package org.terst.feedreader.ui

import android.content.Intent
import android.net.Uri
import android.webkit.WebView
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.pager.HorizontalPager
import androidx.compose.foundation.pager.rememberPagerState
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.Article
import androidx.compose.material.icons.filled.ArrowBack
import androidx.compose.material.icons.filled.Bookmark
import androidx.compose.material.icons.filled.BookmarkBorder
import androidx.compose.material.icons.filled.OpenInBrowser
import androidx.compose.material.icons.outlined.Article
import androidx.compose.material3.CircularProgressIndicator
import androidx.compose.material3.ExperimentalMaterial3Api
import androidx.compose.material3.Icon
import androidx.compose.material3.IconButton
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.Scaffold
import androidx.compose.material3.SnackbarHost
import androidx.compose.material3.SnackbarHostState
import androidx.compose.material3.Text
import androidx.compose.material3.TopAppBar
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.platform.LocalContext
import androidx.compose.ui.text.style.TextOverflow
import androidx.compose.ui.viewinterop.AndroidView
import kotlinx.coroutines.flow.first
import kotlinx.coroutines.launch
import org.terst.feedreader.data.AppDatabase
import org.terst.feedreader.data.ArticleEntity
import org.terst.feedreader.data.FeedEntity
import org.terst.feedreader.data.Net
import org.terst.feedreader.data.Settings
import org.terst.feedreader.readability.ReaderExtractor
import org.terst.feedreader.stash.StashClient
import org.terst.feedreader.stash.StashSaveResult

// Below this length (of the plain feed-provided HTML), assume it's a teaser/summary,
// not the real article body, and auto-fall-back to on-device Readability extraction.
private const val THIN_CONTENT_THRESHOLD = 500

/**
 * Swipeable wrapper: snapshots the article-id order of the list this reader
 * was opened from (Unread/Saved/a specific feed) ONCE at entry, then pages
 * across that fixed queue. Deliberately a snapshot, not a live Flow -- opening
 * an article marks it read, which would otherwise drop it out of the live
 * Unread query mid-swipe and shift every subsequent page underneath the user.
 */
@OptIn(ExperimentalFoundationApi::class)
@Composable
fun ReaderScreen(feedId: String, initialArticleId: String, onBack: () -> Unit) {
    val context = LocalContext.current
    val db = remember { AppDatabase.get(context) }
    var articleIds by remember(feedId) { mutableStateOf<List<String>?>(null) }

    LaunchedEffect(feedId) {
        val flow = when (feedId) {
            UNREAD_FEED_ID -> db.articleDao().observeUnread()
            SAVED_FEED_ID -> db.articleDao().observeSaved()
            else -> db.articleDao().observeByFeed(feedId)
        }
        articleIds = flow.first().map { it.id }
    }

    val ids = articleIds
    if (ids == null) {
        Box(modifier = Modifier.fillMaxSize()) {
            CircularProgressIndicator(modifier = Modifier.align(Alignment.Center))
        }
        return
    }
    // The article may have been opened from somewhere not in this queue (shouldn't normally
    // happen, but fall back to a single-item queue rather than crashing on indexOfFirst = -1).
    val safeIds = if (ids.contains(initialArticleId)) ids else listOf(initialArticleId)
    val initialIndex = safeIds.indexOf(initialArticleId).coerceAtLeast(0)
    val pagerState = rememberPagerState(initialPage = initialIndex) { safeIds.size }

    HorizontalPager(state = pagerState, modifier = Modifier.fillMaxSize()) { page ->
        ReaderContent(articleId = safeIds[page], onBack = onBack)
    }
}

@OptIn(ExperimentalMaterial3Api::class)
@Composable
private fun ReaderContent(articleId: String, onBack: () -> Unit) {
    val context = LocalContext.current
    val db = remember { AppDatabase.get(context) }
    val scope = rememberCoroutineScope()
    val snackbarHostState = remember { SnackbarHostState() }

    var article by remember(articleId) { mutableStateOf<ArticleEntity?>(null) }
    var feed by remember(articleId) { mutableStateOf<FeedEntity?>(null) }
    var feedContent by remember(articleId) { mutableStateOf<String?>(null) }
    var readerContent by remember(articleId) { mutableStateOf<String?>(null) }
    var isReaderMode by remember(articleId) { mutableStateOf(false) }
    var isExtracting by remember(articleId) { mutableStateOf(false) }
    var isSaving by remember(articleId) { mutableStateOf(false) }

    LaunchedEffect(articleId) {
        val loaded = db.articleDao().getById(articleId) ?: return@LaunchedEffect
        article = loaded
        db.articleDao().setRead(articleId, true)
        val loadedFeed = loaded.feedId?.let { db.feedDao().getById(it) }
        feed = loadedFeed

        feedContent = loaded.feedContentHtml
        readerContent = loaded.extractedContent
        val plainLength = feedContent?.replace(Regex("<[^>]*>"), "")?.trim()?.length ?: 0

        if (loadedFeed?.readerModeDisabled != true && readerContent == null && plainLength < THIN_CONTENT_THRESHOLD) {
            // Feed content is too thin to be the real article -- auto-extract, since in this
            // case reader mode isn't really an alternative view, it's the only real content.
            isExtracting = true
            val extracted = ReaderExtractor.extract(context, loaded.link)
            isExtracting = false
            extracted?.content?.let {
                readerContent = it
                db.articleDao().setExtractedContent(articleId, it)
            }
            isReaderMode = true
        }
    }

    fun toggleReaderMode() {
        val a = article ?: return
        if (feed?.readerModeDisabled == true) return
        if (isReaderMode) {
            isReaderMode = false
            return
        }
        if (readerContent != null) {
            isReaderMode = true
            return
        }
        scope.launch {
            isExtracting = true
            val extracted = ReaderExtractor.extract(context, a.link)
            isExtracting = false
            val content = extracted?.content
            if (content != null) {
                readerContent = content
                db.articleDao().setExtractedContent(articleId, content)
                isReaderMode = true
            } else {
                snackbarHostState.showSnackbar("Couldn't extract a reader view for this article")
            }
        }
    }

