1/*
2 * Copyright (C) 2014 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License
15 */
16
17package android.net;
18
19import android.annotation.SystemApi;
20import android.os.Parcel;
21import android.os.Parcelable;
22
23import java.util.Arrays;
24import java.util.Objects;
25
26/**
27 * A curve defining the network score over a range of RSSI values.
28 *
29 * <p>For each RSSI bucket, the score may be any byte. Scores have no absolute meaning and are only
30 * considered relative to other scores assigned by the same scorer. Networks with no score are
31 * treated equivalently to a network with score {@link Byte#MIN_VALUE}, and will not be used.
32 *
33 * <p>For example, consider a curve starting at -110 dBm with a bucket width of 10 and the
34 * following buckets: {@code [-20, -10, 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120]}.
35 * This represents a linear curve between -110 dBm and 30 dBm. It scores progressively higher at
36 * stronger signal strengths.
37 *
38 * <p>A network can be assigned a fixed score independent of RSSI by setting
39 * {@link #rssiBuckets} to a one-byte array whose element is the fixed score. {@link #start}
40 * should be set to the lowest RSSI value at which this fixed score should apply, and
41 * {@link #bucketWidth} should be set such that {@code start + bucketWidth} is equal to the
42 * highest RSSI value at which this fixed score should apply.
43 *
44 * <p>Note that RSSI values below -110 dBm or above 30 dBm are unlikely to cause any difference
45 * in connectivity behavior from those endpoints. That is, the connectivity framework will treat
46 * a network with a -120 dBm signal exactly as it would treat one with a -110 dBm signal.
47 * Therefore, graphs which specify scores outside this range may be truncated to this range by
48 * the system.
49 *
50 * @see ScoredNetwork
51 * @hide
52 */
53@SystemApi
54public class RssiCurve implements Parcelable {
55    private static final int DEFAULT_ACTIVE_NETWORK_RSSI_BOOST = 25;
56
57    /** The starting dBm of the curve. */
58    public final int start;
59
60    /** The width of each RSSI bucket, in dBm. */
61    public final int bucketWidth;
62
63    /** The score for each RSSI bucket. */
64    public final byte[] rssiBuckets;
65
66    /**
67     * The RSSI boost to give this network when active, in dBm.
68     *
69     * <p>When the system is connected to this network, it will pretend that the network has this
70     * much higher of an RSSI. This is to avoid switching networks when another network has only a
71     * slightly higher score.
72     */
73    public final int activeNetworkRssiBoost;
74
75    /**
76     * Construct a new {@link RssiCurve}.
77     *
78     * @param start the starting dBm of the curve.
79     * @param bucketWidth the width of each RSSI bucket, in dBm.
80     * @param rssiBuckets the score for each RSSI bucket.
81     */
82    public RssiCurve(int start, int bucketWidth, byte[] rssiBuckets) {
83        this(start, bucketWidth, rssiBuckets, DEFAULT_ACTIVE_NETWORK_RSSI_BOOST);
84    }
85
86    /**
87     * Construct a new {@link RssiCurve}.
88     *
89     * @param start the starting dBm of the curve.
90     * @param bucketWidth the width of each RSSI bucket, in dBm.
91     * @param rssiBuckets the score for each RSSI bucket.
92     * @param activeNetworkRssiBoost the RSSI boost to apply when this network is active, in dBm.
