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.messaging.util;
18
19/**
20 * Very simple circular array implementation.
21 *
22 * @param <E> The element type of this list.
23 * @LibraryInternal
24 */
25public class CircularArray<E> {
26    private int mNextWriter;
27    private boolean mHasWrapped;
28    private int mMaxCount;
29    Object mList[];
30
31    /**
32     * Constructor for CircularArray.
33     *
34     * @param count Max elements to hold in the list.
35     */
36    public CircularArray(int count) {
37        mMaxCount = count;
38        clear();
39    }
40
41    /**
42     * Reset the list.
43     */
44    public void clear() {
45        mNextWriter = 0;
46        mHasWrapped = false;
47        mList = new Object[mMaxCount];
48    }
49
50    /**
51     * Add an element to the end of the list.
52     *
53     * @param object The object to add.
54     */
55    public void add(E object) {
56        mList[mNextWriter] = object;
57        ++mNextWriter;
58        if (mNextWriter == mMaxCount) {
59            mNextWriter = 0;
60            mHasWrapped = true;
61        }
62    }
63
64    /**
65     * Get the number of elements in the list. This will be 0 <= returned count <= max count
66     *
67     * @return Elements in the circular list.
68     */
69    public int count() {
70        if (mHasWrapped) {
71            return mMaxCount;
72        } else {
73            return mNextWriter;
74        }
75    }
76
77    /**
78     * Return null if the list hasn't wrapped yet. Otherwise return the next object that would be
79     * overwritten. Can be useful to avoid extra allocations.
80     *
81     * @return
82     */
83    @SuppressWarnings("unchecked")
84    public E getFree() {
85        if (!mHasWrapped) {
86            return null;
87        } else {
88            return (E) mList[mNextWriter];
89        }
90    }
91
92    /**
93     * Get the object at index. Index 0 is the oldest item inserted into the list. Index (count() -
94     * 1) is the newest.
95     *
96     * @param index Index to retrieve.
97     * @return Object at index.
98     */
99    @SuppressWarnings("unchecked")
100    public E get(int index) {
101        if (mHasWrapped) {
102            int wrappedIndex = index + mNextWriter;
103            if (wrappedIndex >= mMaxCount) {
104                wrappedIndex -= mMaxCount;
105            }
106            return (E) mList[wrappedIndex];
107        } else {
108            return (E) mList[index];
109        }
110    }
111}
112