Copyright 2018 Netflix, Inc.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
    http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
/**
 * Copyright 2018 Netflix, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.netflix.concurrency.limits.limiter;

import com.netflix.concurrency.limits.Limit;
import com.netflix.concurrency.limits.Limiter;
import com.netflix.concurrency.limits.MetricIds;
import com.netflix.concurrency.limits.MetricRegistry;
import com.netflix.concurrency.limits.internal.EmptyMetricRegistry;
import com.netflix.concurrency.limits.limit.VegasLimit;

import java.util.Optional;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Supplier;

public abstract class AbstractLimiter<ContextT> implements Limiter<ContextT> {
    public static final String ID_TAG = "id";
    public static final String STATUS_TAG = "status";

    public abstract static class Builder<BuilderT extends Builder<BuilderT>> {
        private static final AtomicInteger idCounter = new AtomicInteger();

        private Limit limit = VegasLimit.newDefault();
        private Supplier<Long> clock = System::nanoTime;

        protected String name = "unnamed-" + idCounter.incrementAndGet();
        protected MetricRegistry registry = EmptyMetricRegistry.INSTANCE;

        public BuilderT named(String name) {
            this.name = name;
            return self();
        }

        public BuilderT limit(Limit limit) {
            this.limit = limit;
            return self();
        }

        public BuilderT clock(Supplier<Long> clock) {
            this.clock = clock;
            return self();
        }

        public BuilderT metricRegistry(MetricRegistry registry) {
            this.registry = registry;
            return self();
        }

        protected abstract BuilderT self();
    }

    private final AtomicInteger inFlight = new AtomicInteger();
    private final Supplier<Long> clock;
    private final Limit limitAlgorithm;
    private final MetricRegistry.Counter successCounter;
    private final MetricRegistry.Counter droppedCounter;
    private final MetricRegistry.Counter ignoredCounter;
    private final MetricRegistry.Counter rejectedCounter;

    private volatile int limit;

    protected AbstractLimiter(Builder<?> builder) {
        this.clock = builder.clock;
        this.limitAlgorithm = builder.limit;
        this.limit = limitAlgorithm.getLimit();
        this.limitAlgorithm.notifyOnChange(this::onNewLimit);

        builder.registry.gauge(MetricIds.LIMIT_NAME, this::getLimit);
        this.successCounter = builder.registry.counter(MetricIds.CALL_NAME, ID_TAG, builder.name, STATUS_TAG, "success");
        this.droppedCounter = builder.registry.counter(MetricIds.CALL_NAME, ID_TAG, builder.name, STATUS_TAG, "dropped");
        this.ignoredCounter = builder.registry.counter(MetricIds.CALL_NAME, ID_TAG, builder.name, STATUS_TAG, "ignored");
        this.rejectedCounter = builder.registry.counter(MetricIds.CALL_NAME, ID_TAG, builder.name, STATUS_TAG, "rejected");
    }

    protected Optional<Listener> createRejectedListener() {
        this.rejectedCounter.increment();
        return Optional.empty();
    }

    protected Listener createListener() {
        final long startTime = clock.get();
        final int currentInflight = inFlight.incrementAndGet();
        return new Listener() {
            @Override
            public void onSuccess() {
                inFlight.decrementAndGet();
                successCounter.increment();

                limitAlgorithm.onSample(startTime, clock.get() - startTime, currentInflight, false);
            }

            @Override
            public void onIgnore() {
                inFlight.decrementAndGet();
                ignoredCounter.increment();
            }

            @Override
            public void onDropped() {
                inFlight.decrementAndGet();
                droppedCounter.increment();

                limitAlgorithm.onSample(startTime, clock.get() - startTime, currentInflight, true);
            }
        };
    }

    public int getLimit() {
        return limit;
    }

    public int getInflight() { return inFlight.get(); }

    protected void onNewLimit(int newLimit) {
        limit = newLimit;
    }

}