from __future__ import annotations

from abc import ABC, abstractmethod
from pathlib import Path
import pprint
import random
import time
from typing import Any

import numpy as np
import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.amp import GradScaler

from lib.data import build_dataloader
from lib.tools import build_metrics, compute_metrics, reset_metrics, update_metrics

try:
    import swanlab
except ImportError:
    swanlab = None


class BaseTrainer(ABC):
    """
    训练器基类。

    设计目标：
    - 统一配置入口
    - 统一模型/优化器/调度器创建
    - 不同训练流程只重写最少的方法
    """

    def __init__(self, cfg: dict[str, Any], args: Any | None = None) -> None:
        self.cfg = cfg
        self.args = args
        self._set_random_seed()
        self.device = self._build_device()
        self.output_dir = self._build_output_dir()
        self.start_epoch = 0
        self.best_metric: float | None = None
        self.no_improve_epochs = 0
        self.swanlab_run = None
        self.grad_scaler = GradScaler("cuda", enabled=self._amp_enabled())

    def _set_random_seed(self) -> None:
        seed = int(self.cfg.get("train", {}).get("seed", 42))
        random.seed(seed)
        np.random.seed(seed)
        torch.manual_seed(seed)
        if torch.cuda.is_available():
            torch.cuda.manual_seed(seed)
            torch.cuda.manual_seed_all(seed)

        deterministic = bool(self.cfg.get("train", {}).get("deterministic", False))
        if deterministic:
            torch.backends.cudnn.deterministic = True
            torch.backends.cudnn.benchmark = False
        else:
            torch.backends.cudnn.deterministic = False
            torch.backends.cudnn.benchmark = True

    def _build_device(self) -> torch.device:
        device_name = self.cfg.get("train", {}).get("device", "cpu")
        if device_name == "cuda" and not torch.cuda.is_available():
            device_name = "cpu"
        return torch.device(device_name)

    def _build_output_dir(self) -> Path:
        output_dir = self.cfg.get("checkpoint", {}).get("dir", "outputs/supervised_segmentation")
        path = Path(output_dir)
        path.mkdir(parents=True, exist_ok=True)
        return path

    def _amp_enabled(self) -> bool:
        return bool(self.cfg.get("train", {}).get("amp", False)) and self.device.type == "cuda"

    def _auto_batch_size_cfg(self) -> dict[str, Any]:
        cfg = self.cfg.get("train", {}).get("auto_batch_size", {})
        return cfg if isinstance(cfg, dict) else {}

    def _auto_batch_size_enabled(self) -> bool:
        return bool(self._auto_batch_size_cfg().get("enabled", False))

    def _gpu_total_memory_gb(self) -> float | None:
        if self.device.type != "cuda" or not torch.cuda.is_available():
            return None
        props = torch.cuda.get_device_properties(self.device)
        return float(props.total_memory / (1024 ** 3))

    def _estimate_auto_batch_size(self, *, default_batch_size: int, ssl: bool = False) -> int:
        cfg = self._auto_batch_size_cfg()
        if not cfg.get("enabled", False):
            return int(default_batch_size)

        total_gb = self._gpu_total_memory_gb()
        if total_gb is None:
            return int(default_batch_size)

        target_fraction = float(cfg.get("target_memory_fraction", 0.75))
        target_fraction = min(max(target_fraction, 0.1), 0.95)
        reference_gpu_gb = float(cfg.get("reference_gpu_gb", 8.0))
        reference_batch_size = int(cfg.get("reference_batch_size", default_batch_size))
        max_batch_size = int(cfg.get("max_batch_size", reference_batch_size))
        min_batch_size = int(cfg.get("min_batch_size", 1))

        memory_penalty = float(cfg.get("memory_penalty", 1.0 if not ssl else 1.35))
        scaled = int((reference_batch_size * total_gb * target_fraction) / max(reference_gpu_gb * 0.75 * memory_penalty, 1e-6))
        batch_size = max(min_batch_size, min(max_batch_size, max(default_batch_size, scaled)))
        return int(batch_size)

