function mergeEligibility(detail) {
  if (!detail || detail.state !== 'open' || detail.merged) {
    return { allowed: false, reason: 'Pull request is not open' };
  }
  if (detail.draft) return { allowed: false, reason: 'Draft pull requests cannot be merged' };
  if (!detail.mergeable) return { allowed: false, reason: 'Resolve conflicts before merging' };
  if (detail.ci_state !== 'success') {
    return { allowed: false, reason: 'CI must succeed before merging' };
  }
  if (!detail.head_sha) return { allowed: false, reason: 'Current head is unavailable' };
  return { allowed: true, reason: 'Ready to merge' };
}

function createPullSheet({ fetchJson, storage }) {
  let commentRequest = null;
  let mergeRequest = null;
  const pathFor = item => 'api/v1/repos/' + String(item.repository || '').split('/')
    .map(encodeURIComponent).join('/') + '/pulls/' + encodeURIComponent(item.number);
  const draftKey = item => 'stackchain.pull-comment.v1:' + item.repository + '#' + item.number;

  return {
    load(item) {
      return fetchJson(pathFor(item) + '/detail', { headers: { Accept: 'application/json' } });
    },
    loadDraft(item) {
      try { return storage?.getItem(draftKey(item)) || ''; }
      catch (_error) { return ''; }
    },
    saveDraft(item, body) {
      try { storage?.setItem(draftKey(item), body); }
      catch (_error) { /* The textarea remains the fallback. */ }
    },
    comment(item, body) {
      if (commentRequest) return commentRequest;
      this.saveDraft(item, body);
      commentRequest = fetchJson(pathFor(item) + '/comments', {
        method: 'POST',
        headers: { Accept: 'application/json', 'Content-Type': 'application/json' },
        body: JSON.stringify({ body }),
      }).then(result => {
        try { storage?.removeItem(draftKey(item)); }
        catch (_error) { /* The upstream comment is authoritative. */ }
        return result;
      }).finally(() => { commentRequest = null; });
      return commentRequest;
    },
    merge(item, expectedHeadSha) {
      if (mergeRequest) return mergeRequest;
      mergeRequest = fetchJson(pathFor(item) + '/merge', {
        method: 'POST',
        headers: { Accept: 'application/json', 'Content-Type': 'application/json' },
        body: JSON.stringify({ expected_head_sha: expectedHeadSha }),
      }).then(result => {
        if (!result?.merged) throw new Error('Pull request merge was not confirmed.');
        return result;
      }).finally(() => { mergeRequest = null; });
      return mergeRequest;
    },
  };
}

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