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