"""
Dataset Loaders for Molecular Property Prediction

Supports loading datasets from Hugging Face and PyTorch Geometric.
"""

import torch
import numpy as np
from torch.utils.data import Dataset
from torch_geometric.data import Data, InMemoryDataset
from datasets import load_dataset
from typing import List, Tuple, Optional, Dict
import os


class QM9Dataset(InMemoryDataset):
    """
    QM9 dataset loader from Hugging Face.
    
    Loads the QM9 dataset (133K molecules) with 3D coordinates and quantum properties.
    
    Args:
        root (str): Root directory for dataset storage
        hf_dataset_path (str): Hugging Face dataset path (default: "yairschiff/qm9")
        target_property (str): Target property to predict (default: "homo")
        split (str): Dataset split ("train", "val", "test")
        transform: Optional transform to apply
        pre_transform: Optional pre-transform to apply
    """
    
    def __init__(
        self,
        root: str = "data/qm9",
        hf_dataset_path: str = "yairschiff/qm9",
        target_property: str = "homo",
        split: str = "train",
        transform=None,
        pre_transform=None,
    ):
        self.hf_dataset_path = hf_dataset_path
        self.target_property = target_property
        self.split = split
        
        super().__init__(root, transform, pre_transform)
        self.data, self.slices = torch.load(self.processed_paths[0], weights_only=False)
    
    @property
    def raw_file_names(self) -> List[str]:
        return []  # We load directly from HuggingFace
    
    @property
    def processed_file_names(self) -> List[str]:
        return [f'qm9_{self.split}_processed.pt']
    
    def download(self):
        """Download is handled by HuggingFace datasets library."""
        pass
    
    def process(self):
        """Process raw data into PyTorch Geometric format."""
        print(f"Loading QM9 dataset from Hugging Face: {self.hf_dataset_path}")
        
        # Load dataset directly from Hugging Face
        raw_dataset = load_dataset(self.hf_dataset_path, split=self.split)
        print(f"Loaded {len(raw_dataset)} molecules for {self.split} split")
        
        data_list = []
        
        print("Processing molecules...")
        for idx, sample in enumerate(raw_dataset):
            if idx % 10000 == 0:
                print(f"  Processed {idx}/{len(raw_dataset)} molecules")
            
            # Extract features - use correct column names from HF dataset
            atomic_symbols = sample['atomic_symbols']  # List of atomic symbols like ['C', 'H', 'H', ...]
            positions = torch.tensor(sample['pos'], dtype=torch.float32)  # 3D coordinates
            
            # Convert atomic symbols to atomic numbers
            symbol_to_number = {
                'H': 1, 'He': 2, 'Li': 3, 'Be': 4, 'B': 5, 'C': 6, 
                'N': 7, 'O': 8, 'F': 9, 'Ne': 10
            }
            atomic_numbers = [symbol_to_number.get(sym, 0) for sym in atomic_symbols]
            
            # One-hot encode atomic numbers (H=1 to Ne=10, plus one for unknown)
            num_atoms = len(atomic_numbers)
            node_features = torch.zeros(num_atoms, 11)  # 11 possible atom types
            for i, z in enumerate(atomic_numbers):
                if 1 <= z <= 10:
                    node_features[i, z - 1] = 1.0
                else:
                    node_features[i, 10] = 1.0  # Unknown atom type
            
            # Get target property
            target = torch.tensor([sample[self.target_property]], dtype=torch.float32)
            
            # Distance-based edges (5.0 Angstrom cutoff)
            edge_index = self._get_edge_index(num_atoms, cutoff=5.0, positions=positions)
            
            # Create PyG Data object
            data = Data(
                x=node_features,
                pos=positions,
                edge_index=edge_index,
                y=target,
                num_atoms=num_atoms,
            )
            
            if self.pre_transform is not None:
                data = self.pre_transform(data)
            
            data_list.append(data)
        
        # Save processed data
        data, slices = self.collate(data_list)
        torch.save((data, slices), self.processed_paths[0])
        print(f"Processed {len(data_list)} molecules")
    
    def _get_edge_index(self, num_atoms: int, cutoff: float = 5.0, positions: Optional[torch.Tensor] = None) -> torch.Tensor:
        """
        Create edge index based on distance cutoff.
        
