NavHostController.kt

/*
 * Copyright 2020 The Android Open Source Project
 *
 * 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 androidx.navigation.compose

import android.content.Context
import android.os.Bundle
import androidx.compose.runtime.Composable
import androidx.compose.runtime.DisposableEffect
import androidx.compose.runtime.MutableState
import androidx.compose.runtime.State
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.saveable.Saver
import androidx.compose.runtime.saveable.rememberSaveable
import androidx.compose.ui.platform.LocalContext
import androidx.core.net.toUri
import androidx.navigation.NavBackStackEntry
import androidx.navigation.NavController
import androidx.navigation.NavDeepLinkRequest
import androidx.navigation.NavGraph
import androidx.navigation.NavGraphBuilder
import androidx.navigation.NavHostController
import androidx.navigation.NavOptions
import androidx.navigation.NavOptionsBuilder
import androidx.navigation.navOptions
import androidx.navigation.navigation

/**
 * The route linked to the current destination.
 */
const val KEY_ROUTE = "android-support-nav:controller:route"

/**
 * Gets the current navigation back stack entry as a [MutableState]. When the given navController
 * changes the back stack due to a [NavController.navigate] or [NavController.popBackStack] this
 * will trigger a recompose and return the top entry on the back stack.
 *
 * @return a mutable state of the current back stack entry
 */
@Composable
public fun NavController.currentBackStackEntryAsState(): State<NavBackStackEntry?> {
    val currentNavBackStackEntry = remember { mutableStateOf(currentBackStackEntry) }
    // setup the onDestinationChangedListener responsible for detecting when the
    // current back stack entry changes
    DisposableEffect(this) {
        val callback = NavController.OnDestinationChangedListener { controller, _, _ ->
            currentNavBackStackEntry.value = controller.currentBackStackEntry
        }
        addOnDestinationChangedListener(callback)
        // remove the navController on dispose (i.e. when the composable is destroyed)
        onDispose {
            removeOnDestinationChangedListener(callback)
        }
    }
    return currentNavBackStackEntry
}

/**
 * Creates a NavHostController that handles the adding of the [ComposeNavigator].
 *
 * @see NavHost
 */
@Composable
public fun rememberNavController(): NavHostController {
    val context = LocalContext.current
    return rememberSaveable(saver = NavControllerSaver(context)) {
        createNavController(context)
    }
}

private fun createNavController(context: Context) =
    NavHostController(context).apply {
        navigatorProvider.addNavigator(ComposeNavigator())
    }

/**
 * Saver to save and restore the NavController across config change and process death.
 */
private fun NavControllerSaver(
    context: Context
): Saver<NavHostController, *> = Saver<NavHostController, Bundle>(
    save = { it.saveState() },
    restore = { createNavController(context).apply { restoreState(it) } }
)

/**
 * Navigate to a route in the current NavGraph.
 *
 * @param route route for the destination
 * @param builder DSL for constructing a new [NavOptions]
 */
public fun NavController.navigate(route: String, builder: NavOptionsBuilder.() -> Unit = {}) {
    navigate(
        NavDeepLinkRequest.Builder.fromUri(createRoute(route).toUri()).build(),
        navOptions(builder)
    )
}

/**
 * Construct a new [NavGraph]
 *
 * @param route the route for the graph
 * @param startDestination the route for the start destination
 * @param builder the builder used to construct the graph
 */
fun NavController.createGraph(
    startDestination: String,
    route: String? = null,
    builder: NavGraphBuilder.() -> Unit
): NavGraph = navigatorProvider.navigation(
    if (route != null) createRoute(route).hashCode() else 0,
    createRoute(startDestination).hashCode(),
    builder
)

/**
 * Gets the topmost {@link NavBackStackEntry} for a route.
 * <p>
 * This is always safe to use with {@link #getCurrentDestination() the current destination} or
 * {@link NavDestination#getParent() its parent} or grandparent navigation graphs as these
 * destinations are guaranteed to be on the back stack.
 *
 * @param route route of a destination that exists on the back stack
 * @throws IllegalArgumentException if the destination is not on the back stack
 */
public fun NavController.getBackStackEntry(route: String): NavBackStackEntry {
    try {
        return getBackStackEntry(createRoute(route).hashCode())
    } catch (e: IllegalArgumentException) {
        throw IllegalArgumentException(
            "No destination with route $route is on the NavController's back stack. The current " +
                "destination is $currentDestination"
        )
    }
}

internal fun createRoute(route: String) = "android-app://androidx.navigation.compose/$route"