    def _resolve_batch_size(self, key: str, default: int, *, ssl: bool = False) -> int:
        train_cfg = self.cfg.get("train", {})
        configured = int(train_cfg.get(key, default))
        batch_size = self._estimate_auto_batch_size(default_batch_size=configured, ssl=ssl)
        if self._auto_batch_size_enabled() and batch_size != configured:
            print(
                {
                    "message": "auto_batch_size adjusted",
                    "key": key,
                    "configured": configured,
                    "resolved": batch_size,
                    "gpu_total_gb": self._gpu_total_memory_gb(),
                }
            )
        return batch_size

    def _dataset_cfg(self) -> dict[str, Any]:
        return self.cfg.get("dataset", {})

    def _dataset_name(self) -> str:
        dataset_cfg = self._dataset_cfg()
        dataset_name = dataset_cfg.get("dataset_name") or dataset_cfg.get("name")
        if not dataset_name:
            raise ValueError("dataset.dataset_name is required.")
        return str(dataset_name)

    def _dataset_root(self) -> str:
        dataset_cfg = self._dataset_cfg()
        root = dataset_cfg.get("root")
        if not root:
            raise ValueError("dataset.root is required.")
        return str(root)

    def _image_size(self) -> tuple[int, int]:
        dataset_cfg = self._dataset_cfg()
        image_size = dataset_cfg.get("image_size")
        if image_size is None:
            raise ValueError("dataset.image_size is required.")
        return int(image_size[0]), int(image_size[1])

    def _build_resize_transform(self, *, mode: str) -> Any:
        height, width = self._image_size()
        interpolation_mode = "bilinear" if mode == "image" else "nearest"

        def _transform(tensor: torch.Tensor) -> torch.Tensor:
            resized = F.interpolate(
                tensor.unsqueeze(0),
                size=(height, width),
                mode=interpolation_mode,
                align_corners=False if interpolation_mode != "nearest" else None,
            )
            return resized.squeeze(0)

        return _transform

    def _build_segmentation_loader(
            self,
            *,
            split: str,
            batch_size: int,
            shuffle: bool,
            split_file: str | None = None,
            augmentation_config: dict[str, Any] | None = None,
    ):
        dataset_cfg = self._dataset_cfg()
        train_cfg = self.cfg.get("train", {})
        num_workers = max(0, int(train_cfg.get("num_workers", 0)))
        persistent_workers = bool(train_cfg.get("persistent_workers", False)) if num_workers > 0 else False
        loader = build_dataloader(
            dataset_name=self._dataset_name(),
            root=self._dataset_root(),
            split=split,
            split_file=split_file,
            batch_size=batch_size,
            shuffle=shuffle,
            num_workers=num_workers,
            augmentation_config=augmentation_config,
            image_transform=self._build_resize_transform(mode="image"),
            mask_transform=self._build_resize_transform(mode="mask"),
            pin_memory=bool(train_cfg.get("pin_memory", self.device.type == "cuda")),
            persistent_workers=persistent_workers,
            prefetch_factor=train_cfg.get("prefetch_factor") if num_workers > 0 else None,
        )
        return loader

    def _build_val_loader(
            self,
            *,
            batch_size: int,
            shuffle: bool = False,
    ):
        dataset_cfg = self._dataset_cfg()
        val_split = dataset_cfg.get("val_split", "val")
        if val_split is None:
            return None
        return self._build_segmentation_loader(
            split=str(val_split),
            split_file=dataset_cfg.get("val_split_file"),
            batch_size=batch_size,
            shuffle=shuffle,
            augmentation_config=self.cfg.get("augmentation", {}).get("val"),
        )

    def _checkpoint_cfg(self) -> dict[str, Any]:
        return self.cfg.get("checkpoint", {})

    def _logging_cfg(self) -> dict[str, Any]:
        return self.cfg.get("logging", {})

