/*
 * Copyright (C) 2021 The Android Open Source Project
 *
 * 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.android.car.telemetry.publisher;

import com.android.car.telemetry.databroker.DataSubscriber;

import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;

/**
 * Abstract class for publishers. It is 1-1 with data source and manages sending data to
 * subscribers. Publisher stops itself when there are no subscribers.
 *
 * <p>Note that it doesn't map 1-1 to {@link com.android.car.telemetry.TelemetryProto.Publisher}
 * configuration. Single publisher instance can send data as several
 * {@link com.android.car.telemetry.TelemetryProto.Publisher} to subscribers.
 *
 * <p>Not thread-safe.
 */
public abstract class AbstractPublisher {
    private final HashSet<DataSubscriber> mDataSubscribers = new HashSet<>();

    /**
     * Adds a subscriber that listens for data produced by this publisher.
     *
     * @param subscriber a subscriber to receive data
     * @throws IllegalArgumentException if an invalid subscriber was provided.
     */
    public void addDataSubscriber(DataSubscriber subscriber) {
        // This method can throw exceptions if data is invalid - do now swap these 2 lines.
        onDataSubscriberAdded(subscriber);
        mDataSubscribers.add(subscriber);
    }

    /**
     * Removes the subscriber from the publisher. Publisher stops if necessary.
     *
     * @throws IllegalArgumentException if the subscriber was not found.
     */
    public void removeDataSubscriber(DataSubscriber subscriber) {
        if (!mDataSubscribers.remove(subscriber)) {
            throw new IllegalArgumentException("Failed to remove, subscriber not found");
        }
        onDataSubscribersRemoved(Collections.singletonList(subscriber));
    }

    /**
     * Removes all the subscribers from the publisher. The publisher may stop.
     */
    public void removeAllDataSubscribers() {
        onDataSubscribersRemoved(mDataSubscribers);
        mDataSubscribers.clear();
    }

    /**
     * Called when a new subscriber is added to the publisher.
     *
     * @throws IllegalArgumentException if the invalid subscriber was provided.
     */
    protected abstract void onDataSubscriberAdded(DataSubscriber subscriber);

    /** Called when subscribers are removed from the publisher. */
    protected abstract void onDataSubscribersRemoved(Collection<DataSubscriber> subscribers);

    protected HashSet<DataSubscriber> getDataSubscribers() {
        return mDataSubscribers;
    }
}