common/device-side/bedstead/eventlib/src/main/java/com/android/eventlib/Events.java

/*
 * Copyright (C) 2020 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.eventlib;

import android.content.Context;
import android.util.Log;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.time.Duration;
import java.time.Instant;
import java.util.ArrayDeque;
import java.util.Collections;
import java.util.Deque;
import java.util.Queue;
import java.util.Set;
import java.util.WeakHashMap;
import java.util.concurrent.ConcurrentLinkedDeque;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.atomic.AtomicBoolean;

/** Event store for the current package. */
final class Events {

    private static final String TAG = "EventLibEvents";
    private static final String EVENT_LOG_FILE_NAME = "Events";
    private static final Duration MAX_LOG_AGE = Duration.ofMinutes(5);
    private static final int BYTES_PER_INT = 4;

    private static final ExecutorService sExecutor = Executors.newSingleThreadExecutor();
    private AtomicBoolean mLoadedHistory = new AtomicBoolean(false);

    /** Interface used to be informed when new events are logged. */
    interface EventListener {
        void onNewEvent(Event e);
    }

    private static Events mInstance;

    static Events getInstance(Context context, boolean needsHistory) {
        if (mInstance == null) {
            synchronized (Events.class) {
                if (mInstance == null) {
                    mInstance = new Events(context.getApplicationContext());
                }
            }
        }

        if (needsHistory) {
            mInstance.loadHistory();
        }

        return mInstance;
    }

    private final Context mContext; // ApplicationContext
    private FileOutputStream mOutputStream;

    private Events(Context context) {
        this.mContext = context;
    }

    private void loadHistory() {
        if (mLoadedHistory.getAndSet(true)) {
            return;
        }

        loadEventsFromFile();
    }

    private void loadEventsFromFile() {
        synchronized (mEventList) {
            mEventList.clear();
            Instant now = Instant.now();
            Deque<Event> eventQueue = new ArrayDeque<>();
            try (FileInputStream fileInputStream = mContext.openFileInput(EVENT_LOG_FILE_NAME)) {
                Event event = readEvent(fileInputStream);

                while (event != null) {
                    // I'm not sure if we need this
                    if (event.mTimestamp.plus(MAX_LOG_AGE).isAfter(now)) {
                        eventQueue.addFirst(event);
                    }
                    event = readEvent(fileInputStream);
                }

                for (Event e : eventQueue) {
                    mEventList.addFirst(e);
                }
            } catch (FileNotFoundException e) {
                // Ignore this exception as if there's no file there's nothing to load
                Log.i(TAG, "No existing event file");
            } catch (IOException e) {
                Log.e(TAG, "Error when loading events from file", e);
            }
        }
    }

    private Event readEvent(FileInputStream fileInputStream) throws IOException {
        if (fileInputStream.available() < BYTES_PER_INT) {
            return null;
        }
        byte[] sizeBytes = new byte[BYTES_PER_INT];
        fileInputStream.read(sizeBytes);

        int size = ByteBuffer.wrap(sizeBytes).getInt();

        byte[] eventBytes = new byte[size];
        fileInputStream.read(eventBytes);

        return Event.fromBytes(eventBytes);
    }

    /** Saves the event so it can be queried. */
    void log(Event event) {
        sExecutor.execute(() -> {
            Log.d(TAG, event.toString());
            synchronized (mEventList) {
                mEventList.add(event); // TODO: This should be made immutable before adding
                writeEventToFile(event);
            }
            triggerEventListeners(event);
        });
    }

    private void writeEventToFile(Event event) {
        try {
            if (mOutputStream == null) {
                mOutputStream = mContext.openFileOutput(
                        EVENT_LOG_FILE_NAME, Context.MODE_PRIVATE | Context.MODE_APPEND);
            }

            Log.e(TAG, "writing event to file: " + event);
            byte[] eventBytes = event.toBytes();
            mOutputStream.write(
                    ByteBuffer.allocate(BYTES_PER_INT).putInt(eventBytes.length).array());
            mOutputStream.write(eventBytes);
        } catch (IOException e) {
            throw new IllegalStateException("Error writing event to log", e);
        }
    }

    private final Deque<Event> mEventList = new ConcurrentLinkedDeque<>();
    // This is a weak set so we don't retain listeners from old tests
    private final Set<EventListener> mEventListeners
            = Collections.newSetFromMap(new WeakHashMap<>());

    /** Get all logged events. */
    public Queue<Event> getEvents() {
        return mEventList;
    }

    /** Register an {@link EventListener} to be called when a new {@link Event} is logged. */
    public Queue<Event> registerEventListener(EventListener listener) {
        synchronized (mEventList) {
            synchronized (mEventListeners) {
                mEventListeners.add(listener);

                return getEvents();
            }
        }
    }

    private void triggerEventListeners(Event event) {
        synchronized (mEventListeners) {
            for (EventListener listener : mEventListeners) {
                listener.onNewEvent(event);
            }
        }
    }

}