package edu.neu.ccs.evergreen.state;

import java.util.Random;

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;

/**
 * Use a biased coin to decide if the next variable is true or false.
 */
public abstract class BiasNextState implements NextState {
	private static final Logger LOGGER = Logger.getLogger(BiasNextState.class);

	protected Random random;
	protected double refresh = 0.5;
	protected boolean doRefresh = true;
	protected double bias;
	
	abstract protected boolean doRefresh();
	abstract protected double calculateBias(State state, int maxOriginalVariable, Assignments bestAssignments);

	/**
	 * @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) {
		if (doRefresh()) {
			bias = calculateBias(state, maxOriginalVariable, bestAssignments
					);
			doRefresh = false;
			LOGGER.debug("Bias refreshed and is now " + bias + " which solves " + state.satisfiedPercentage(bias));
		}
		// TODO maybe track set of unavailable variables
		for (int variable = 1; variable <= maxOriginalVariable; variable++) {
			if (state.unassigned(variable)) {
				State testState = state.clone();
				int value = 0;
				try {
					// if bias = 1 we always set true, that's why <=
					if (random.nextDouble() < bias) {
						value = 1;
					}
					LOGGER.trace("Trying " + variable + "=" + value);
					testState.addAssignment(new Assignment(variable, value));
				} catch (ContradictionException contradictionException) {
					LOGGER.trace(variable + "=" + value
							+ " caused contradiction");
					Constraint errorConstraint = contradictionException
							.getConstraint();
					throw new ContradictionException("Variable " + variable
							+ " leads to a contradiction", testState,
							errorConstraint);
				}
				return testState;
			}
		}
		LOGGER.debug("No unassigned variables");
		throw new ContradictionException("No unassigned variables");
	}
	
	/**
	 * @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;
	}
}