package de.ugoe.cs.eventbench.coverage;

import java.security.InvalidParameterException;
import java.util.Collection;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Set;

import de.ugoe.cs.eventbench.data.Event;
import de.ugoe.cs.eventbench.models.IStochasticProcess;

/**
 * <p>
 * This class gathers some helper functions to work with sequences.
 * </p>
 * 
 * @author Steffen Herbold
 * @version 1.0
 */
public class SequenceTools {
	
	/**
	 * <p>
	 * Private constructor to prevent initializing of the class.
	 * </p>
	 */
	private SequenceTools() {
		
	}

	/**
	 * <p>
	 * Calculates the weights for all sequences passed to this function as
	 * defined by the stochastic process and stores them in a {@link Map}. The
	 * weights are normalized, i.e., the sum of all weights contained in this
	 * map is 1.
	 * </p>
	 * 
	 * @param process
	 *            process used for weight calculation
	 * @param sequences
	 *            sequences for which the weights are calculated
	 * @return {@link Map} of weights
	 */
	public static Map<List<? extends Event<?>>, Double> generateWeights(
			IStochasticProcess process,
			Collection<List<? extends Event<?>>> sequences) {
		Map<List<? extends Event<?>>, Double> subSeqWeights = new LinkedHashMap<List<? extends Event<?>>, Double>();
		if (sequences != null && !sequences.isEmpty()) {
			if (process != null) {
				double sum = 0.0;
				for (List<? extends Event<?>> sequence : sequences) {
					double prob = process.getProbability(sequence);
					subSeqWeights.put(sequence, prob);
					sum += prob;
				}
				if (sum < 1.0) {
					for (Map.Entry<List<? extends Event<?>>, Double> entry : subSeqWeights
							.entrySet()) {
						entry.setValue(entry.getValue() / sum);
					}
				}
			} else {
				for( List<? extends Event<?>> sequence : sequences ) {
					subSeqWeights.put(sequence, 0.0d);
				}
			}
		}
		return subSeqWeights;
	}

	/**
	 * <p>
	 * Calculates the number of all existing sequences of a given length,
	 * regardless whether they are possible or not.
	 * </p>
	 * 
	 * @param process
	 *            stochastic process whose symbols are the basis for this
	 *            calculation
	 * @param length
	 *            lenght of the sequences
	 * @return numStates^length
	 * @throws InvalidParameterException
	 *             thrown if length less or equal to 0
	 */
	public static long numSequences(IStochasticProcess process, int length) {
		if (length <= 0) {
			throw new InvalidParameterException(
					"length must be a positive integer");
		}
		long result = 0;
		if (process != null) {
			result = (long) Math.pow(process.getNumSymbols(), length);
		}
		return result;
	}

	/**
	 * <p>
	 * Creates a {@link Set} of all subsequences of a given length that are
	 * contained in a sequence collection.
	 * </p>
	 * 
	 * @param sequences
	 *            sequences from which the subsequences are extracted
	 * @param length
	 *            length of the subsequences
	 * @return {@link Set} of all subsequences
	 * @throws InvalidParameterException
	 *             thrown if length less or equal to 0
	 */
	public static Set<List<? extends Event<?>>> containedSubSequences(
			Collection<List<? extends Event<?>>> sequences, int length) {
		if (length <= 0) {
			throw new InvalidParameterException(
					"length must be a positive integer");
		}
		Set<List<? extends Event<?>>> containedSubSeqs = new LinkedHashSet<List<? extends Event<?>>>();
		if (sequences != null) {
			for (List<? extends Event<?>> sequence : sequences) {
				List<Event<?>> subSeq = new LinkedList<Event<?>>();
				boolean minLengthReached = false;
				for (Event<?> event : sequence) {
					subSeq.add(event);
					if (!minLengthReached) {
						if (subSeq.size() == length) {
							minLengthReached = true;
						}
					} else {
						subSeq.remove(0);
					}
					if (minLengthReached) {
						if (!containedSubSeqs.contains(subSeq)) {
							containedSubSeqs.add(new LinkedList<Event<?>>(
									subSeq));
						}
					}
				}
			}
		}
		return containedSubSeqs;
	}
}