from __future__ import annotations

from pathlib import Path
from typing import Dict, Iterable, Optional

import numpy as np
import torch
from PIL import Image
from torch.utils.data import DataLoader, Dataset
from utils.dataset_cache import dataloader_kwargs, print_dataloader_policy

try:
    from torchvision import transforms
except Exception:  # pragma: no cover - torchvision import errors are environment-specific.
    transforms = None


IMG_EXTS = {".png", ".jpg", ".jpeg", ".tif", ".tiff", ".bmp"}
MASK_DIR_CANDIDATES = ("Mask", "mask", "label", "labels", "OUT", "gt")


def _scan(folder: Path) -> Dict[str, Path]:
    return {
        p.stem: p
        for p in sorted(folder.iterdir())
        if p.is_file() and not p.name.startswith(".") and p.suffix.lower() in IMG_EXTS
    }


def _resolve(root: Path, value: str | Path) -> Path:
    p = Path(value)
    return p if p.is_absolute() else root / p


def _configured_dirs(root: Path, split: str, cfg: dict) -> Optional[tuple[Path, Path, Path]]:
    if "splits" in cfg:
        split_dir = root / cfg.get("splits", {}).get(split, split)
        a_dir = split_dir / cfg.get("image_a_folder", "A")
        b_dir = split_dir / cfg.get("image_b_folder", "B")
        m_dir = split_dir / cfg.get("mask_folder", "label")
        return a_dir, b_dir, m_dir
    source = cfg.get("split", {}).get("source_folders", {})
    a_rel = source.get(f"{split}_a") or source.get("a")
    b_rel = source.get(f"{split}_b") or source.get("b")
    m_rel = source.get(f"{split}_mask") or source.get("mask")
    if not (a_rel and b_rel and m_rel):
        return None
    return _resolve(root, a_rel), _resolve(root, b_rel), _resolve(root, m_rel)


def _mask_dir(split_dir: Path) -> Path:
    for name in MASK_DIR_CANDIDATES:
        candidate = split_dir / name
        if candidate.is_dir():
            return candidate
    tried = ", ".join(MASK_DIR_CANDIDATES)
    raise FileNotFoundError(f"No mask directory under {split_dir}; tried {tried}")


class CDDataset(Dataset):
    """Configurable binary change-detection dataset.

    This is the shared root loader for CD-Models. It intentionally supports the
    folder conventions found in mamba-cd and the nested research repos instead
    of adding another WildFire-specific loader.
    """

    def __init__(
        self,
        root: str | Path,
        split: str,
        cfg: Optional[dict] = None,
        image_size: Optional[int] = None,
        normalize: bool = True,
        return_format: str = "dict",
    ) -> None:
        self.root = Path(root)
        self.split = split
        self.cfg = cfg or {}
        self.return_format = return_format
        ds_cfg = self.cfg.get("dataset", self.cfg)
        self.image_size = int(image_size or ds_cfg.get("image_size", ds_cfg.get("img_size", 256)))
        self.threshold = int(ds_cfg.get("binary_threshold", ds_cfg.get("mask_threshold", 127)))
        self.mean = ds_cfg.get("mean", ds_cfg.get("mean_a", [0.485, 0.456, 0.406]))
        self.std = ds_cfg.get("std", ds_cfg.get("std_a", [0.229, 0.224, 0.225]))
        if not self.root.is_dir():
            dataset_name = ds_cfg.get("_dataset_name", ds_cfg.get("name", "unknown"))
            raise FileNotFoundError(
                f"\n{'=' * 60}\n"
                f"Dataset root directory not found:\n  {self.root}\n\n"
                f"For dataset '{dataset_name}', either:\n"
                f"  1. Download the dataset and place it at the above path\n"
                f"  2. Update DATA_ROOT: export DATA_ROOT=/correct/path\n"
                f"  3. Edit configs/datasets/{dataset_name}.yaml\n"
                f"{'=' * 60}"
            )