    def _validation_cfg(self) -> dict[str, Any]:
        return self.cfg.get("validation", {})

    def _checkpoint_enabled(self) -> bool:
        return bool(self._checkpoint_cfg().get("save", True))

    def _best_mode(self) -> str:
        return str(self._checkpoint_cfg().get("monitor_mode", "min"))

    def _is_better_metric(self, metric: float) -> bool:
        if self.best_metric is None:
            return True
        if self._best_mode() == "max":
            return metric > self.best_metric
        return metric < self.best_metric

    def _save_checkpoint(self, filename: str, state: dict[str, Any]) -> Path | None:
        if not self._checkpoint_enabled():
            return None
        path = self.output_dir / filename
        torch.save(state, path)
        return path

    def _resume_checkpoint_path(self) -> Path | None:
        resume_path = self._checkpoint_cfg().get("resume")
        if not resume_path:
            return None
        path = Path(str(resume_path))
        if not path.is_absolute():
            path = Path.cwd() / path
        return path

    def _maybe_resume(
            self,
            *,
            module_map: dict[str, Any],
            optimizer: Any | None = None,
            scheduler: Any | None = None,
    ) -> dict[str, Any] | None:
        path = self._resume_checkpoint_path()
        if path is None:
            return None
        if not path.exists():
            raise FileNotFoundError(f"Resume checkpoint not found: {path}")

        checkpoint = torch.load(path, map_location="cpu")
        strict = bool(self._checkpoint_cfg().get("resume_strict", True))
        for key, module in module_map.items():
            if module is None:
                continue
            state_dict = checkpoint.get(key)
            if state_dict is not None:
                module.load_state_dict(state_dict, strict=strict)

        if optimizer is not None and checkpoint.get("optimizer") is not None:
            optimizer.load_state_dict(checkpoint["optimizer"])
        if scheduler is not None and checkpoint.get("scheduler") is not None:
            scheduler.load_state_dict(checkpoint["scheduler"])
        if checkpoint.get("grad_scaler") is not None:
            self.grad_scaler.load_state_dict(checkpoint["grad_scaler"])

        if checkpoint.get("best_metric") is not None:
            self.best_metric = float(checkpoint["best_metric"])
        elif checkpoint.get("metrics") is not None:
            monitor_name = str(self._checkpoint_cfg().get("monitor", "total"))
            monitor_value = checkpoint["metrics"].get(f"val_{monitor_name}")
            if monitor_value is None:
                monitor_value = checkpoint["metrics"].get(monitor_name)
            if monitor_value is not None:
                self.best_metric = float(monitor_value)
        if checkpoint.get("no_improve_epochs") is not None:
            self.no_improve_epochs = int(checkpoint["no_improve_epochs"])

        if bool(self._checkpoint_cfg().get("resume_training", True)):
            self.start_epoch = int(checkpoint.get("epoch", -1)) + 1
        return checkpoint

    def _validation_enabled(self) -> bool:
        return bool(self._validation_cfg().get("enabled", True))

    def _validation_interval(self) -> int:
        return max(1, int(self._validation_cfg().get("interval", 1)))

    def _should_validate(self, epoch: int) -> bool:
        return self._validation_enabled() and ((epoch + 1) % self._validation_interval() == 0)

    def _metric_task_mode(self) -> str:
        validation_cfg = self._validation_cfg()
        metrics_cfg = validation_cfg.get("metrics", self.cfg.get("metrics"))
        if isinstance(metrics_cfg, dict):
            return str(metrics_cfg.get("task_mode", "binary"))
        return "binary"

    def _metric_threshold(self) -> float:
        validation_cfg = self._validation_cfg()
        threshold = validation_cfg.get("threshold", 0.5)
        return float(threshold)

    def _build_validation_metrics(self) -> dict[str, Any]:
        validation_cfg = self._validation_cfg()
        metrics_cfg = validation_cfg.get("metrics", self.cfg.get("metrics"))
        if metrics_cfg is None:
            return {}
        return build_metrics(metrics_cfg)

