Kucoin: Subscription configuration

* Simplify GenerateDefaultSubs
* Improve TestGenSubs coverage
* Test Candle Sub generation
* Support Candle intervals
* Full responsibility for formatting Channel name on GenerateDefaultSubs
  OR consumer of Subscribe
* Simplify generatePayloads as a result

currency/currencies.go

@@ -20,6 +20,14 @@ func NewCurrenciesFromStringArray(currencies []string) Currencies {
 // Currencies define a range of supported currency codes
 type Currencies []Code
 
+// Add adds a currency to the list if it doesn't exist
+func (c Currencies) Add(a Code) Currencies {
+	if !c.Contains(a) {
+		c = append(c, a)
+	}
+	return c
+}
+
 // Strings returns an array of currency strings
 func (c Currencies) Strings() []string {
 	list := make([]string, len(c))

currency/currencies_test.go

@@ -3,6 +3,8 @@ package currency
 import (
 	"encoding/json"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
 func TestCurrenciesUnmarshalJSON(t *testing.T) {
@@ -62,3 +64,13 @@ func TestMatch(t *testing.T) {
 		t.Fatal("should not match")
 	}
 }
+
+func TestCurrenciesAdd(t *testing.T) {
+	c := Currencies{}
+	c = c.Add(BTC)
+	assert.Len(t, c, 1, "Should have one currency")
+	c = c.Add(ETH)
+	assert.Len(t, c, 2, "Should have one currency")
+	c = c.Add(BTC)
+	assert.Len(t, c, 2, "Adding a duplicate should not change anything")
+}

exchanges/kucoin/kucoin_types.go

@@ -33,6 +33,8 @@ var (
 	errSizeOrFundIsRequired      = errors.New("at least one required among size and funds")
 	errInvalidLeverage           = errors.New("invalid leverage value")
 	errInvalidClientOrderID      = errors.New("no client order ID supplied, this endpoint requires a UUID or similar string")
+	errInvalidMsgType            = errors.New("message type field not valid")
+	errSubscriptionPairRequired  = errors.New("pair required for manual subscriptions")
 
 	subAccountRegExp           = regexp.MustCompile("^[a-zA-Z0-9]{7-32}$")
 	subAccountPassphraseRegExp = regexp.MustCompile("^[a-zA-Z0-9]{7-24}$")