function createFindWork({ fetchJson, onItems, onPagination, onStatus }) {
  let available = [];
  let pagination = { page: 1, total: 0, has_more: false };
  let loadRequest = null;
  let claimRequest = null;

  function apply(result, append) {
    const incoming = Array.isArray(result?.items) ? result.items : [];
    if (append) {
      const byId = new Map(available.map(item => [item.id, item]));
      incoming.forEach(item => {
        if (item && !byId.has(item.id)) byId.set(item.id, { ...item });
      });
      available = Array.from(byId.values());
    } else {
      available = incoming.map(item => ({ ...item }));
    }
    pagination = {
      page: Number(result?.page) || 1,
      total: Number(result?.total) || available.length,
      has_more: result?.has_more === true,
    };
    onItems(available.slice());
    onPagination({ ...pagination });
  }

  function loadPage(page, append) {
    if (loadRequest) return loadRequest;
    loadRequest = fetchJson('api/v1/available-issues?page=' + page, {
      headers: { Accept: 'application/json' },
    }).then(result => {
      apply(result, append);
      return result;
    }).finally(() => { loadRequest = null; });
    return loadRequest;
  }

  return {
    reset(result) {
      apply(result, false);
    },
    load() {
      return loadPage(1, false);
    },
    loadMore() {
      if (!pagination.has_more) return Promise.resolve(false);
      return loadPage(pagination.page + 1, true);
    },
    items() {
      return available.slice();
    },
    claim(item) {
      if (claimRequest) return claimRequest;
      const key = item.repository + '#' + item.number;
      onStatus('Assigning ' + key + '…');
      const path = 'api/v1/repos/' + item.repository.split('/').map(encodeURIComponent).join('/') +
        '/issues/' + encodeURIComponent(item.number) + '/claim';
      claimRequest = fetchJson(path, {
        method: 'PATCH',
        headers: { Accept: 'application/json' },
      }).then(confirmed => {
        if (!Array.isArray(confirmed?.assignees) || !confirmed.assignees.length) {
          throw new Error('Issue assignment was not confirmed.');
        }
        available = available.filter(candidate =>
          candidate.repository !== item.repository || candidate.number !== item.number
        );
        onItems(available.slice());
        onStatus('Assigned ' + key + ' to you.');
        return confirmed;
      }).finally(() => { claimRequest = null; });
      return claimRequest;
    },
  };
}

if (typeof module !== 'undefined' && module.exports) module.exports = createFindWork;