Calculating each exchange's fees (#188)

* Adds some constants for fee types
Adds some fee calculation in an attempt to be generic
Adds fee stuff to Bittrex
Adds fee stuff to bitstamp

* Fixes bitstamp fee calculation

* Tests
Tests all scenarios for GetFeeByType

* Adds method to wrapper
Adds err to response
Checks for err

* Adds support for Bittrex fees

* Adds maker/taker dynamic to fees
Updates tests
Adds bitmex fee support
Removes unused switch case scenarios to not waste space

* Adds bithumb support for fee calculation

* Adds Bitfinex fee support
Adds list of currencies as const strings
Sets up bitflyer

* Fixes arguments

* Greatly expands symbols
Adds Binance fee calculation support
Cleans up previous exchanges

* Fixes errors for fee calculations

* Adds ANX fee support

* Adds btcc fee support
Adds alphapoint fee wrapper support
Renames method to match "enum"
Uses symbols in tests, not inline strings

* Adds support for BTCMarkets fee calculation
Adds new method to retrieve fee amount from BTCMarkets
Adds new fee type struct: FeeBuilder
Updates ANX and BTCMarkets to use new FeeBuilder type struct
Standardises the tests to run when it comes to fee calculation

* Migrates all existing exchange fee to use new feebuilder type struct
Uses standard testing model

* Fixes unit tests

* Updates maker taker fees in test config

* Removes parallel from fee testing

* Removes more parallel from tests

* Adds coinbasepro fee support

* Adds Coinut fee support

* Adds Exmo fee support
Adds maker fee support to coinut
Introduces a type for fees and bank transfers to prevent random strings being used

* Adds partial bitflyer support
Moves bitflyer to feeBuilder struct

* Adds gateio fee support

* Adds Gemini fee support

* Adds hitbtc fee support

* Adds huobi fee support

* Adds HuobiHadax fee support

* Adds itbit fee support

* Adds partial kraken fee support with trading fees

* Finishes basic Kraken fee support

* Adds basic LakeBTC fee support

* Adds basic liqui fee support

* Adds localbitcoins fee support.......

* Adds basic okcoin fee support

* Adds simple OKEX fee support
Adds many new currency symbols
Fixes liqui's fees

* Adds poloniex fee support

* Adds fee support for Yobit

* Adds WEX fee support

* Adds ZB fee support

* Removes bad reference

* Improves accuracy of variable name

* trading fee method names are now consistent

(cherry picked from commit 21c82e8b90cae590cfd73d365d7be39e1a00e973)

* Fixes rebasing issues

* Fixes issues from rebase
Removes "IsTaker" as IsMaker bool can imply taker
Updates tests to actually work.

* Adds a zero to the test

* Fixes bitfinex api endpoints and fixes fee calculations

* Updates btcmarkets trading fee calculation

* Verifies tests with apis for all exchanges except coinbasepro, itbit and bitflyer
Removes taker fee test as taker is default

* Removes redundant all exchange wrapper error checks due to the error checks being redundant

* Addresses review comments:
- Renames variables
- Changes how functions return data
- Fixes typo

exchanges/itbit/itbit.go

@@ -101,14 +101,6 @@ func (i *ItBit) Setup(exch config.ExchangeConfig) {
 	}
 }
 
-// GetFee returns the maker or taker fee
-func (i *ItBit) GetFee(maker bool) float64 {
-	if maker {
-		return i.MakerFee
-	}
-	return i.TakerFee
-}
-
 // GetTicker returns ticker info for a specified market.
 // currencyPair - example "XBTUSD" "XBTSGD" "XBTEUR"
 func (i *ItBit) GetTicker(currencyPair string) (Ticker, error) {
@@ -376,3 +368,27 @@ func (i *ItBit) SendAuthenticatedHTTPRequest(method string, path string, params
 
 	return i.SendPayload(method, url, headers, bytes.NewBuffer([]byte(PayloadJSON)), result, true, i.Verbose)
 }
+
+// GetFee returns an estimate of fee based on type of transaction
+func (i *ItBit) GetFee(feeBuilder exchange.FeeBuilder) (float64, error) {
+	var fee float64
+	switch feeBuilder.FeeType {
+	case exchange.CryptocurrencyTradeFee:
+		fee = calculateTradingFee(feeBuilder.PurchasePrice, feeBuilder.Amount, feeBuilder.IsMaker)
+	}
+	if fee < 0 {
+		fee = 0
+	}
+
+	return fee, nil
+}
+
+func calculateTradingFee(purchasePrice, amount float64, isMaker bool) float64 {
+	// TODO: Itbit has volume discounts, but not API endpoint to get the exact volume numbers
+	// When support is added, this needs to be updated to calculate the accurate volume fee
+	feePercent := 0.0025
+	if isMaker {
+		feePercent = 0
+	}
+	return feePercent * purchasePrice * amount
+}