WebView.kt

/*
 * Copyright 2021 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
 *
 *      https://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.google.accompanist.web

import android.graphics.Bitmap
import android.view.ViewGroup
import android.webkit.WebChromeClient
import android.webkit.WebResourceError
import android.webkit.WebResourceRequest
import android.webkit.WebView
import android.webkit.WebViewClient
import androidx.activity.compose.BackHandler
import androidx.compose.runtime.Composable
import androidx.compose.runtime.Immutable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.Stable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateListOf
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.runtime.setValue
import androidx.compose.ui.Modifier
import androidx.compose.ui.platform.LocalInspectionMode
import androidx.compose.ui.viewinterop.AndroidView
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.flow.MutableSharedFlow
import kotlinx.coroutines.launch
import kotlinx.coroutines.withContext

/**
 * A wrapper around the Android View WebView to provide a basic WebView composable.
 *
 * If you require more customisation you are most likely better rolling your own and using this
 * wrapper as an example.
 *
 * @param state The webview state holder where the Uri to load is defined.
 * @param captureBackPresses Set to true to have this Composable capture back presses and navigate
 * the WebView back.
 * @param navigator An optional navigator object that can be used to control the WebView's
 * navigation from outside the composable.
 * @param onCreated Called when the WebView is first created, this can be used to set additional
 * settings on the WebView. WebChromeClient and WebViewClient should not be set here as they will be
 * subsequently overwritten after this lambda is called.
 * @param client Provides access to WebViewClient via subclassing
 * @param chromeClient Provides access to WebChromeClient via subclassing
 * @sample com.google.accompanist.sample.webview.BasicWebViewSample
 */
@Composable
fun WebView(
    state: WebViewState,
    modifier: Modifier = Modifier,
    captureBackPresses: Boolean = true,
    navigator: WebViewNavigator = rememberWebViewNavigator(),
    onCreated: (WebView) -> Unit = {},
    client: AccompanistWebViewClient = remember { AccompanistWebViewClient() },
    chromeClient: AccompanistWebChromeClient = remember { AccompanistWebChromeClient() }
) {
    var webView by remember { mutableStateOf<WebView?>(null) }

    BackHandler(captureBackPresses && navigator.canGoBack) {
        webView?.goBack()
    }

    LaunchedEffect(webView, navigator) {
        with(navigator) { webView?.handleNavigationEvents() }
    }

    // Set the state of the client and chrome client
    // This is done internally to ensure they always are the same instance as the
    // parent Web composable
    client.state = state
    client.navigator = navigator
    chromeClient.state = state

    val runningInPreview = LocalInspectionMode.current

    AndroidView(
        factory = { context ->
            WebView(context).apply {
                onCreated(this)

                layoutParams = ViewGroup.LayoutParams(
                    ViewGroup.LayoutParams.MATCH_PARENT,
                    ViewGroup.LayoutParams.MATCH_PARENT
                )

                webChromeClient = chromeClient
                webViewClient = client
            }.also { webView = it }
        },
        modifier = modifier
    ) { view ->
        // AndroidViews are not supported by preview, bail early
        if (runningInPreview) return@AndroidView

        when (val content = state.content) {
            is WebContent.Url -> {
                val url = content.url

                if (url.isNotEmpty() && url != view.url) {
                    view.loadUrl(url, content.additionalHttpHeaders.toMutableMap())
                }
            }
            is WebContent.Data -> {
                view.loadDataWithBaseURL(content.baseUrl, content.data, null, "utf-8", null)
            }
        }

        navigator.canGoBack = view.canGoBack()
        navigator.canGoForward = view.canGoForward()
    }
}

/**
 * AccompanistWebViewClient
 *
 * A parent class implementation of WebViewClient that can be subclassed to add custom behaviour.
 *
 * As Accompanist Web needs to set its own web client to function, it provides this intermediary
 * class that can be overriden if further custom behaviour is required.
 */
open class AccompanistWebViewClient : WebViewClient() {
    open lateinit var state: WebViewState
        internal set
    open lateinit var navigator: WebViewNavigator
        internal set

    override fun onPageStarted(view: WebView?, url: String?, favicon: Bitmap?) {
        super.onPageStarted(view, url, favicon)
        state.loadingState = LoadingState.Loading(0.0f)
        state.errorsForCurrentRequest.clear()
        state.pageTitle = null
        state.pageIcon = null
    }

