/**

  Rules -

  https://zh.wikipedia.org/wiki/%E8%81%94%E7%AB%8B%E5%88%B6

  https://en.wikipedia.org/wiki/Mixed-member_proportional_representation

  1)各政黨總當選名額，以全國總應選名額依各政黨在第二張投政黨名單的得票比率分配。（假設使用與目前不分區算法相同的最大餘數法）

  2)扣除該黨在選舉區已得議席

  3)其差額再由政黨比例代表名額中補足。

  @param {Number} totalSeat - 總席次數量，正整數。

  @param {Number} threshold - 小黨門檻（5 代表 5%）。程式本身沒有檢查說加起來要 = 100%，未滿 100% 的部分，視同未過門檻的小黨們的和。

  @param {Number[]} partyVotePercentages - 各黨政黨票（不分區）得票率百分比（34 表示 34%）

  @param {Number[]} localSeats - 各黨區域立委席次

  @return {Object()} list of seats - 各黨總席次

*/

function calculateSeatsMMP(totalSeat, threshold, partyVotePercentages, localSeats) {

  let expectedSeats = calculateSeats(totalSeat, partyVotePercentages, threshold).map(party => party.seat)

  return localSeats.map((localSeat, idx) => expectedSeats[idx] < localSeat ? localSeat : expectedSeats[idx])

}

​

​

// Test cases.

//

console.table([

  {

    // The one in wikipedia ( https://zh.wikipedia.org/wiki/%E8%81%94%E7%AB%8B%E5%88%B6 )

    //

    actual:calculateSeatsMMP(100, 5, [25, 5, 40, 30], [15, 6, 19, 20]),

    expected: [25, 6, 40, 30]

  },

  {

    // 增額增到爆炸：小黨都沒超過門檻(6%)，單一大黨過門檻；

    // 小黨的區域當選，全都變成增額名額，大黨把席次全吃下來。

    //

    actual:calculateSeatsMMP(10, 6, [5,5,90], [1,2,5]),

    expected: [1,2,10]

  },

  {

    // 測試 threshold。沒有增額。

    //

    actual:calculateSeatsMMP(41, 5, [2,3,50,45], [0,0,10,10]),

    expected: [0,0,22,19]

  }

])

​

​

​

// Libraries

//

// From: https://github.com/g0v/partyvote2016/blob/gh-pages/main.js

//

function calculateSeats(totalSeat, stage1votes, threshold) {

  // Apply rule 5 & rule 1

  //

  var stage1sum = stage1votes.reduce(function(s, p){

    return s + (p >= threshold ? p : 0)

  }, 0);

​

  var stage2votes = stage1votes.map(function(p){

    return p >= threshold ? +(p * 100 / stage1sum).toFixed(2) : 0

  });

​

  // Apply rule 2

  //

  var stage2totalSeat = 0

  var partiesData = stage2votes.map(function(p, idx){

    var seat = totalSeat * p / 100, flooredSeat = Math.floor(seat);

​

    stage2totalSeat += flooredSeat;

​

    return {

      id: idx, // partiesData will be sorted later, thus requires idx

      seat: flooredSeat,

      remain: seat - flooredSeat

    }

  })

​

  var result = stage2votes.map(function(p, idx){

    return {

      stage1votes: stage1votes[idx],

      value: p,

      seat: partiesData[idx].seat

    }

  });

​

  // Apply rule 3

  //

  shuffle(partiesData).sort(function(a, b){return b.remain-a.remain})

  while(stage2totalSeat < totalSeat) {

    var partyData = partiesData.shift();

    result[partyData.id].seat += 1;

    stage2totalSeat += 1;

  }

​

  return result;

}

​

​

function shuffle(array) {

  var currentIndex = array.length, temporaryValue, randomIndex;

​

  // While there remain elements to shuffle...

  while (0 !== currentIndex) {

​

    // Pick a remaining element...

    randomIndex = Math.floor(Math.random() * currentIndex);

    currentIndex -= 1;

​

    // And swap it with the current element.

    temporaryValue = array[currentIndex];

    array[currentIndex] = array[randomIndex];

    array[randomIndex] = temporaryValue;

  }

​

  return array;

}