// server/utils/cache.ts - 简单内存缓存，按题目、题型和选项生成缓存键
import { createHash } from "node:crypto";

import { serverEnv } from "~~/server/utils/env";

/**
 * 旧 Python 服务使用进程内字典缓存答案
 *
 * Nuxt 版保持同样的“内存缓存”语义：服务重启后缓存清空，不跨实例共享；
 * 这对个人题库服务足够简单，也避免为了缓存引入数据库或 Redis
 */
export class SimpleCache {
  /** Map key 是题目、题型和选项计算出的 md5；value 保存写入时间和答案 */
  private readonly cache = new Map<
    string,
    {
      timestamp: number;
      value: string;
    }
  >();

  constructor(private readonly expirationSeconds: number) {}

  /**
   * 根据题目、题型和选项生成缓存键
   *
   * 同一道题如果选项不同，不能复用旧答案，所以三个字段都参与计算
   */
  private generateKey(question: string, questionType = "", options = "") {
    return createHash("md5")
      .update(`${question}|${questionType}|${options}`, "utf8")
      .digest("hex");
  }

  /**
   * 读取缓存答案
   *
   * 命中过期项时会顺手删除，避免长时间运行后堆积无效缓存
   */
  get(question: string, questionType = "", options = "") {
    const key = this.generateKey(question, questionType, options);
    const item = this.cache.get(key);
    if (!item) return undefined;

    if (Date.now() - item.timestamp < this.expirationSeconds * 1000) {
      return item.value;
    }

    this.cache.delete(key);
    return undefined;
  }

  /** 写入答案缓存，时间戳使用当前进程时间即可 */
  set(question: string, answer: string, questionType = "", options = "") {
    const key = this.generateKey(question, questionType, options);
    this.cache.set(key, {
      timestamp: Date.now(),
      value: answer
    });
  }

  /** 清空全部缓存，对应 `/api/cache/clear` */
  clear() {
    this.cache.clear();
  }

  /**
   * 批量移除过期项
   *
   * 目前在统计缓存大小时调用，避免 stats 返回已经过期的数量
   */
  removeExpired() {
    const now = Date.now();
    let removedCount = 0;

    for (const [key, item] of this.cache.entries()) {
      if (now - item.timestamp >= this.expirationSeconds * 1000) {
        this.cache.delete(key);
        removedCount += 1;
      }
    }

    return removedCount;
  }

  /** 获取当前有效缓存数量 */
  size() {
    this.removeExpired();
    return this.cache.size;
  }
}

/**
 * 全局答案缓存实例
 *
 * 如果 `ENABLE_CACHE=false`，导出 undefined，调用处用可选链即可保持逻辑简洁
 */
export const answerCache = serverEnv.enableCache
  ? new SimpleCache(serverEnv.cacheExpiration)
  : undefined;