/**
 * 加权随机选取
 */
export class WeightedPick {
    /**
     * 按 weight 加权随机一项；weight≤0 不参与
     * @param list 候选列表
     */
    static pick<T extends { weight?: number }>(list: T[]): T | null {
        if (!list?.length) return null;
        let total = 0;
        for (const x of list) {
            const w = Number(x.weight) || 0;
            if (w > 0) total += w;
        }
        if (total <= 0) return null;
        let r = Math.random() * total;
        for (const x of list) {
            const w = Number(x.weight) || 0;
            if (w <= 0) continue;
            r -= w;
            if (r <= 0) return x;
        }
        return list[list.length - 1] ?? null;
    }
}