from __future__ import annotations

from typing import Any

from torch import nn

try:
    from monai.losses.dice import DiceCELoss, DiceFocalLoss, GeneralizedDiceFocalLoss
    from monai.losses.hausdorff_loss import HausdorffDTLoss
except ImportError as exc:
    DiceCELoss = None
    DiceFocalLoss = None
    GeneralizedDiceFocalLoss = None
    HausdorffDTLoss = None
    _MONAI_IMPORT_ERROR = exc
else:
    _MONAI_IMPORT_ERROR = None

LOSS_REGISTRY = {
    "dicece": DiceCELoss,
    "dicefocal": DiceFocalLoss,
    "generalized_dice_focal": GeneralizedDiceFocalLoss,
    "gdl_focal": GeneralizedDiceFocalLoss,
    "hausdorff": HausdorffDTLoss,
}

DEFAULT_TASK_LOSS = {
    "lun": {
        "name": "dicece",
        "params": {
            "include_background": True,
            "lambda_dice": 0.7,
            "lambda_ce": 0.3,
        },
    },
    "pe": {
        "name": "dicece",
        "params": {
            "include_background": True,
            "lambda_dice": 0.7,
            "lambda_ce": 0.3,
        },
    },
    "b": {
        "name": "dicefocal",
        "params": {
            "include_background": True,
            "lambda_dice": 1.0,
            "lambda_focal": 1.0,
            "gamma": 2.0,
        },
    },
}


def _require_monai() -> None:
    if _MONAI_IMPORT_ERROR is not None:
        raise ImportError(
            "MONAI is required for lib.tools.tools. Install monai before building losses."
        ) from _MONAI_IMPORT_ERROR


def _mode_defaults(task_mode: str) -> dict[str, Any]:
    mode = task_mode.lower()
    if mode == "binary":
        return {
            "sigmoid": True,
            "softmax": False,
            "to_onehot_y": False,
            "reduction": "mean",
        }
    if mode == "multiclass":
        return {
            "sigmoid": False,
            "softmax": True,
            "to_onehot_y": True,
            "reduction": "mean",
        }
    raise ValueError(f"Unsupported task_mode '{task_mode}'. Expected 'binary' or 'multiclass'.")


def _get_task_config(task_name: str) -> dict[str, Any]:
    task = task_name.lower()
    if task not in DEFAULT_TASK_LOSS:
        raise ValueError(f"Unsupported task '{task_name}'. Expected one of: {', '.join(DEFAULT_TASK_LOSS)}.")
    task_cfg = DEFAULT_TASK_LOSS[task]
    return {
        "name": task_cfg["name"],
        "params": dict(task_cfg.get("params", {})),
    }


def build_loss(config: dict[str, Any]) -> nn.Module:
    """Build a MONAI tools from a plain yaml-style config dict.

    Supported examples:
    {"task_name": "lun"}
    {"name": "dicece", "task_mode": "binary", "params": {"lambda_ce": 0.5}}
    {"name": "dicece", "task_mode": "multiclass", "params": {"include_background": True}}
    """

    _require_monai()

    if not isinstance(config, dict) or not config:
        raise ValueError("Loss config must be a non-empty dict.")

    task_mode = config.get("task_mode", "binary")
    if not isinstance(task_mode, str):
        raise ValueError("Loss config field 'task_mode' must be a string.")

    if "task_name" in config and config["task_name"] is not None:
        if not isinstance(config["task_name"], str):
            raise ValueError("Loss config field 'task_name' must be a string.")
        merged = _get_task_config(config["task_name"])
        merged["params"].update(config.get("params", {}))
        if "name" in config:
            merged["name"] = config["name"]
    else:
        name = config.get("name")
        if not isinstance(name, str) or not name:
            raise ValueError("Loss config must provide 'name' or 'task_name'.")
        merged = {
            "name": name,
            "params": dict(config.get("params", {})),
        }

    if not isinstance(merged["params"], dict):
        raise ValueError("Loss config field 'params' must be a dict if provided.")

    params = _mode_defaults(task_mode)
    params.update(merged["params"])

    loss_name = merged["name"].lower()
    loss_cls = LOSS_REGISTRY.get(loss_name)
    if loss_cls is None:
        raise ValueError(
            f"Unsupported tools '{merged['name']}'. Expected one of: {', '.join(LOSS_REGISTRY)}."
        )

    return loss_cls(**params)


__all__ = ["DEFAULT_TASK_LOSS", "LOSS_REGISTRY", "build_loss"]