application/mov/match/fee_strategy.go

   1 package match
   2
   3 import (
   4         "math"
   5
   6         "github.com/bytom/vapor/errors"
   7         "github.com/bytom/vapor/protocol/bc"
   8 )
   9
  10 var (
  11         // ErrAmountOfFeeOutOfRange represent The fee charged is out of range
  12         ErrAmountOfFeeOutOfRange = errors.New("amount of fee is out of range")
  13 )
  14
  15 // AllocatedAssets represent reallocated assets after calculating fees
  16 type AllocatedAssets struct {
  17         Receives []*bc.AssetAmount
  18         Refunds  RefundAssets
  19         Fees     []*bc.AssetAmount
  20 }
  21
  22 // RefundAssets represent alias for assetAmount array, because each transaction participant can be refunded multiple assets
  23 type RefundAssets [][]*bc.AssetAmount
  24
  25 // Add used to add a refund to specify order
  26 func (r RefundAssets) Add(index int, asset bc.AssetID, amount uint64) {
  27         if index >= len(r) {
  28                 index = 0
  29         }
  30
  31         for _, assetAmount := range r[index] {
  32                 if *assetAmount.AssetId == asset {
  33                         assetAmount.Amount += amount
  34                         return
  35                 }
  36         }
  37         r[index] = append(r[index], &bc.AssetAmount{AssetId: &asset, Amount: amount})
  38 }
  39
  40 // FeeStrategy used to indicate how to charge a matching fee
  41 type FeeStrategy interface {
  42         // Allocate will allocate the price differential in matching transaction to the participants and the fee
  43         // @param receiveAmounts the amount of assets that the participants in the matching transaction can received when no fee is considered
  44         // @param priceDiffs price differential of matching transaction
  45         // @return reallocated assets after calculating fees
  46         Allocate(receiveAmounts, priceDiffs []*bc.AssetAmount) *AllocatedAssets
  47
  48         // Validate verify that the fee charged for a matching transaction is correct
  49         Validate(receiveAmounts []*bc.AssetAmount, feeAmounts map[bc.AssetID]uint64) error
  50 }
  51
  52 // DefaultFeeStrategy represent the default fee charge strategy
  53 type DefaultFeeStrategy struct {}
  54
  55 // NewDefaultFeeStrategy return a new instance of DefaultFeeStrategy
  56 func NewDefaultFeeStrategy() *DefaultFeeStrategy {
  57         return &DefaultFeeStrategy{}
  58 }
  59
  60 // Allocate will allocate the price differential in matching transaction to the participants and the fee
  61 func (d *DefaultFeeStrategy) Allocate(receiveAmounts, priceDiffs []*bc.AssetAmount) *AllocatedAssets {
  62         feeMap := make(map[bc.AssetID]uint64)
  63         for _, priceDiff := range priceDiffs {
  64                 feeMap[*priceDiff.AssetId] = priceDiff.Amount
  65         }
  66
  67         var fees []*bc.AssetAmount
  68         refunds := make([][]*bc.AssetAmount, len(receiveAmounts))
  69         receives := make([]*bc.AssetAmount, len(receiveAmounts))
  70
  71         for i, receiveAmount := range receiveAmounts {
  72                 amount := receiveAmount.Amount
  73                 minFeeAmount := d.calcMinFeeAmount(amount)
  74                 receives[i] = &bc.AssetAmount{AssetId: receiveAmount.AssetId, Amount: amount - minFeeAmount}
  75                 feeMap[*receiveAmount.AssetId] += minFeeAmount
  76
  77                 maxFeeAmount := d.calcMaxFeeAmount(amount)
  78                 feeAmount, reminder := feeMap[*receiveAmount.AssetId], uint64(0)
  79                 if feeAmount > maxFeeAmount {
  80                         reminder = feeAmount - maxFeeAmount
  81                         feeAmount = maxFeeAmount
  82                 }
  83
  84                 fees = append(fees, &bc.AssetAmount{AssetId: receiveAmount.AssetId, Amount: feeAmount})
  85
  86                 // There is the remaining amount after paying the handling fee, assign it evenly to participants in the transaction
  87                 averageAmount := reminder / uint64(len(receiveAmounts))
  88                 if averageAmount == 0 {
  89                         averageAmount = 1
  90                 }
  91
  92                 for j := 0; j < len(receiveAmounts) && reminder > 0; j++ {
  93                         refundAmount := averageAmount
  94                         if j == len(receiveAmounts)-1 {
  95                                 refundAmount = reminder
  96                         }
  97                         refunds[j] = append(refunds[j], &bc.AssetAmount{AssetId: receiveAmount.AssetId, Amount: refundAmount})
  98                         reminder -= averageAmount
  99                 }
 100         }
 101         return &AllocatedAssets{Receives: receives, Refunds: refunds, Fees: fees}
 102 }
 103
 104 // Validate verify that the fee charged for a matching transaction is correct
 105 func (d *DefaultFeeStrategy) Validate(receiveAmounts []*bc.AssetAmount, feeAmounts map[bc.AssetID]uint64) error {
 106         for _, receiveAmount := range receiveAmounts {
 107                 feeAmount := feeAmounts[*receiveAmount.AssetId]
 108                 maxFeeAmount := d.calcMaxFeeAmount(receiveAmount.Amount)
 109                 minFeeAmount := d.calcMinFeeAmount(receiveAmount.Amount)
 110                 if feeAmount < minFeeAmount || feeAmount > maxFeeAmount {
 111                         return ErrAmountOfFeeOutOfRange
 112                 }
 113         }
 114         return nil
 115 }
 116
 117 func (d *DefaultFeeStrategy) calcMinFeeAmount(amount uint64) uint64 {
 118         return uint64(math.Ceil(float64(amount) / 1000))
 119 }
 120
 121 func (d *DefaultFeeStrategy) calcMaxFeeAmount(amount uint64) uint64 {
 122         return uint64(math.Ceil(float64(amount) * 0.05))
 123 }