#!/usr/bin/env python3
"""
按 JSON 每条记录里的 "task" 字段划分 train / test，保证同一 task 只出现在一侧（无 overlap）。
先在「唯一 task」集合上做 8:2 划分，再把属于各 task 的样本归入对应集合。

用法:
  python split_metadata_by_task.py \\
    --input train_metadata_100.json \\
    --out_train train_metadata_100_train.json \\
    --out_test train_metadata_100_test.json \\
    --ratio_train 0.8 \\
    --seed 42
"""

from __future__ import annotations

import argparse
import json
import random
from collections import Counter


def main():
    p = argparse.ArgumentParser(description="Split metadata JSON by task (no task overlap between splits).")
    p.add_argument("--input", "-i", type=str, default="train_metadata_100.json")
    p.add_argument("--out_train", type=str, default="train_metadata_100_train.json")
    p.add_argument("--out_test", type=str, default="train_metadata_100_test.json")
    p.add_argument("--ratio_train", type=float, default=0.8, help="Fraction of unique tasks assigned to train (default 0.8).")
    p.add_argument("--seed", type=int, default=42, help="Shuffle seed for reproducible task split.")
    args = p.parse_args()

    if not 0.0 < args.ratio_train < 1.0:
        raise ValueError("ratio_train must be in (0, 1).")

    with open(args.input, "r", encoding="utf-8") as f:
        records = json.load(f)
    if not isinstance(records, list):
        raise ValueError("Top-level JSON must be a list of objects.")

    for i, r in enumerate(records):
        if "task" not in r:
            raise KeyError(f"Record {i} missing 'task' field.")

    unique_tasks = sorted({r["task"] for r in records})
    n_tasks = len(unique_tasks)

    rng = random.Random(args.seed)
    shuffled = list(unique_tasks)
    rng.shuffle(shuffled)

    if n_tasks < 2:
        print("Warning: only one unique task; all records -> train, test is empty.")
        train_tasks = set(shuffled)
        test_tasks = set()
    else:
        # 在「唯一 task」个数上做比例：例如 100 个 task、0.8 -> 80 个进 train、20 个进 test
        n_train_tasks = int(n_tasks * args.ratio_train)
        n_train_tasks = max(1, min(n_tasks - 1, n_train_tasks))
        train_tasks = set(shuffled[:n_train_tasks])
        test_tasks = set(shuffled[n_train_tasks:])

    train_records = [r for r in records if r["task"] in train_tasks]
    test_records = [r for r in records if r["task"] in test_tasks]

    overlap = train_tasks & test_tasks
    if overlap:
        raise RuntimeError(f"Internal error: overlapping tasks {overlap}")

    # 校验：每条样本的 task 必须落在某一侧
    missing = [r["task"] for r in records if r["task"] not in train_tasks and r["task"] not in test_tasks]
    if missing:
        raise RuntimeError(f"Some tasks not in split: {set(missing)}")

    with open(args.out_train, "w", encoding="utf-8") as f:
        json.dump(train_records, f, indent=4, ensure_ascii=False)
    with open(args.out_test, "w", encoding="utf-8") as f:
        json.dump(test_records, f, indent=4, ensure_ascii=False)

    ct_train = Counter(r["task"] for r in train_records)
    ct_test = Counter(r["task"] for r in test_records)

    print(f"Input: {args.input}")
    print(f"  total records: {len(records)}")
    print(f"  unique tasks:  {n_tasks}")
    print(f"Split (by task): train_tasks={len(train_tasks)}, test_tasks={len(test_tasks)} (ratio ~ {args.ratio_train:.1f} : {1-args.ratio_train:.1f})")
    print(f"  train records: {len(train_records)}")
    print(f"  test records:  {len(test_records)}")
    print(f"  seed: {args.seed}")
    print(f"Wrote: {args.out_train}")
    print(f"Wrote: {args.out_test}")

    # 快速断言：无 task 同时出现在两侧
    train_task_keys = set(ct_train.keys())
    test_task_keys = set(ct_test.keys())
    assert not (train_task_keys & test_task_keys), "task overlap between train and test samples"


if __name__ == "__main__":
    main()