package net.i2p.router.tunnel.pool;

import net.i2p.data.Hash;
import net.i2p.router.RouterContext;
import net.i2p.util.ObjectCounter;
import net.i2p.util.SimpleTimer;

/**
 * Count how often we have accepted a tunnel with the peer
 * as the previous or next hop.
 * We limit each peer to a percentage of all participating tunnels,
 * subject to minimum and maximum values for the limit.
 *
 * This offers basic protection against simple attacks
 * but is not a complete solution, as by design, we don't know
 * the originator of a tunnel request.
 *
 * This also effectively limits the number of tunnels between
 * any given pair of routers, which probably isn't a bad thing.
 *
 * Note that the actual limits will be higher than specified
 * by up to 1 / LIFETIME_PORTION because the counter window resets.
 *
 * Note that the counts are of previous + next hops, so the total will
 * be higher than the participating tunnel count, and will also grow
 * as the network uses more 3-hop tunnels.
 *
 * @since 0.8.4
 */
class ParticipatingThrottler {
    private final RouterContext context;
    private final ObjectCounter<Hash> counter;

    /** portion of the tunnel lifetime */
    private static final int LIFETIME_PORTION = 3;
    private static final int MIN_LIMIT = 18 / LIFETIME_PORTION;
    private static final int MAX_LIMIT = 66 / LIFETIME_PORTION;
    private static final int PERCENT_LIMIT = 12 / LIFETIME_PORTION;
    private static final long CLEAN_TIME = 11*60*1000 / LIFETIME_PORTION;

    ParticipatingThrottler(RouterContext ctx) {
        this.context = ctx;
        this.counter = new ObjectCounter<Hash>();
        ctx.simpleTimer2().addPeriodicEvent(new Cleaner(), CLEAN_TIME);
    }

    /** increments before checking */
    boolean shouldThrottle(Hash h) {
        int numTunnels = this.context.tunnelManager().getParticipatingCount();
        int limit = Math.max(MIN_LIMIT, Math.min(MAX_LIMIT, numTunnels * PERCENT_LIMIT / 100));
        return this.counter.increment(h) > limit;
    }

    private class Cleaner implements SimpleTimer.TimedEvent {
        public void timeReached() {
            ParticipatingThrottler.this.counter.clear();
        }
    }
}
