/*
 * Copyright (C) 2014 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.net;

import android.content.Context;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.os.Messenger;
import android.util.Log;
import android.util.SparseArray;

import com.android.internal.annotations.VisibleForTesting;
import com.android.internal.util.IndentingPrintWriter;
import com.android.internal.util.Protocol;

import java.io.FileDescriptor;
import java.io.PrintWriter;

A NetworkFactory is an entity that creates NetworkAgent objects. The bearers register with ConnectivityService using register and their factory will start receiving scored NetworkRequests. NetworkRequests can be filtered 3 ways: by NetworkCapabilities, by score and more complexly by overridden function. All of these can be dynamic - changing NetworkCapabilities or score forces re-evaluation of all current requests. If any requests pass the filter some overrideable functions will be called. If the bearer only cares about very simple start/stopNetwork callbacks, those functions can be overridden. If the bearer needs more interaction, it can override addNetworkRequest and removeNetworkRequest which will give it each request that passes their current filters. 
@hide
/**
 * A NetworkFactory is an entity that creates NetworkAgent objects.
 * The bearers register with ConnectivityService using {@link #register} and
 * their factory will start receiving scored NetworkRequests.  NetworkRequests
 * can be filtered 3 ways: by NetworkCapabilities, by score and more complexly by
 * overridden function.  All of these can be dynamic - changing NetworkCapabilities
 * or score forces re-evaluation of all current requests.
 *
 * If any requests pass the filter some overrideable functions will be called.
 * If the bearer only cares about very simple start/stopNetwork callbacks, those
 * functions can be overridden.  If the bearer needs more interaction, it can
 * override addNetworkRequest and removeNetworkRequest which will give it each
 * request that passes their current filters.
 * @hide
 **/
public class NetworkFactory extends Handler {
    private static final boolean DBG = true;
    private static final boolean VDBG = false;

    private static final int BASE = Protocol.BASE_NETWORK_FACTORY;
    
Pass a network request to the bearer.  If the bearer believes it can
satisfy the request it should connect to the network and create a
NetworkAgent.  Once the NetworkAgent is fully functional it will
register itself with ConnectivityService using registerNetworkAgent.
If the bearer cannot immediately satisfy the request (no network,
user disabled the radio, lower-scored network) it should remember
any NetworkRequests it may be able to satisfy in the future.  It may
disregard any that it will never be able to service, for example
those requiring a different bearer.
msg.obj = NetworkRequest
msg.arg1 = score - the score of the any network currently satisfying this
           request.  If this bearer knows in advance it cannot
           exceed this score it should not try to connect, holding the request
           for the future.
           Note that subsequent events may give a different (lower
           or higher) score for this request, transmitted to each
           NetworkFactory through additional CMD_REQUEST_NETWORK msgs
           with the same NetworkRequest but an updated score.
           Also, network conditions may change for this bearer
           allowing for a better score in the future.
/**
     * Pass a network request to the bearer.  If the bearer believes it can
     * satisfy the request it should connect to the network and create a
     * NetworkAgent.  Once the NetworkAgent is fully functional it will
     * register itself with ConnectivityService using registerNetworkAgent.
     * If the bearer cannot immediately satisfy the request (no network,
     * user disabled the radio, lower-scored network) it should remember
     * any NetworkRequests it may be able to satisfy in the future.  It may
     * disregard any that it will never be able to service, for example
     * those requiring a different bearer.
     * msg.obj = NetworkRequest
     * msg.arg1 = score - the score of the any network currently satisfying this
     *            request.  If this bearer knows in advance it cannot
     *            exceed this score it should not try to connect, holding the request
     *            for the future.
     *            Note that subsequent events may give a different (lower
     *            or higher) score for this request, transmitted to each
     *            NetworkFactory through additional CMD_REQUEST_NETWORK msgs
     *            with the same NetworkRequest but an updated score.
     *            Also, network conditions may change for this bearer
     *            allowing for a better score in the future.
     */
    public static final int CMD_REQUEST_NETWORK = BASE;

    
Cancel a network request
msg.obj = NetworkRequest
/**
     * Cancel a network request
     * msg.obj = NetworkRequest
     */
    public static final int CMD_CANCEL_REQUEST = BASE + 1;

