From f6bce891c4f664418082d960bc0db6f8258e5eb5 Mon Sep 17 00:00:00 2001
From: Adrian Gallagher <thrasher@addictionsoftware.com>
Date: Fri, 5 Oct 2018 15:21:06 +1000
Subject: [PATCH] Add additional helper functions to pairs package

---
 config/config.go           |  2 +-
 currency/pair/pair.go      | 20 ++++++++++++++++
 currency/pair/pair_test.go | 49 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 70 insertions(+), 1 deletion(-)

diff --git a/config/config.go b/config/config.go
index 6bd023d6..a849d82a 100644
--- a/config/config.go
+++ b/config/config.go
@@ -497,7 +497,7 @@ func (c *Config) CheckPairConsistency(exchName string) error {
 	}
 
 	if len(pairs) == 0 {
-		exchCfg.EnabledPairs = availPairs[0].Pair().String()
+		exchCfg.EnabledPairs = pair.RandomPairFromPairs(availPairs).Pair().String()
 	} else {
 		exchCfg.EnabledPairs = common.JoinStrings(pair.PairsToStringArray(pairs), ",")
 	}
diff --git a/currency/pair/pair.go b/currency/pair/pair.go
index 8eabacac..dd989c95 100644
--- a/currency/pair/pair.go
+++ b/currency/pair/pair.go
@@ -1,6 +1,7 @@
 package pair
 
 import (
+	"math/rand"
 	"strings"
 
 	"github.com/thrasher-/gocryptotrader/common"
@@ -80,6 +81,14 @@ func (c CurrencyPair) Swap() CurrencyPair {
 	return p
 }
 
+// Empty returns whether or not the pair is empty
+func (c CurrencyPair) Empty() bool {
+	if c.FirstCurrency == "" || c.SecondCurrency == "" {
+		return true
+	}
+	return false
+}
+
 // NewCurrencyPairDelimiter splits the desired currency string at delimeter,
 // the returns a CurrencyPair struct
 func NewCurrencyPairDelimiter(currency, delimiter string) CurrencyPair {
@@ -216,3 +225,14 @@ func PairsToStringArray(pairs []CurrencyPair) []string {
 	}
 	return p
 }
+
+// RandomPairFromPairs returns a random pair from a list of pairs
+func RandomPairFromPairs(pairs []CurrencyPair) CurrencyPair {
+	pairsLen := len(pairs)
+
+	if pairsLen == 0 {
+		return CurrencyPair{}
+	}
+
+	return pairs[rand.Intn(pairsLen)]
+}
diff --git a/currency/pair/pair_test.go b/currency/pair/pair_test.go
index 798865d7..2ae662ff 100644
--- a/currency/pair/pair_test.go
+++ b/currency/pair/pair_test.go
@@ -154,6 +154,19 @@ func TestSwap(t *testing.T) {
 	}
 }
 
+func TestEmpty(t *testing.T) {
+	t.Parallel()
+	pair := NewCurrencyPair("BTC", "USD")
+	if pair.Empty() {
+		t.Error("Test failed. Empty() returned true when the pair was initialised")
+	}
+
+	var p CurrencyPair
+	if !p.Empty() {
+		t.Error("Test failed. Empty() returned true when the pair wasn't initialised")
+	}
+}
+
 func TestNewCurrencyPair(t *testing.T) {
 	t.Parallel()
 	pair := NewCurrencyPair("BTC", "USD")
@@ -370,3 +383,39 @@ func TestPairsToStringArray(t *testing.T) {
 		t.Error("Test failed. TestPairsToStringArray: Unexpected values")
 	}
 }
+
+func TestRandomPairFromPairs(t *testing.T) {
+	// Test that an empty pairs array returns an empty currency pair
+	result := RandomPairFromPairs([]CurrencyPair{})
+	if !result.Empty() {
+		t.Error("Test failed. TestRandomPairFromPairs: Unexpected values")
+	}
+
+	// Test that a populated pairs array returns a non-empty currency pair
+	var pairs []CurrencyPair
+	pairs = append(pairs, NewCurrencyPair("BTC", "USD"))
+	result = RandomPairFromPairs(pairs)
+
+	if result.Empty() {
+		t.Error("Test failed. TestRandomPairFromPairs: Unexpected values")
+	}
+
+	// Test that a populated pairs array over a number of attempts returns ALL
+	// currency pairs
+	pairs = append(pairs, NewCurrencyPair("ETH", "USD"))
+	expectedResults := make(map[string]bool)
+	for i := 0; i < 50; i++ {
+		p := RandomPairFromPairs(pairs).Pair().String()
+		_, ok := expectedResults[p]
+		if !ok {
+			expectedResults[p] = true
+		}
+	}
+
+	for x := range pairs {
+		_, ok := expectedResults[pairs[x].Pair().String()]
+		if !ok {
+			t.Error("Test failed. TestRandomPairFromPairs: Unexpected values")
+		}
+	}
+}