import { createSubgraph } from "../../subgraph.js";
import { books } from "./data.js";

export default createSubgraph("c", {
  typeDefs: /* GraphQL */ `
    extend schema
      @link(url: "https://specs.apollo.dev/federation/v2.3", import: ["@key"])

    type Book @key(fields: "id") {
      id: ID!
      author: Author
    }

    type Author {
      id: ID!
      name: String
    }
  `,
  resolvers: {
    Book: {
      __resolveReference(reference: { id: String } | { upc: String }) {
        if (reference != null) {
          let book:
            | { id: string; author: { id: string; name: string } }
            | undefined;
          if ("id" in reference && reference.id !== null) {
            book = books.find((book) => book.id === reference.id);
          }
          if ("upc" in reference && reference.upc !== null) {
            book = books.find((book) => book.upc === reference.upc);
          }
          if (book != null) {
            return {
              __typename: "Book",
              id: book.id,
              author: {
                __typename: "Author",
                id: book.author.id,
                name: book.author.name,
              },
            };
          }
        }
        throw new Error("Invalid reference");
      },
    },
  },
});