1 /*
<lambda>null2  * Copyright 2023 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 
17 package androidx.compose.foundation.lazy.layout
18 
19 /**
20  * Common parts backing the interval-based content of lazy layout defined through `item` DSL.
21  *
22  * Note: this class is a part of [LazyLayout] harness that allows for building custom lazy layouts.
23  * LazyLayout and all corresponding APIs are still under development and are subject to change.
24  */
25 abstract class LazyLayoutIntervalContent<Interval : LazyLayoutIntervalContent.Interval> {
26     abstract val intervals: IntervalList<Interval>
27 
28     /** The total amount of items in all the intervals. */
29     val itemCount: Int
30         get() = intervals.size
31 
32     /** Returns item key based on a global index. */
33     fun getKey(index: Int): Any =
34         withInterval(index) { localIndex, content ->
35             content.key?.invoke(localIndex) ?: getDefaultLazyLayoutKey(index)
36         }
37 
38     /** Returns content type based on a global index. */
39     fun getContentType(index: Int): Any? =
40         withInterval(index) { localIndex, content -> content.type.invoke(localIndex) }
41 
42     /**
43      * Runs a [block] on the content of the interval associated with the provided [globalIndex] with
44      * providing a local index in the given interval.
45      */
46     inline fun <T> withInterval(
47         globalIndex: Int,
48         block: (localIntervalIndex: Int, content: Interval) -> T
49     ): T {
50         val interval = intervals[globalIndex]
51         val localIntervalIndex = globalIndex - interval.startIndex
52         return block(localIntervalIndex, interval.value)
53     }
54 
55     /**
56      * Common content of individual intervals in `item` DSL of lazy layouts.
57      *
58      * Note: this class is a part of [LazyLayout] harness that allows for building custom lazy
59      * layouts. LazyLayout and all corresponding APIs are still under development and are subject to
60      * change.
61      */
62     interface Interval {
63         /** Returns item key based on a local index for the current interval. */
64         val key: ((index: Int) -> Any)?
65             get() = null
66 
67         /** Returns item type based on a local index for the current interval. */
68         val type: ((index: Int) -> Any?)
69             get() = { null }
70     }
71 }
72