/* Copyright 2012, Sebastian Reichel <sre@ring0.de>
 * Copyright 2012, Ted Carancho
 *
 * Ported from AeroQuad
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

public class PID {
	double P;
	double I;
	double D;

	double lastPosition;
	uint64 previousPIDTime;
	double integratedError;
	double windupGuard;

	public double update(double targetPosition, double currentPosition) {
		/* calculate time delta */
		uint64 currentTime = time_t();
		uint64 deltaPIDTime = currentTime - previousPIDTime;
		previousPIDTime = currentTime;

		/* calculate error */
		double error = targetPosition - currentPosition;
		integratedError += error * deltaPIDTime;
		integratedError = constrain(integratedError, -windupGuard, windupGuard);

		double dTerm = D * (currentPosition - lastPosition) / (deltaPIDTime * 100);
		lastPosition = currentPosition;

		return P * error + I * integratedError + dTerm;
	}

	public void clear() {
		integratedError = 0;
		previousPIDTime = time_t();
	}
}