/*
 * Copyright (C) 2008 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.os;

import android.util.Log;

import java.util.ArrayList;
import java.util.HashMap;

UEventObserver is an abstract class that receives UEvents from the kernel.

Subclass UEventObserver, implementing onUEvent(UEvent event), then call
startObserving() with a match string. The UEvent thread will then call your
onUEvent() method when a UEvent occurs that contains your match string.

Call stopObserving() to stop receiving UEvents.

There is only one UEvent thread per process, even if that process has
multiple UEventObserver subclass instances. The UEvent thread starts when
the startObserving() is called for the first time in that process. Once
started the UEvent thread will not stop (although it can stop notifying
UEventObserver's via stopObserving()).

@hide
/**
 * UEventObserver is an abstract class that receives UEvents from the kernel.<p>
 *
 * Subclass UEventObserver, implementing onUEvent(UEvent event), then call
 * startObserving() with a match string. The UEvent thread will then call your
 * onUEvent() method when a UEvent occurs that contains your match string.<p>
 *
 * Call stopObserving() to stop receiving UEvents.<p>
 *
 * There is only one UEvent thread per process, even if that process has
 * multiple UEventObserver subclass instances. The UEvent thread starts when
 * the startObserving() is called for the first time in that process. Once
 * started the UEvent thread will not stop (although it can stop notifying
 * UEventObserver's via stopObserving()).<p>
 *
 * @hide
*/
public abstract class UEventObserver {
    private static final String TAG = "UEventObserver";
    private static final boolean DEBUG = false;

    private static UEventThread sThread;

    private static native void nativeSetup();
    private static native String nativeWaitForNextEvent();
    private static native void nativeAddMatch(String match);
    private static native void nativeRemoveMatch(String match);

    public UEventObserver() {
    }

    @Override
    protected void finalize() throws Throwable {
        try {
            stopObserving();
        } finally {
            super.finalize();
        }
    }

    private static UEventThread getThread() {
        synchronized (UEventObserver.class) {
            if (sThread == null) {
                sThread = new UEventThread();
                sThread.start();
            }
            return sThread;
        }
    }

    private static UEventThread peekThread() {
        synchronized (UEventObserver.class) {
            return sThread;
        }
    }

    
Begin observation of UEvents.

This method will cause the UEvent thread to start if this is the first
invocation of startObserving in this process.

Once called, the UEvent thread will call onUEvent() when an incoming
UEvent matches the specified string.

This method can be called multiple times to register multiple matches.
Only one call to stopObserving is required even with multiple registered
matches.
Params:
match – A substring of the UEvent to match.  Try to be as specific
as possible to avoid incurring unintended additional cost from processing
irrelevant messages.  Netlink messages can be moderately high bandwidth and
are expensive to parse.  For example, some devices may send one netlink message
for each vsync period./**
     * Begin observation of UEvents.<p>
     * This method will cause the UEvent thread to start if this is the first
     * invocation of startObserving in this process.<p>
     * Once called, the UEvent thread will call onUEvent() when an incoming
     * UEvent matches the specified string.<p>
     * This method can be called multiple times to register multiple matches.
     * Only one call to stopObserving is required even with multiple registered
     * matches.
     *
     * @param match A substring of the UEvent to match.  Try to be as specific
     * as possible to avoid incurring unintended additional cost from processing
     * irrelevant messages.  Netlink messages can be moderately high bandwidth and
     * are expensive to parse.  For example, some devices may send one netlink message
     * for each vsync period.
     */
    public final void startObserving(String match) {
        if (match == null || match.isEmpty()) {
            throw new IllegalArgumentException("match substring must be non-empty");
        }

        final UEventThread t = getThread();
        t.addObserver(match, this);
    }

    
End observation of UEvents.

