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package org.daisy.common.messaging;

import java.math.BigDecimal;
import java.util.function.Consumer;
import java.util.List;
import java.util.Set;

import org.daisy.common.messaging.Message.Level;

import com.google.common.collect.ImmutableSet;

/**
 * Gives access to the stored messages.
 */
public abstract class MessageAccessor {

	/**
	 * Gets the errors.
	 *
	 * @return the error messages
	 */
	public List getErrors() {
		return getMessagesFrom(Level.ERROR);
	}

	/**
	 * Gets the warnings.
	 *
	 * @return the warning messages
	 */
	public List getWarnings(){
		return getMessagesFrom(Level.WARNING);
	}

	/**
	 * Gets the infos.
	 *
	 * @return the info messages
	 */
	public List getInfos(){
		return getMessagesFrom(Level.INFO);
	};

	/**
	 * Gets the debugs.
	 *
	 * @return the debug messages
	 */
	public List getDebugs(){
		return getMessagesFrom(Level.DEBUG);
	}

	/**
	 * Gets the traces.
	 *
	 * @return the trace messages
	 */
	public List getTraces(){
		return getMessagesFrom(Level.TRACE);
	}

	private List getMessagesFrom(Level level) {
		return createFilter().filterLevels(fromLevel(level)).getMessages();
	}

	private Set fromLevel(Level level) {
		ImmutableSet.Builder b = new ImmutableSet.Builder<>();
		for (Level l : Level.values())
			if (l.compareTo(level) <= 0)
				b.add(l);
		return b.build();
	}

	/**
	 * Gets the messgages from a set of levels
	 *
	 * @param fromLevels levels
	 * @return the messages
	 */
	public abstract List getAll();

	/**
	 * Register a callback that is called whenever a new (top-level) message arrives, a message is
	 * updated with descendant messages, or the progress of a message changes.
	 *
	 * The argument must be a function that accepts a sequence number representing the event. This
	 * sequence number can then be used to get the list of all messages affected by the change, via
	 * createFilter().inRange(...).getMessages().
	 *
	 * A sequence number is never null and never lower than the sequence numbers previously
	 * received, but the same sequence number may occur more than once.
	 */
	public abstract void listen(Consumer callback);
	public abstract void unlisten(Consumer callback);

	public abstract BigDecimal getProgress();

	public abstract MessageFilter createFilter();

	public interface MessageFilter {
		public MessageFilter filterLevels(Set levels);
		public MessageFilter greaterThan(int sequence);
		/**
		 * Get all the top-level messages affected by the events between (and including) "start" en
		 * "end". A top-level message may have been added, or a message may have been changed by a
		 * progress update or a new child message, or by a change of any of its already contained
		 * child messages.
		 */
		public MessageFilter inRange(int start, int end);
		public List getMessages();
	}
}