From 50f4b8350491446ce09a7571412139f722172d08 Mon Sep 17 00:00:00 2001
From: Fabio Scotto di Santolo <fabio.scottodisantolo@gmail.com>
Date: Fri, 6 Jan 2023 11:42:00 +0100
Subject: [PATCH] Implemented Queue data structure

---
 pkg/collection/queue.go      | 59 ++++++++++++++++++++++
 pkg/collection/queue_test.go | 94 ++++++++++++++++++++++++++++++++++++
 2 files changed, 153 insertions(+)
 create mode 100644 pkg/collection/queue.go
 create mode 100644 pkg/collection/queue_test.go

diff --git a/pkg/collection/queue.go b/pkg/collection/queue.go
new file mode 100644
index 0000000..4eec96b
--- /dev/null
+++ b/pkg/collection/queue.go
@@ -0,0 +1,59 @@
+package collection
+
+import (
+	"fmt"
+	"strings"
+)
+
+var (
+	ErrEmptyQueue = fmt.Errorf("empty queue")
+)
+
+type Queue[E any] struct {
+	items []E
+}
+
+func NewQueue[E any](items ...E) *Queue[E] {
+	if items == nil {
+		items = make([]E, 0)
+	}
+	return &Queue[E]{items}
+}
+
+func (q *Queue[E]) Empty() bool {
+	return q.Size() == 0
+}
+
+func (q *Queue[E]) Size() int {
+	return len(q.items)
+}
+
+func (q *Queue[E]) Enqueue(item E) {
+	q.items = append(q.items, item)
+}
+
+func (q *Queue[E]) Dequeue() (E, error) {
+	if q.Empty() {
+		return *new(E), ErrEmptyQueue
+	}
+	item := q.items[0]
+	q.items = q.items[1:]
+	return item, nil
+}
+
+func (q *Queue[E]) String() string {
+	var sb strings.Builder
+	sb.WriteString("[")
+	for i := 0; i < q.Size(); i++ {
+		var s string
+		item := q.items[i]
+		if i >= q.Size()-1 {
+			s = fmt.Sprintf("%v", item)
+		} else {
+			s = fmt.Sprintf("%v, ", item)
+		}
+		sb.WriteString(s)
+	}
+	sb.WriteString("]")
+	return sb.String()
+}
diff --git a/pkg/collection/queue_test.go b/pkg/collection/queue_test.go
new file mode 100644
index 0000000..70f4728
--- /dev/null
+++ b/pkg/collection/queue_test.go
@@ -0,0 +1,94 @@
+package collection
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestQueue_Empty(t *testing.T) {
+	useCases := []struct {
+		description string
+		queue       *Queue[int]
+		want        bool
+	}{
+		{description: "empty queue", queue: NewQueue[int](), want: true},
+		{description: "non empty queue", queue: NewQueue(1), want: false},
+	}
+
+	for _, tt := range useCases {
+		result := tt.queue.Empty()
+		if result != tt.want {
+			t.Errorf("test: %s, want %v got %v", tt.description, tt.want, result)
+		}
+	}
+}
+
+func TestQueue_Size(t *testing.T) {
+	useCases := []struct {
+		description string
+		queue       *Queue[int]
+		want        int
+	}{
+		{description: "empty queue", queue: NewQueue[int](), want: 0},
+		{description: "non empty queue", queue: NewQueue(1), want: 1},
+	}
+
+	for _, tt := range useCases {
+		result := tt.queue.Size()
+		if result != tt.want {
+			t.Errorf("test: %s, want %v got %v", tt.description, tt.want, result)
+		}
+	}
+}
+
+func TestQueue_Enqueue(t *testing.T) {
+	useCases := []struct {
+		description string
+		original    *Queue[int]
+		modified    *Queue[int]
+		item        int
+	}{
+		{description: "enqueue one item in empty queue", original: NewQueue[int](), modified: NewQueue(1), item: 1},
+		{description: "enqueue one item in full queue", original: NewQueue(1, 2, 3), modified: NewQueue(1, 2, 3, 4), item: 4},
+	}
+
+	for _, tt := range useCases {
+		tt.original.Enqueue(tt.item)
+		if !reflect.DeepEqual(tt.original.items, tt.modified.items) {
+			t.Errorf("test: %s, want %v got %v", tt.description, tt.modified, tt.original)
+		}
+	}
+}
+
+func TestQueue_Dequeue(t *testing.T) {
+	useCases := []struct {
+		description string
+		original    *Queue[int]
+		modified    *Queue[int]
+		item        int
+		err         error
+	}{
+		{description: "dequeue one item in empty queue",
+			original: NewQueue[int](),
+			modified: NewQueue[int](),
+			item:     0,
+			err:      ErrEmptyQueue},
+		{description: "dequeue one item in single item queue",
+			original: NewQueue(1),
+			modified: NewQueue[int](),
+			item:     1,
+			err:      nil},
+		{description: "dequeue one item in full queue",
+			original: NewQueue(1, 2, 3),
+			modified: NewQueue(2, 3),
+			item:     1,
+			err:      nil},
+	}
+
+	for _, tt := range useCases {
+		_, err := tt.original.Dequeue()
+		if !reflect.DeepEqual(tt.original.items, tt.modified.items) || err != tt.err {
+			t.Errorf("test: %s, want %v got %v", tt.description, tt.modified, tt.original)
+		}
+	}
+}