1/*
2 * Copyright (C) 2014 Google Inc.
3 * Licensed to The Android Open Source Project.
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 *      http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18package com.android.mail.ui;
19
20import android.support.v4.view.ViewPager;
21
22import com.android.mail.utils.ViewUtils;
23
24/**
25 * Helper class for adding RTL support to a ViewPager. Note that this also requires a PagerAdapter
26 * that returns the pages in reversed order in the RTL case.
27 */
28public class BidiViewPagerHelper {
29    private ViewPager mViewPager;
30
31    public BidiViewPagerHelper(ViewPager viewPager) {
32        mViewPager = viewPager;
33    }
34
35    public int getFirstPage() {
36        return getIndexFromBidiIndex(0);
37    }
38
39    public int getLastPage() {
40        return getIndexFromBidiIndex(mViewPager.getAdapter().getCount() - 1);
41    }
42
43    public int getPreviousPage() {
44        return clampToBounds(getIndexFromBidiIndex(getBidiIndex(mViewPager.getCurrentItem()) - 1));
45    }
46
47    public int getNextPage() {
48        return clampToBounds(getIndexFromBidiIndex(getBidiIndex(mViewPager.getCurrentItem()) + 1));
49    }
50
51    private int clampToBounds(int position) {
52        return Math.max(0, Math.min(mViewPager.getAdapter().getCount() - 1, position));
53    }
54
55    private int getBidiIndex(int position) {
56        if (ViewUtils.isViewRtl(mViewPager)) {
57            return mViewPager.getAdapter().getCount() - 1 - position;
58        } else {
59            return position;
60        }
61    }
62
63    /** Inverse of {@link #getBidiIndex} function. */
64    private int getIndexFromBidiIndex(int position) {
65        // getBidiIndex is equal to its inverse function so we are just calling getBidiIndex.
66        return getBidiIndex(position);
67    }
68}
69