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from __future__ import annotations

import argparse
import json
import math
import time
from pathlib import Path
from typing import Dict, Any

import psutil
import torch
import torch.nn as nn
from accelerate import init_empty_weights
from accelerate.utils import set_module_tensor_to_device
from transformers import AutoConfig, AutoModelForCausalLM, AutoTokenizer

from rotorquant_weights import load_quantized_package, _unpack_3bit, _deterministic_rotor_matrix


def rss_gb() -> float:
    return psutil.Process().memory_info().rss / (1024 ** 3)


def _get_parent_module(root: nn.Module, module_path: str):
    if not module_path:
        return None, ""
    parts = module_path.split(".")
    parent = root
    for p in parts[:-1]:
        parent = getattr(parent, p)
    return parent, parts[-1]


class FusedRotorLinear(nn.Module):
    def __init__(
        self,
        in_features: int,
        out_features: int,
        bias: torch.Tensor | None,
        qt_raw: Dict[str, Any],
        seed: int,
        block_size: int,
        rotor_angle_scale: float,
        layer_name: str,
        out_chunk_size: int = 64,
        cache_weight: bool = True,
    ):
        super().__init__()
        self.in_features = in_features
        self.out_features = out_features
        self.block_size = block_size
        self.rotor_angle_scale = rotor_angle_scale
        self.layer_name = layer_name
        self.out_chunk_size = out_chunk_size
        self.cache_weight = cache_weight

        self.row_size = int(qt_raw["row_size"])
        self.row_rot_size = int(qt_raw["row_rot_size"])
        self.row_padded_size = int(qt_raw["row_padded_size"])
        self.n_rows = int(qt_raw["n_rows"])

        packed = qt_raw["packed_indices"].to(torch.uint8)
        n_values = self.n_rows * self.row_padded_size
        idx = _unpack_3bit(packed, n_values=n_values, device=torch.device("cpu"))
        idx = idx.reshape(self.n_rows, self.row_padded_size).to(torch.uint8)

        self.register_buffer("indices", idx)
        self.register_buffer("centers", qt_raw["centers"].to(torch.float16))
        self.register_buffer("scales", qt_raw["scales"].to(torch.float16))
        self.register_buffer("codebook", qt_raw["codebook"].to(torch.float16))

        lowrank_A = qt_raw.get("lowrank_A")
        lowrank_B = qt_raw.get("lowrank_B")
        if lowrank_A is not None and lowrank_B is not None:
            self.register_buffer("lowrank_A", lowrank_A.to(torch.float16))
            self.register_buffer("lowrank_B", lowrank_B.to(torch.float16))
        else:
            self.lowrank_A = None
            self.lowrank_B = None

        R = _deterministic_rotor_matrix(
            name=layer_name,
            seed=seed,
            device=torch.device("cpu"),
            dtype=torch.float32,
            angle_scale=rotor_angle_scale,
        )
        self.register_buffer("R", R.to(torch.float16))

        if bias is not None:
            self.bias = nn.Parameter(bias.to(torch.float32), requires_grad=False)
        else:
            self.register_parameter("bias", None)
        self.register_buffer("_cached_weight", None, persistent=False)

    def _decode_weight_chunk(self, s: int, e: int) -> torch.Tensor:
        rows = e - s
        idx = self.indices[s:e].long()
        vals = self.codebook[idx]

        n_blocks = self.row_padded_size // self.block_size
        vals_b = vals.view(rows, n_blocks, self.block_size)

        centers = self.centers[s * n_blocks : e * n_blocks].view(rows, n_blocks, 1)
        scales = self.scales[s * n_blocks : e * n_blocks].view(rows, n_blocks, 1)
        w_rot = (vals_b * scales + centers).view(rows, self.row_padded_size)
        w_rot = w_rot[:, : self.row_rot_size]

        R = self.R.to(dtype=torch.float32)
        w = (w_rot.to(torch.float32).view(rows, -1, 3) @ R).view(rows, self.row_rot_size)
        w = w[:, : self.row_size]

        if self.lowrank_A is not None and self.lowrank_B is not None:
            A = self.lowrank_A[s:e].to(torch.float32)
            B = self.lowrank_B.to(torch.float32)
            w = w + (A @ B)

        return w[:, : self.in_features]

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        orig_shape = x.shape[:-1]
        x2 = x.reshape(-1, x.shape[-1]).to(torch.float32)

        if self.cache_weight and self._cached_weight is None:
            parts = []
            for s in range(0, self.out_features, self.out_chunk_size):
                e = min(self.out_features, s + self.out_chunk_size)
                parts.append(self._decode_weight_chunk(s, e))
            self._cached_weight = torch.cat(parts, dim=0).to(torch.float16)

        if self._cached_weight is not None:
            w = self._cached_weight.to(device=x2.device, dtype=torch.float32)
            out = x2 @ w.T
        else:
            out = torch.empty(x2.shape[0], self.out_features, dtype=torch.float32, device=x2.device)
            for s in range(0, self.out_features, self.out_chunk_size):
                e = min(self.out_features, s + self.out_chunk_size)
                w = self._decode_weight_chunk(s, e).to(x2.device)
                out[:, s:e] = x2 @ w.T

        if self.bias is not None:
            out = out + self.bias
        return out.reshape(*orig_shape, self.out_features)


def load_fused_model(pkg_path: str, out_chunk_size: int = 64):
    t0 = time.perf_counter()
    pkg = load_quantized_package(pkg_path)
    model_id = pkg["model_id"]
    seed = int(pkg.get("seed", 1337))
    block_size = int(pkg.get("block_size", 128))
    rotor_angle_scale = float(pkg.get("rotor_angle_scale", 1.0))