        Args:
            num_atoms: Number of atoms in molecule
            cutoff: Distance cutoff in Angstroms
            positions: Atom positions [num_atoms, 3] (optional)
            
        Returns:
            edge_index: Edge indices [2, num_edges]
        """
        if positions is not None:
            # Distance-based edges (more realistic!)
            dist_matrix = torch.cdist(positions, positions)
            
            # Create edges within cutoff distance
            within_cutoff = (dist_matrix < cutoff) & (dist_matrix > 0)  # Exclude self-loops
            edge_index = within_cutoff.nonzero().t()
            
        else:
            # Fallback: fully connected (for backward compatibility)
            row = []
            col = []
            for i in range(num_atoms):
                for j in range(num_atoms):
                    if i != j:
                        row.append(i)
                        col.append(j)
            edge_index = torch.tensor([row, col], dtype=torch.long)
        
        return edge_index


class MolecularDatasetWrapper:
    """
    Wrapper for molecular datasets with preprocessing and normalization.
    
    Args:
        dataset: Base dataset (e.g., QM9Dataset)
        normalize_targets: Whether to normalize target values
        rotation_augmentation: Whether to apply random rotations
    """
    
    def __init__(
        self,
        dataset: InMemoryDataset,
        normalize_targets: bool = True,
        rotation_augmentation: bool = False,
        target_mean: Optional[float] = None,
        target_std: Optional[float] = None,
    ):
        self.dataset = dataset
        self.normalize_targets = normalize_targets
        self.rotation_augmentation = rotation_augmentation
        
        # Use provided stats or compute from dataset
        if normalize_targets:
            if target_mean is not None and target_std is not None:
                # Use provided normalization stats (for val/test)
                self.target_mean = target_mean
                self.target_std = target_std
            else:
                # Compute from this dataset (for train)
                self.target_mean, self.target_std = self._compute_normalization_stats()
        else:
            self.target_mean = 0.0
            self.target_std = 1.0
    
    def _compute_normalization_stats(self) -> Tuple[float, float]:
        """Compute mean and std of target values."""
        targets = []
        for i in range(len(self.dataset)):
            data = self.dataset[i]
            targets.append(data.y.item())
        
        targets = np.array(targets)
        return targets.mean(), targets.std()
    
    def __len__(self) -> int:
        return len(self.dataset)
    
    def __getitem__(self, idx: int) -> Data:
        data = self.dataset[idx].clone()
        
        # Normalize targets
        if self.normalize_targets:
            data.y = (data.y - self.target_mean) / self.target_std
        
        # Apply rotation augmentation (only if enabled)
        if self.rotation_augmentation:
            data.pos = self._random_rotation(data.pos)
        
        return data
    
    def _random_rotation(self, pos: torch.Tensor) -> torch.Tensor:
        """Apply random 3D rotation."""
        # Random rotation matrix
        angles = torch.rand(3) * 2 * np.pi
        
        # Rotation around x-axis
        Rx = torch.tensor([
            [1, 0, 0],
            [0, torch.cos(angles[0]), -torch.sin(angles[0])],
            [0, torch.sin(angles[0]), torch.cos(angles[0])]
        ], dtype=pos.dtype)
        
        # Rotation around y-axis
        Ry = torch.tensor([
            [torch.cos(angles[1]), 0, torch.sin(angles[1])],
            [0, 1, 0],
            [-torch.sin(angles[1]), 0, torch.cos(angles[1])]
        ], dtype=pos.dtype)
        
