#!/usr/bin/env python3
"""Create nested random-sampled structure subsets from SPICE XYZ datasets.

Uses random sampling for subset selection (no descriptor-based selection).
Smaller subsets are nested within larger ones (strict prefixes).

Usage:
    python sample_nested_subsets_random.py --input data/train_large_neut_no_bad_clean.xyz --percentages 50 20 10 5 1
    python sample_nested_subsets_random.py --input data/test_large_neut_all.xyz --percentages 50 20 10 5 1
"""

from __future__ import annotations

import argparse
import logging
import sys
from pathlib import Path

import numpy as np
from ase.io import read, write


def setup_logging() -> None:
    """Configure logging to stdout."""
    logging.basicConfig(
        level=logging.INFO,
        format="%(asctime)s | %(levelname)s | %(message)s",
        stream=sys.stdout,
    )


def count_structures(filepath: Path) -> int:
    """Count the number of structures in an XYZ file efficiently."""
    logging.info(f"Counting structures in {filepath.name}...")
    count = 0
    with open(filepath, "r") as f:
        while True:
            line = f.readline()
            if not line:
                break
            try:
                natoms = int(line.strip())
                f.readline()  # Skip comment
                for _ in range(natoms):
                    f.readline()  # Skip atom lines
                count += 1
            except (ValueError, StopIteration):
                break
    return count


def random_sample_structures(
    input_path: Path,
    output_path: Path,
    num_samples: int,
    seed: int = 42,
) -> list:
    """
    Randomly sample structures from an XYZ file.
    
    Args:
        input_path: Path to input XYZ file
        output_path: Path to output XYZ file
        num_samples: Number of samples to select
        seed: Random seed for reproducibility
    
    Returns:
        List of sampled ASE Atoms objects
    """
    logging.info(f"Loading structures from {input_path.name}...")
    all_atoms = read(str(input_path), index=":")
    total = len(all_atoms)
    
    if num_samples > total:
        logging.warning(f"Requested {num_samples} samples but only {total} available. Using all structures.")
        num_samples = total
    
    # Set random seed for reproducibility
    np.random.seed(seed)
    
    # Generate random indices
    logging.info(f"Randomly sampling {num_samples} structures from {total} total...")
    indices = np.random.choice(total, size=num_samples, replace=False)
    indices = np.sort(indices)  # Sort to maintain some order
    
    # Select structures
    sampled_atoms = [all_atoms[i] for i in indices]
    
    # Write to file
    logging.info(f"Writing {len(sampled_atoms)} structures to {output_path.name}...")
    write(str(output_path), sampled_atoms, format="extxyz")
    
    return sampled_atoms


def create_nested_subsets_from_parent(
    parent_atoms: list,
    output_dir: Path,
    base_name: str,
    subset_sizes: dict[float, int],
) -> None:
    """
    Create nested subsets from the parent atom list.
    
    Args:
        parent_atoms: List of ASE Atoms objects from the largest subset
        output_dir: Directory for output files
        base_name: Base name for output files
        subset_sizes: Dict mapping percentages to counts (excluding the largest)
    """
    logging.info(f"Creating nested subsets from {len(parent_atoms)} parent structures")
    
    # Create smaller nested subsets
    for pct in sorted(subset_sizes.keys(), reverse=True):
        size = subset_sizes[pct]
        output_path = output_dir / f"{base_name}{pct}pct_{size}.xyz"
        
        logging.info(f"Creating {pct}% subset ({size} structures)...")
        subset_atoms = parent_atoms[:size]
        
        write(str(output_path), subset_atoms, format="extxyz")
        logging.info(f"Wrote {len(subset_atoms)} structures to {output_path.name}")


