"""
split_dataset.py — ERYON reproducible train/val/test splitter.

Splits at the PATIENT level (not slice level) to prevent leakage.
Writes a splits.json: {series_id: "train" | "val" | "test"}.

Ratios default to 70/15/15.  Seed is fixed and written into the output
so splits can be reproduced exactly from the JSON alone.

Usage:
    python split_dataset.py \\
        --manifest manifests/lidc/manifest_v1.0.0.jsonl \\
        --train 0.70 --val 0.15 --test 0.15 \\
        --seed 42 \\
        --out manifests/lidc/splits_v1.0.0.json
"""

import argparse
import json
import random
from collections import defaultdict
from pathlib import Path


def load_manifest(path: Path) -> list[dict]:
    return [json.loads(line) for line in path.read_text().splitlines() if line.strip()]


def split_patients(
    records: list[dict],
    train_ratio: float,
    val_ratio: float,
    seed: int,
) -> dict[str, str]:
    patient_to_series: dict[str, set] = defaultdict(set)
    for r in records:
        patient_to_series[r["patient_id"]].add(r["series_id"])

    patients = sorted(patient_to_series.keys())
    rng = random.Random(seed)
    rng.shuffle(patients)

    n = len(patients)
    n_train = int(n * train_ratio)
    n_val   = int(n * val_ratio)

    train_patients = set(patients[:n_train])
    val_patients   = set(patients[n_train : n_train + n_val])
    test_patients  = set(patients[n_train + n_val :])

    series_split: dict[str, str] = {}
    for pid, series_set in patient_to_series.items():
        if pid in train_patients:
            split = "train"
        elif pid in val_patients:
            split = "val"
        else:
            split = "test"
        for sid in series_set:
            series_split[sid] = split

    return series_split


def main() -> None:
    parser = argparse.ArgumentParser()
    parser.add_argument("--manifest", required=True)
    parser.add_argument("--train", type=float, default=0.70)
    parser.add_argument("--val",   type=float, default=0.15)
    parser.add_argument("--test",  type=float, default=0.15)
    parser.add_argument("--seed",  type=int,   default=42)
    parser.add_argument("--out",   required=True)
    args = parser.parse_args()

    assert abs(args.train + args.val + args.test - 1.0) < 1e-6, "Ratios must sum to 1.0"

    records = load_manifest(Path(args.manifest))
    splits  = split_patients(records, args.train, args.val, args.seed)

    out = {
        "seed": args.seed,
        "ratios": {"train": args.train, "val": args.val, "test": args.test},
        "splits": splits,
    }
    out_path = Path(args.out)
    out_path.parent.mkdir(parents=True, exist_ok=True)
    out_path.write_text(json.dumps(out, indent=2))

    counts = {"train": 0, "val": 0, "test": 0}
    for s in splits.values():
        counts[s] += 1
    print(f"Split complete: {counts}  →  {out_path}")


if __name__ == "__main__":
    main()