【Redis】Sorted Setからランダムに要素を取得する方法

const levelRandomRange = 100000


func Add(ctx context.Context, userID string,myLevel int32) error {
  // DIした方が良いけど、ここでは簡略化の為適宜Newを行う
  redisClient := redis.NewClient(&redis.Options{})
  
  score := createSearchScore(myLevel)
  zMember := &redis.Z{
    Score: score,
    Member: userID,
  }
  if cmd := redisClient.ZAdd(ctx, "search", zMember);cmd.Err() != nil {
    return err
  }
  
  return nil
}

func createSearchScore(level int32) float64 {
  return float64(int(level)*levelRandomRange + rand.Intn(levelRandomRange))
}
type searchScoreInfo struct {
  minScore float64
  maxScore float64
  isDesc   bool
}

func Search(ctx context.Context, userID string, myLevel int32) error {
  minLevel,maxLevel := getMinAndMaxLv(myLevel)
  
  // 自分のレベルより下の範囲、自分のレベルより上の範囲で、それぞれ基準とするレベルを決める。
  minTargetLevel := rand.Intn(myLevel - minLevel + 1) + minLevel
  maxTargetLevel := rand.Intn(maxLevel - myLevel + 1) + myLevel
  
  // それぞれの範囲で昇順、降順で検索するかを確定する。
  lowerInfo := getLowerSearchScoreInfo(minLevel, minTargetLevel, myLevel)
  higherInfo := getHigherSearchScoreInfo(maxLevel, maxTargetLevel, myLevel)
  
  // Redisにアクセス
  lowerIDs := rangeByScore(lowerInfo.minScore, lowerInfo.maxScore, 10,lowerInfo.isDesc)
  higherIDs := rangeByScore(higherInfo.minScore, higherInfo.maxScore, 10,higherInfo.isDesc)
  
  // 5対5になるように仕分けてappend
  lowerTargetIDs, lowerSurplusIDs := assortIDs(lowerIDs)
  higherTargetIDs, higherSurplusIDs := assortIDs(higherIDs)
  
  targetUserIDs := make([]string, 0, 10)
  targetUserIDs = append(targetUserIDs, lowerTargetIDs...)
  targetUserIDs = append(targetUserIDs, higherTargetIDs...)
  
  // 表示件数に足りなければ、下か上の範囲で余っている方で補う
  if len(targetUserIDs) < 10 {
     surplusUserIDs := make([]string, 0, len(lowerSurplusIDs)+len(higherSurplusIDs))
     surplusUserIDs = append(surplusUserIDs, lowerTargetIDs...)
     surplusUserIDs = append(surplusUserIDs, higherTargetIDs...)
     
     for _, id := range surplusUserIDs {
       targetUserIDs = append(targetUserIDs, id)
       if len(targetUserIDs) < 10 {
         break
       }
     }
  }
  
  return nil
}

func getMinAndMaxLv(myLevel int32) (int32, int32) {
  minLevel := myLevel - 10
  maxLevel := myLevel + 10

  // 下限と上限を超えてたらそれぞれ丸める
  if minLevel < 1 {
     minLevel = 1
  }
  if maxLevel < 1 {
     maxLevel = 1
  }
  if minLevel > 100 {
     minLevel = 100
  }
  if maxLevel > 100 {
     maxLevel = 100
  }
  
  return minMlv, maxMlv
}

func getLowerSearchScoreInfo(minLevel, targetLevel, myLevel int32) searchScoreInfo {
  /*
   自分のLevel: 50

   targetLevelが45 ~ 50なら、minLevel ← targetLevelの降順
   targetLevelが40 ~ 44なら、targetLevel → myLevelの昇順
  */

  isDesc := (targetLevel - minLevel) >= 5
  var min float64
  var max float64
  if isDesc {
    min = createSearchScore(minLevel)
    max = createSearchScore(targetLevel)
  } else {
    min = createSearchScore(targetLevel)
    max = createSearchScore(myLevel)   
  }

  return searchScoreInfo {
    minScore: min
    maxScore: max
    isDesc:   isDesc,
  }
}

func getHigherSearchScoreInfo(maxLevel, targetLevel, myLevel int32) searchScoreInfo {
  /*
   自分のLevel: 50

   targetLevelが55 ~ 60なら、myLevel ← targetLevelの降順
   targetLevelが50 ~ 54なら、targetLevel → maxLevelの昇順
  */

  isDesc := (maxLevel - targetLevel) <= 5
  var min float64
  var max float64
  if isDesc {
    min = createSearchScore(myLevel)
    max = createSearchScore(targetLevel)
  } else {
    min = createSearchScore(targetLevel)
    max = createSearchScore(maxLevel)   
  }

  return searchScoreInfo {
    minScore: min
    maxScore: max
    isDesc:   isDesc,
  }
}


func rangeByScore(min,max,count int64, isDesc bool) ([]string,error) {
  // DIした方が良いけど、ここでは簡略化の為適宜Newを行う
  redisClient := redis.NewClient(&redis.Options{})
  
  rangeBy := &redis.ZRangeBy{
    Min:    strconv.FormatInt(min, 10)
    Max:    strconv.FormatInt(max, 10)
    Offset: 0,
    Count:  count,
  }
  
  var cmd *redis.StringSliceCmd
  if isDesc {
    cmd = redisClient.ZRevRangeByScore(ctx, key, rangeBy)
  } else {
    cmd = s.redisClient.ZRangeByScore(ctx, key, rangeBy)
  }
  
  if cmd.Err() != nil {
    return err
  }
  
  return cmd.Val()
}

func assortIDs(ids []string) ([]string, []string) {
  targetUserIDs := make([]string, 0, 5)
  surplusUserIDs := make([]string, 0, 5)
  for _, id := range ids {
   if len(targetUserIDs) < 5 {
      targetUserIDs = append(targetUserIDs, id)
    } else {
      surplusUserIDs = append(surplusUserIDs, id)
    }
   }

  return targetUserIDs, surplusUserIDs
}