/*
 * Copyright 2018 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.annotation.NonNull;
import android.annotation.Nullable;
import android.net.MacAddress;
import android.net.wifi.ScanResult;
import android.net.wifi.WifiConfiguration;
import android.util.ArrayMap;

import com.android.internal.util.Preconditions;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Map;
import java.util.Objects;
import java.util.StringJoiner;

/**
 * Candidates for network selection
 */
public class WifiCandidates {
    private static final String TAG = "WifiCandidates";

    WifiCandidates(@NonNull WifiScoreCard wifiScoreCard) {
        mWifiScoreCard = Preconditions.checkNotNull(wifiScoreCard);
    }
    private final WifiScoreCard mWifiScoreCard;

    /**
     * Represents a connectable candidate.
     */
    public interface Candidate {
        /**
         * Gets the Key, which contains the SSID, BSSID, security type, and config id.
         *
         * Generally, a CandidateScorer should not need to use this.
         */
        @Nullable Key getKey();
        /**
         * Gets the ScanDetail associate with the candidate.
         */
        @Nullable ScanDetail getScanDetail();
        /**
         * Gets the config id.
         */
        int getNetworkConfigId();
        /**
         * Returns true for an open network.
         */
        boolean isOpenNetwork();
        /**
         * Returns true for a passpoint network.
         */
        boolean isPasspoint();
        /**
         * Returns true for an ephemeral network.
         */
        boolean isEphemeral();
        /**
         * Returns true for a trusted network.
         */
        boolean isTrusted();
        /**
         * Returns the ID of the evaluator that provided the candidate.
         */
        @WifiNetworkSelector.NetworkEvaluator.EvaluatorId int getEvaluatorId();
        /**
         * Gets the score that was provided by the evaluator.
         *
         * Not all evaluators provide a useful score. Scores from different evaluators
         * are not directly comparable.
         */
        int getEvaluatorScore();
        /**
         * Returns true if the candidate is in the same network as the
         * current connection.
         */
        boolean isCurrentNetwork();
        /**
         * Return true if the candidate is currently connected.
         */
        boolean isCurrentBssid();
        /**
         * Returns a value between 0 and 1.
         *
         * 1.0 means the network was recently selected by the user or an app.
         * 0.0 means not recently selected by user or app.
         */
        double getLastSelectionWeight();
        /**
         * Gets the scan RSSI.
         */
        int getScanRssi();
        /**
         * Gets the scan frequency.
         */
        int getFrequency();
        /**
         * Gets statistics from the scorecard.
         */
        @Nullable WifiScoreCardProto.Signal getEventStatistics(WifiScoreCardProto.Event event);
    }

    /**
     * Represents a connectable candidate
     */
    static class CandidateImpl implements Candidate {
        public final Key key;                   // SSID/sectype/BSSID/configId
        public final ScanDetail scanDetail;
        public final WifiConfiguration config;
        // First evaluator to nominate this config
        public final @WifiNetworkSelector.NetworkEvaluator.EvaluatorId int evaluatorId;
        public final int evaluatorScore;        // Score provided by first nominating evaluator
        public final double lastSelectionWeight; // Value between 0 and 1

        private WifiScoreCard.PerBssid mPerBssid; // For accessing the scorecard entry
        private final boolean mIsCurrentNetwork;
        private final boolean mIsCurrentBssid;

        CandidateImpl(Key key,
                ScanDetail scanDetail,
                WifiConfiguration config,
                @WifiNetworkSelector.NetworkEvaluator.EvaluatorId int evaluatorId,
                int evaluatorScore,
                WifiScoreCard.PerBssid perBssid,
                double lastSelectionWeight,
                boolean isCurrentNetwork,
                boolean isCurrentBssid) {
            this.key = key;
            this.scanDetail = scanDetail;
            this.config = config;
            this.evaluatorId = evaluatorId;
            this.evaluatorScore = evaluatorScore;
            this.mPerBssid = perBssid;
            this.lastSelectionWeight = lastSelectionWeight;
            this.mIsCurrentNetwork = isCurrentNetwork;
            this.mIsCurrentBssid = isCurrentBssid;
        }

        @Override
        public Key getKey() {
            return key;
        }

        @Override
        public int getNetworkConfigId() {
            return key.networkId;
        }

        @Override
        public ScanDetail getScanDetail() {
            return scanDetail;
        }

        @Override
        public boolean isOpenNetwork() {
            // TODO - should be able to base this on key.matchInfo.securityType
            return WifiConfigurationUtil.isConfigForOpenNetwork(config);
        }

        @Override
        public boolean isPasspoint() {
            return config.isPasspoint();
        }

        @Override
        public boolean isEphemeral() {
            return config.ephemeral;
        }

        @Override
        public boolean isTrusted() {
            return config.trusted;
        }