        configured = _configured_dirs(self.root, split, self.cfg)
        if configured is None:
            split_dir = self.root / split
            a_dir = split_dir / "A"
            b_dir = split_dir / "B"
            m_dir = _mask_dir(split_dir)
        else:
            a_dir, b_dir, m_dir = configured

        for label, folder in (("A", a_dir), ("B", b_dir), ("mask", m_dir)):
            if not folder.is_dir():
                raise FileNotFoundError(f"{label} directory not found: {folder}")

        a_files = _scan(a_dir)
        b_files = _scan(b_dir)
        m_files = _scan(m_dir)
        stems = sorted(set(a_files) & set(b_files) & set(m_files))
        if not stems:
            raise RuntimeError(f"No matched A/B/mask triplets found for {self.root} split {split}")
        self.samples = [(a_files[s], b_files[s], m_files[s], s) for s in stems]

        if transforms is None:
            self.image_tf = None
        else:
            ops: list = [transforms.Resize((self.image_size, self.image_size)), transforms.ToTensor()]
            if normalize:
                ops.append(transforms.Normalize(mean=self.mean, std=self.std))
            self.image_tf = transforms.Compose(ops)

    def __len__(self) -> int:
        return len(self.samples)

    def _image(self, path: Path) -> torch.Tensor:
        img = Image.open(path).convert("RGB")
        if self.image_tf is not None:
            return self.image_tf(img)
        img = img.resize((self.image_size, self.image_size), Image.BILINEAR)
        arr = np.array(img, dtype=np.float32) / 255.0
        return torch.from_numpy(arr).permute(2, 0, 1)

    def _mask(self, path: Path) -> torch.Tensor:
        mask = Image.open(path).convert("L").resize((self.image_size, self.image_size), Image.NEAREST)
        arr = np.array(mask, dtype=np.uint8)
        if arr.max() <= 1:
            bin_mask = (arr > 0).astype(np.float32)
        else:
            bin_mask = (arr > self.threshold).astype(np.float32)
        return torch.from_numpy(bin_mask).unsqueeze(0)

    def __getitem__(self, index: int):
        a_path, b_path, mask_path, name = self.samples[index]
        a = self._image(a_path)
        b = self._image(b_path)
        mask = self._mask(mask_path)
        if self.return_format == "tuple":
            return a, b, mask, name
        if self.return_format == "legacy":
            return {"A": a, "B": b, "L": mask.squeeze(0).long(), "name": name}
        return {"a": a, "b": b, "mask": mask, "name": name}


def build_dataloader(
    cfg: dict,
    split: str,
    shuffle: Optional[bool] = None,
    return_format: str = "dict",
) -> DataLoader:
    ds_cfg = cfg.get("dataset", cfg)
    dataset = CDDataset(
        ds_cfg.get("root", ds_cfg["data_root"]),
        split=split,
        cfg=cfg,
        image_size=int(ds_cfg.get("image_size", ds_cfg.get("img_size", 256))),
        return_format=return_format,
    )
    batch_size = int(ds_cfg.get("batch_size", 8))
    num_workers = int(ds_cfg.get("num_workers", 4))
    if shuffle is None:
        shuffle = split == "train"
    print_dataloader_policy({**ds_cfg, "num_workers": num_workers}, torch.cuda.is_available())
    return DataLoader(
        dataset,
        batch_size=batch_size,
        shuffle=shuffle,
        **dataloader_kwargs({**ds_cfg, "num_workers": num_workers}, torch.cuda.is_available()),
        drop_last=split == "train",
    )


def available_splits(cfg: dict) -> Iterable[str]:
    ds_cfg = cfg.get("dataset", cfg)
    root = Path(ds_cfg.get("root", ds_cfg["data_root"]))
    if "splits" in cfg:
        yield from cfg["splits"]
        return
    source = cfg.get("split", {}).get("source_folders", {})
    for split in ("train", "val", "test"):
        if source.get(f"{split}_a") and source.get(f"{split}_b") and source.get(f"{split}_mask"):
            yield split
        elif (root / split).is_dir():
            yield split