    Scaffold(
        topBar = {
            TopAppBar(
                title = {
                    Column {
                        Text(article?.title.orEmpty(), maxLines = 1, overflow = TextOverflow.Ellipsis)
                        feed?.title?.let {
                            Text(
                                it,
                                maxLines = 1,
                                overflow = TextOverflow.Ellipsis,
                                style = MaterialTheme.typography.labelSmall,
                                color = MaterialTheme.colorScheme.onSurfaceVariant
                            )
                        }
                    }
                },
                navigationIcon = {
                    IconButton(onClick = onBack) {
                        Icon(Icons.Default.ArrowBack, contentDescription = "Back")
                    }
                },
                actions = {
                    val currentArticle = article
                    // Only offer the toggle when there's an actual feed-provided alternative to
                    // switch back to (if we already had to auto-extract for thin feed content,
                    // reader mode IS the only content) and the feed hasn't opted out of it.
                    if (feedContent != null && feed?.readerModeDisabled != true) {
                        IconButton(enabled = !isExtracting, onClick = { toggleReaderMode() }) {
                            Icon(
                                if (isReaderMode) Icons.Filled.Article else Icons.Outlined.Article,
                                contentDescription = "Toggle reader view"
                            )
                        }
                    }
                    IconButton(onClick = {
                        val a = currentArticle ?: return@IconButton
                        val browserIntent = Intent(Intent.ACTION_VIEW, Uri.parse(a.link))
                        context.startActivity(browserIntent)
                    }) {
                        Icon(Icons.Default.OpenInBrowser, contentDescription = "Open in browser")
                    }
                    IconButton(
                        enabled = !isSaving,
                        onClick = {
                            val a = currentArticle ?: return@IconButton
                            isSaving = true
                            scope.launch {
                                val settings = Settings(context)
                                val client = StashClient(Net.client, settings.stashBaseUrlNow(), settings.stashApiKeyNow())
                                when (val result = client.saveArticle(a.link, a.title)) {
                                    is StashSaveResult.Saved -> {
                                        db.articleDao().setSaved(a.id, true)
                                        db.articleDao().setStashArtifactId(a.id, result.artifact.id)
                                        snackbarHostState.showSnackbar("Saved to Stash")
                                    }
                                    is StashSaveResult.AlreadySaved -> {
                                        db.articleDao().setSaved(a.id, true)
                                        db.articleDao().setStashArtifactId(a.id, result.existingId)
                                        snackbarHostState.showSnackbar("Already in Stash")
                                    }
                                    is StashSaveResult.Failed ->
                                        snackbarHostState.showSnackbar("Save failed: ${result.message}")
                                }
                                isSaving = false
                            }
                        }
                    ) {
                        Icon(
                            if (currentArticle?.isSaved == true) Icons.Default.Bookmark else Icons.Default.BookmarkBorder,
                            contentDescription = "Save to Stash"
                        )
                    }
                }
            )
        },
        snackbarHost = { SnackbarHost(snackbarHostState) }
    ) { padding ->
        Box(modifier = Modifier.fillMaxSize().padding(padding)) {
            val content = if (isReaderMode) readerContent else (feedContent ?: readerContent)
            val baseUrl = article?.link
            if (content != null) {
                // AndroidView's update lambda reruns on every recomposition of this
                // composable -- including ones unrelated to content, like isSaving
                // flipping while a Stash save is in flight. Reloading the WebView's HTML
                // on those unrelated recompositions was resetting scroll position mid-swipe,
                // which is what made scrolling feel unsmooth/janky. Track what's actually
                // loaded and only reload when the content string itself changes.
                val loadedContent = remember(articleId) { mutableStateOf<String?>(null) }
                AndroidView(
                    modifier = Modifier.fillMaxSize(),
                    factory = { ctx ->
                        WebView(ctx).apply {
                            settings.javaScriptEnabled = false
                            loadDataWithBaseURL(baseUrl, wrapHtml(content), "text/html", "UTF-8", null)
                            loadedContent.value = content
                        }
                    },
                    update = { webView ->
                        if (loadedContent.value != content) {
                            webView.loadDataWithBaseURL(baseUrl, wrapHtml(content), "text/html", "UTF-8", null)
                            loadedContent.value = content
                        }
                    },
                    // AndroidView does not destroy() the underlying WebView on its own --
                    // without this, swiping through many articles (each page holding its own
                    // WebView) leaks a WebView's native resources per page and eventually
                    // exhausts memory over a long reading session.
                    onRelease = { webView -> webView.destroy() }
                )
            } else if (isExtracting) {
                CircularProgressIndicator(modifier = Modifier.align(Alignment.Center))
            }
        }
    }
}

// Hardcoded dark palette, not @media (prefers-color-scheme) -- the app itself always
// forces dark colorScheme() regardless of system setting (see MainActivity), so the
// reader content should match rather than following a system light/dark that the rest
// of the app ignores.
private fun wrapHtml(bodyContent: String): String = """
    <html><head><meta name="viewport" content="width=device-width, initial-scale=1">
    <style>
    body { font-family: sans-serif; font-size: 18px; line-height: 1.5; padding: 16px;
           background-color: #121212; color: #e1e1e1; }
    a { color: #8ab4f8; }
    img { max-width: 100%; height: auto; }
    </style></head>
    <body>$bodyContent</body></html>
""".trimIndent()