        @Override
        public @WifiNetworkSelector.NetworkEvaluator.EvaluatorId int getEvaluatorId() {
            return evaluatorId;
        }

        @Override
        public int getEvaluatorScore() {
            return evaluatorScore;
        }

        @Override
        public double getLastSelectionWeight() {
            return lastSelectionWeight;
        }

        @Override
        public boolean isCurrentNetwork() {
            return mIsCurrentNetwork;
        }

        @Override
        public boolean isCurrentBssid() {
            return mIsCurrentBssid;
        }

        @Override
        public int getScanRssi() {
            return scanDetail.getScanResult().level;
        }

        @Override
        public int getFrequency() {
            return scanDetail.getScanResult().frequency;
        }

        /**
         * Accesses statistical information from the score card
         */
        @Override
        public WifiScoreCardProto.Signal
                getEventStatistics(WifiScoreCardProto.Event event) {
            if (mPerBssid == null) return null;
            WifiScoreCard.PerSignal perSignal = mPerBssid.lookupSignal(event, getFrequency());
            if (perSignal == null) return null;
            return perSignal.toSignal();
        }

    }

    /**
     * Represents a scoring function
     */
    public interface CandidateScorer {
        /**
         * The scorer's name, and perhaps important parameterization/version.
         */
        String getIdentifier();

        /**
         * Calculates the score for a group of candidates that belong
         * to the same network.
         */
        @Nullable ScoredCandidate scoreCandidates(@NonNull Collection<Candidate> group);

        /**
         * Returns true if the legacy user connect choice logic should be used.
         *
         * @returns false to disable the legacy logic
         */
        boolean userConnectChoiceOverrideWanted();
    }

    /**
     * Represents a candidate with a real-valued score, along with an error estimate.
     *
     * Larger values reflect more desirable candidates. The range is arbitrary,
     * because scores generated by different sources are not compared with each
     * other.
     *
     * The error estimate is on the same scale as the value, and should
     * always be strictly positive. For instance, it might be the standard deviation.
     */
    public static class ScoredCandidate {
        public final double value;
        public final double err;
        public final Key candidateKey;
        public ScoredCandidate(double value, double err, Candidate candidate) {
            this.value = value;
            this.err = err;
            this.candidateKey = (candidate == null) ? null : candidate.getKey();
        }
        /**
         * Represents no score
         */
        public static final ScoredCandidate NONE =
                new ScoredCandidate(Double.NEGATIVE_INFINITY, Double.POSITIVE_INFINITY, null);
    }

    /**
     * The key used for tracking candidates, consisting of SSID, security type, BSSID, and network
     * configuration id.
     */
    // TODO (b/123014687) unify with similar classes in the framework
    public static class Key {
        public final ScanResultMatchInfo matchInfo; // Contains the SSID and security type
        public final MacAddress bssid;
        public final int networkId;                 // network configuration id

        public Key(ScanResultMatchInfo matchInfo,
                   MacAddress bssid,
                   int networkId) {
            this.matchInfo = matchInfo;
            this.bssid = bssid;
            this.networkId = networkId;
        }

        @Override
        public boolean equals(Object other) {
            if (!(other instanceof Key)) return false;
            Key that = (Key) other;
            return (this.matchInfo.equals(that.matchInfo)
                    && this.bssid.equals(that.bssid)
                    && this.networkId == that.networkId);
        }

        @Override
        public int hashCode() {
            return Objects.hash(matchInfo, bssid, networkId);
        }
    }

    private final Map<Key, CandidateImpl> mCandidates = new ArrayMap<>();

    private int mCurrentNetworkId = -1;
    @Nullable private MacAddress mCurrentBssid = null;

    /**
     * Sets up information about the currently-connected network.
     */
    public void setCurrent(int currentNetworkId, String currentBssid) {
        mCurrentNetworkId = currentNetworkId;
        mCurrentBssid = null;
        if (currentBssid == null) return;
        try {
            mCurrentBssid = MacAddress.fromString(currentBssid);
        } catch (RuntimeException e) {
            failWithException(e);
        }
    }

