import { Injectable } from '@nestjs/common';
import { InjectEntityManager, InjectRepository } from '@nestjs/typeorm';
import { EntityManager, Repository, TreeRepository } from 'typeorm';
import { NewItemInput } from './dto/new-item.input';
import { Item } from './items.entity';
import { ItemModel } from './items.model';

@Injectable()
export class ItemsService {
  constructor(
    @InjectRepository(Item)
    private itemRepository: Repository<Item>,
    @InjectEntityManager()
    private entityManager: EntityManager,
  ) {
    this.treeRepository = this.entityManager.getTreeRepository(Item);
  }
  treeRepository: TreeRepository<Item>;

  async getItem(id: string): Promise<Item | undefined> {
    return this.itemRepository.findOne(id);
  }

  async getItemParent(item: ItemModel): Promise<Item | undefined> {
    const childItem = await this.itemRepository.findOneOrFail(item.id, {
      relations: ['parent'],
    });
    return childItem.parent;
  }

  async getItemChildren(item: ItemModel): Promise<Item[]> {
    return this.itemRepository.find({
      where: {
        parent: item.id,
      },
    });
  }

  async getItemDescendents(item: ItemModel): Promise<Item[]> {
    const parentItem = await this.itemRepository.findOneOrFail(item.id, {
      relations: ['parent'],
    });
    // TreeRepository.findDescendants()[0] is always the parent item
    return (await this.treeRepository.findDescendants(parentItem)).slice(1);
  }

  async createItem(input: NewItemInput): Promise<Item> {
    // must use Repository.save() for the closure table to work,
    // so we have to check whether the provided ID exists in the first place
    if (input.id && (await this.itemRepository.count({ id: input.id })) !== 0) {
      throw new Error('Item with this ID already exists');
    }

    const highestId = input.id
      ? // nobody cares in this case
        null
      : (
          await this.itemRepository.findOne({
            select: ['id'],
            order: { id: 'DESC' },
          })
        )?.id || '139999999999';

    const item = this.itemRepository.create({
      ...input,
      // if id not provided, use the highest one in db +1
      id: highestId ? (BigInt(highestId) + 1n).toString(10) : input.id,
      parent: input.parent
        ? await this.itemRepository.findOneOrFail(input.parent)
        : undefined,
    });

    await this.itemRepository.save(item);

    return item;
  }
}