    override fun onPageFinished(view: WebView?, url: String?) {
        super.onPageFinished(view, url)
        state.loadingState = LoadingState.Finished
        navigator.canGoBack = view?.canGoBack() ?: false
        navigator.canGoForward = view?.canGoForward() ?: false
    }

    override fun doUpdateVisitedHistory(
        view: WebView?,
        url: String?,
        isReload: Boolean
    ) {
        super.doUpdateVisitedHistory(view, url, isReload)
        // WebView will often update the current url itself.
        // This happens in situations like redirects and navigating through
        // history. We capture this change and update our state holder url.
        // On older APIs (28 and lower), this method is called when loading
        // html data. We don't want to update the state in this case as that will
        // overwrite the html being loaded.
        if (url != null &&
            !url.startsWith("data:text/html") &&
            state.content.getCurrentUrl() != url
        ) {
            state.content = state.content.withUrl(url)
        }
    }

    override fun onReceivedError(
        view: WebView?,
        request: WebResourceRequest?,
        error: WebResourceError?
    ) {
        super.onReceivedError(view, request, error)

        if (error != null) {
            state.errorsForCurrentRequest.add(WebViewError(request, error))
        }
    }

    override fun shouldOverrideUrlLoading(
        view: WebView?,
        request: WebResourceRequest?
    ): Boolean {
        // Override all url loads to make the single source of truth
        // of the URL the state holder Url
        request?.let {
            state.content = state.content.withUrl(it.url.toString())
        }
        return true
    }
}

/**
 * AccompanistWebChromeClient
 *
 * A parent class implementation of WebChromeClient that can be subclassed to add custom behaviour.
 *
 * As Accompanist Web needs to set its own web client to function, it provides this intermediary
 * class that can be overriden if further custom behaviour is required.
 */
open class AccompanistWebChromeClient : WebChromeClient() {
    open lateinit var state: WebViewState
        internal set

    override fun onReceivedTitle(view: WebView?, title: String?) {
        super.onReceivedTitle(view, title)
        state.pageTitle = title
    }

    override fun onReceivedIcon(view: WebView?, icon: Bitmap?) {
        super.onReceivedIcon(view, icon)
        state.pageIcon = icon
    }

    override fun onProgressChanged(view: WebView?, newProgress: Int) {
        super.onProgressChanged(view, newProgress)
        if (state.loadingState is LoadingState.Finished) return
        state.loadingState = LoadingState.Loading(newProgress / 100.0f)
    }
}

sealed class WebContent {
    data class Url(
        val url: String,
        val additionalHttpHeaders: Map<String, String> = emptyMap(),
    ) : WebContent()

    data class Data(val data: String, val baseUrl: String? = null) : WebContent()

    fun getCurrentUrl(): String? {
        return when (this) {
            is Url -> url
            is Data -> baseUrl
        }
    }
}

internal fun WebContent.withUrl(url: String) = when (this) {
    is WebContent.Url -> copy(url = url)
    else -> WebContent.Url(url)
}

/**
 * Sealed class for constraining possible loading states.
 * See [Loading] and [Finished].
 */
sealed class LoadingState {
    /**
     * Describes a WebView that has not yet loaded for the first time.
     */
    object Initializing : LoadingState()

    /**
     * Describes a webview between `onPageStarted` and `onPageFinished` events, contains a
     * [progress] property which is updated by the webview.
     */
    data class Loading(val progress: Float) : LoadingState()

    /**
     * Describes a webview that has finished loading content.
     */
    object Finished : LoadingState()
}

/**
 * A state holder to hold the state for the WebView. In most cases this will be remembered
 * using the rememberWebViewState(uri) function.
 */
@Stable
class WebViewState(webContent: WebContent) {
    /**
     *  The content being loaded by the WebView
     */
    var content by mutableStateOf<WebContent>(webContent)

    /**
     * Whether the WebView is currently [LoadingState.Loading] data in its main frame (along with
     * progress) or the data loading has [LoadingState.Finished]. See [LoadingState]
     */
    var loadingState: LoadingState by mutableStateOf(LoadingState.Initializing)
        internal set

    /**
     * Whether the webview is currently loading data in its main frame
     */
    val isLoading: Boolean
        get() = loadingState !is LoadingState.Finished

