'use strict';

const IMPORTED_FIELDS = ['title', 'altTitles', 'authors', 'status', 'year', 'tags', 'description'];
const same = (a, b) => JSON.stringify(a) === JSON.stringify(b);
const { normalizeWorkIdentity, sameWorkIdentity } = require('./work-identity');

// The effective fields remain at the top of manga.json. A snapshot of the last
// imported values lets later imports refresh unchanged fields without replacing
// values somebody edited in the library. Legacy files have no snapshot, so their
// existing values are conservatively treated as intentional.
function mergeImportedMetadata(prior, imported, fallbackTitle) {
  const previous = prior['x-metadata']?.imported || {};
  const result = { ...prior };
  for (const field of IMPORTED_FIELDS) {
    if (!Object.hasOwn(imported, field)) continue;
    if (result[field] === undefined || result[field] === null || result[field] === ''
      || (Object.hasOwn(previous, field) && same(result[field], previous[field]))) {
      result[field] = imported[field];
    }
  }
  if (!result.title) result.title = fallbackTitle;

  const oldId = prior['x-anilist']?.id;
  const newId = imported['x-anilist']?.id;
  if (oldId != null && newId != null && String(oldId) !== String(newId)) {
    throw new Error(`AniList identity conflict: existing ${oldId}, imported ${newId}; review the manga match`);
  }
  if (imported['x-anilist']) result['x-anilist'] = { ...(prior['x-anilist'] || {}), ...imported['x-anilist'] };
  const oldWorkIdentity = normalizeWorkIdentity(prior['x-work-identity']);
  const newWorkIdentity = normalizeWorkIdentity(imported['x-work-identity']);
  if (oldWorkIdentity && newWorkIdentity && !sameWorkIdentity(oldWorkIdentity, newWorkIdentity)) {
    throw new Error(`MangaCircus work identity conflict: existing ${oldWorkIdentity.kind} identity differs from imported ${newWorkIdentity.kind} identity`);
  }
  if (newWorkIdentity) result['x-work-identity'] = newWorkIdentity;
  const snapshot = { ...previous };
  for (const field of IMPORTED_FIELDS) if (Object.hasOwn(imported, field)) snapshot[field] = imported[field];
  if (Object.keys(snapshot).length) result['x-metadata'] = { ...(prior['x-metadata'] || {}), imported: snapshot };
  return result;
}

module.exports = { mergeImportedMetadata, IMPORTED_FIELDS };