dataSelection

/**
 * @param {Array<{user: number, duration: number, equipment: Array<string>}>} sessions
 * @param {{user?: number, minDuration?: number, equipment?: Array<string>, merge?: boolean}} [options]
 * @return {Array<{user: number, duration: number, equipment: Array<string>}>>}
 */
export default function selectData(sessions, options = {}) {
  const {
    user,
    minDuration,
    equipment,
    merge = false,
  } = options || {};

  const hasUserFilter = user !== undefined;
  const hasMinDurationFilter = minDuration !== undefined;
  const hasEquipmentFilter = equipment !== undefined;
  const equipmentFilterSet = hasEquipmentFilter ? new Set(equipment) : null;

  /**
   * @param {{user: number, duration: number, equipment: Array<string>}} session
   * @returns {boolean}
   */
  const matchesFilters = (session) => {
    if (hasUserFilter && session.user !== user) {
      return false;
    }

    if (hasMinDurationFilter && session.duration < minDuration) {
      return false;
    }

    if (hasEquipmentFilter) {
      let found = false;

      for (const item of session.equipment) {
        if (equipmentFilterSet.has(item)) {
          found = true;
          break;
        }
      }

      if (!found) {
        return false;
      }
    }

    return true;
  };

  if (!merge) {
    return sessions.filter(matchesFilters);
  }

  const mergedByUser = new Map();

  for (let i = 0; i < sessions.length; i++) {
    const session = sessions[i];
    const existing = mergedByUser.get(session.user);

    if (!existing) {
      mergedByUser.set(session.user, {
        user: session.user,
        duration: session.duration,
        equipmentSet: new Set(session.equipment),
        lastIndex: i,
      });
      continue;
    }

    existing.duration += session.duration;
    existing.lastIndex = i;

    for (const item of session.equipment) {
      existing.equipmentSet.add(item);
    }
  }

  const mergedRows = Array.from(mergedByUser.values())
    .sort((a, b) => a.lastIndex - b.lastIndex)
    .map((row) => ({
      user: row.user,
      duration: row.duration,
      equipment: Array.from(row.equipmentSet).sort(),
    }));

  return mergedRows.filter(matchesFilters);
}


/** Test cases for the selectData function
selectData(sessions);
// [
//   { user: 8, duration: 50, equipment: ['bench'] },
//   { user: 7, duration: 150, equipment: ['dumbbell', 'kettlebell'] },
//   { user: 1, duration: 10, equipment: ['barbell'] },
//   { user: 7, duration: 100, equipment: ['bike', 'kettlebell'] },
//   { user: 7, duration: 200, equipment: ['bike'] },
//   { user: 2, duration: 200, equipment: ['treadmill'] },
//   { user: 2, duration: 200, equipment: ['bike'] },
// ];

selectData(sessions, { user: 2 });
// [
//   { user: 2, duration: 200, equipment: ['treadmill'] },
//   { user: 2, duration: 200, equipment: ['bike'] },
// ];

selectData(sessions, { minDuration: 200 });
// [
//   { user: 7, duration: 200, equipment: ['bike'] },
//   { user: 2, duration: 200, equipment: ['treadmill'] },
//   { user: 2, duration: 200, equipment: ['bike'] },
// ];

selectData(sessions, { minDuration: 400 });
// [];

selectData(sessions, { equipment: ['bike', 'dumbbell'] });
// [
//   { user: 7, duration: 150, equipment: ['dumbbell', 'kettlebell'] },
//   { user: 7, duration: 100, equipment: ['bike', 'kettlebell'] },
//   { user: 7, duration: 200, equipment: ['bike'] },
//   { user: 2, duration: 200, equipment: ['bike'] },
// ];

selectData(sessions, { merge: true });
// [
//   { user: 8, duration: 50, equipment: ['bench'] },
//   { user: 1, duration: 10, equipment: ['barbell'] },
//   { user: 7, duration: 450, equipment: ['bike', 'dumbbell', 'kettlebell'] },
//   { user: 2, duration: 400, equipment: ['bike', 'treadmill'] },
// ];

selectData(sessions, { merge: true, minDuration: 400 });
// [
//   { user: 7, duration: 450, equipment: ['bike', 'dumbbell', 'kettlebell'] },
//   { user: 2, duration: 400, equipment: ['bike', 'treadmill'] },
// ];

*/