1/*
2 * Copyright (C) 2015 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 com.android.tv.recommendation;
18
19import java.util.concurrent.TimeUnit;
20
21public class RecentChannelEvaluator extends Recommender.Evaluator {
22    private static final long WATCH_DURATION_MS_LOWER_BOUND = TimeUnit.MINUTES.toMillis(3);
23    private static final long WATCH_DURATION_MS_UPPER_BOUND = TimeUnit.MINUTES.toMillis(7);
24
25    private static final double MAX_SCORE_FOR_LOWER_BOUND = 0.1;
26
27    private long mLastWatchLogUpdateTimeMs;
28
29    public RecentChannelEvaluator() {
30        mLastWatchLogUpdateTimeMs = System.currentTimeMillis();
31    }
32
33    @Override
34    public void onNewWatchLog(ChannelRecord channelRecord) {
35        mLastWatchLogUpdateTimeMs = System.currentTimeMillis();
36    }
37
38    @Override
39    public double evaluateChannel(long channelId) {
40        ChannelRecord cr = getRecommender().getChannelRecord(channelId);
41        if (cr == null) {
42            return NOT_RECOMMENDED;
43        }
44        WatchedProgram[] watchHistory = cr.getWatchHistory();
45        double maxScore = 0.0;
46        for (int i = watchHistory.length - 1; i >= 0; --i) {
47            double recentWatchScore =
48                    (double) watchHistory[i].getWatchEndTimeMs() / mLastWatchLogUpdateTimeMs;
49            double watchDurationScore;
50            double watchDuration = watchHistory[i].getWatchedDurationMs();
51            if (watchDuration < WATCH_DURATION_MS_LOWER_BOUND) {
52                watchDurationScore = MAX_SCORE_FOR_LOWER_BOUND;
53            } else if (watchDuration < WATCH_DURATION_MS_UPPER_BOUND) {
54                watchDurationScore = (watchDuration - WATCH_DURATION_MS_LOWER_BOUND)
55                        / (WATCH_DURATION_MS_UPPER_BOUND - WATCH_DURATION_MS_LOWER_BOUND)
56                        * (1 - MAX_SCORE_FOR_LOWER_BOUND) + MAX_SCORE_FOR_LOWER_BOUND;
57            } else {
58                watchDurationScore = 1.0;
59            }
60            maxScore = Math.max(maxScore, watchDurationScore * recentWatchScore);
61        }
62        return (maxScore > 0.0) ? maxScore : NOT_RECOMMENDED;
63    }
64}