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MultiStackNav.kt
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MultiStackNav.kt
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/*
* Copyright 2021 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.tunjid.treenav
/**
* A compound immutable navigation [Node] whose [children] are comprised of independent [StackNav]
* instances
*/
data class MultiStackNav(
val name: String,
val indexHistory: List<Int> = listOf(0),
val currentIndex: Int = 0,
val stacks: List<StackNav> = listOf()
) : Node {
override val id: String get() = name
override val children: List<Node> get() = stacks
}
/**
* Switches out the [current] for [Node]
*/
fun MultiStackNav.swap(node: Node): MultiStackNav = atCurrentIndex { swap(node) }
/**
* Pushes [node] on top of the [StackNav] at [MultiStackNav.currentIndex]
*/
fun MultiStackNav.push(node: Node): MultiStackNav = atCurrentIndex { push(node) }
/**
* Tries to pop the active [StackNav]. If unsuccessful, it tries to go to the last
* [MultiStackNav.currentIndex] before the active [MultiStackNav.currentIndex]
*/
fun MultiStackNav.pop(): MultiStackNav = when (val changed = atCurrentIndex(StackNav::pop)) {
// There was nothing to pop, try switching the active index
this -> indexHistory.dropLast(1).let { newIndexHistory ->
when (val newIndex = newIndexHistory.lastOrNull()) {
null -> this
else -> copy(
indexHistory = newIndexHistory,
currentIndex = newIndex
)
}
}
else -> changed
}
/**
* Switches the [MultiStackNav.currentIndex] to [toIndex]
*/
fun MultiStackNav.switch(toIndex: Int): MultiStackNav = copy(
currentIndex = toIndex,
indexHistory = (indexHistory - toIndex) + toIndex
)
/**
* Performs the given [operation] with the [StackNav] at [MultiStackNav.currentIndex]
*/
private inline fun MultiStackNav.atCurrentIndex(operation: StackNav.() -> StackNav) = copy(
stacks = stacks.mapIndexed { index, stack ->
if (index == currentIndex) operation(stack)
else stack
}
)
val MultiStackNav.current: Node? get() = stacks.getOrNull(currentIndex)?.children?.lastOrNull()