package envoy.server.data;

import java.time.LocalDateTime;
import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;

import envoy.data.User.UserStatus;
import envoy.server.net.ConnectionManager;

/**
 * Project: <strong>envoy-server-standalone</strong><br>
 * File: <strong>PersistenceManager.java</strong><br>
 * Created: <strong>1 Jan 2020</strong><br>
 *
 * @author Leon Hofmeister
 * @author Maximilian K&auml;fer
 * @since Envoy Server Standalone v0.1-alpha
 */
public class PersistenceManager {

	private final EntityManager		entityManager	= Persistence.createEntityManagerFactory("envoy").createEntityManager();
	private final EntityTransaction	transaction		= entityManager.getTransaction();

	private static final PersistenceManager persistenceManager = new PersistenceManager();

	/**
	 * Creates the singleton instance of the @link{PersistenceManager}.
	 *
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	private PersistenceManager() {
		Runtime.getRuntime().addShutdownHook(new Thread(() -> {
			transaction.begin();
			ConnectionManager.getInstance()
				.getOnlineUsers()
				.stream()
				.map(this::getUserByID)
				.forEach(user -> { user.setStatus(UserStatus.OFFLINE); user.setLastSeen(LocalDateTime.now()); entityManager.merge(user); });
			transaction.commit();
		}));
	}

	/**
	 * @return the {@link PersistenceManager} singleton
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public static PersistenceManager getInstance() { return persistenceManager; }

	/**
	 * Adds a {@link Contact} to the database.
	 *
	 * @param contact the {@link Contact} to add to the database
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public void addContact(Contact contact) { persist(contact); }

	/**
	 * Adds a {@link Message} to the database.
	 *
	 * @param message the {@link Message} to add to the database
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public void addMessage(Message message) { persist(message); }

	/**
	 * Adds a {@link ConfigItem} to the database.
	 *
	 * @param configItem the {@link ConfigItem} to add to the database
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public void addConfigItem(ConfigItem configItem) { persist(configItem); }

	/**
	 * Updates a {@link Contact} in the database
	 *
	 * @param contact the {@link Contact} to add to the database
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public void updateContact(Contact contact) { merge(contact); }

	/**
	 * Updates a {@link Message} in the database.
	 *
	 * @param message the message to update
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public void updateMessage(Message message) { merge(message); }

	/**
	 * Updates a {@link ConfigItem} in the database.
	 *
	 * @param configItem the configItem to update
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public void updateConfigItem(ConfigItem configItem) { merge(configItem); }

	/**
	 * Deletes a {@link Contact} in the database.
	 *
	 * @param contact the {@link Contact} to delete
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public void deleteContact(Contact contact) { remove(contact); }

	/**
	 * Deletes a {@link Message} in the database.
	 *
	 * @param message the {@link Message} to delete
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public void deleteMessage(Message message) { remove(message); }

	/**
	 * Searches for a {@link User} with a specific ID.
	 *
	 * @param id the id to search for
	 * @return the user with the specified ID or {@code null} if none was found
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public User getUserByID(long id) { return entityManager.find(User.class, id); }

	/**
	 * Searches for a {@link Group} with a specific ID.
	 *
	 * @param id the id to search for
	 * @return the group with the specified ID or {@code null} if none was found
	 * @since Envoy Server Standalone v0.1-beta
	 */
	public Group getGroupByID(long id) { return entityManager.find(Group.class, id); }

	/**
	 * Searches for a {@link Contact} with a specific ID.
	 *
	 * @param id the id to search for
	 * @return the contact with the specified ID or {@code null} if none was found
	 * @since Envoy Server Standalone v0.1-beta
	 */
	public Contact getContactByID(long id) { return entityManager.find(Contact.class, id); }

	/**
	 * Searched for a {@link User} with a specific name.
	 *
	 * @param name the name of the user
	 * @return the user with the specified name
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public User getUserByName(String name) {
		return (User) entityManager.createNamedQuery(User.findByName).setParameter("name", name).getSingleResult();
	}

	/**
	 * Searched for a {@link Group} with a specific name.
	 *
	 * @param name the name of the group
	 * @return the group with the specified name
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public Group getGroupByName(String name) {
		return (Group) entityManager.createNamedQuery(Group.findByName).setParameter("name", name).getSingleResult();
	}

	/**
	 * Searches for a {@link Message} with a specific id.
	 *
	 * @param id the id to search for
	 * @return the message with the specified ID or {@code null} if none is found
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public Message getMessageByID(long id) { return entityManager.find(Message.class, id); }

	/**
	 * @param key the name of this {@link ConfigItem}
	 * @return the {@link ConfigItem} with the given name
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public ConfigItem getConfigItemByID(String key) { return entityManager.find(ConfigItem.class, key); }

	/**
	 * Returns all messages received while being offline or the ones that have
	 * changed.
	 *
	 * @param user the user who wants to receive his unread messages
	 * @return all messages that the client does not yet have (unread messages)
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public List<Message> getPendingMessages(User user) {
		return entityManager
			.createNamedQuery(Message.getPending)
			.setParameter("user", user)
			.setParameter("lastSeen", user.getLastSeen())
			.getResultList();
	}

	/**
	 * Returns all groupMessages received while being offline or the ones that have
	 * changed.
	 *
	 * @param user the user who wants to receive his unread groupMessages
	 * @return all groupMessages that the client does not yet have (unread
	 *         groupMessages)
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public List<GroupMessage> getPendingGroupMessages(User user) {
		return entityManager.createNamedQuery(GroupMessage.getPendingGroupMsg)
			.setParameter("userId", user.getID())
			.setParameter("lastSeen", user.getLastSeen())
			.getResultList();
	}

	/**
	 * Searches for users matching a search phrase. Contacts of the attached user
	 * and the attached user is ignored.
	 *
	 * @param searchPhrase the search phrase
	 * @param userId       the ID of the user in whose context the search is
	 *                     performed
	 * @return a list of all users who matched the criteria
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public List<User> searchUsers(String searchPhrase, long userId) {
		return entityManager.createNamedQuery(
				User.searchByName)
			.setParameter("searchPhrase", searchPhrase + "%")
			.setParameter("context", getUserByID(userId))
			.getResultList();
	}

	/**
	 * Adds a contact to the contact list of another contact and vice versa.
	 *
	 * @param contactID1 the ID of the first contact
	 * @param contactID2 the ID of the second contact
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public void addContactBidirectional(long contactID1, long contactID2) {

		// Get users by ID
		Contact	c1	= getContactByID(contactID1);
		Contact	c2	= getContactByID(contactID2);

		// Add users to each others contact lists
		c1.getContacts().add(c2);
		c2.getContacts().add(c1);

		// Synchronize changes with the database
		transaction.begin();
		entityManager.merge(c1);
		entityManager.merge(c2);
		transaction.commit();
	}

	/**
	 * @param user the User whose contacts should be retrieved
	 * @return the contacts of this User
	 * @since Envoy Server Standalone v0.1-alpha
	 */
	public List<User> getContacts(User user) {
		return entityManager.createNamedQuery(User.findContacts).setParameter("user", user).getResultList();
	}

	private void persist(Object obj) {
		transaction.begin();
		entityManager.persist(obj);
		transaction.commit();
	}

	private void merge(Object obj) {
		transaction.begin();
		entityManager.merge(obj);
		transaction.commit();
	}

	private void remove(Object obj) {
		transaction.begin();
		entityManager.remove(obj);
		transaction.commit();
	}
}