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81 lines
2.5 KiB
81 lines
2.5 KiB
const BN = require('ethereumjs-util').BN
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const normalize = require('eth-sig-util').normalize
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class PendingBalanceCalculator {
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/**
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* Used for calculating a users "pending balance": their current balance minus the total possible cost of all their
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* pending transactions.
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*
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* @typedef {Object} PendingBalanceCalculator
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* @param {Function} getBalance Returns a promise of a BN of the current balance in Wei
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* @param {Function} getPendingTransactions Returns an array of TxMeta Objects, which have txParams properties,
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* which include value, gasPrice, and gas, all in a base=16 hex format.
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*
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*/
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constructor ({ getBalance, getPendingTransactions }) {
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this.getPendingTransactions = getPendingTransactions
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this.getNetworkBalance = getBalance
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}
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/**
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* Returns the users "pending balance": their current balance minus the total possible cost of all their
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* pending transactions.
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*
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* @returns {Promise<string>} Promises a base 16 hex string that contains the user's "pending balance"
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*
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*/
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async getBalance () {
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const results = await Promise.all([
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this.getNetworkBalance(),
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this.getPendingTransactions(),
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])
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const [ balance, pending ] = results
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if (!balance) {
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return undefined
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}
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const pendingValue = pending.reduce((total, tx) => {
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return total.add(this.calculateMaxCost(tx))
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}, new BN(0))
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return `0x${balance.sub(pendingValue).toString(16)}`
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}
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/**
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* Calculates the maximum possible cost of a single transaction, based on the value, gas price and gas limit.
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*
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* @param {object} tx Contains all that data about a transaction.
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* @property {object} tx.txParams Contains data needed to calculate the maximum cost of the transaction: gas,
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* gasLimit and value.
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*
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* @returns {string} Returns a base 16 hex string that contains the maximum possible cost of the transaction.
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*/
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calculateMaxCost (tx) {
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const txValue = tx.txParams.value
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const value = this.hexToBn(txValue)
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const gasPrice = this.hexToBn(tx.txParams.gasPrice)
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const gas = tx.txParams.gas
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const gasLimit = tx.txParams.gasLimit
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const gasLimitBn = this.hexToBn(gas || gasLimit)
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const gasCost = gasPrice.mul(gasLimitBn)
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return value.add(gasCost)
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}
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/**
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* Converts a hex string to a BN object
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*
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* @param {string} hex A number represented as a hex string
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* @returns {Object} A BN object
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*
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*/
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hexToBn (hex) {
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return new BN(normalize(hex).substring(2), 16)
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}
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}
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module.exports = PendingBalanceCalculator
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