This process's UEvent thread will never call onUEvent() on this
UEventObserver after this call. Repeated calls have no effect.
/**
     * End observation of UEvents.<p>
     * This process's UEvent thread will never call onUEvent() on this
     * UEventObserver after this call. Repeated calls have no effect.
     */
    public final void stopObserving() {
        final UEventThread t = peekThread();
        if (t != null) {
            t.removeObserver(this);
        }
    }

    
Subclasses of UEventObserver should override this method to handle
UEvents.
/**
     * Subclasses of UEventObserver should override this method to handle
     * UEvents.
     */
    public abstract void onUEvent(UEvent event);

    
Representation of a UEvent.
/**
     * Representation of a UEvent.
     */
    public static final class UEvent {
        // collection of key=value pairs parsed from the uevent message
        private final HashMap<String,String> mMap = new HashMap<String,String>();

        public UEvent(String message) {
            int offset = 0;
            int length = message.length();

            while (offset < length) {
                int equals = message.indexOf('=', offset);
                int at = message.indexOf('\0', offset);
                if (at < 0) break;

                if (equals > offset && equals < at) {
                    // key is before the equals sign, and value is after
                    mMap.put(message.substring(offset, equals),
                            message.substring(equals + 1, at));
                }

                offset = at + 1;
            }
        }

        public String get(String key) {
            return mMap.get(key);
        }

        public String get(String key, String defaultValue) {
            String result = mMap.get(key);
            return (result == null ? defaultValue : result);
        }

        public String toString() {
            return mMap.toString();
        }
    }

    private static final class UEventThread extends Thread {
        
Many to many mapping of string match to observer.
 Multimap would be better, but not available in android, so use
 an ArrayList where even elements are the String match and odd
 elements the corresponding UEventObserver observer /** Many to many mapping of string match to observer.
         *  Multimap would be better, but not available in android, so use
         *  an ArrayList where even elements are the String match and odd
         *  elements the corresponding UEventObserver observer */
        private final ArrayList<Object> mKeysAndObservers = new ArrayList<Object>();

        private final ArrayList<UEventObserver> mTempObserversToSignal =
                new ArrayList<UEventObserver>();

        public UEventThread() {
            super("UEventObserver");
        }

        @Override
        public void run() {
            nativeSetup();

            while (true) {
                String message = nativeWaitForNextEvent();
                if (message != null) {
                    if (DEBUG) {
                        Log.d(TAG, message);
                    }
                    sendEvent(message);
                }
            }
        }

        private void sendEvent(String message) {
            synchronized (mKeysAndObservers) {
                final int N = mKeysAndObservers.size();
                for (int i = 0; i < N; i += 2) {
                    final String key = (String)mKeysAndObservers.get(i);
                    if (message.contains(key)) {
                        final UEventObserver observer =
                                (UEventObserver)mKeysAndObservers.get(i + 1);
                        mTempObserversToSignal.add(observer);
                    }
                }
            }

            if (!mTempObserversToSignal.isEmpty()) {
                final UEvent event = new UEvent(message);
                final int N = mTempObserversToSignal.size();
                for (int i = 0; i < N; i++) {
                    final UEventObserver observer = mTempObserversToSignal.get(i);
                    observer.onUEvent(event);
                }
                mTempObserversToSignal.clear();
            }
        }

        public void addObserver(String match, UEventObserver observer) {
            synchronized (mKeysAndObservers) {
                mKeysAndObservers.add(match);
                mKeysAndObservers.add(observer);
                nativeAddMatch(match);
            }
        }

        
Removes every key/value pair where value=observer from mObservers /** Removes every key/value pair where value=observer from mObservers */
        public void removeObserver(UEventObserver observer) {
            synchronized (mKeysAndObservers) {
                for (int i = 0; i < mKeysAndObservers.size(); ) {
                    if (mKeysAndObservers.get(i + 1) == observer) {
                        mKeysAndObservers.remove(i + 1);
                        final String match = (String)mKeysAndObservers.remove(i);
                        nativeRemoveMatch(match);
                    } else {
                        i += 2;
                    }
                }
            }
        }
    }
}