1/*
2 * Copyright 2018 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 androidx.paging;
18
19import androidx.annotation.NonNull;
20import androidx.arch.core.util.Function;
21
22import java.util.IdentityHashMap;
23import java.util.List;
24
25class WrapperItemKeyedDataSource<K, A, B> extends ItemKeyedDataSource<K, B> {
26    private final ItemKeyedDataSource<K, A> mSource;
27    private final Function<List<A>, List<B>> mListFunction;
28
29    private final IdentityHashMap<B, K> mKeyMap = new IdentityHashMap<>();
30
31    WrapperItemKeyedDataSource(ItemKeyedDataSource<K, A> source,
32            Function<List<A>, List<B>> listFunction) {
33        mSource = source;
34        mListFunction = listFunction;
35    }
36
37    @Override
38    public void addInvalidatedCallback(@NonNull InvalidatedCallback onInvalidatedCallback) {
39        mSource.addInvalidatedCallback(onInvalidatedCallback);
40    }
41
42    @Override
43    public void removeInvalidatedCallback(@NonNull InvalidatedCallback onInvalidatedCallback) {
44        mSource.removeInvalidatedCallback(onInvalidatedCallback);
45    }
46
47    @Override
48    public void invalidate() {
49        mSource.invalidate();
50    }
51
52    @Override
53    public boolean isInvalid() {
54        return mSource.isInvalid();
55    }
56
57    private List<B> convertWithStashedKeys(List<A> source) {
58        List<B> dest = convert(mListFunction, source);
59        synchronized (mKeyMap) {
60            // synchronize on mKeyMap, since multiple loads may occur simultaneously.
61            // Note: manually sync avoids locking per-item (e.g. Collections.synchronizedMap)
62            for (int i = 0; i < dest.size(); i++) {
63                mKeyMap.put(dest.get(i), mSource.getKey(source.get(i)));
64            }
65        }
66        return dest;
67    }
68
69    @Override
70    public void loadInitial(@NonNull LoadInitialParams<K> params,
71            final @NonNull LoadInitialCallback<B> callback) {
72        mSource.loadInitial(params, new LoadInitialCallback<A>() {
73            @Override
74            public void onResult(@NonNull List<A> data, int position, int totalCount) {
75                callback.onResult(convertWithStashedKeys(data), position, totalCount);
76            }
77
78            @Override
79            public void onResult(@NonNull List<A> data) {
80                callback.onResult(convertWithStashedKeys(data));
81            }
82        });
83    }
84
85    @Override
86    public void loadAfter(@NonNull LoadParams<K> params,
87            final @NonNull LoadCallback<B> callback) {
88        mSource.loadAfter(params, new LoadCallback<A>() {
89            @Override
90            public void onResult(@NonNull List<A> data) {
91                callback.onResult(convertWithStashedKeys(data));
92            }
93        });
94    }
95
96    @Override
97    public void loadBefore(@NonNull LoadParams<K> params,
98            final @NonNull LoadCallback<B> callback) {
99        mSource.loadBefore(params, new LoadCallback<A>() {
100            @Override
101            public void onResult(@NonNull List<A> data) {
102                callback.onResult(convertWithStashedKeys(data));
103            }
104        });
105    }
106
107    @NonNull
108    @Override
109    public K getKey(@NonNull B item) {
110        synchronized (mKeyMap) {
111            return mKeyMap.get(item);
112        }
113    }
114}
115