backend/buisnesslogic/src/main/java/com/plannaplan/services/GroupService.java

package com.plannaplan.services;

import java.util.HashMap;
import java.util.List;
import java.util.Objects;
import java.util.Optional;
import java.util.stream.Collectors;
import java.util.function.Function;

import com.plannaplan.entities.Assignment;
import com.plannaplan.entities.Groups;
import com.plannaplan.repositories.GroupRepository;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

/**
 * Service of GroupService which can find(optional), get(By Course, Groups
 * Ammount, Group By Id, find Not Existing Group), save, delete group.
 */

@Service
public class GroupService {
    @Autowired
    private GroupRepository repo;

    public GroupService() {
    }

    public Optional<Groups> find(int time, int capacity, String room) {
        return this.repo.find(time, room, capacity);
    }

    public Optional<Groups> find(Integer zajCykId, Integer nrGr) {
        return this.repo.find(zajCykId, nrGr);
    }

    public List<Groups> getGroupsByCourse(Long id) {
        return this.repo.getByCourse(id);
    }

    public Groups save(Groups group) {
        return this.repo.save(group);
    }

    public void delete(Groups groups) {
        this.repo.delete(groups);
    }

    public int getGroupsAmmount() {
        return (int) this.repo.count();
    }

    public Optional<Groups> getGroupById(Long id) {
        return this.repo.findById(id);
    }

    public Optional<Long> findNotExistingGroup(List<Long> ids) {
        for (Long oneId : ids) {
            if (this.repo.existsById(oneId) == false) {
                return Optional.of(oneId);
            }
        }
        return Optional.empty();

    }

    /**
     * 
     * @param assignments list of assignments you want to get taken places ammount
     * @return HashMap of Long to Integer where Long is group id and Integer is how
     *         many places in gorup is already taken
     */
    public HashMap<Long, Integer> getTakenPlacesOfAssignments(List<Assignment> assignments) {
        return getTakenPlaces(assignments.stream().map(Assignment::getGroup).collect(Collectors.toList()));
    }

    /**
     * 
     * @param groups list of groups you want to get taken places ammount
     * @return HashMap of Long to Integer where Long is group id and Integer is how
     *         many places in gorup is already taken
     */
    public HashMap<Long, Integer> getTakenPlaces(List<Groups> groups) {
        HashMap<Long, Integer> response = new HashMap<>();

        if (groups.size() == 0) {
            return response;
        }

        List<Object[]> respoonses = this.repo
                .getAssignedAmounts(groups.stream().filter(Objects::nonNull).map(new Function<Groups, Long>() {
                    @Override
                    public Long apply(Groups p) {
                        final Long id = p.getId();
                        response.put(id, 0);
                        return id;
                    }
                }).collect(Collectors.toList()));

        for (Object[] element : respoonses) {
            response.put(((Groups) element[0]).getId(), ((Long) element[1]).intValue());
        }

        return response;
    }
}