const formatTime = date => {
  const year = date.getFullYear()
  const month = date.getMonth() + 1
  const day = date.getDate()
  const hour = date.getHours()
  const minute = date.getMinutes()
  const second = date.getSeconds()
  return `${[year, month, day].map(formatNumber).join('/')} ${[hour, minute, second].map(formatNumber).join(':')}`
}

const formatNumber = n => {
  n = n.toString()
  return n[1] ? n : `0${n}`
}

const promisify =  (api) => {
  return (options, ...params) => {
      return new Promise((resolve, reject) => {
          api(Object.assign({}, options, { success: resolve, fail: reject }), ...params);
      });
  }
}

const BeaconUtils = {
  
// 计算距离
calculateAccuracy:function(txPower, rssi, n) {
  // return (0.89976) * Math.pow(rssi / txPower, 7.7095) + 0.111

  return Math.pow(10, Math.abs(rssi - txPower) / (10 * n))
},

//求数组平均值
arrayAverage:function (arr) {
   let tmp = arr.reduce((acc, val) => acc + val, 0) / arr.length
   return tmp
},

//数组分类:按照关键词key
//data = {1003:[{},{},···],1002:[{},{},···],1001:[{},{},···]}
classification:function (list,key) {
  let data = {}
  for(var i = 0; i < list.length; i++) {
      if(!data[list[i][key]]) {
          var arr = [];
          arr.push(list[i]);
          data[list[i][key]] = arr;
      }else {
          data[list[i][key]].push(list[i])
      }
  }

  return data
},

//求一维队列某点的高斯模糊权重 @param(队列长度，目标位置, 平均差)
getOneGuassionArray: function(size, kerR, sigma) {
    // if (size % 2 > 0) {
    //   size -= 1
    // }
    // if (!size) {
    //   return []
    // }
    if (kerR > size-1){
      return []
    }
    let sum = 0;
    let arr = new Array(size);
    //进来的列表的元素可能是一样的，防止平均差为0的情况
    if(sigma == 0){
      let weight = 1 / size;
      return arr.fill(weight)
    }
    for (let i = 0; i < size; i++) {
      arr[i] = Math.exp(-((i - kerR) * (i - kerR)) / (2 * sigma * sigma)) / (sigma * Math.pow(2*Math.PI,0.5));
      sum += arr[i];
    }

    return arr.map(e => e / sum);
  },

  //计算数组平均差
  //list：rssi数组
  //average:rssi平均值
  getMeanDeviation: function(list,average){
    let length = list.length;
    //数组的每一个数都要减去一个平均数，结果取绝对值
    let arr = list.map(num=>Math.abs(num-average))
    return arr.reduce((prev,curr)=>prev+curr) / length;
  },

  //计算数组方差
  // list:待计算数组
  // average：数组元素平均值
  getVariance:function(list,average){
    let sum = 0;
    for(let element of list){
      sum += Math.pow((element - average),2)
    }
    return sum / list.length
  },

  //js实现字符串重复的repeat函数
  repeat:function(src, n) {
    return (new Array(n + 1)).join(src);
  },

  //计算椭圆长度
  //R是预设的有效范围半径
  //L是椭圆长度
  getLR:function(R,L){
    let d = L - R 
    let r = (R - d) / 2
    let h = r + d
    return 2*Math.pow((R*R - h*h),0.5)
  }
}

module.exports = {
  formatTime,
  promisify,
  BeaconUtils
}