import { PrismaService } from "@cv/core";
import { Injectable, Scope } from "@nestjs/common";
import DataLoader from "dataloader";
import type { ApplicationStatusRelation } from "./application.entity";

@Injectable({ scope: Scope.REQUEST })
export class ApplicationStatusDataLoaderService {
  private loader: DataLoader<string, ApplicationStatusRelation | null>;

  constructor(readonly prisma: PrismaService) {
    this.loader = new DataLoader<string, ApplicationStatusRelation | null>(
      async (ids: readonly string[]) => {
        const statuses = await prisma.applicationStatus.findMany({
          where: {
            id: { in: [...ids] },
          },
          select: {
            id: true,
            name: true,
            description: true,
            createdAt: true,
            updatedAt: true,
          },
        });

        const statusMap = new Map<string, ApplicationStatusRelation>();
        for (const {
          id,
          name,
          description,
          createdAt,
          updatedAt,
        } of statuses) {
          statusMap.set(id, {
            id,
            name,
            description,
            createdAt,
            updatedAt,
          });
        }

        return ids.map((id) => statusMap.get(id) ?? null);
      },
    );
  }

  async load(key: string): Promise<ApplicationStatusRelation | null> {
    return this.loader.load(key);
  }

  async loadMany(
    keys: readonly string[],
  ): Promise<(ApplicationStatusRelation | null)[]> {
    const results = await this.loader.loadMany(keys);
    return results.map((result) => (result instanceof Error ? null : result));
  }
}