    /**
     * Adds a new candidate
     *
     * @returns true if added or replaced, false otherwise
     */
    public boolean add(ScanDetail scanDetail,
                    WifiConfiguration config,
                    @WifiNetworkSelector.NetworkEvaluator.EvaluatorId int evaluatorId,
                    int evaluatorScore,
                    double lastSelectionWeightBetweenZeroAndOne) {
        if (config == null) return failure();
        if (scanDetail == null) return failure();
        ScanResult scanResult = scanDetail.getScanResult();
        if (scanResult == null) return failure();
        MacAddress bssid;
        try {
            bssid = MacAddress.fromString(scanResult.BSSID);
        } catch (RuntimeException e) {
            return failWithException(e);
        }
        ScanResultMatchInfo key1 = ScanResultMatchInfo.fromWifiConfiguration(config);
        ScanResultMatchInfo key2 = ScanResultMatchInfo.fromScanResult(scanResult);
        if (!key1.equals(key2)) return failure(key1, key2);
        Key key = new Key(key1, bssid, config.networkId);
        CandidateImpl old = mCandidates.get(key);
        if (old != null) {
            // check if we want to replace this old candidate
            if (evaluatorId < old.evaluatorId) return failure();
            if (evaluatorId > old.evaluatorId) return false;
            if (evaluatorScore <= old.evaluatorScore) return false;
            remove(old);
        }
        WifiScoreCard.PerBssid perBssid = mWifiScoreCard.lookupBssid(
                key.matchInfo.networkSsid,
                key.bssid.toString());
        perBssid.setSecurityType(
                WifiScoreCardProto.SecurityType.forNumber(key.matchInfo.networkType));
        perBssid.setNetworkConfigId(config.networkId);
        CandidateImpl candidate = new CandidateImpl(key,
                scanDetail, config, evaluatorId, evaluatorScore, perBssid,
                Math.min(Math.max(lastSelectionWeightBetweenZeroAndOne, 0.0), 1.0),
                config.networkId == mCurrentNetworkId,
                bssid.equals(mCurrentBssid));
        mCandidates.put(key, candidate);
        return true;
    }
    /** Adds a new candidate with no user selection weight. */
    public boolean add(ScanDetail scanDetail,
                    WifiConfiguration config,
                    @WifiNetworkSelector.NetworkEvaluator.EvaluatorId int evaluatorId,
                    int evaluatorScore) {
        return add(scanDetail, config, evaluatorId, evaluatorScore, 0.0);
    }

    /**
     * Removes a candidate
     * @returns true if the candidate was successfully removed
     */
    public boolean remove(Candidate candidate) {
        if (!(candidate instanceof CandidateImpl)) return failure();
        return mCandidates.remove(((CandidateImpl) candidate).key, (CandidateImpl) candidate);
    }

    /**
     * Returns the number of candidates (at the BSSID level)
     */
    public int size() {
        return mCandidates.size();
    }

    /**
     * Returns the candidates, grouped by network.
     */
    public Collection<Collection<Candidate>> getGroupedCandidates() {
        Map<Integer, Collection<Candidate>> candidatesForNetworkId = new ArrayMap<>();
        for (CandidateImpl candidate : mCandidates.values()) {
            Collection<Candidate> cc = candidatesForNetworkId.get(candidate.key.networkId);
            if (cc == null) {
                cc = new ArrayList<>(2); // Guess 2 bssids per network
                candidatesForNetworkId.put(candidate.key.networkId, cc);
            }
            cc.add(candidate);
        }
        return candidatesForNetworkId.values();
    }

    /**
     * Make a choice from among the candidates, using the provided scorer.
     *
     * @returns the chosen scored candidate, or ScoredCandidate.NONE.
     */
    public @NonNull ScoredCandidate choose(@NonNull CandidateScorer candidateScorer) {
        Preconditions.checkNotNull(candidateScorer);
        ScoredCandidate choice = ScoredCandidate.NONE;
        for (Collection<Candidate> group : getGroupedCandidates()) {
            ScoredCandidate scoredCandidate = candidateScorer.scoreCandidates(group);
            if (scoredCandidate != null && scoredCandidate.value > choice.value) {
                choice = scoredCandidate;
            }
        }
        return choice;
    }

    /**
     * After a failure indication is returned, this may be used to get details.
     */
    public RuntimeException getLastFault() {
        return mLastFault;
    }

    /**
     * Returns the number of faults we have seen
     */
    public int getFaultCount() {
        return mFaultCount;
    }

    /**
     * Clears any recorded faults
     */
    public void clearFaults() {
        mLastFault = null;
        mFaultCount = 0;
    }

    /**
     * Controls whether to immediately raise an exception on a failure
     */
    public WifiCandidates setPicky(boolean picky) {
        mPicky = picky;
        return this;
    }

    /**
     * Records details about a failure
     *
     * This captures a stack trace, so don't bother to construct a string message, just
     * supply any culprits (convertible to strings) that might aid diagnosis.
     *
     * @returns false
     * @throws RuntimeException (if in picky mode)
     */
    private boolean failure(Object... culprits) {
        StringJoiner joiner = new StringJoiner(",");
        for (Object c : culprits) {
            joiner.add("" + c);
        }
        return failWithException(new IllegalArgumentException(joiner.toString()));
    }

    /**
     * As above, if we already have an exception.
     */
    private boolean failWithException(RuntimeException e) {
        mLastFault = e;
        mFaultCount++;
        if (mPicky) {
            throw e;
        }
        return false;
    }

    private boolean mPicky = false;
    private RuntimeException mLastFault = null;
    private int mFaultCount = 0;

}