package edu.neu.ccs.evergreen.state;

import org.apache.log4j.Logger;

import edu.neu.ccs.evergreen.exception.ContradictionException;
import edu.neu.ccs.evergreen.model.Assignment;
import edu.neu.ccs.evergreen.model.Assignments;
import edu.neu.ccs.evergreen.model.Constraint;
import edu.neu.ccs.evergreen.model.State;

/**
 * Uses the app mean algorithm to order the variables and values.
 */
public class AppMeanNextState implements NextState {
	private static final Logger LOGGER = Logger.getLogger(AppMeanNextState.class);

	/**
	 * @see edu.neu.ccs.evergreen.state.NextState#getNextState(edu.neu.ccs.evergreen.model.State,
	 *      int, edu.neu.ccs.evergreen.model.Assignments)
	 */
	public State getNextState(State state, int maxOriginalVariable, Assignments bestAssignments) {
		State nextState = null;
		double best = Double.MIN_VALUE;

		// TODO maybe track set of unavailable variables
		for (int variable = 1; variable <= maxOriginalVariable; variable++) {
			if (state.unassigned(variable)) {
				State testState = null;
				Constraint errorConstraint = null;
				for (int value = 0; value < 2; value++) {
					try {
						LOGGER.trace("Trying " + variable + "=" + value);
						testState = state.clone();
						testState
								.addAssignment(new Assignment(variable, value));
						double test = testState.appMean();
						if (test > best) {
							nextState = testState;
							best = test;
						}
					} catch (ContradictionException contradictionException) {
						LOGGER.trace(variable + "=" + value
								+ " caused contradiction");
						errorConstraint = contradictionException
								.getConstraint();
						throw new ContradictionException("Variable " + variable
								+ " leads to a contradiction", testState,
								errorConstraint);
					}
				}
			}
		}
		if (nextState == null) {
			LOGGER
					.debug("Every possible decision variable leads to a contradiction");
			throw new ContradictionException(
					"Every possible decision variable leads to a contradiction");
		}
		LOGGER.debug("getNextState picked " + nextState.getLastDecision());
		return nextState;
	}

	/**
	 * @see edu.neu.ccs.evergreen.state.NextState#initBestAssignments(edu.neu.ccs.evergreen.model.State)
	 */
	public Assignments initBestAssignments(State state) {
		// Ignore
		return null;
	}

	/**
	 * @see edu.neu.ccs.evergreen.state.NextState#updateBestAssignments(edu.neu.ccs.evergreen.model.State, edu.neu.ccs.evergreen.model.Assignments)
	 */
	public Assignments updateBestAssignments(State state, Assignments bestAssignments) {
		// Ignore
		return null;
	}
}