/*
 * Copyright (C) 2016 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.server.wifi;

import android.os.Binder;
import android.os.IBinder;
import android.os.RemoteException;
import android.util.Slog;

import com.android.internal.app.IBatteryStats;

import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

/**
 * WifiMulticastLockManager tracks holders of multicast locks and
 * triggers enabling and disabling of filtering.
 *
 * @hide
 */
public class WifiMulticastLockManager {
    private static final String TAG = "WifiMulticastLockManager";
    private final List<Multicaster> mMulticasters = new ArrayList<>();
    private int mMulticastEnabled = 0;
    private int mMulticastDisabled = 0;
    private boolean mVerboseLoggingEnabled = false;
    private final IBatteryStats mBatteryStats;
    private final FilterController mFilterController;

    /** Delegate for handling state change events for multicast filtering. */
    public interface FilterController {
        /** Called when multicast filtering should be enabled */
        void startFilteringMulticastPackets();

        /** Called when multicast filtering should be disabled */
        void stopFilteringMulticastPackets();
    }

    public WifiMulticastLockManager(FilterController filterController, IBatteryStats batteryStats) {
        mBatteryStats = batteryStats;
        mFilterController = filterController;
    }

    private class Multicaster implements IBinder.DeathRecipient {
        String mTag;
        int mUid;
        IBinder mBinder;

        Multicaster(String tag, IBinder binder) {
            mTag = tag;
            mUid = Binder.getCallingUid();
            mBinder = binder;
            try {
                mBinder.linkToDeath(this, 0);
            } catch (RemoteException e) {
                binderDied();
            }
        }

        @Override
        public void binderDied() {
            Slog.e(TAG, "Multicaster binderDied");
            synchronized (mMulticasters) {
                int i = mMulticasters.indexOf(this);
                if (i != -1) {
                    removeMulticasterLocked(i, mUid);
                }
            }
        }

        void unlinkDeathRecipient() {
            mBinder.unlinkToDeath(this, 0);
        }

        public int getUid() {
            return mUid;
        }

        public String toString() {
            return "Multicaster{" + mTag + " uid=" + mUid  + "}";
        }
    }

    protected void dump(PrintWriter pw) {
        pw.println("mMulticastEnabled " + mMulticastEnabled);
        pw.println("mMulticastDisabled " + mMulticastDisabled);
        pw.println("Multicast Locks held:");
        for (Multicaster l : mMulticasters) {
            pw.print("    ");
            pw.println(l);
        }
    }

    protected void enableVerboseLogging(int verbose) {
        if (verbose > 0) {
            mVerboseLoggingEnabled = true;
        } else {
            mVerboseLoggingEnabled = false;
        }
    }

    /** Start filtering if  no multicasters exist. */
    public void initializeFiltering() {
        synchronized (mMulticasters) {
            // if anybody had requested filters be off, leave off
            if (mMulticasters.size() != 0) {
                return;
            } else {
                mFilterController.startFilteringMulticastPackets();
            }
        }
    }

    /**
     * Acquire a multicast lock.
     * @param binder a binder used to ensure caller is still alive
     * @param tag string name of the caller.
     */
    public void acquireLock(IBinder binder, String tag) {
        synchronized (mMulticasters) {
            mMulticastEnabled++;
            mMulticasters.add(new Multicaster(tag, binder));
            // Note that we could call stopFilteringMulticastPackets only when
            // our new size == 1 (first call), but this function won't
            // be called often and by making the stopPacket call each
            // time we're less fragile and self-healing.
            mFilterController.stopFilteringMulticastPackets();
        }

        int uid = Binder.getCallingUid();
        final long ident = Binder.clearCallingIdentity();
        try {
            mBatteryStats.noteWifiMulticastEnabled(uid);
        } catch (RemoteException e) {
        } finally {
            Binder.restoreCallingIdentity(ident);
        }
    }

    /** Releases a multicast lock */
    public void releaseLock() {
        int uid = Binder.getCallingUid();
        synchronized (mMulticasters) {
            mMulticastDisabled++;
            int size = mMulticasters.size();
            for (int i = size - 1; i >= 0; i--) {
                Multicaster m = mMulticasters.get(i);
                if ((m != null) && (m.getUid() == uid)) {
                    removeMulticasterLocked(i, uid);
                }
            }
        }
    }

    private void removeMulticasterLocked(int i, int uid) {
        Multicaster removed = mMulticasters.remove(i);

        if (removed != null) {
            removed.unlinkDeathRecipient();
        }
        if (mMulticasters.size() == 0) {
            mFilterController.startFilteringMulticastPackets();
        }

        final long ident = Binder.clearCallingIdentity();
        try {
            mBatteryStats.noteWifiMulticastDisabled(uid);
        } catch (RemoteException e) {
        } finally {
            Binder.restoreCallingIdentity(ident);
        }
    }

    /** Returns whether multicast should be allowed (filterning disabled). */
    public boolean isMulticastEnabled() {
        synchronized (mMulticasters) {
            return (mMulticasters.size() > 0);
        }
    }
}