#!/usr/bin/env python3
"""数苗打卡抽奖 — 开奖结果独立复算脚本(不依赖服务端任何代码)。

用法:
  1. 打开验证页,下载「验证数据 .json」
  2. python3 verify_draw.py shumiao-verify-*.json

复算三件事:
  - 快照哈希:   sha256(canonical_json({"period": 期次, "groups": 组号, "members": [[组号,姓名,学号],...]}))
                (v1 老快照无 members 字段,自动兼容)
  - 承诺哈希:   sha256("shumiao-commit-v1|期次|seed|快照哈希") 与冻结时公布的一致(防 seed 被换)
  - 中奖顺序:   seed 经 HMAC-SHA256 熵流 + 拒绝采样无偏 Fisher-Yates 洗牌(以个人为奖池单位)
"""
import hashlib
import hmac
import json
import sys


def mask_name(n: str) -> str:
    n = (n or "").strip()
    if len(n) <= 1:
        return n
    if len(n) == 2:
        return n[0] + "*"
    return n[0] + "*" * (len(n) - 2) + n[-1]


def canonical_snapshot(period_id: int, groups: list, members: list | None = None) -> str:
    d = {"period": period_id, "groups": sorted(groups)}
    if members is not None:
        d["members"] = sorted(members)
    return json.dumps(d, ensure_ascii=False, separators=(",", ":"))


def snapshot_hash(period_id: int, groups: list, members: list | None = None) -> str:
    return hashlib.sha256(canonical_snapshot(period_id, groups, members).encode("utf-8")).hexdigest()


def make_commitment(period_id: int, seed_hex: str, snap_hash: str) -> str:
    msg = f"shumiao-commit-v1|{period_id}|{seed_hex}|{snap_hash}"
    return hashlib.sha256(msg.encode("utf-8")).hexdigest()


def _stream(seed_hex: str):
    seed = bytes.fromhex(seed_hex)
    i = 0
    while True:
        block = hmac.new(seed, f"shumiao-draw-{i}".encode("utf-8"), hashlib.sha256).digest()
        for off in range(0, 32, 8):
            yield int.from_bytes(block[off:off + 8], "big")
        i += 1


def _rand_below(gen, n: int) -> int:
    limit = (1 << 64) - ((1 << 64) % n)
    while True:
        v = next(gen)
        if v < limit:
            return v % n


def permutation(items: list, seed_hex: str) -> list:
    a = sorted(items)
    gen = _stream(seed_hex)
    for i in range(len(a) - 1, 0, -1):
        j = _rand_below(gen, i + 1)
        a[i], a[j] = a[j], a[i]
    return a


def main(path: str) -> int:
    d = json.load(open(path, encoding="utf-8"))
    need = ["period_id", "groups", "seed_hex", "commitment", "snapshot_hash"]
    missing = [k for k in need if k not in d]
    if missing:
        print(f"缺少字段: {missing}"); return 2

    pid = d["period_id"]
    groups = [g["group_no"] if isinstance(g, dict) else g for g in d["groups"]]
    members = d.get("snapshot", {}).get("members")
    ok = True

    h = snapshot_hash(pid, groups, members)
    if h == d["snapshot_hash"]:
        print(f"[PASS] 快照哈希一致: {h}")
    else:
        print(f"[FAIL] 快照哈希不一致: 本地 {h} vs 公布 {d['snapshot_hash']}"); ok = False

    if not d["seed_hex"]:
        print("[INFO] 本期尚未开奖: seed 未公布,暂时只能核对快照哈希。开奖后重跑本脚本即可完整验证。")
        print("结论: " + ("快照核对通过 ✔" if ok else "快照不一致 ✘"))
        return 0 if ok else 1

    seed_hex = d["seed_hex"]
    c = make_commitment(pid, seed_hex, d["snapshot_hash"])
    if c == d["commitment"]:
        print(f"[PASS] 承诺哈希一致(冻结前公布的 commitment 确由该 seed 生成): {c}")
    else:
        print(f"[FAIL] 承诺哈希不一致: seed 与冻结时公布的 commitment 对不上"); ok = False

    pool = members if members else groups  # v1 老快照:奖池单位是组
    order = permutation(pool, seed_hex)
    total = sum(t["count"] for t in d.get("tiers", []))
    print(f"[INFO] 洗牌后完整顺序(前 {max(total, len(order))} 名):")
    for i, item in enumerate(order):
        if members:
            g, name, sid = item
            print(f"   {i + 1:>3}. 第{g}组 {mask_name(name)}({sid})")
        else:
            print(f"   {i + 1:>3}. {item}号组")

    if d.get("winners"):
        expect = order[:len(d["winners"])]
        if members:
            expect = [(g, sid) for g, _n, sid in expect]
            got = [(w["group_no"], w.get("student_id", "")) for w in d["winners"]]
        else:
            expect = list(expect)
            got = [w["group_no"] for w in d["winners"]]
        if expect == got:
            print(f"[PASS] 中奖顺序与公布结果完全一致")
        else:
            print(f"[FAIL] 中奖顺序不一致: 本地 {expect} vs 公布 {got}"); ok = False

    print("结论: " + ("全部通过,开奖结果可信 ✔" if ok else "存在不一致,请向管理员反映 ✘"))
    return 0 if ok else 1


if __name__ == "__main__":
    if len(sys.argv) != 2:
        print(__doc__)
        sys.exit(2)
    sys.exit(main(sys.argv[1]))