    
Internally used to set our best-guess score.
msg.arg1 = new score
/**
     * Internally used to set our best-guess score.
     * msg.arg1 = new score
     */
    private static final int CMD_SET_SCORE = BASE + 2;

    
Internally used to set our current filter for coarse bandwidth changes with
technology changes.
msg.obj = new filter
/**
     * Internally used to set our current filter for coarse bandwidth changes with
     * technology changes.
     * msg.obj = new filter
     */
    private static final int CMD_SET_FILTER = BASE + 3;

    private final Context mContext;
    private final String LOG_TAG;

    private final SparseArray<NetworkRequestInfo> mNetworkRequests =
            new SparseArray<NetworkRequestInfo>();

    private int mScore;
    private NetworkCapabilities mCapabilityFilter;

    private int mRefCount = 0;
    private Messenger mMessenger = null;

    public NetworkFactory(Looper looper, Context context, String logTag,
            NetworkCapabilities filter) {
        super(looper);
        LOG_TAG = logTag;
        mContext = context;
        mCapabilityFilter = filter;
    }

    public void register() {
        if (DBG) log("Registering NetworkFactory");
        if (mMessenger == null) {
            mMessenger = new Messenger(this);
            ConnectivityManager.from(mContext).registerNetworkFactory(mMessenger, LOG_TAG);
        }
    }

    public void unregister() {
        if (DBG) log("Unregistering NetworkFactory");
        if (mMessenger != null) {
            ConnectivityManager.from(mContext).unregisterNetworkFactory(mMessenger);
            mMessenger = null;
        }
    }

    @Override
    public void handleMessage(Message msg) {
        switch (msg.what) {
            case CMD_REQUEST_NETWORK: {
                handleAddRequest((NetworkRequest)msg.obj, msg.arg1);
                break;
            }
            case CMD_CANCEL_REQUEST: {
                handleRemoveRequest((NetworkRequest) msg.obj);
                break;
            }
            case CMD_SET_SCORE: {
                handleSetScore(msg.arg1);
                break;
            }
            case CMD_SET_FILTER: {
                handleSetFilter((NetworkCapabilities) msg.obj);
                break;
            }
        }
    }

    private class NetworkRequestInfo {
        public final NetworkRequest request;
        public int score;
        public boolean requested; // do we have a request outstanding, limited by score

        public NetworkRequestInfo(NetworkRequest request, int score) {
            this.request = request;
            this.score = score;
            this.requested = false;
        }

        @Override
        public String toString() {
            return "{" + request + ", score=" + score + ", requested=" + requested + "}";
        }
    }

    @VisibleForTesting
    protected void handleAddRequest(NetworkRequest request, int score) {
        NetworkRequestInfo n = mNetworkRequests.get(request.requestId);
        if (n == null) {
            if (DBG) log("got request " + request + " with score " + score);
            n = new NetworkRequestInfo(request, score);
            mNetworkRequests.put(n.request.requestId, n);
        } else {
            if (VDBG) log("new score " + score + " for exisiting request " + request);
            n.score = score;
        }
        if (VDBG) log("  my score=" + mScore + ", my filter=" + mCapabilityFilter);

        evalRequest(n);
    }

    @VisibleForTesting
    protected void handleRemoveRequest(NetworkRequest request) {
        NetworkRequestInfo n = mNetworkRequests.get(request.requestId);
        if (n != null) {
            mNetworkRequests.remove(request.requestId);
            if (n.requested) releaseNetworkFor(n.request);
        }
    }

    private void handleSetScore(int score) {
        mScore = score;
        evalRequests();
    }

    private void handleSetFilter(NetworkCapabilities netCap) {
        mCapabilityFilter = netCap;
        evalRequests();
    }

