import sys
import traceback


class Item:
    SPACE = ' '
    DASH_SPACE = ' - '
    def __init__(self, key, name, function, parent=None):
        self.key = str(key)
        self.name = name
        self.function = function
        self.parent = parent

        if parent:
            parent.add_item(self)

    def __str__(self):
        return self.SPACE + self.key + self.DASH_SPACE + self.name

    def execute(self):
        print('\n' + self.name + '\n')
        return self.function()


class Menu:
    def __init__(self, name, items=None):
        self.name = name
        self.items = items or []

    def add_item(self, item):
        self.items.append(item)
        if item.parent != self:
            item.parent = self

    def remove_item(self, item):
        self.items.remove(item)
        if item.parent == self:
            item.parent = None

    def __str__(self):
        all = ['', self.name, '']
        for item in self.items:
            all.append(str(item))
        return '\n'.join(all)

    def get_item(self, key):
        for item in self.items:
            if item.key == key:
                return item

    def execute(self):
        while True:
            try:
                print(self)
                choice = raw_input(" >>  ")
                try:
                    item = self.get_item(choice)

                    try:
                        item.execute()
                    except Exception:
                        traceback.print_exc()

                except Exception:
                    print('Invalid selection, please try again.\n')
            except KeyboardInterrupt:
                sys.exit()


if __name__ == "__main__":
    # Pass in methods to run for each menu item
    menu_items = [
        Item(1, 'View Running tasks', view_running_tasks),
        Item(2, 'View Task', view_task),
        # ...
        Item(9, 'Exit', exit)]
    menu = Menu('Task Management', items=menu_items)

    menu.execute()