/*
 * Copyright (C) 2019 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 android.graphics;

import android.annotation.NonNull;
import android.os.Handler;

import com.android.internal.util.VirtualRefBasePtr;

import java.lang.ref.WeakReference;

/**
 * Provides streaming access to frame stats information from HardwareRenderer to apps.
 *
 * @hide
 */
public final class HardwareRendererObserver {
    private final long[] mFrameMetrics;
    private final Handler mHandler;
    private final OnFrameMetricsAvailableListener mListener;
    private VirtualRefBasePtr mNativePtr;

    /**
     * Interface for clients that want frame timing information for each frame rendered.
     * @hide
     */
    public interface OnFrameMetricsAvailableListener {
        /**
         * Called when information is available for the previously rendered frame.
         *
         * Reports can be dropped if this callback takes too long to execute, as the report producer
         * cannot wait for the consumer to complete.
         *
         * It is highly recommended that clients copy the metrics array within this method
         * and defer additional computation or storage to another thread to avoid unnecessarily
         * dropping reports.
         *
         * @param dropCountSinceLastInvocation the number of reports dropped since the last time
         * this callback was invoked.
         */
        void onFrameMetricsAvailable(int dropCountSinceLastInvocation);
    }

    /**
     * Creates a FrameMetricsObserver
     *
     * @param frameMetrics the available metrics. This array is reused on every call to the listener
     * and thus <strong>this reference should only be used within the scope of the listener callback
     * as data is not guaranteed to be valid outside the scope of that method</strong>.
     * @param handler the Handler to use when invoking callbacks
     */
    public HardwareRendererObserver(@NonNull OnFrameMetricsAvailableListener listener,
            @NonNull long[] frameMetrics, @NonNull Handler handler, boolean waitForPresentTime) {
        if (handler == null || handler.getLooper() == null) {
            throw new NullPointerException("handler and its looper cannot be null");
        }

        if (handler.getLooper().getQueue() == null) {
            throw new IllegalStateException("invalid looper, null message queue\n");
        }

        mFrameMetrics = frameMetrics;
        mHandler = handler;
        mListener = listener;
        mNativePtr = new VirtualRefBasePtr(nCreateObserver(
                new WeakReference<>(this), waitForPresentTime));
    }

    /*package*/ long getNativeInstance() {
        return mNativePtr.get();
    }

    private void notifyDataAvailable() {
        mHandler.post(() -> {
            boolean hasMoreData = true;
            while (hasMoreData) {
                // a drop count of -1 is a sentinel that no more buffers are available
                int dropCount = nGetNextBuffer(mNativePtr.get(), mFrameMetrics);
                if (dropCount >= 0) {
                    mListener.onFrameMetricsAvailable(dropCount);
                } else {
                    hasMoreData = false;
                }
            }
        });
    }

    /**
     * called by native
     * @hide
     * @return true to keep listening, false if this is a dead observer
     */
    static boolean invokeDataAvailable(WeakReference<HardwareRendererObserver> weakObserver) {
        HardwareRendererObserver observer = weakObserver.get();
        if (observer != null) {
            observer.notifyDataAvailable();
            return true;
        }
        return false;
    }

    private static native long nCreateObserver(WeakReference<HardwareRendererObserver> observer,
            boolean waitForPresentTime);
    private static native int nGetNextBuffer(long nativePtr, long[] data);
}