    /**
     * The title received from the loaded content of the current page
     */
    var pageTitle: String? by mutableStateOf(null)
        internal set

    /**
     * the favicon received from the loaded content of the current page
     */
    var pageIcon: Bitmap? by mutableStateOf(null)
        internal set

    /**
     * A list for errors captured in the last load. Reset when a new page is loaded.
     * Errors could be from any resource (iframe, image, etc.), not just for the main page.
     * For more fine grained control use the OnError callback of the WebView.
     */
    val errorsForCurrentRequest = mutableStateListOf<WebViewError>()
}

/**
 * Allows control over the navigation of a WebView from outside the composable. E.g. for performing
 * a back navigation in response to the user clicking the "up" button in a TopAppBar.
 *
 * @see [rememberWebViewNavigator]
 */
@Stable
class WebViewNavigator(private val coroutineScope: CoroutineScope) {

    private enum class NavigationEvent { BACK, FORWARD, RELOAD, STOP_LOADING }

    private val navigationEvents: MutableSharedFlow<NavigationEvent> = MutableSharedFlow()

    // Use Dispatchers.Main to ensure that the webview methods are called on UI thread
    internal suspend fun WebView.handleNavigationEvents(): Nothing = withContext(Dispatchers.Main) {
        navigationEvents.collect { event ->
            when (event) {
                NavigationEvent.BACK -> goBack()
                NavigationEvent.FORWARD -> goForward()
                NavigationEvent.RELOAD -> reload()
                NavigationEvent.STOP_LOADING -> stopLoading()
            }
        }
    }

    /**
     * True when the web view is able to navigate backwards, false otherwise.
     */
    var canGoBack: Boolean by mutableStateOf(false)
        internal set

    /**
     * True when the web view is able to navigate forwards, false otherwise.
     */
    var canGoForward: Boolean by mutableStateOf(false)
        internal set

    /**
     * Navigates the webview back to the previous page.
     */
    fun navigateBack() {
        coroutineScope.launch { navigationEvents.emit(NavigationEvent.BACK) }
    }

    /**
     * Navigates the webview forward after going back from a page.
     */
    fun navigateForward() {
        coroutineScope.launch { navigationEvents.emit(NavigationEvent.FORWARD) }
    }

    /**
     * Reloads the current page in the webview.
     */
    fun reload() {
        coroutineScope.launch { navigationEvents.emit(NavigationEvent.RELOAD) }
    }

    /**
     * Stops the current page load (if one is loading).
     */
    fun stopLoading() {
        coroutineScope.launch { navigationEvents.emit(NavigationEvent.STOP_LOADING) }
    }
}

/**
 * Creates and remembers a [WebViewNavigator] using the default [CoroutineScope] or a provided
 * override.
 */
@Composable
fun rememberWebViewNavigator(
    coroutineScope: CoroutineScope = rememberCoroutineScope()
) = remember(coroutineScope) { WebViewNavigator(coroutineScope) }

/**
 * A wrapper class to hold errors from the WebView.
 */
@Immutable
data class WebViewError(
    /**
     * The request the error came from.
     */
    val request: WebResourceRequest?,
    /**
     * The error that was reported.
     */
    val error: WebResourceError
)

/**
 * Creates a WebView state that is remembered across Compositions.
 *
 * @param url The url to load in the WebView
 * @param additionalHttpHeaders Optional, additional HTTP headers that are passed to [WebView.loadUrl].
 *                              Note that these headers are used for all subsequent requests of the WebView.
 */
@Composable
fun rememberWebViewState(url: String, additionalHttpHeaders: Map<String, String> = emptyMap()) =
    // Rather than using .apply {} here we will recreate the state, this prevents
    // a recomposition loop when the webview updates the url itself.
    remember(url, additionalHttpHeaders) {
        WebViewState(
            WebContent.Url(
                url = url,
                additionalHttpHeaders = additionalHttpHeaders
            )
        )
    }

/**
 * Creates a WebView state that is remembered across Compositions.
 *
 * @param data The uri to load in the WebView
 */
@Composable
fun rememberWebViewStateWithHTMLData(data: String, baseUrl: String? = null) =
    remember(data, baseUrl) {
        WebViewState(WebContent.Data(data, baseUrl))
    }