Calculate steam market fees

steamMarket.js

// Steam market fee calculator:tm:

// The price you're selling at, in cents
var sellPrice = 100

// Handy toggles
var inMarketPage = !!g_rgWalletInfo;
var hasItemSelectred = !!g_ActiveInventory.selectedItem.description.market_fee;

// Steam values, may vary per region or game, defaults at the end.
var steamFeePercent = inMarketPage ? g_rgWalletInfo['wallet_fee_percent'] : 0.05
var steamFeeMinimum = inMarketPage ? g_rgWalletInfo['wallet_fee_minimum'] : 1
var steamFeeBase = inMarketPage ? g_rgWalletInfo['wallet_fee_base'] : 0
var publisherFeePercent = hasItemSelectred ? g_ActiveInventory.selectedItem.description.market_fee : 0.10

var calculateFees = (receivedAmount) => {
    var steamFee = Math.floor(Math.max(receivedAmount * steamFeePercent, steamFeeMinimum) + steamFeeBase)
    var publisherFee = Math.floor(publisherFeePercent > 0 ? Math.max(receivedAmount * publisherFeePercent, 1) : 0);
    return {
        steamFee,
        publisherFee,
        totalFees: steamFee + publisherFee,
        amountToSellAt: receivedAmount + steamFee + publisherFee
    }
}

var iterations = 0;
var estimateReceived = parseInt((sellPrice - steamFeeBase) / (steamFeePercent + publisherFeePercent + 1));
var fees = calculateFees(estimateReceived);
var everUndershot = false;

// Precision calculation due to Math.floor
while (fees.amountToSellAt != sellPrice && iterations < 10) {
    if (fees.amountToSellAt > sellPrice) {
        if (everUndershot) {
            fees = calculateFees(estimateReceived - 1);
            fees.steamFee += (amount - fees.amountSoldAt);
            fees.totalFees += (amount - fees.amountSoldAt);
            fees.amountSoldAt = amount;
            break;
        } else {
            estimateReceived--;
        }
    } else {
        everUndershot = true;
        estimateReceived++;
    }

    fees = calculateFees(estimateReceived);
    iterations++;
}

// Ignore how ugly this looks
console.log(`From ${(sellPrice / 100).toFixed(2)} you get ${((sellPrice - fees.totalFees) / 100).toFixed(2)}, to get ${(sellPrice / 100).toFixed(2)} sell at ${(calculateFees(sellPrice).amountToSellAt / 100).toFixed(2)}`)