From 3de08b76e4f52c35e7b01fd8f67b343913903537 Mon Sep 17 00:00:00 2001
From: Adrian Gallagher <thrasher@addictionsoftware.com>
Date: Sun, 19 Feb 2017 18:30:41 +1100
Subject: [PATCH] Add CalculatePercentageGainOrLoss function

---
 common.go      |  6 +++++-
 common_test.go | 17 ++++++++++++++---
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/common.go b/common.go
index 33f32374..cb231f0d 100644
--- a/common.go
+++ b/common.go
@@ -175,8 +175,12 @@ func CalculateFee(amount, fee float64) float64 {
 	return amount * (fee / 100)
 }
 
+func CalculatePercentageGainOrLoss(priceNow, priceThen float64) float64 {
+	return (priceNow - priceThen) / priceThen * 100
+}
+
 func CalculatePercentageDifference(amount, secondAmount float64) float64 {
-	return (secondAmount - amount) / amount * 100
+	return (amount - secondAmount) / ((amount + secondAmount) / 2) * 100
 }
 
 func CalculateNetProfit(amount, priceThen, priceNow, costs float64) float64 {
diff --git a/common_test.go b/common_test.go
index 4f9781cc..653e2ffb 100644
--- a/common_test.go
+++ b/common_test.go
@@ -183,11 +183,22 @@ func TestCalculateAmountWithFee(t *testing.T) {
 	}
 }
 
+func TestCalculatePercentageGainOrLoss(t *testing.T) {
+	t.Parallel()
+	originalInput := float64(9300)
+	secondInput := float64(9000)
+	expectedOutput := 3.3333333333333335
+	actualResult := CalculatePercentageGainOrLoss(originalInput, secondInput)
+	if expectedOutput != actualResult {
+		t.Error(fmt.Sprintf("Test failed. Expected '%f'. Actual '%f'.", expectedOutput, actualResult))
+	}
+}
+
 func TestCalculatePercentageDifference(t *testing.T) {
 	t.Parallel()
-	originalInput := float64(5)
-	secondAmount := float64(10)
-	expectedOutput := float64(100)
+	originalInput := float64(10)
+	secondAmount := float64(5)
+	expectedOutput := 66.66666666666666
 	actualResult := CalculatePercentageDifference(originalInput, secondAmount)
 	if expectedOutput != actualResult {
 		t.Error(fmt.Sprintf("Test failed. Expected '%f'. Actual '%f'.", expectedOutput, actualResult))