    config = AutoConfig.from_pretrained(model_id)
    with init_empty_weights():
        model = AutoModelForCausalLM.from_config(config)
    model.eval()

    passthrough = pkg["passthrough"]
    quantized = pkg["quantized"]

    consumed = set()
    for w_name, qt_raw in quantized.items():
        if not w_name.endswith(".weight"):
            continue
        mod_name = w_name[:-7]
        parent, child = _get_parent_module(model, mod_name)
        if parent is None or not hasattr(parent, child):
            continue
        old = getattr(parent, child)
        if not isinstance(old, nn.Linear):
            continue
        if "n_rows" not in qt_raw:
            continue

        bias_name = f"{mod_name}.bias"
        bias = passthrough.get(bias_name)

        fused = FusedRotorLinear(
            in_features=old.in_features,
            out_features=old.out_features,
            bias=bias,
            qt_raw=qt_raw,
            seed=seed,
            block_size=block_size,
            rotor_angle_scale=rotor_angle_scale,
            layer_name=w_name,
            out_chunk_size=out_chunk_size,
            cache_weight=True,
        )
        setattr(parent, child, fused)
        consumed.add(w_name)
        if bias is not None:
            consumed.add(bias_name)

    for name, t in passthrough.items():
        if name in consumed:
            continue
        set_module_tensor_to_device(model, name, "cpu", value=t)

    for name, qt_raw in quantized.items():
        if name in consumed:
            continue
        if "n_rows" not in qt_raw:
            from rotorquant_weights import dequantize_to_state_dict
            sd = dequantize_to_state_dict({
                "bits": pkg["bits"],
                "block_size": pkg["block_size"],
                "seed": pkg["seed"],
                "lowrank_rank": pkg.get("lowrank_rank", 0),
                "rotor_angle_scale": pkg.get("rotor_angle_scale", 1.0),
                "rowwise": False,
                "quantized": {name: qt_raw},
                "passthrough": {},
            }, dtype=torch.float32, device="cpu")
            set_module_tensor_to_device(model, name, "cpu", value=sd[name])
        else:
            from rotorquant_weights import dequantize_to_state_dict
            sd = dequantize_to_state_dict({
                "bits": pkg["bits"],
                "block_size": pkg["block_size"],
                "seed": pkg["seed"],
                "lowrank_rank": pkg.get("lowrank_rank", 0),
                "rotor_angle_scale": pkg.get("rotor_angle_scale", 1.0),
                "rowwise": pkg.get("rowwise", True),
                "quantized": {name: qt_raw},
                "passthrough": {},
            }, dtype=torch.float32, device="cpu")
            set_module_tensor_to_device(model, name, "cpu", value=sd[name])

    model = model.to(torch.float32)
    load_s = time.perf_counter() - t0
    return model, model_id, load_s


def run_prompt(model, tokenizer, prompt: str, max_new_tokens: int) -> str:
    messages = [
        {"role": "system", "content": "You are Qwen, created by Alibaba Cloud. You are a helpful assistant."},
        {"role": "user", "content": prompt},
    ]
    text = tokenizer.apply_chat_template(messages, tokenize=False, add_generation_prompt=True)
    inp = tokenizer([text], return_tensors="pt")
    with torch.no_grad():
        out = model.generate(**inp, max_new_tokens=max_new_tokens, do_sample=False)
    new = out[:, inp["input_ids"].shape[1]:]
    return tokenizer.batch_decode(new, skip_special_tokens=True)[0]


def parse_args():
    p = argparse.ArgumentParser(description="Run fused RotorQuant runtime")
    sub = p.add_subparsers(dest="cmd", required=True)

    r = sub.add_parser("run")
    r.add_argument("--pkg", default="artifacts/qwen2.5-0.5b-rotorq3-mlp-only.pt")
    r.add_argument("--prompt", default="Explain quantization in one paragraph.")
    r.add_argument("--max-new-tokens", type=int, default=64)
    r.add_argument("--out-chunk-size", type=int, default=64)

    b = sub.add_parser("bench")
    b.add_argument("--pkg", default="artifacts/qwen2.5-0.5b-rotorq3-mlp-only.pt")
    b.add_argument("--out", default="artifacts/fused_runtime_meta.json")
    b.add_argument("--out-chunk-size", type=int, default=64)

    return p.parse_args()


def main():
    args = parse_args()

    if args.cmd == "run":
        model, model_id, load_s = load_fused_model(args.pkg, out_chunk_size=args.out_chunk_size)
        tok = AutoTokenizer.from_pretrained(model_id)
        ans = run_prompt(model, tok, args.prompt, args.max_new_tokens)
        print(f"load_s={load_s:.3f}")
        print("\n=== Prompt ===")
        print(args.prompt)
        print("\n=== Response ===")
        print(ans)

    elif args.cmd == "bench":
        rss0 = rss_gb()
        model, model_id, load_s = load_fused_model(args.pkg, out_chunk_size=args.out_chunk_size)
        rss1 = rss_gb()
        tok = AutoTokenizer.from_pretrained(model_id)
        t0 = time.perf_counter()
        _ = run_prompt(model, tok, "warmup", 32)
        t1 = time.perf_counter() - t0
        rss2 = rss_gb()

        out = {
            "pkg": args.pkg,
            "load_s": load_s,
            "warmup_generate_s": t1,
            "rss_before_gb": rss0,
            "rss_after_load_gb": rss1,
            "rss_after_warmup_gb": rss2,
            "out_chunk_size": args.out_chunk_size,
        }
        Path(args.out).write_text(json.dumps(out, indent=2), encoding="utf-8")
        print(json.dumps(out, indent=2))


if __name__ == "__main__":
    main()