# Copyright 2016 Google Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import threading


class ShelfInfo:
    """The contents of a single shelf."""

    def __init__(self, shelf):
        self._shelf = shelf
        self._last_book_id = 0
        self._books = dict()


class Bookstore:
    """An in-memory backend for storing Bookstore data."""

    def __init__(self):
        self._last_shelf_id = 0
        self._shelves = dict()
        self._lock = threading.Lock()

    def list_shelf(self):
        with self._lock:
            return [s._shelf for (_, s) in self._shelves.items()]

    def create_shelf(self, shelf):
        with self._lock:
            self._last_shelf_id += 1
            shelf_id = self._last_shelf_id
        shelf.id = shelf_id
        self._shelves[shelf_id] = ShelfInfo(shelf)
        return (shelf, shelf_id)

    def get_shelf(self, shelf_id):
        with self._lock:
            return self._shelves[shelf_id]._shelf

    def delete_shelf(self, shelf_id):
        with self._lock:
            del self._shelves[shelf_id]

    def list_books(self, shelf_id):
        with self._lock:
            return [book for (_, book) in self._shelves[shelf_id]._books.items()]

    def create_book(self, shelf_id, book):
        with self._lock:
            shelf_info = self._shelves[shelf_id]
            shelf_info._last_book_id += 1
            book_id = shelf_info._last_book_id
            book.id = book_id
            shelf_info._books[book_id] = book
            return book

    def get_book(self, shelf_id, book_id):
        with self._lock:
            return self._shelves[shelf_id]._books[book_id]

    def delete_book(self, shelf_id, book_id):
        with self._lock:
            del self._shelves[shelf_id]._books[book_id]