def parse_args() -> argparse.Namespace:
    parser = argparse.ArgumentParser(
        description=__doc__,
        formatter_class=argparse.RawDescriptionHelpFormatter,
    )
    parser.add_argument(
        "--input",
        type=str,
        required=True,
        help="Path to input XYZ file",
    )
    parser.add_argument(
        "--percentages",
        nargs="+",
        type=float,
        required=True,
        help="Subset percentages (e.g., 50 20 10 5 1 for 50%%, 20%%, etc.)",
    )
    parser.add_argument(
        "--output-dir",
        type=str,
        default=None,
        help="Output directory (defaults to 'random_subsets' in same dir as input)",
    )
    parser.add_argument(
        "--prefix",
        type=str,
        default=None,
        help="Output file prefix (defaults to input filename + _random_)",
    )
    parser.add_argument(
        "--seed",
        type=int,
        default=42,
        help="Random seed for reproducibility (default: 42)",
    )
    return parser.parse_args()


def main() -> None:
    args = parse_args()
    setup_logging()
    
    input_path = Path(args.input).expanduser().resolve()
    if not input_path.is_file():
        raise FileNotFoundError(f"Input file not found: {input_path}")
    
    # Validate and sort percentages
    percentages = sorted([p for p in args.percentages if p > 0], reverse=True)
    if not percentages:
        raise ValueError("At least one positive percentage must be provided")
    
    if any(p > 100 for p in percentages):
        raise ValueError("Percentages must be <= 100")
    
    # Count total structures
    total_structures = count_structures(input_path)
    logging.info(f"Total structures in dataset: {total_structures}")
    
    # Calculate subset sizes
    subset_sizes = {}
    for pct in percentages:
        size = int(np.round(total_structures * pct / 100))
        if size == 0:
            logging.warning(f"Percentage {pct}% results in 0 structures, skipping")
            continue
        subset_sizes[pct] = size
    
    if not subset_sizes:
        raise ValueError("No valid subset sizes after conversion")
    
    # Log planned subsets
    logging.info("\nPlanned subsets:")
    for pct in sorted(subset_sizes.keys(), reverse=True):
        size = subset_sizes[pct]
        logging.info(f"  {pct}% = {size} structures")
    
    # Setup output - use 'random_subsets' folder by default
    if args.output_dir:
        output_dir = Path(args.output_dir).expanduser().resolve()
    else:
        output_dir = input_path.parent / "random_subsets"
    
    output_dir.mkdir(parents=True, exist_ok=True)
    logging.info(f"Output directory: {output_dir}")
    
    # Use '_random_' prefix by default
    prefix = args.prefix or f"{input_path.stem}_random_"
    
    # Get largest subset size and create it using random sampling
    largest_pct = max(subset_sizes.keys())
    largest_size = subset_sizes[largest_pct]
    
    logging.info(f"\n{'='*60}")
    logging.info(f"Creating largest subset ({largest_pct}% = {largest_size} structures) using random sampling")
    logging.info(f"Random seed: {args.seed}")
    logging.info(f"{'='*60}\n")
    
    largest_output = output_dir / f"{prefix}{largest_pct}pct_{largest_size}.xyz"
    
    parent_atoms = random_sample_structures(
        input_path=input_path,
        output_path=largest_output,
        num_samples=largest_size,
        seed=args.seed,
    )
    
    # Create smaller nested subsets from the largest one
    if len(subset_sizes) > 1:
        logging.info(f"\n{'='*60}")
        logging.info("Creating nested smaller subsets from largest subset")
        logging.info(f"{'='*60}\n")
        
        smaller_sizes = {pct: size for pct, size in subset_sizes.items() if pct < largest_pct}
        create_nested_subsets_from_parent(
            parent_atoms=parent_atoms,
            output_dir=output_dir,
            base_name=prefix,
            subset_sizes=smaller_sizes,
        )
    
    logging.info("\n" + "="*60)
    logging.info("All nested random subsets created successfully!")
    logging.info(f"Output location: {output_dir}")
    logging.info("="*60)


if __name__ == "__main__":
    main()