1 /*
2 * Copyright (C) 2024 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 com.android.systemui.scene.data.model
18
19 import com.android.compose.animation.scene.SceneKey
20
21 /** An immutable stack of [SceneKey]s backed by a singly-linked list. */
22 sealed interface SceneStack
23
24 private data object EmptyStack : SceneStack
25
26 private data class StackedNodes(val head: SceneKey, val tail: SceneStack) : SceneStack
27
28 /** Returns the scene at the head of the stack, or `null` if empty. O(1) */
SceneStacknull29 fun SceneStack.peek(): SceneKey? =
30 when (this) {
31 EmptyStack -> null
32 is StackedNodes -> head
33 }
34
35 /** Returns a stack with the head removed, or `null` if empty. O(1) */
SceneStacknull36 fun SceneStack.pop(): SceneStack? =
37 when (this) {
38 EmptyStack -> null
39 is StackedNodes -> tail
40 }
41
42 /** Returns a stack with [sceneKey] as the head on top of [this]. O(1) */
SceneStacknull43 fun SceneStack.push(sceneKey: SceneKey): SceneStack = StackedNodes(sceneKey, this)
44
45 /** Returns an iterable that produces all elements in the stack, from head to tail. */
46 fun SceneStack.asIterable(): Iterable<SceneKey> = Iterable {
47 iterator {
48 when (this@asIterable) {
49 EmptyStack -> {}
50 is StackedNodes -> {
51 yield(head)
52 yieldAll(tail.asIterable())
53 }
54 }
55 }
56 }
57
58 /**
59 * Returns a new [SceneStack] containing the given [scenes], ordered such that the first argument is
60 * the head returned from [peek], then the second, and so forth.
61 */
sceneStackOfnull62 fun sceneStackOf(vararg scenes: SceneKey): SceneStack {
63 var result: SceneStack = EmptyStack
64 for (sceneKey in scenes.reversed()) {
65 result = result.push(sceneKey)
66 }
67 return result
68 }
69