3 files changed, 90 insertions, 2 deletions
diff --git a/todolist/app.go b/todolist/app.go
index 1ab6b20..20a35ef 100644
--- a/todolist/app.go
+++ b/todolist/app.go
@@ -183,6 +183,13 @@ func (a *App) getGroups(input string, todos []*Todo) *GroupedTodos {
 	return grouped
 }
 
+func (a *App) GarbageCollect() {
+	a.Load()
+	a.TodoList.GarbageCollect()
+	a.Save()
+	fmt.Println("Garbage collection complete.")
+}
+
 func (a *App) Load() error {
 	todos, err := a.TodoStore.Load()
 	if err != nil {
diff --git a/todolist/todo_list.go b/todolist/todo_list.go
index d7e1f83..ea8ecbe 100644
--- a/todolist/todo_list.go
+++ b/todolist/todo_list.go
@@ -78,14 +78,32 @@ func (t *TodoList) Todos() []*Todo {
 	return t.Data
 }
 
-func (t *TodoList) NextId() int {
+func (t *TodoList) MaxId() int {
 	maxId := 0
 	for _, todo := range t.Data {
 		if todo.Id > maxId {
 			maxId = todo.Id
 		}
 	}
-	return maxId + 1
+	return maxId
+}
+
+func (t *TodoList) NextId() int {
+	var found bool
+	maxID := t.MaxId()
+	for i := 1; i <= maxID; i++ {
+		found = false
+		for _, todo := range t.Data {
+			if todo.Id == i {
+				found = true
+				break
+			}
+		}
+		if !found {
+			return i
+		}
+	}
+	return maxID + 1
 }
 
 func (t *TodoList) FindById(id int) *Todo {
@@ -96,3 +114,15 @@ func (t *TodoList) FindById(id int) *Todo {
 	}
 	return nil
 }
+
+func (t *TodoList) GarbageCollect() {
+	var toDelete []*Todo
+	for _, todo := range t.Data {
+		if todo.Archived {
+			toDelete = append(toDelete, todo)
+		}
+	}
+	for _, todo := range toDelete {
+		t.Delete(todo.Id)
+	}
+}
diff --git a/todolist/todo_list_test.go b/todolist/todo_list_test.go
index 8a40b14..eb0bc84 100644
--- a/todolist/todo_list_test.go
+++ b/todolist/todo_list_test.go
@@ -8,8 +8,42 @@ import (
 
 func TestNextId(t *testing.T) {
 	assert := assert.New(t)
+	todo := &Todo{Subject: "testing", Completed: false, Archived: false}
 	list := &TodoList{}
 	assert.Equal(1, list.NextId())
+	list.Add(todo)
+	assert.Equal(2, list.NextId())
+}
+
+func TestNextIdWhenTodoDeleted(t *testing.T) {
+	assert := assert.New(t)
+	todo := &Todo{Subject: "testing", Completed: false, Archived: false}
+	todo2 := &Todo{Subject: "testing2", Completed: false, Archived: false}
+	todo3 := &Todo{Subject: "testing3", Completed: false, Archived: false}
+	list := &TodoList{}
+
+	list.Add(todo)
+	list.Add(todo2)
+	list.Add(todo3)
+
+	list.Delete(2)
+	assert.Equal(2, list.NextId())
+	list.Add(todo2)
+	assert.Equal(4, list.NextId())
+	list.Delete(1)
+	assert.Equal(1, list.NextId())
+}
+
+func TestMaxId(t *testing.T) {
+	assert := assert.New(t)
+	todo := &Todo{Subject: "testing", Completed: false, Archived: false}
+	todo2 := &Todo{Subject: "testing 2", Completed: false, Archived: false}
+	list := &TodoList{}
+	assert.Equal(0, list.MaxId())
+	list.Add(todo)
+	assert.Equal(1, list.MaxId())
+	list.Add(todo2)
+	assert.Equal(2, list.MaxId())
 }
 
 func TestIndexOf(t *testing.T) {
@@ -77,3 +111,20 @@ func TestUncomplete(t *testing.T) {
 	list.Uncomplete(2)
 	assert.Equal(false, list.FindById(2).Completed)
 }
+
+func TestGarbageCollect(t *testing.T) {
+	assert := assert.New(t)
+	list := &TodoList{}
+	todo := &Todo{Subject: "testing", Completed: false, Archived: true}
+	todo2 := &Todo{Subject: "testing2", Completed: false, Archived: false}
+	todo3 := &Todo{Subject: "testing3", Completed: false, Archived: true}
+	list.Add(todo)
+	list.Add(todo2)
+	list.Add(todo3)
+
+	list.GarbageCollect()
+
+	assert.Equal(len(list.Data), 1)
+	assert.Equal(1, list.NextId())
+	assert.Equal(2, list.MaxId())
+}