import os
from typing import Dict, List, Tuple

import numpy as np
import rasterio
import torch
from huggingface_hub import hf_hub_download
from torch.utils.data import Dataset

from config import DEFAULT_PATCH_SIZE, NUM_CHANNELS, NUM_CLASSES, IGNORE_INDEX, CLASS_NAMES

DATASET_REPO = os.environ.get("DATASET_REPO", "")
HF_TOKEN     = os.environ.get("HF_TOKEN", "") or None

BAND_FILES      = [f"H_{i}.tif" for i in range(1, 8)]
TRAIN_MASK_FILE = "TRAINING.tif"
VAL_MASK_FILE   = "GROUND TRUTH.tif"


# ── File helpers ─────────────────────────────────────────────

def _get_path(filename: str) -> str:
    """Use local file if it exists, otherwise download from HuggingFace."""
    if os.path.exists(filename):
        return filename
    if not DATASET_REPO:
        raise EnvironmentError(
            f"'{filename}' not found locally and DATASET_REPO is not set."
        )
    return hf_hub_download(
        repo_id=DATASET_REPO,
        filename=filename,
        repo_type="dataset",
        token=HF_TOKEN,
    )


def _read_band(path: str) -> np.ndarray:
    with rasterio.open(path) as src:
        data = src.read(1).astype(np.float32)
        if src.nodata is not None:
            data[data == src.nodata] = np.nan
    return data


def _read_mask_raw(path: str) -> Tuple[np.ndarray, object, str]:
    with rasterio.open(path) as src:
        data   = src.read(1)
        nodata = src.nodata
        info   = f"shape={src.shape} dtype={src.dtypes[0]} nodata={nodata}"
    return data, nodata, info


def _normalize(image: np.ndarray) -> np.ndarray:
    out = np.zeros_like(image, dtype=np.float32)
    for b in range(image.shape[0]):
        band   = image[b]
        finite = band[np.isfinite(band)]
        if len(finite) == 0:
            continue
        lo, hi = np.percentile(finite, 2), np.percentile(finite, 98)
        out[b]  = np.clip((np.nan_to_num(band) - lo) / max(hi - lo, 1e-6), 0.0, 1.0)
    return out


def _compute_ndvi(raw_image: np.ndarray) -> np.ndarray:
    """NDVI = (NIR - Red) / (NIR + Red).  H_5=NIR (idx 4), H_4=Red (idx 3)."""
    nir = raw_image[4].astype(np.float32)
    red = raw_image[3].astype(np.float32)
    denom = nir + red
    return np.where(np.abs(denom) > 1e-6, (nir - red) / denom, 0.0).clip(-1.0, 1.0)


def _compute_ndwi(raw_image: np.ndarray) -> np.ndarray:
    """NDWI = (Green - NIR) / (Green + NIR).  H_3=Green (idx 2), H_5=NIR (idx 4)."""
    green = raw_image[2].astype(np.float32)
    nir   = raw_image[4].astype(np.float32)
    denom = green + nir
    return np.where(np.abs(denom) > 1e-6, (green - nir) / denom, 0.0).clip(-1.0, 1.0)


def _remap_mask(raw: np.ndarray, nodata_val) -> Tuple[np.ndarray, List[int]]:
    """
    Map raw pixel values -> 0..NUM_CLASSES-1.
    Value 0 and nodata -> IGNORE_INDEX.
    """
    if nodata_val is not None:
        nodata_px = raw == int(nodata_val)
    else:
        nodata_px = np.zeros(raw.shape, dtype=bool)

    ignore_px  = nodata_px | (raw == 0)
    valid      = ~ignore_px
    raw_unique = sorted(int(v) for v in np.unique(raw[valid]))

    mask = np.full(raw.shape, IGNORE_INDEX, dtype=np.int64)
    for cls_idx, raw_val in enumerate(raw_unique[:NUM_CLASSES]):
        mask[raw == raw_val] = cls_idx

    return mask, raw_unique


def _extract_patches(
    image: np.ndarray,
    mask:  np.ndarray,
    patch_size: int,
) -> Tuple[np.ndarray, np.ndarray]:
    _, H_img, W_img = image.shape
    H_msk, W_msk   = mask.shape
    H = min(H_img, H_msk)
    W = min(W_img, W_msk)
    stride = patch_size // 2
    imgs, masks = [], []

    def steps(size):
        s = list(range(0, size - patch_size + 1, stride))
        if not s:
            s = [0] if size >= patch_size else []
        elif s[-1] < size - patch_size:
            s.append(size - patch_size)
        return s

    for y in steps(H):
        for x in steps(W):
            pm = mask[y : y + patch_size, x : x + patch_size]
            pi = image[:, y : y + patch_size, x : x + patch_size]
            if pm.shape == (patch_size, patch_size) and (pm != IGNORE_INDEX).any():
                imgs.append(pi)
                masks.append(pm)

