BasicBulletShielder

package wiki;

import java.awt.Color;
import java.awt.geom.Line2D;
import java.awt.geom.Point2D;
import java.util.ArrayDeque;
import robocode.AdvancedRobot;
import robocode.BulletHitEvent;
import robocode.HitByBulletEvent;
import robocode.Rules;
import robocode.ScannedRobotEvent;
import robocode.util.Utils;

public class BasicBulletShielder extends AdvancedRobot {
	public void run() {
		setAdjustGunForRobotTurn(true);
		setAdjustRadarForGunTurn(true);
		
		setAllColors(Color.WHITE);
		
		/* Setup Radar */
		turnRadarRightRadians(Double.POSITIVE_INFINITY);
	    while(true) scan();
	}
	
	ArrayDeque<Double> pastAngles = new ArrayDeque<Double>();
	
	static final double BULLET_START_POWER = 0.15;
	
	Point2D lastPosition = null;
	double lastEnemyEnergy = 100;
	double lastMoveDistance = 0;
	double aimAngle = 0;
	double firePower = BULLET_START_POWER;
	long fireOnTick = 0;
	
	public void onScannedRobot(ScannedRobotEvent e) {
		double angleToEnemy = getHeadingRadians() + e.getBearingRadians();
		
		Point2D enemyPosition = project(getPosition(),angleToEnemy,e.getDistance());
		
		pastAngles.addFirst(angleToEnemy);
		if(pastAngles.size() > 3)
			pastAngles.removeLast();
	
		long time = getTime();
		
		/* Radar */
		setTurnRadarRightRadians(1.9*Utils.normalRelativeAngle(angleToEnemy - getRadarHeadingRadians()));
		
		double enemyEnergy = e.getEnergy();
		double deltaEnergy = lastEnemyEnergy - enemyEnergy;
		lastEnemyEnergy = enemyEnergy;
		
		if(deltaEnergy > 0 && deltaEnergy <= 3) {
			double bulletAngle = pastAngles.getLast() + Math.PI;
			double bulletSpeed = Rules.getBulletSpeed(deltaEnergy);
			
			/* how much time till the next time they can fire? */
			int minTimeTillNextFire = (int)(Rules.getGunHeat(deltaEnergy)/getGunCoolingRate());
			
			/* we have to move there and back, so divide the time we have in half */
			int maxTestDistance = getMaxMoveDistanceForTime(minTimeTillNextFire/2);
			
			double bestDeviation = Double.POSITIVE_INFINITY;
			
			double myBulletSpeed = Rules.getBulletSpeed(BULLET_START_POWER);
			
			for(int move = -maxTestDistance; move <= maxTestDistance; ++move) {
				/* shielding with a move of zero is dangerous and we shouldn't attempt it */
				if(move == 0)
					continue;
				
				/* calculate where we will be when we finish moving */
				Point2D myFirePosition = getMoveEnd(move);
				
				/* determine how long it will take to get there */
				long timeToMove = TIME_TO_MOVE[Math.abs(move)];
				
				/* the bullet position at the time time we start */
				Point2D bulletStart = project(lastPosition,bulletAngle,bulletSpeed*(timeToMove+1));
				
				/* calculate our target position */
				Point2D target = intercept(myFirePosition,myBulletSpeed,bulletStart,bulletAngle,bulletSpeed);
				
				double eGoalTime = Math.ceil(bulletStart.distance(target) / bulletSpeed);
				
				/* Update our target */
				target = project(bulletStart, bulletAngle, (eGoalTime-0.5)*bulletSpeed);
				double myGunAim = angleFromTo(myFirePosition,target);
				
				/* determine if they intersect */
				Line2D eLine = new Line2D.Double(
						project(bulletStart,bulletAngle,bulletSpeed*(eGoalTime-1)),
						project(bulletStart,bulletAngle,bulletSpeed*eGoalTime)
						);
				
				double myTargetTime = myFirePosition.distance(target) / myBulletSpeed;
				double myGoalTime = Math.ceil(myTargetTime);
				
				Line2D myLine = new Line2D.Double(
						project(myFirePosition,myGunAim,myBulletSpeed*(myGoalTime-1)),
						project(myFirePosition,myGunAim,myBulletSpeed*myGoalTime)
						);
				
				if(myLine.intersectsLine(eLine)) {
					double dB = myTargetTime - (myGoalTime - 0.5);
					double deviation = dB*dB;
					
					if(deviation < bestDeviation) {
						bestDeviation = deviation;
						lastMoveDistance = move;
						
						fireOnTick = time + timeToMove;
						
						/* tweak our power so that ours is more centered as well */
						double goalSpeed = myFirePosition.distance(target) / (myGoalTime-0.5);
						firePower = Math.max(0.1,Math.min((20-goalSpeed)/3,0.2));
						
						aimAngle = myGunAim;
						setTurnRightRadians(0);
						setAhead(lastMoveDistance);
					}
				}
			} /* for(int move ... */
		} /* if(deltaEnergy ... */
		
		if(time == fireOnTick) {
			setFire(firePower);
		}
		
		if(time == fireOnTick + 1) {
			setAhead(-lastMoveDistance);
		}
		
		if(time > fireOnTick && getDistanceRemaining() == 0) {
			aimAngle = angleToEnemy;
			setTurnRightRadians(Utils.normalRelativeAngle(angleToEnemy + Math.PI/2.0 - Math.PI/4.0 - getHeadingRadians()));
		}
		
		setTurnGunRightRadians(Utils.normalRelativeAngle(aimAngle - getGunHeadingRadians()));
		
		lastPosition = enemyPosition;
	}
	
	public void onBulletHit(final BulletHitEvent e) {
		lastEnemyEnergy -= Rules.getBulletDamage(e.getBullet().getPower());
	}

	public void onHitByBullet(final HitByBulletEvent e) {
		lastEnemyEnergy += Rules.getBulletHitBonus(e.getPower());
	}
	
	static final int[] TIME_TO_MOVE = new int[] {0,1,2,2,3,3,4,4,4};
	static final int[] MAX_MOVE_DIST = new int[] {0,1,3,5,8};
	public int getMaxMoveDistanceForTime(int time) {
		if(time >= MAX_MOVE_DIST.length)
			return MAX_MOVE_DIST[MAX_MOVE_DIST.length-1];
		return MAX_MOVE_DIST[time];
	}
	
	public Point2D getMoveEnd(double distance) {
		return project(getPosition(),getHeadingRadians(),distance);
	}
	
	public Point2D getPosition() {
		return new Point2D.Double(getX(),getY());
	}
	
	public Point2D project(Point2D start, double angle, double length) {
		return new Point2D.Double(
					start.getX() + Math.sin(angle) * length,
					start.getY() + Math.cos(angle) * length
				);
	}
	
	public Point2D intercept(Point2D pos, double vel, Point2D tPos, double tHeading, double tVel) {
		double tVelX = Math.sin(tHeading)*tVel;
		double tVelY = Math.cos(tHeading)*tVel;
		double relX = tPos.getX() - pos.getX();
		double relY = tPos.getY() - pos.getY();
		double b = relX * tVelX + relY * tVelY;
		double a = vel * vel - tVel * tVel;
		b = (b + Math.sqrt(b * b + a * (relX * relX + relY * relY))) / a;
		return new Point2D.Double(tVelX*b+tPos.getX(),tVelY*b+tPos.getY());
	}

	public double angleFromTo(Point2D a, Point2D b) {
		return Math.atan2(b.getX() - a.getX(), b.getY() - a.getY());
	}
}