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"""
Phase 1: Data splitting with contract-level leakage prevention

This module implements contract-level train/val/test splitting, ensuring
that no contract text appears in more than one split.

CRITICAL: This prevents data leakage and ensures honest evaluation.
"""

import logging
import random
from typing import List, Tuple, Set, Dict
from pathlib import Path
import json

from data.loaders import Contract

logger = logging.getLogger(__name__)

class ContractLevelSplitter:
    """Split contracts into train/val/test with zero-leakage guarantee."""
    
    def __init__(self, random_seed: int = 42):
        """
        Initialize splitter.
        
        Args:
            random_seed: Seed for reproducibility
        """
        self.random_seed = random_seed
        random.seed(random_seed)
    
    def split(
        self,
        contracts: List[Contract],
        train_frac: float = 0.70,
        val_frac: float = 0.15,
        test_frac: float = 0.15,
    ) -> Tuple[List[Contract], List[Contract], List[Contract]]:
        """
        Split contracts at the contract level (never split a contract across splits).
        
        Args:
            contracts: List of contracts to split
            train_frac: Fraction for training
            val_frac: Fraction for validation
            test_frac: Fraction for testing
        
        Returns:
            Tuple of (train_contracts, val_contracts, test_contracts)
        
        Raises:
            AssertionError: If fractions don't sum to 1.0 or leakage is detected
        """
        assert abs(train_frac + val_frac + test_frac - 1.0) < 1e-6, \
            f"Fractions must sum to 1.0, got {train_frac + val_frac + test_frac}"
        
        # Shuffle contracts
        shuffled = list(contracts)
        random.shuffle(shuffled)
        
        n = len(shuffled)
        train_end = int(n * train_frac)
        val_end = train_end + int(n * val_frac)
        
        train = shuffled[:train_end]
        val = shuffled[train_end:val_end]
        test = shuffled[val_end:]
        
        # Verify zero leakage
        self._verify_no_leakage(train, val, test)
        
        logger.info(f"Split {n} contracts:")
        logger.info(f"  Train: {len(train)} ({len(train)/n*100:.1f}%)")
        logger.info(f"  Val:   {len(val)} ({len(val)/n*100:.1f}%)")
        logger.info(f"  Test:  {len(test)} ({len(test)/n*100:.1f}%)")
        
        return train, val, test
    
    @staticmethod
    def _verify_no_leakage(
        train: List[Contract],
        val: List[Contract],
        test: List[Contract]
    ) -> None:
        """
        Verify that no contract appears in multiple splits.
        
        Raises:
            AssertionError: If leakage is detected
        """
        train_ids = {c.id for c in train}
        val_ids = {c.id for c in val}
        test_ids = {c.id for c in test}
        
        # Check for overlaps
        train_val_overlap = train_ids & val_ids
        val_test_overlap = val_ids & test_ids
        train_test_overlap = train_ids & test_ids
        
        assert len(train_val_overlap) == 0, \
            f"LEAKAGE: {len(train_val_overlap)} contracts in both train and val: {train_val_overlap}"
        assert len(val_test_overlap) == 0, \
            f"LEAKAGE: {len(val_test_overlap)} contracts in both val and test: {val_test_overlap}"
        assert len(train_test_overlap) == 0, \
            f"LEAKAGE: {len(train_test_overlap)} contracts in both train and test: {train_test_overlap}"
        
        # Check for duplicate text (additional verification)
        train_texts = {c.text for c in train}
        val_texts = {c.text for c in val}
        test_texts = {c.text for c in test}
        
        # Duplicates within splits are OK; duplicates across splits are NOT OK
        assert len(train_texts & val_texts) == 0, \
            "LEAKAGE: Duplicate contract text in train and val"
        assert len(val_texts & test_texts) == 0, \
            "LEAKAGE: Duplicate contract text in val and test"
        assert len(train_texts & test_texts) == 0, \
            "LEAKAGE: Duplicate contract text in train and test"
        
        logger.info("✓ Leakage verification passed: zero contract overlap across splits")

class DatasetStatistics:
    """Compute and log dataset statistics."""
    
    @staticmethod
    def compute(
        datasets: Dict[str, List[Contract]],
        output_file: str = None
    ) -> Dict:
        """
        Compute statistics across all datasets.
        
        Args:
            datasets: Dict of {name: [contracts]}
            output_file: Optional path to save statistics as JSON
        
        Returns:
            Dict of statistics
        """
        stats = {}
        
        for dataset_name, contracts in datasets.items():
            if not contracts:
                continue
            
            # Basic counts
            num_contracts = len(contracts)
            num_clauses = sum(len(c.clauses) for c in contracts)
            
            # Text statistics
            text_lengths = [len(c.text) for c in contracts]
            clause_counts = [len(c.clauses) for c in contracts]
            
            # Category distribution (for CUAD/MAUD)
            category_counts = {}
            for contract in contracts:
                for clause in contract.clauses:
                    cat = clause.get("category", "unknown")
                    category_counts[cat] = category_counts.get(cat, 0) + 1
            
            stats[dataset_name] = {
                "num_contracts": num_contracts,
                "num_clauses": num_clauses,
                "clauses_per_contract": {
                    "mean": sum(clause_counts) / len(clause_counts),
                    "median": sorted(clause_counts)[len(clause_counts)//2],
                    "min": min(clause_counts),
                    "max": max(clause_counts),
                },
                "text_length_chars": {
                    "mean": sum(text_lengths) / len(text_lengths),
                    "median": sorted(text_lengths)[len(text_lengths)//2],
                    "min": min(text_lengths),
                    "max": max(text_lengths),
                },
                "categories": category_counts,
            }
        
        # Log summary
        logger.info("\n" + "=" * 70)
        logger.info("DATASET STATISTICS")
        logger.info("=" * 70)
        for dataset_name, ds_stats in stats.items():
            logger.info(f"\n{dataset_name}:")
            logger.info(f"  Contracts: {ds_stats['num_contracts']}")
            logger.info(f"  Clauses: {ds_stats['num_clauses']}")
            logger.info(f"  Clauses/contract (mean): {ds_stats['clauses_per_contract']['mean']:.1f}")
            logger.info(f"  Text length chars (mean): {ds_stats['text_length_chars']['mean']:.0f}")
            
            if ds_stats['categories']:
                logger.info(f"  Categories: {len(ds_stats['categories'])}")
                sorted_cats = sorted(
                    ds_stats['categories'].items(),
                    key=lambda x: x[1],
                    reverse=True
                )
                for cat, count in sorted_cats[:5]:
                    logger.info(f"    - {cat}: {count}")
        
        logger.info("=" * 70 + "\n")
        
        # Save to file if requested
        if output_file:
            with open(output_file, "w") as f:
                json.dump(stats, f, indent=2)
            logger.info(f"Statistics saved to {output_file}")
        
        return stats

if __name__ == "__main__":
    logging.basicConfig(level=logging.INFO)
    
    from data.loaders import load_all_datasets
    
    # Load all datasets
    datasets = load_all_datasets()
    
    # Example: split CUAD train/test
    if "cuad_train" in datasets and datasets["cuad_train"]:
        splitter = ContractLevelSplitter(random_seed=42)
        train, val, test = splitter.split(
            datasets["cuad_train"],
            train_frac=0.70,
            val_frac=0.15,
            test_frac=0.15
        )
        
        logger.info(f"✓ Successfully split CUAD: {len(train)} train, {len(val)} val, {len(test)} test")
    
    # Compute statistics
    stats = DatasetStatistics.compute(datasets, output_file="data/statistics.json")