/*
 * 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.TelemetryProto;
import com.android.car.telemetry.databroker.DataSubscriber;

import java.util.List;

/**
 * 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>The methods must be called from the telemetry thread.
 */
public abstract class AbstractPublisher {
    private final PublisherFailureListener mFailureListener;

    /**
     * Listener for publisher failures, such as failing to connect to a underlying service or
     * invalid Publisher configuration. When publishers fail, the affected configs should be
     * disabled, because the associated scripts cannot receive data from the failed publishers.
     */
    public interface PublisherFailureListener {
        /** Called by publishers when they fail. */
        void onPublisherFailure(
                AbstractPublisher publisher,
                List<TelemetryProto.MetricsConfig> affectedConfigs, Throwable error);
    }

    AbstractPublisher(PublisherFailureListener failureListener) {
        mFailureListener = failureListener;
    }

    /**
     * Adds a subscriber that listens for data produced by this publisher.
     *
     * <p>DataBroker may call this method when a new {@code MetricsConfig} is added,
     * {@code CarTelemetryService} is restarted or the device is restarted.
     *
     * @param subscriber a subscriber to receive data
     * @throws IllegalArgumentException if the subscriber is invalid.
     * @throws IllegalStateException if there are internal errors.
     */
    public abstract void addDataSubscriber(DataSubscriber subscriber);

    /**
     * Removes the subscriber from the publisher. Publisher stops if necessary.
     *
     * <p>It does nothing if subscriber is not found.
     */
    public abstract void removeDataSubscriber(DataSubscriber subscriber);

    /**
     * Removes all the subscribers from the publisher. The publisher may stop.
     *
     * <p>This method also cleans-up internal publisher and the data source persisted state.
     */
    public abstract void removeAllDataSubscribers();

    /** Returns true if the publisher already has this data subscriber. */
    public abstract boolean hasDataSubscriber(DataSubscriber subscriber);

    /**
     * Notifies the failure Listener that this publisher failed. See
     * {@link PublisherFailureListener} for details.
     */
    protected void onPublisherFailure(
            List<TelemetryProto.MetricsConfig> affectedConfigs, Throwable error) {
        mFailureListener.onPublisherFailure(this, affectedConfigs, error);
    }
}