ReadaBook/apps/api/src/metadata/adapters/open-library.provider.ts

import { Injectable } from "@nestjs/common";
import { MetadataLookup, MetadataMatch, MetadataProvider, MetadataProviderConfig } from "../metadata.types.js";
import { toIsbn13 } from "../use-cases/extract-identifiers.js";

@Injectable()
export class OpenLibraryProvider implements MetadataProvider {
  readonly id = "openlibrary" as const;

  async lookup(lookup: MetadataLookup, _config: MetadataProviderConfig): Promise<MetadataMatch | null> {
    const isbn = lookup.identifiers.isbn13 ?? lookup.identifiers.isbn10;
    if (isbn) {
      return this.lookupIsbn(isbn, lookup.identifiers.isbn13);
    }
    const query = `title:${lookup.title}${lookup.author ? ` author:${lookup.author}` : ""}`;
    const url = new URL("https://openlibrary.org/search.json");
    url.searchParams.set("q", query);
    url.searchParams.set("limit", "1");
    const response = await fetch(url, {
      headers: { "User-Agent": "ReadaBook/0.1 local-library-manager" },
      signal: AbortSignal.timeout(4000)
    });
    if (!response.ok) return null;
    const data = (await response.json()) as { docs?: Array<Record<string, unknown>> };
    const doc = data.docs?.[0];
    if (!doc) return null;
    return {
      title: stringValue(doc.title) ?? undefined,
      author: arrayJoin(doc.author_name),
      language: firstArrayValue(doc.language),
      publisher: firstArrayValue(doc.publisher),
      publishedDate: String(doc.first_publish_year ?? "") || null,
      isbn: bestIsbn(doc.isbn, lookup.identifiers.isbn13)
    };
  }

  private async lookupIsbn(isbn: string, expectedIsbn13: string | null): Promise<MetadataMatch | null> {
    const response = await fetch(`https://openlibrary.org/isbn/${encodeURIComponent(isbn)}.json`, {
      headers: { "User-Agent": "ReadaBook/0.1 local-library-manager" },
      signal: AbortSignal.timeout(4000)
    });
    if (!response.ok) return null;
    const edition = (await response.json()) as Record<string, unknown>;
    const author = await this.lookupAuthorName(edition.authors);
    return {
      title: stringValue(edition.title) ?? undefined,
      author,
      description: descriptionValue(edition.description),
      isbn: bestIsbn([...(asStringArray(edition.isbn_13)), ...(asStringArray(edition.isbn_10))], expectedIsbn13),
      language: languageValue(edition.languages),
      publisher: firstArrayValue(edition.publishers),
      publishedDate: stringValue(edition.publish_date)
    };
  }

  private async lookupAuthorName(value: unknown): Promise<string | null> {
    const key = (Array.isArray(value) ? value[0] : undefined)?.key;
    if (typeof key !== "string") return null;
    const response = await fetch(`https://openlibrary.org${key}.json`, {
      headers: { "User-Agent": "ReadaBook/0.1 local-library-manager" },
      signal: AbortSignal.timeout(3000)
    });
    if (!response.ok) return null;
    const author = (await response.json()) as Record<string, unknown>;
    return stringValue(author.name);
  }
}

function stringValue(value: unknown): string | null {
  return typeof value === "string" && value.trim() ? value.trim() : null;
}

function firstArrayValue(value: unknown): string | null {
  if (!Array.isArray(value) || !value.length) return null;
  return String(value[0]);
}

function arrayJoin(value: unknown): string | null {
  return Array.isArray(value) && value.length ? value.map(String).join(", ") : null;
}

function bestIsbn(value: unknown, expectedIsbn13: string | null): string | null {
  if (!Array.isArray(value)) return null;
  const values = value.map(String);
  return values.find((candidate) => toIsbn13(candidate) === expectedIsbn13) ?? values.find((candidate) => toIsbn13(candidate)) ?? null;
}

function asStringArray(value: unknown): string[] {
  return Array.isArray(value) ? value.map(String) : [];
}

function descriptionValue(value: unknown): string | null {
  if (typeof value === "string") return value.trim() || null;
  if (typeof value === "object" && value && "value" in value) return stringValue(value.value);
  return null;
}

function languageValue(value: unknown): string | null {
  const key = (Array.isArray(value) ? value[0] : undefined)?.key;
  return typeof key === "string" ? key.split("/").pop() ?? null : null;
}