rcon2mc 0.1.0

/*
 * // Copyright (c) 2026 Jack Wang
 * //
 * // Permission is hereby granted, free of charge, to any person obtaining a copy
 * // of this software and associated documentation files (the "Software"), to deal
 * // in the Software without restriction, including without limitation the rights
 * // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * // copies of the Software, and to permit persons to whom the Software is
 * // furnished to do so, subject to the following conditions:
 * //
 * // The above copyright notice and this permission notice shall be included in all
 * // copies or substantial portions of the Software.
 * //
 * // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * // SOFTWARE.
 * //
 * // Author: Jack Wang <wang@rjack.cn>
 * // GitHub: https://github.com/nearlyheadlessjack/rcon2mc
 */
use std::cell::RefCell;
use std::time::{SystemTime, UNIX_EPOCH};

thread_local! {
    static RNG_STATE: RefCell<u64> = const { RefCell::new(0) };
}

#[inline]
fn xorshift64(state: &mut u64) -> u64 {
    let mut x = *state;
    x ^= x << 13;
    x ^= x >> 7;
    x ^= x << 17;
    *state = x;
    x
}

fn init_seed() -> u64 {
    let dur = SystemTime::now()
        .duration_since(UNIX_EPOCH)
        .expect("系统时间早于 UNIX_EPOCH");
    let seed = dur.as_nanos() as u64;
    if seed == 0 {
        1
    } else {
        seed
    }
}

pub fn gen_rand_i32(lower: i32, upper: i32) -> i32 {
    let range = (upper as i64 - lower as i64 + 1) as u64;
    debug_assert!(range > 0, "lower 必须小于等于 upper");

    RNG_STATE.with(|cell| {
        let mut state = cell.borrow_mut();
        if *state == 0 {
            *state = init_seed();
        }

        let rand_val = xorshift64(&mut *state); // 0 ..= u64::MAX
        let offset = (rand_val % range) as i64; // 0 .. range-1
        (lower as i64 + offset) as i32
    })
}