    def _early_stopping_enabled(self) -> bool:
        return bool(self._validation_cfg().get("early_stopping", False))

    def _early_stopping_patience(self) -> int:
        return max(1, int(self._validation_cfg().get("early_stopping_patience", 10)))

    def _early_stopping_min_delta(self) -> float:
        return float(self._validation_cfg().get("early_stopping_min_delta", 0.0))

    def _update_validation_metrics(
            self,
            metrics: dict[str, Any],
            *,
            logits: torch.Tensor,
            target: torch.Tensor,
    ) -> None:
        if not metrics:
            return
        update_metrics(
            metrics,
            logits,
            target,
            task_mode=self._metric_task_mode(),
            threshold=self._metric_threshold(),
            num_classes=int(self._dataset_cfg().get("num_classes", 1)),
        )

    def _compute_validation_metric_values(self, metrics: dict[str, Any]) -> dict[str, float]:
        if not metrics:
            return {}
        values = compute_metrics(metrics)
        reset_metrics(metrics)
        return values

    def _init_swanlab(self) -> None:
        logging_cfg = self._logging_cfg()
        if not bool(logging_cfg.get("use_swanlab", False)):
            return
        if swanlab is None:
            print("SwanLab is not installed. Logging will continue without SwanLab.")
            return

        run_name = logging_cfg.get("experiment_name") or self.output_dir.name
        self.swanlab_run = swanlab.init(
            project=logging_cfg.get("project", "X_SSL_Net"),
            name=run_name,
            config=self.cfg,
            logdir=logging_cfg.get("swanlab_logdir", "swanlog"),
            mode=logging_cfg.get("swanlab_mode"),
        )

    def _log_metrics(self, metrics: dict[str, float], *, step: int) -> None:
        if self.swanlab_run is None:
            return
        swanlab.log(metrics, step=step)

    def _close_loggers(self) -> None:
        if self.swanlab_run is not None:
            swanlab.finish()
            self.swanlab_run = None

    def _log_interval(self) -> int:
        return max(1, int(self._logging_cfg().get("log_interval", 20)))

    def _grad_clip_cfg(self) -> dict[str, Any]:
        cfg = self.cfg.get("train", {}).get("grad_clip", {})
        return cfg if isinstance(cfg, dict) else {}

    def _grad_clip_enabled(self) -> bool:
        return bool(self._grad_clip_cfg().get("enabled", False))

    def _accum_steps(self) -> int:
        return max(1, int(self.cfg.get("train", {}).get("accum_steps", 1)))

    def _clip_gradients(self, module: nn.Module | None) -> float | None:
        if module is None or not self._grad_clip_enabled():
            return None
        cfg = self._grad_clip_cfg()
        max_norm = float(cfg.get("max_norm", 1.0))
        norm_type = float(cfg.get("norm_type", 2.0))
        params = [param for param in module.parameters() if param.requires_grad and param.grad is not None]
        if not params:
            return None
        total_norm = torch.nn.utils.clip_grad_norm_(params, max_norm=max_norm, norm_type=norm_type)
        return float(total_norm.detach().cpu() if isinstance(total_norm, torch.Tensor) else total_norm)

    def _current_lrs(self, optimizer: Any | None) -> list[float]:
        if optimizer is None:
            return []
        return [float(group.get("lr", 0.0)) for group in optimizer.param_groups]

    @staticmethod
    def _count_parameters(module: nn.Module | None) -> dict[str, int]:
        if module is None:
            return {"total": 0, "trainable": 0}
        total = sum(param.numel() for param in module.parameters())
        trainable = sum(param.numel() for param in module.parameters() if param.requires_grad)
        return {"total": int(total), "trainable": int(trainable)}

