"""Model checkpoint serialization helpers."""

import io
import json
import time
from dataclasses import dataclass, field
from pathlib import Path
from typing import Any, Callable, Dict, Optional, Union

import safetensors.torch as st
import torch
import torch.distributed as dist

from astrai.parallel.setup import get_rank

_META_FILE = "meta.json"
_CONFIG_FILE = "config.json"
_WEIGHTS_FILE = "model.safetensors"


def save_safetensors(state_dict: dict, path: Union[str, Path]):
    st.save_file(state_dict, str(path))


def _broadcast_load(loader: Callable[[], dict], broadcast: bool) -> dict:
    """Load on rank 0 and broadcast the object to all ranks."""
    if not broadcast or not dist.is_initialized():
        return loader()
    rank = get_rank()
    if rank == 0:
        data = loader()
    else:
        data = {}
    tmp = [data]
    dist.broadcast_object_list(tmp, src=0)
    return tmp[0]


def load_safetensors(path: Union[str, Path], broadcast: bool = False) -> dict:
    return _broadcast_load(lambda: st.load_file(str(path)), broadcast)


def save_json(data: dict, path: Union[str, Path]):
    with open(str(path), "w") as f:
        json.dump(data, f, indent=2)


def load_json(path: Union[str, Path], broadcast: bool = False) -> dict:
    return _broadcast_load(lambda: json.loads(Path(path).read_text()), broadcast)


def save_torch(obj: Any, path: Union[str, Path]):
    torch.save(obj, str(path))


def load_torch(path: Union[str, Path], broadcast: bool = False) -> Any:
    if not broadcast or not dist.is_initialized():
        return torch.load(str(path), map_location="cpu", weights_only=False)

    path = Path(path)
    rank = get_rank()

    if rank == 0:
        with open(path, "rb") as f:
            raw = f.read()
        data_tensor = torch.frombuffer(bytearray(raw), dtype=torch.uint8)
        num_bytes = torch.tensor([len(raw)], dtype=torch.long)
    else:
        num_bytes = torch.tensor([0], dtype=torch.long)

    dist.broadcast(num_bytes, src=0)

    if rank != 0:
        data_tensor = torch.empty(num_bytes.item(), dtype=torch.uint8)

    dist.broadcast(data_tensor, src=0)

    buf = io.BytesIO(data_tensor.numpy().tobytes())
    return torch.load(buf, map_location="cpu", weights_only=False)


def save_model(config: dict, state_dict: dict, save_directory: str):
    save_path = Path(save_directory)
    save_path.mkdir(parents=True, exist_ok=True)
    save_json(config, save_path / _CONFIG_FILE)
    save_safetensors(state_dict, save_path / _WEIGHTS_FILE)


def load_model_config(save_directory: str) -> dict:
    return load_json(Path(save_directory) / _CONFIG_FILE)


def load_model_weights(save_directory: str) -> dict:
    save_path = Path(save_directory)
    weights_file = save_path / _WEIGHTS_FILE
    if weights_file.exists():
        return load_state_dict(weights_file)

    index_path = save_path / "model.safetensors.index.json"
    if index_path.exists():
        index = load_json(index_path)
        weight_map = index.get("weight_map", {})
        state_dict = {}
        for shard in sorted(set(weight_map.values())):
            state_dict.update(load_state_dict(save_path / shard))
        return state_dict

    raise FileNotFoundError(f"No model weights found in {save_directory}")


def load_state_dict(path: Union[str, Path], broadcast: bool = False) -> dict:
    path = Path(path)
    if not broadcast or not dist.is_initialized():
        return load_safetensors(path)

    rank = get_rank()
    if rank == 0:
        state_dict = load_safetensors(path)
        specs = [
            (k, list(state_dict[k].shape), str(state_dict[k].dtype).split(".")[-1])
            for k in sorted(state_dict)
        ]
    else:
        state_dict = {}
        specs = []

    specs_list = [specs]
    dist.broadcast_object_list(specs_list, src=0)
    specs = specs_list[0]

    for key, shape, dtype_name in specs:
        dtype = getattr(torch, dtype_name)
        if rank != 0:
            tensor = torch.empty(shape, dtype=dtype, device="cpu")
        else:
            tensor = state_dict[key].contiguous().cpu()
        dist.broadcast(tensor, src=0)
        if rank != 0:
            state_dict[key] = tensor
    return state_dict


@dataclass
class Checkpoint:
    state_dict: Dict[str, Any] = field(default_factory=dict)
    epoch: int = 0
    consumed_samples: int = 0
    extra: Dict[str, Any] = field(default_factory=dict)
    meta: Dict[str, Any] = field(default_factory=dict)
    config: Dict[str, Any] = field(default_factory=dict)

    def save(self, save_dir: str):
        save_path = Path(save_dir)
        save_path.mkdir(parents=True, exist_ok=True)

        meta = {
            "epoch": self.epoch,
            "consumed_samples": self.consumed_samples,
            "timestamp": time.strftime("%Y-%m-%dT%H:%M:%S"),
            **self.meta,
        }
        save_json(meta, save_path / _META_FILE)
        save_json(self.config, save_path / _CONFIG_FILE)
        save_safetensors(self.state_dict, save_path / _WEIGHTS_FILE)
        for key, value in self.extra.items():
            save_torch(value, save_path / f"{key}.pt")

    @classmethod
    def load(cls, save_dir: str, broadcast: bool = False) -> "Checkpoint":
        save_path = Path(save_dir)

        meta = load_json(save_path / _META_FILE, broadcast)
        config = load_json(save_path / _CONFIG_FILE, broadcast)
        state_dict = load_state_dict(save_path / _WEIGHTS_FILE, broadcast=broadcast)

        extra = {}
        for f in sorted(save_path.iterdir()):
            if f.suffix == ".pt":
                extra[f.stem] = load_torch(f, broadcast=broadcast)

        return cls(
            state_dict=state_dict,
            epoch=meta.get("epoch", 0),
            consumed_samples=meta.get("consumed_samples", 0),
            extra=extra,
            meta=meta,
            config=config,
        )

    @classmethod
    def load_any(cls, save_dir: str, broadcast: bool = False) -> Optional["Checkpoint"]:
        save_path = Path(save_dir)
        meta_path = save_path / _META_FILE
        weights_path = save_path / _WEIGHTS_FILE

        if meta_path.exists():
            return cls.load(save_dir, broadcast=broadcast)

        weights_path = save_path / _WEIGHTS_FILE
        index_path = save_path / "model.safetensors.index.json"
        if weights_path.exists() or index_path.exists():
            state_dict = load_model_weights(save_dir)
            config = {}
            config_path = save_path / _CONFIG_FILE
            if config_path.exists():
                config = load_json(config_path, broadcast)
            return cls(state_dict=state_dict, config=config)

        return None