    
Overridable function to provide complex filtering. Called for every request every time a new NetworkRequest is seen and whenever the filterScore or filterNetworkCapabilities change. acceptRequest can be overridden to provide complex filter behavior for the incoming requests For output, this class will call needNetworkFor and releaseNetworkFor for every request that passes the filters. If you don't need to see every request, you can leave the base implementations of those two functions and instead override startNetwork and stopNetwork. If you want to see every score fluctuation on every request, set your score filter to a very high number and watch needNetworkFor. 
Returns:
true to accept the request./**
     * Overridable function to provide complex filtering.
     * Called for every request every time a new NetworkRequest is seen
     * and whenever the filterScore or filterNetworkCapabilities change.
     *
     * acceptRequest can be overridden to provide complex filter behavior
     * for the incoming requests
     *
     * For output, this class will call {@link #needNetworkFor} and
     * {@link #releaseNetworkFor} for every request that passes the filters.
     * If you don't need to see every request, you can leave the base
     * implementations of those two functions and instead override
     * {@link #startNetwork} and {@link #stopNetwork}.
     *
     * If you want to see every score fluctuation on every request, set
     * your score filter to a very high number and watch {@link #needNetworkFor}.
     *
     * @return {@code true} to accept the request.
     */
    public boolean acceptRequest(NetworkRequest request, int score) {
        return true;
    }

    private void evalRequest(NetworkRequestInfo n) {
        if (VDBG) log("evalRequest");
        if (n.requested == false && n.score < mScore &&
                n.request.networkCapabilities.satisfiedByNetworkCapabilities(
                mCapabilityFilter) && acceptRequest(n.request, n.score)) {
            if (VDBG) log("  needNetworkFor");
            needNetworkFor(n.request, n.score);
            n.requested = true;
        } else if (n.requested == true &&
                (n.score > mScore || n.request.networkCapabilities.satisfiedByNetworkCapabilities(
                mCapabilityFilter) == false || acceptRequest(n.request, n.score) == false)) {
            if (VDBG) log("  releaseNetworkFor");
            releaseNetworkFor(n.request);
            n.requested = false;
        } else {
            if (VDBG) log("  done");
        }
    }

    private void evalRequests() {
        for (int i = 0; i < mNetworkRequests.size(); i++) {
            NetworkRequestInfo n = mNetworkRequests.valueAt(i);

            evalRequest(n);
        }
    }

    
Post a command, on this NetworkFactory Handler, to re-evaluate all
oustanding requests. Can be called from a factory implementation.
/**
     * Post a command, on this NetworkFactory Handler, to re-evaluate all
     * oustanding requests. Can be called from a factory implementation.
     */
    protected void reevaluateAllRequests() {
        post(() -> {
            evalRequests();
        });
    }

    // override to do simple mode (request independent)
    protected void startNetwork() { }
    protected void stopNetwork() { }

    // override to do fancier stuff
    protected void needNetworkFor(NetworkRequest networkRequest, int score) {
        if (++mRefCount == 1) startNetwork();
    }

    protected void releaseNetworkFor(NetworkRequest networkRequest) {
        if (--mRefCount == 0) stopNetwork();
    }


    public void addNetworkRequest(NetworkRequest networkRequest, int score) {
        sendMessage(obtainMessage(CMD_REQUEST_NETWORK,
                new NetworkRequestInfo(networkRequest, score)));
    }

    public void removeNetworkRequest(NetworkRequest networkRequest) {
        sendMessage(obtainMessage(CMD_CANCEL_REQUEST, networkRequest));
    }

    public void setScoreFilter(int score) {
        sendMessage(obtainMessage(CMD_SET_SCORE, score, 0));
    }

    public void setCapabilityFilter(NetworkCapabilities netCap) {
        sendMessage(obtainMessage(CMD_SET_FILTER, new NetworkCapabilities(netCap)));
    }

    @VisibleForTesting
    protected int getRequestCount() {
        return mNetworkRequests.size();
    }

    protected void log(String s) {
        Log.d(LOG_TAG, s);
    }

    public void dump(FileDescriptor fd, PrintWriter writer, String[] args) {
        final IndentingPrintWriter pw = new IndentingPrintWriter(writer, "  ");
        pw.println(toString());
        pw.increaseIndent();
        for (int i = 0; i < mNetworkRequests.size(); i++) {
            pw.println(mNetworkRequests.valueAt(i));
        }
        pw.decreaseIndent();
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("{").append(LOG_TAG).append(" - ScoreFilter=").
                append(mScore).append(", Filter=").append(mCapabilityFilter).append(", requests=").
                append(mNetworkRequests.size()).append(", refCount=").append(mRefCount).
                append("}");
        return sb.toString();
    }
}