package geniusweb.bidspace;

import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

import geniusweb.issuevalue.Bid;
import geniusweb.profile.DefaultPartialOrdering;
import geniusweb.profile.PartialOrdering;
import geniusweb.profile.utilityspace.UtilitySpace;
import tudelft.utilities.immutablelist.ListWithRemove;
import tudelft.utilities.immutablelist.Tuple;
import tudelft.utilities.immutablelist.Tuples;

/**
 * Simple demo converting a {@link UtilitySpace} into a {@link PartialOrdering}.
 * Notice, a UtilitySpace IS a PartialOrdering, but a special one that is in
 * fact a full ordering. This converter makes it a space that really has all
 * info removed except for a few basic "isBetter" informations.
 */
public class PartialSpaceFromUtility extends DefaultPartialOrdering {
	public PartialSpaceFromUtility(UtilitySpace space, int nRankings) {
		super(space.getName() + "_" + nRankings, space.getDomain(), space.getReservationBid(),
				pickBetter(space, nRankings));
	}

	/**
	 * Pick subset of static isbetter rankings. Notice, ShuffledList currently can't
	 * handle really large lists which also limits this. This has to be fixed.
	 * 
	 * @param space     the space to sample from
	 * @param nRankings the number of rankings to be placed in the PartialOrdering.
	 * @return a subset creating a partial profile of the geiven UtilitySpace
	 */
	private static Map<Bid, Set<Bid>> pickBetter(UtilitySpace space, int nRankings) {
		Map<Bid, Set<Bid>> eqOrBetter = new HashMap<>();

		AllBidsList allbids = new AllBidsList(space.getDomain());
		ListWithRemove<Tuple<Bid, Bid>> available = new ListWithRemove<>(new Tuples<Bid, Bid>(allbids, allbids));
		for (int n = 0; n < nRankings; n++) {
			BigInteger sel = rnd(available.size());
			Tuple<Bid, Bid> tuple = available.get(sel);
			Bid bid1 = tuple.get1();
			Bid bid2 = tuple.get2();
			switch (space.getUtility(bid1).compareTo(space.getUtility(bid2))) {
			case -1: // bid1 is worse
				add(eqOrBetter, bid2, bid1);
				break;
			case 0:
				add(eqOrBetter, bid2, bid1);
				add(eqOrBetter, bid1, bid2);
				break;
			case 1:// bid1 is better
				add(eqOrBetter, bid1, bid2);
				break;
			}
			available = available.remove(sel);
		}
		return eqOrBetter;
	}

	/**
	 * 
	 * @param eqOrBetter map to be extended with (key=bid1, value=bid2)
	 * @param bid1       the key to add a value to
	 * @param bid2       the value to be added
	 */
	private static void add(Map<Bid, Set<Bid>> eqOrBetter, Bid bid1, Bid bid2) {
		Set<Bid> set = eqOrBetter.get(bid1);
		if (set == null) {
			set = new HashSet<Bid>();
		}
		set.add(bid2);
		eqOrBetter.put(bid1, set);
	}

	/**
	 * Bit simplistic way to generate random in [0,n>. Simplistic because the mod()
	 * operator that we use causes bias in the random numbers.
	 * 
	 * @param n the maximum value for the random number
	 * @return random in [0,n>
	 * 
	 */
	private static final BigInteger rnd(BigInteger n) {
		return new BigInteger(n.bitLength(), new SecureRandom()).mod(n);
	}
}