session-grouper.js

function groupSessions(sessions, config = {}) {
  const now = config.now ? new Date(config.now) : new Date();

  const startOfToday = Date.UTC(now.getUTCFullYear(), now.getUTCMonth(), now.getUTCDate());
  const startOfYesterday = startOfToday - 86400000;

  const dayOfWeek = now.getUTCDay();
  const startOfWeek = startOfToday - (dayOfWeek * 86400000);

  const buckets = {
    Today: [],
    Yesterday: [],
    'This Week': []
  };

  for (const session of sessions) {
    const modified = new Date(session.modified);
    const startOfModified = Date.UTC(
      modified.getUTCFullYear(),
      modified.getUTCMonth(),
      modified.getUTCDate()
    );

    if (startOfModified === startOfToday) {
      buckets.Today.push(session);
    } else if (startOfModified === startOfYesterday) {
      buckets.Yesterday.push(session);
    } else if (startOfModified >= startOfWeek && startOfModified < startOfYesterday) {
      buckets['This Week'].push(session);
    } else {
      const monthNames = [
        'January', 'February', 'March', 'April', 'May', 'June',
        'July', 'August', 'September', 'October', 'November', 'December'
      ];
      const monthKey = `${monthNames[modified.getUTCMonth()]} ${modified.getUTCFullYear()}`;
      if (!buckets[monthKey]) buckets[monthKey] = [];
      buckets[monthKey].push(session);
    }
  }

  const defaultExpanded = config.expandedGroups || ['Today', 'Yesterday'];
  const result = [];

  for (const name of ['Today', 'Yesterday', 'This Week']) {
    if (buckets[name] && buckets[name].length > 0) {
      result.push({
        name,
        expanded: defaultExpanded.includes(name),
        sessions: buckets[name]
      });
    }
  }

  const monthKeys = Object.keys(buckets).filter(
    k => !['Today', 'Yesterday', 'This Week'].includes(k)
  );

  monthKeys.sort((a, b) => {
    const dateA = new Date(buckets[a][0].modified);
    const dateB = new Date(buckets[b][0].modified);
    return dateB - dateA;
  });

  for (const name of monthKeys) {
    result.push({
      name,
      expanded: defaultExpanded.includes(name),
      sessions: buckets[name]
    });
  }

  return result;
}

module.exports = { groupSessions };