, map_location="cpu", weights_only=True)


def load_ymodel3_eval(path: Union[str, Path], config: Optional[YConfig3] = None, strict: bool = True) -> YForCausalLM3:
    if config is None:
        config_path = Path(path) / "config.json" if Path(path).is_dir() else Path(path).with_name("config.json")
        if not config_path.exists():
            raise FileNotFoundError("config is required when config.json is not next to the checkpoint")
        config = YConfig3.from_json_file(str(config_path))
    model = YForCausalLM3(config)
    state = _load_state_dict(path)
    model.load_state_dict(state, strict=strict)
    model.eval()
    return model


# ── Backward-compatible aliases ────────────────────────────────────

YModel3Eval = YModel3
YForCausalLM3Eval = YForCausalLM3