    @staticmethod
    def _loader_summary(loader: Any | None) -> dict[str, Any] | None:
        if loader is None:
            return None
        dataset = getattr(loader, "dataset", None)
        return {
            "dataset_size": len(dataset) if dataset is not None else None,
            "num_batches": len(loader),
            "batch_size": getattr(loader, "batch_size", None),
            "num_workers": getattr(loader, "num_workers", None),
            "pin_memory": getattr(loader, "pin_memory", None),
            "persistent_workers": getattr(loader, "persistent_workers", None),
            "prefetch_factor": getattr(loader, "prefetch_factor", None),
            "drop_last": getattr(loader, "drop_last", None),
        }

    def _training_setup_summary(
            self,
            *,
            model_map: dict[str, nn.Module | None],
            loader_map: dict[str, Any | None],
            optimizer: Any | None = None,
            scheduler: Any | None = None,
    ) -> dict[str, Any]:
        return {
            "trainer": self.cfg.get("trainer", {}).get("name"),
            "device": str(self.device),
            "amp_enabled": self._amp_enabled(),
            "output_dir": str(self.output_dir),
            "start_epoch": self.start_epoch,
            "train": self.cfg.get("train", {}),
            "dataset": self.cfg.get("dataset", {}),
            "model": self.cfg.get("model", {}),
            "optimizer": self.cfg.get("optimizer", {}),
            "scheduler": self.cfg.get("scheduler"),
            "current_lrs": self._current_lrs(optimizer),
            "validation": self.cfg.get("validation", {}),
            "checkpoint": self.cfg.get("checkpoint", {}),
            "logging": self.cfg.get("logging", {}),
            "model_parameters": {
                name: self._count_parameters(module)
                for name, module in model_map.items()
            },
            "loaders": {
                name: self._loader_summary(loader)
                for name, loader in loader_map.items()
            },
            "cuda": {
                "available": torch.cuda.is_available(),
                "device_name": torch.cuda.get_device_name(self.device) if self.device.type == "cuda" else None,
                "device_count": torch.cuda.device_count(),
            },
        }

    def _print_training_setup(
            self,
            *,
            model_map: dict[str, nn.Module | None],
            loader_map: dict[str, Any | None],
            optimizer: Any | None = None,
            scheduler: Any | None = None,
    ) -> None:
        if not bool(self._logging_cfg().get("print_training_setup", True)):
            return
        summary = self._training_setup_summary(
            model_map=model_map,
            loader_map=loader_map,
            optimizer=optimizer,
            scheduler=scheduler,
        )
        print("========== TRAINING SETUP ==========")
        pprint.pprint(summary, sort_dicts=False, width=120)
        print("======== END TRAINING SETUP ========")

    def _gpu_memory_mb(self) -> float:
        if self.device.type != "cuda" or not torch.cuda.is_available():
            return 0.0
        return float(torch.cuda.max_memory_allocated(device=self.device) / (1024 ** 2))

    def _performance_snapshot(
            self,
            *,
            epoch: int,
            step: int,
            num_steps: int,
            data_time: float,
            iter_time: float,
            metrics: dict[str, float],
            prefix: str = "train",
    ) -> dict[str, float | int]:
        snapshot: dict[str, float | int] = {
            "epoch": epoch,
            "step": step,
            "num_steps": num_steps,
            "data_time": data_time,
            "iter_time": iter_time,
            "gpu_memory_mb": self._gpu_memory_mb(),
        }
        lrs = self._current_lrs(getattr(self, "optimizer", None))
        if lrs:
            snapshot["lr"] = lrs[0]
        for key, value in metrics.items():
            snapshot[f"{prefix}_{key}"] = value
        return snapshot

    def _maybe_log_step(
            self,
            *,
            epoch: int,
            step: int,
            num_steps: int,
            data_time: float,
            iter_time: float,
            metrics: dict[str, float],
            prefix: str = "train",
    ) -> None:
        if step % self._log_interval() != 0 and step != num_steps:
            return
        snapshot = self._performance_snapshot(
            epoch=epoch,
            step=step,
            num_steps=num_steps,
            data_time=data_time,
            iter_time=iter_time,
            metrics=metrics,
            prefix=prefix,
        )
        print(snapshot)
        log_metrics = {
            f"{prefix}/{key}": value
            for key, value in metrics.items()
        }
        log_metrics.update(
            {
                f"{prefix}/data_time": data_time,
                f"{prefix}/iter_time": iter_time,
                f"{prefix}/gpu_memory_mb": float(snapshot["gpu_memory_mb"]),
            }
        )
        if "lr" in snapshot:
            log_metrics[f"{prefix}/lr"] = float(snapshot["lr"])

