Adapt Task to consider subtasks and implement service to create Subtasks

backend/src/main/java/core/entities/timemanager/Task.java

@@ -33,6 +33,13 @@ public class Task {
     @OneToOne(mappedBy = "task", cascade = CascadeType.ALL, orphanRemoval = true)
     private TaskSerieItem taskSerieItem;
 
+    @OneToMany(mappedBy = "parent", cascade = CascadeType.ALL, orphanRemoval = true)
+    private Set<Task> subtasks;
+
+    @ManyToOne
+    @JoinColumn(name = "parent")
+    private Task parent;
+
     public Task() {
         this.basicTaskSchedules = new ArrayList<>();
     }
@@ -149,6 +156,27 @@ public class Task {
         this.basicTaskSchedules = basicTaskSchedules;
     }
 
+    public void addSubtask(Task subtask) {
+        subtask.setParent(this);
+        this.subtasks.add(subtask);
+    }
+
+    public Set<Task> getSubtasks() {
+        return subtasks;
+    }
+
+    public void setSubtasks(Set<Task> subtasks) {
+        this.subtasks = subtasks;
+    }
+
+    public Task getParent() {
+        return parent;
+    }
+
+    public void setParent(Task parent) {
+        this.parent = parent;
+    }
+
     @Override
     public boolean equals(Object o) {
         if (this == o) return true;

backend/src/main/java/core/services/TaskService.java

@@ -49,6 +49,21 @@ public class TaskService {
         return new ServiceResult<>(task);
     }
 
+    public ServiceResult<Task> createSubTask(Task parentTask, TaskFieldInfo taskFieldInfo) {
+        if(taskFieldInfo.getStartDate().isBefore(parentTask.getStartDate()) ||
+                taskFieldInfo.getDeadline().isAfter(parentTask.getDeadline()) ||
+                taskFieldInfo.getDeadline().isBefore(taskFieldInfo.getStartDate())) {
+            return new ServiceResult<>(ServiceExitCode.INVALID_PARAMETER);
+        }
+
+        Task task = new Task(parentTask.getTaskgroup(), taskFieldInfo);
+        parentTask.getTaskgroup().getTasks().add(task);
+        parentTask.addSubtask(task);
+
+        taskRepository.save(task);
+        return new ServiceResult<>(task);
+    }
+
     private boolean existTaskByName(Collection<Task> tasks, String name) {
         for(Task task : tasks) {
             if(task.getTaskName().equals(name)) {
@@ -94,7 +109,6 @@ public class TaskService {
             taskSeriesService.deleteTaskSeriesItem(task);
         }
         taskRepository.delete(task);
-
     }
 
     public void clearTasks(Taskgroup taskgroup) {