From f35d68c85ddbfd8895d444331ba9e0da269b932a Mon Sep 17 00:00:00 2001
From: Emir Pasic <emirpasic@hotmail.com>
Date: Wed, 22 Jun 2016 06:04:14 +0200
Subject: [PATCH] - add iterator to linked list stack

---
 stacks/linkedliststack/linkedliststack.go     | 30 ++++++++++++++++
 .../linkedliststack/linkedliststack_test.go   | 34 +++++++++++++++++++
 2 files changed, 64 insertions(+)

diff --git a/stacks/linkedliststack/linkedliststack.go b/stacks/linkedliststack/linkedliststack.go
index 5cc08e6..14b720f 100644
--- a/stacks/linkedliststack/linkedliststack.go
+++ b/stacks/linkedliststack/linkedliststack.go
@@ -33,6 +33,7 @@ package linkedliststack
 
 import (
 	"fmt"
+	"github.com/emirpasic/gods/containers"
 	"github.com/emirpasic/gods/lists/singlylinkedlist"
 	"github.com/emirpasic/gods/stacks"
 	"strings"
@@ -40,6 +41,7 @@ import (
 
 func assertInterfaceImplementation() {
 	var _ stacks.Stack = (*Stack)(nil)
+	var _ containers.Iterator = (*Iterator)(nil)
 }
 
 type Stack struct {
@@ -90,6 +92,29 @@ func (stack *Stack) Values() []interface{} {
 	return stack.list.Values()
 }
 
+type Iterator struct {
+	stack *Stack
+	index int
+}
+
+func (stack *Stack) Iterator() Iterator {
+	return Iterator{stack: stack, index: -1}
+}
+
+func (iterator *Iterator) Next() bool {
+	iterator.index += 1
+	return iterator.stack.withinRange(iterator.index)
+}
+
+func (iterator *Iterator) Value() interface{} {
+	value, _ := iterator.stack.list.Get(iterator.index) // in reverse (LIFO)
+	return value
+}
+
+func (iterator *Iterator) Index() interface{} {
+	return iterator.index
+}
+
 func (stack *Stack) String() string {
 	str := "LinkedListStack\n"
 	values := []string{}
@@ -99,3 +124,8 @@ func (stack *Stack) String() string {
 	str += strings.Join(values, ", ")
 	return str
 }
+
+// Check that the index is withing bounds of the list
+func (stack *Stack) withinRange(index int) bool {
+	return index >= 0 && index < stack.list.Size()
+}
diff --git a/stacks/linkedliststack/linkedliststack_test.go b/stacks/linkedliststack/linkedliststack_test.go
index dea7ba0..2e082ff 100644
--- a/stacks/linkedliststack/linkedliststack_test.go
+++ b/stacks/linkedliststack/linkedliststack_test.go
@@ -84,7 +84,41 @@ func TestLinkedListStack(t *testing.T) {
 	if actualValue := stack.Values(); len(actualValue) != 0 {
 		t.Errorf("Got %v expected %v", actualValue, "[]")
 	}
+}
 
+func TestLinkedListStackIterator(t *testing.T) {
+	stack := New()
+	stack.Push("a")
+	stack.Push("b")
+	stack.Push("c")
+
+	// Iterator
+	it := stack.Iterator()
+	for it.Next() {
+		index := it.Index()
+		value := it.Value()
+		switch index {
+		case 0:
+			if actualValue, expectedValue := value, "c"; actualValue != expectedValue {
+				t.Errorf("Got %v expected %v", actualValue, expectedValue)
+			}
+		case 1:
+			if actualValue, expectedValue := value, "b"; actualValue != expectedValue {
+				t.Errorf("Got %v expected %v", actualValue, expectedValue)
+			}
+		case 2:
+			if actualValue, expectedValue := value, "a"; actualValue != expectedValue {
+				t.Errorf("Got %v expected %v", actualValue, expectedValue)
+			}
+		default:
+			t.Errorf("Too many")
+		}
+	}
+	stack.Clear()
+	it = stack.Iterator()
+	for it.Next() {
+		t.Errorf("Shouldn't iterate on empty stack")
+	}
 }
 
 func BenchmarkLinkedListStack(b *testing.B) {