import Big, { BigSource } from 'big.js'
import LRU from 'lru-cache'

const calcOperateMap = {
  '+': 'add',
  '-': 'sub',
  '*': 'mul',
  '/': 'div'
} as const

/**
 * 数值计算（数值计算最好交由后端处理）
 * @param number1 数字1
 * @param number2 数字2
 * @param operate 操作符 默认‘+’
 * @returns 计算后的结果
 */
export function calc (number1: BigSource, number2: BigSource, operate: '+'|'-'|'*'|'/' = '+') {
  const operateMethod = calcOperateMap[operate]
  if (operateMethod === undefined) return new Big(number1).toNumber()
  const result: Big = new Big(number1)[operateMethod](number2)
  return result.toNumber()
}

/**
 * 获取缓存方法
 * @param fn 需要被缓存的方法
 * @param max 最大缓存数
 * @returns [缓存方法，清除缓存方法]
 */
export function getCahceFn<T, U> (fn: (val: U) =>T, max = 20) {
  const cache = new LRU<U, T>({
    max,
    maxAge: 60 * 1000
  })
  return [(val: U) => {
    // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
    if (cache.has(val)) return cache.get(val)!
    const result = fn(val)
    cache.set(val, result)
    return result
  }, () => { cache.clear() }]
}