        # Rotation around z-axis
        Rz = torch.tensor([
            [torch.cos(angles[2]), -torch.sin(angles[2]), 0],
            [torch.sin(angles[2]), torch.cos(angles[2]), 0],
            [0, 0, 1]
        ], dtype=pos.dtype)
        
        # Combined rotation
        R = Rz @ Ry @ Rx
        
        return pos @ R.T
    
    def denormalize(self, normalized_values: torch.Tensor) -> torch.Tensor:
        """Denormalize predictions back to original scale."""
        return normalized_values * self.target_std + self.target_mean


def create_qm9_dataloaders(
    root: str = "data/qm9",
    hf_dataset_path: str = "yairschiff/qm9",
    target_property: str = "homo",
    batch_size: int = 32,
    num_workers: int = 4,
    normalize_targets: bool = True,
    rotation_augmentation: bool = True,
    train_split: float = 0.8,
    val_split: float = 0.1,
) -> Dict[str, torch.utils.data.DataLoader]:
    """
    Create train/val/test dataloaders for QM9.
    
    Args:
        root: Root directory for dataset
        hf_dataset_path: Hugging Face dataset path
        target_property: Target property to predict
        batch_size: Batch size
        num_workers: Number of data loading workers
        normalize_targets: Whether to normalize targets
        rotation_augmentation: Whether to use rotation augmentation
        train_split: Fraction for training (default: 0.8)
        val_split: Fraction for validation (default: 0.1)
        
    Returns:
        Dictionary with 'train', 'val', 'test' dataloaders
    """
    from torch_geometric.loader import DataLoader
    from torch.utils.data import random_split
    
    # Load the full dataset (only 'train' split exists in HF)
    print("Loading full QM9 dataset...")
    full_dataset = QM9Dataset(
        root=root,
        hf_dataset_path=hf_dataset_path,
        target_property=target_property,
        split="train"  # HF only has 'train' split
    )
    
    # Calculate split sizes
    total_size = len(full_dataset)
    train_size = int(train_split * total_size)
    val_size = int(val_split * total_size)
    test_size = total_size - train_size - val_size
    
    print(f"Splitting dataset: train={train_size}, val={val_size}, test={test_size}")
    
    # Random split
    train_dataset, val_dataset, test_dataset = random_split(
        full_dataset,
        [train_size, val_size, test_size],
        generator=torch.Generator().manual_seed(42)
    )
    
    # Wrap datasets - compute normalization from TRAINING set only!
    train_wrapped = MolecularDatasetWrapper(
        train_dataset,
        normalize_targets=normalize_targets,
        rotation_augmentation=rotation_augmentation
    )
    
    # Val and test use TRAINING set's normalization stats
    val_wrapped = MolecularDatasetWrapper(
        val_dataset,
        normalize_targets=normalize_targets,
        rotation_augmentation=False,  # No augmentation for validation
        target_mean=train_wrapped.target_mean if normalize_targets else None,
        target_std=train_wrapped.target_std if normalize_targets else None,
    )
    
    test_wrapped = MolecularDatasetWrapper(
        test_dataset,
        normalize_targets=normalize_targets,
        rotation_augmentation=False,  # No augmentation for test
        target_mean=train_wrapped.target_mean if normalize_targets else None,
        target_std=train_wrapped.target_std if normalize_targets else None,
    )
    
    # Create dataloaders
    train_loader = DataLoader(
        train_wrapped,
        batch_size=batch_size,
        shuffle=True,
        num_workers=num_workers,
        pin_memory=True
    )
    
    val_loader = DataLoader(
        val_wrapped,
        batch_size=batch_size,
        shuffle=False,
        num_workers=num_workers,
        pin_memory=True
    )
    
    test_loader = DataLoader(
        test_wrapped,
        batch_size=batch_size,
        shuffle=False,
        num_workers=num_workers,
        pin_memory=True
    )
    
    return {
        'train': train_loader,
        'val': val_loader,
        'test': test_loader,
        'train_dataset': train_wrapped,  # For denormalization
    }