    if not imgs:
        ph = min(patch_size, H)
        pw = min(patch_size, W)
        img_pad  = np.zeros((image.shape[0], patch_size, patch_size), dtype=np.float32)
        mask_pad = np.full((patch_size, patch_size), IGNORE_INDEX, dtype=np.int64)
        img_pad[:, :ph, :pw]  = image[:, :ph, :pw]
        mask_pad[:ph, :pw]    = mask[:ph, :pw]
        imgs.append(img_pad)
        masks.append(mask_pad)

    return np.stack(imgs).astype(np.float32), np.stack(masks).astype(np.int64)


# ── Spectral analysis ─────────────────────────────────────────

def compute_spectral_signatures(full_image: np.ndarray, full_mask: np.ndarray) -> Dict:
    """Per-class mean and std across the 7 normalized bands, from labeled pixels."""
    sigs = {}
    for cls_idx in range(NUM_CLASSES):
        px = full_mask == cls_idx
        if px.sum() == 0:
            sigs[cls_idx] = {
                "mean": np.zeros(NUM_CHANNELS, dtype=np.float32),
                "std":  np.zeros(NUM_CHANNELS, dtype=np.float32),
                "n":    0,
            }
        else:
            vals = full_image[:, px]  # (7, N)
            sigs[cls_idx] = {
                "mean": vals.mean(axis=1).astype(np.float32),
                "std":  vals.std(axis=1).astype(np.float32),
                "n":    int(px.sum()),
            }
    return sigs


# ── Dataset class ─────────────────────────────────────────────

class MultiSpectralDataset(Dataset):
    def __init__(self, images: np.ndarray, masks: np.ndarray):
        self.images = images.astype(np.float32)
        self.masks  = masks.astype(np.int64)

    def __len__(self):
        return len(self.images)

    def __getitem__(self, idx: int):
        return torch.from_numpy(self.images[idx]), torch.from_numpy(self.masks[idx])


# ── Public API ────────────────────────────────────────────────

def load_data(patch_size: int = DEFAULT_PATCH_SIZE) -> Dict:
    # Read raw bands
    raw_bands = [_read_band(_get_path(f)) for f in BAND_FILES]
    raw_image = np.stack(raw_bands, axis=0)  # (7, H, W) raw float32

    # Compute spectral indices from raw values (ratio, so must use raw)
    ndvi = _compute_ndvi(raw_image)
    ndwi = _compute_ndwi(raw_image)

    # Normalize
    image = _normalize(raw_image)  # (7, H, W) normalized [0,1]

    # Read masks
    raw_train, nd_train, info_train = _read_mask_raw(_get_path(TRAIN_MASK_FILE))
    raw_val,   nd_val,   info_val   = _read_mask_raw(_get_path(VAL_MASK_FILE))

    # Remap
    train_mask, train_vals = _remap_mask(raw_train, nd_train)
    val_mask,   val_vals   = _remap_mask(raw_val,   nd_val)

    if not train_vals:
        raise ValueError(
            f"TRAINING.tif has no labeled pixels. Info: {info_train} | "
            f"Unique raw values: {np.unique(raw_train).tolist()}"
        )

    # Patches
    tr_imgs, tr_masks = _extract_patches(image, train_mask, patch_size)
    va_imgs, va_masks = _extract_patches(image, val_mask,   patch_size)

    # Spectral signatures from training labels
    signatures = compute_spectral_signatures(image, train_mask)

    train_labeled = int((train_mask != IGNORE_INDEX).sum())
    val_labeled   = int((val_mask   != IGNORE_INDEX).sum())

    def _class_dist(mask, total):
        parts = []
        for i, name in enumerate(CLASS_NAMES):
            n = int((mask == i).sum())
            parts.append(f"{name}: {n:,} ({n / max(1, total) * 100:.1f}%)")
        return " | ".join(parts)

    status = "\n".join([
        f"Train patches: **{len(tr_imgs)}** | Val patches: **{len(va_imgs)}** | Patch: **{patch_size}x{patch_size}**",
        f"Training labels: **{train_labeled:,}** px — {_class_dist(train_mask, train_labeled)}",
        f"Validation labels: **{val_labeled:,}** px — {_class_dist(val_mask, val_labeled)}",
    ])

    return {
        "full_image":       image,
        "full_train_mask":  train_mask,
        "full_val_mask":    val_mask,
        "ndvi":             ndvi,
        "ndwi":             ndwi,
        "signatures":       signatures,
        "train_images":     tr_imgs,
        "train_masks":      tr_masks,
        "val_images":       va_imgs,
        "val_masks":        va_masks,
        "status":           status,
    }