    @staticmethod
    def _average_metric_sums(metric_sums: dict[str, float], steps: int) -> dict[str, float]:
        if steps <= 0:
            return {}
        return {key: value / steps for key, value in metric_sums.items()}

    def _base_checkpoint_state(self, *, epoch: int, metrics: dict[str, float] | None = None) -> dict[str, Any]:
        state = {
            "epoch": epoch,
            "cfg": self.cfg,
            "metrics": metrics or {},
            "grad_scaler": self.grad_scaler.state_dict(),
            "no_improve_epochs": self.no_improve_epochs,
        }
        return state

    def _finalize_epoch(
            self,
            *,
            epoch: int,
            train_metrics: dict[str, float],
            val_metrics: dict[str, float] | None,
            checkpoint_state: dict[str, Any],
    ) -> tuple[dict[str, Any], bool]:
        merged_metrics = dict(train_metrics)
        if val_metrics is not None:
            merged_metrics.update({f"val_{key}": value for key, value in val_metrics.items()})

        improved = False
        if val_metrics is not None:
            monitor_name = str(self._checkpoint_cfg().get("monitor", "total"))
            if monitor_name not in val_metrics:
                raise KeyError(f"Checkpoint monitor '{monitor_name}' not found in val metrics.")
            monitor_value = float(val_metrics[monitor_name])
            delta = self._early_stopping_min_delta()
            previous_best = self.best_metric
            is_better = self._is_better_metric(monitor_value)
            if previous_best is not None and self._best_mode() == "max":
                is_better = monitor_value > (previous_best + delta)
            elif previous_best is not None and self._best_mode() == "min":
                is_better = monitor_value < (previous_best - delta)

            if is_better:
                self.best_metric = monitor_value
                self.no_improve_epochs = 0
                improved = True
                best_state = dict(checkpoint_state)
                best_state.update(
                    self._base_checkpoint_state(
                        epoch=epoch,
                        metrics=merged_metrics,
                    )
                )
                best_state["best_metric"] = self.best_metric
                self._save_checkpoint("best.pth", best_state)
            else:
                self.no_improve_epochs += 1

        save_last = bool(self._checkpoint_cfg().get("save_last", True))
        if save_last:
            last_state = dict(checkpoint_state)
            last_state.update(self._base_checkpoint_state(epoch=epoch, metrics=merged_metrics))
            if self.best_metric is not None:
                last_state["best_metric"] = self.best_metric
            self._save_checkpoint("last.pth", last_state)

        summary = {"epoch": epoch}
        summary.update(train_metrics)
        if val_metrics is not None:
            summary.update({f"val_{key}": value for key, value in val_metrics.items()})
        if self.best_metric is not None:
            summary["best_metric"] = float(self.best_metric)
        summary["no_improve_epochs"] = self.no_improve_epochs
        lrs = self._current_lrs(getattr(self, "optimizer", None))
        if lrs:
            summary["lr"] = lrs[0]
        self._log_metrics(summary, step=epoch)
        should_stop = False
        if val_metrics is not None and self._early_stopping_enabled():
            should_stop = self.no_improve_epochs >= self._early_stopping_patience()
            summary["early_stop"] = should_stop
            summary["improved"] = improved
        return summary, should_stop

    @abstractmethod
    def build(self) -> None:
        """
        创建模型、优化器、数据加载器等运行所需对象。
        """

    @abstractmethod
    def train(self) -> None:
        """
        执行完整训练流程。
        """