93     */
94    public RssiCurve(int start, int bucketWidth, byte[] rssiBuckets, int activeNetworkRssiBoost) {
95        this.start = start;
96        this.bucketWidth = bucketWidth;
97        if (rssiBuckets == null || rssiBuckets.length == 0) {
98            throw new IllegalArgumentException("rssiBuckets must be at least one element large.");
99        }
100        this.rssiBuckets = rssiBuckets;
101        this.activeNetworkRssiBoost = activeNetworkRssiBoost;
102    }
103
104    private RssiCurve(Parcel in) {
105        start = in.readInt();
106        bucketWidth = in.readInt();
107        int bucketCount = in.readInt();
108        rssiBuckets = new byte[bucketCount];
109        in.readByteArray(rssiBuckets);
110        activeNetworkRssiBoost = in.readInt();
111    }
112
113    @Override
114    public int describeContents() {
115        return 0;
116    }
117
118    @Override
119    public void writeToParcel(Parcel out, int flags) {
120        out.writeInt(start);
121        out.writeInt(bucketWidth);
122        out.writeInt(rssiBuckets.length);
123        out.writeByteArray(rssiBuckets);
124        out.writeInt(activeNetworkRssiBoost);
125    }
126
127    /**
128     * Lookup the score for a given RSSI value.
129     *
130     * @param rssi The RSSI to lookup. If the RSSI falls below the start of the curve, the score at
131     *         the start of the curve will be returned. If it falls after the end of the curve, the
132     *         score at the end of the curve will be returned.
133     * @return the score for the given RSSI.
134     */
135    public byte lookupScore(int rssi) {
136        return lookupScore(rssi, false /* isActiveNetwork */);
137    }
138
139    /**
140     * Lookup the score for a given RSSI value.
141     *
142     * @param rssi The RSSI to lookup. If the RSSI falls below the start of the curve, the score at
143     *         the start of the curve will be returned. If it falls after the end of the curve, the
144     *         score at the end of the curve will be returned.
145     * @param isActiveNetwork Whether this network is currently active.
146     * @return the score for the given RSSI.
147     */
148    public byte lookupScore(int rssi, boolean isActiveNetwork) {
149        if (isActiveNetwork) {
150            rssi += activeNetworkRssiBoost;
151        }
152
153        int index = (rssi - start) / bucketWidth;
154
155        // Snap the index to the closest bucket if it falls outside the curve.
156        if (index < 0) {
157            index = 0;
158        } else if (index > rssiBuckets.length - 1) {
159            index = rssiBuckets.length - 1;
160        }
161
162        return rssiBuckets[index];
163    }
164
165    /**
166     * Determine if two RSSI curves are defined in the same way.
167     *
168     * <p>Note that two curves can be equivalent but defined differently, e.g. if one bucket in one
169     * curve is split into two buckets in another. For the purpose of this method, these curves are
170     * not considered equal to each other.
171     */
172    @Override
173    public boolean equals(Object o) {
174        if (this == o) return true;
175        if (o == null || getClass() != o.getClass()) return false;
176
177        RssiCurve rssiCurve = (RssiCurve) o;
178
179        return start == rssiCurve.start &&
180                bucketWidth == rssiCurve.bucketWidth &&
181                Arrays.equals(rssiBuckets, rssiCurve.rssiBuckets) &&
182                activeNetworkRssiBoost == rssiCurve.activeNetworkRssiBoost;
183    }
184
185    @Override
186    public int hashCode() {
187        return Objects.hash(start, bucketWidth, rssiBuckets, activeNetworkRssiBoost);
188    }
189
190    @Override
191    public String toString() {
192        StringBuilder sb = new StringBuilder();
193        sb.append("RssiCurve[start=")
194                .append(start)
195                .append(",bucketWidth=")
196                .append(bucketWidth)
197                .append(",activeNetworkRssiBoost=")
198                .append(activeNetworkRssiBoost);
199
200        sb.append(",buckets=");
201        for (int i = 0; i < rssiBuckets.length; i++) {
202            sb.append(rssiBuckets[i]);
203            if (i < rssiBuckets.length - 1) {
204                sb.append(",");
205            }
206        }
207        sb.append("]");
208
209        return sb.toString();
210    }
211
212    public static final Creator<RssiCurve> CREATOR =
213            new Creator<RssiCurve>() {
214                @Override
215                public RssiCurve createFromParcel(Parcel in) {
216                    return new RssiCurve(in);
217                }
218
219                @Override
220                public RssiCurve[] newArray(int size) {
221                    return new RssiCurve[size];
222                }
223            };
224}
225