/*
 * Copyright (C) 2017 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.connectivity.tethering;

import static android.provider.Settings.Global.TETHER_OFFLOAD_DISABLED;

import android.content.ContentResolver;
import android.net.IpPrefix;
import android.net.LinkProperties;
import android.net.RouteInfo;
import android.net.util.SharedLog;
import android.os.Handler;
import android.provider.Settings;

import java.net.Inet4Address;
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.Set;

/**
 * A class to encapsulate the business logic of programming the tethering
 * hardware offload interface.
 *
 * @hide
 */
public class OffloadController {
    private static final String TAG = OffloadController.class.getSimpleName();

    private final Handler mHandler;
    private final OffloadHardwareInterface mHwInterface;
    private final ContentResolver mContentResolver;
    private final SharedLog mLog;
    private boolean mConfigInitialized;
    private boolean mControlInitialized;
    private LinkProperties mUpstreamLinkProperties;
    private Set<IpPrefix> mExemptPrefixes;

    public OffloadController(Handler h, OffloadHardwareInterface hwi,
            ContentResolver contentResolver, SharedLog log) {
        mHandler = h;
        mHwInterface = hwi;
        mContentResolver = contentResolver;
        mLog = log.forSubComponent(TAG);
    }

    public void start() {
        if (started()) return;

        if (isOffloadDisabled()) {
            mLog.i("tethering offload disabled");
            return;
        }

        if (!mConfigInitialized) {
            mConfigInitialized = mHwInterface.initOffloadConfig();
            if (!mConfigInitialized) {
                mLog.i("tethering offload config not supported");
                stop();
                return;
            }
        }

        mControlInitialized = mHwInterface.initOffloadControl(
                new OffloadHardwareInterface.ControlCallback() {
                    @Override
                    public void onOffloadEvent(int event) {
                        mLog.log("got offload event: " + event);
                    }

                    @Override
                    public void onNatTimeoutUpdate(int proto,
                                                   String srcAddr, int srcPort,
                                                   String dstAddr, int dstPort) {
                        mLog.log(String.format("NAT timeout update: %s (%s,%s) -> (%s,%s)",
                                proto, srcAddr, srcPort, dstAddr, dstPort));
                    }
                });
        if (!mControlInitialized) {
            mLog.i("tethering offload control not supported");
            stop();
        }
        mLog.log("tethering offload started");
    }

    public void stop() {
        final boolean wasStarted = started();
        mUpstreamLinkProperties = null;
        mHwInterface.stopOffloadControl();
        mControlInitialized = false;
        mConfigInitialized = false;
        if (wasStarted) mLog.log("tethering offload stopped");
    }

    public void setUpstreamLinkProperties(LinkProperties lp) {
        if (!started()) return;

        mUpstreamLinkProperties = (lp != null) ? new LinkProperties(lp) : null;
        // TODO: examine return code and decide what to do if programming
        // upstream parameters fails (probably just wait for a subsequent
        // onOffloadEvent() callback to tell us offload is available again and
        // then reapply all state).
        pushUpstreamParameters();
    }

    public void updateExemptPrefixes(Set<IpPrefix> exemptPrefixes) {
        if (!started()) return;

        mExemptPrefixes = exemptPrefixes;
        // TODO:
        //     - add IP addresses from all downstream link properties
        //     - add routes from all non-tethering downstream link properties
        //     - remove any 64share prefixes
        //     - push this to the HAL
    }

    public void notifyDownstreamLinkProperties(LinkProperties lp) {
        if (!started()) return;

        // TODO: Cache LinkProperties on a per-ifname basis and compute the
        // deltas, calling addDownstream()/removeDownstream() accordingly.
    }

    public void removeDownstreamInterface(String ifname) {
        if (!started()) return;

        // TODO: Check cache for LinkProperties of ifname and, if present,
        // call removeDownstream() accordingly.
    }

    private boolean isOffloadDisabled() {
        // Defaults to |false| if not present.
        return (Settings.Global.getInt(mContentResolver, TETHER_OFFLOAD_DISABLED, 0) != 0);
    }

    private boolean started() {
        return mConfigInitialized && mControlInitialized;
    }

    private boolean pushUpstreamParameters() {
        if (mUpstreamLinkProperties == null) {
            return mHwInterface.setUpstreamParameters(null, null, null, null);
        }

        // A stacked interface cannot be an upstream for hardware offload.
        // Consequently, we examine only the primary interface name, look at
        // getAddresses() rather than getAllAddresses(), and check getRoutes()
        // rather than getAllRoutes().
        final String iface = mUpstreamLinkProperties.getInterfaceName();
        final ArrayList<String> v6gateways = new ArrayList<>();
        String v4addr = null;
        String v4gateway = null;

        for (InetAddress ip : mUpstreamLinkProperties.getAddresses()) {
            if (ip instanceof Inet4Address) {
                v4addr = ip.getHostAddress();
                break;
            }
        }

        // Find the gateway addresses of all default routes of either address family.
        for (RouteInfo ri : mUpstreamLinkProperties.getRoutes()) {
            if (!ri.hasGateway()) continue;

            final String gateway = ri.getGateway().getHostAddress();
            if (ri.isIPv4Default()) {
                v4gateway = gateway;
            } else if (ri.isIPv6Default()) {
                v6gateways.add(gateway);
            }
        }

        return mHwInterface.setUpstreamParameters(
                iface, v4addr, v4gateway, (v6gateways.isEmpty() ? null : v6gateways));
    }
}