package org.terst.feedreader.ui

import androidx.compose.foundation.clickable
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.Spacer
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.width
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.items
import androidx.compose.material.icons.Icons
import androidx.compose.material.icons.filled.Add
import androidx.compose.material.icons.filled.Article
import androidx.compose.material.icons.filled.Delete
import androidx.compose.material.icons.filled.ExpandLess
import androidx.compose.material.icons.filled.ExpandMore
import androidx.compose.material.icons.filled.MoreVert
import androidx.compose.material.icons.filled.Refresh
import androidx.compose.material.icons.filled.Settings
import androidx.compose.material.icons.outlined.Article
import androidx.compose.material3.DropdownMenu
import androidx.compose.material3.DropdownMenuItem
import androidx.compose.material3.ExperimentalMaterial3Api
import androidx.compose.material3.FloatingActionButton
import androidx.compose.material3.HorizontalDivider
import androidx.compose.material3.Icon
import androidx.compose.material3.IconButton
import androidx.compose.material3.ListItem
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.collectAsState
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.unit.dp
import kotlinx.coroutines.flow.combine
import kotlinx.coroutines.launch
import org.terst.feedreader.data.AppDatabase
import org.terst.feedreader.data.FeedEntity
import org.terst.feedreader.data.setReaderModeEnabled
import org.terst.feedreader.work.FeedFetchWorker

@OptIn(ExperimentalMaterial3Api::class)
@Composable
fun FeedListScreen(
    onOpenFeed: (String) -> Unit,
    onOpenUnread: () -> Unit,
    onOpenOlder: () -> Unit,
    onOpenSaved: () -> Unit,
    onAddFeed: () -> Unit,
    onSettings: () -> Unit
) {
    val context = LocalContext.current
    val db = remember { AppDatabase.get(context) }
    val scope = rememberCoroutineScope()
    val cutoff = remember { System.currentTimeMillis() - RECENT_WINDOW_MS }

    val feeds by remember {
        combine(db.feedDao().observeAll(), db.articleDao().observeUnreadCounts()) { feeds, counts ->
            val countsByFeed = counts.associate { it.feedId to it.count }
            feeds.map { it to (countsByFeed[it.id] ?: 0) }
        }
    }.collectAsState(initial = emptyList())

    val recentUnreadCount by remember { db.articleDao().observeUnreadCount(cutoff) }.collectAsState(initial = 0)
    val olderUnreadCount by remember { db.articleDao().observeOlderUnreadCount(cutoff) }.collectAsState(initial = 0)
    val savedCount by remember { db.articleDao().observeSavedCount() }.collectAsState(initial = 0)
    var menuExpanded by remember { mutableStateOf(false) }
    var pendingDelete by remember { mutableStateOf<FeedEntity?>(null) }
    // Folders start collapsed -- that's the whole point of grouping once there are enough
    // feeds/folders that the flat list was worth organizing in the first place. Session-only
    // (not persisted): which folders were open isn't something worth remembering across app
    // restarts, per the app's "simple design" scope.
    var expandedFolders by remember { mutableStateOf(setOf<String>()) }
    val snackbarHostState = remember { SnackbarHostState() }

    pendingDelete?.let { feed ->
        ConfirmDialog(
            title = "Unsubscribe from ${feed.title.ifBlank { feed.id }}?",
            text = "Removes its articles. Anything you've saved is kept.",
            confirmLabel = "Unsubscribe",
            onConfirm = {
                scope.launch {
                    db.articleDao().deleteUnsavedByFeed(feed.id)
                    db.feedDao().delete(feed.id)
                }
                pendingDelete = null
            },
            onDismiss = { pendingDelete = null }
        )
    }

    Scaffold(
        topBar = {
            TopAppBar(
                title = { Text("Feeds") },
                actions = {
                    IconButton(onClick = { FeedFetchWorker.fetchNow(context) }) {
                        Icon(Icons.Default.Refresh, contentDescription = "Refresh all")
                    }
                    IconButton(onClick = onSettings) {
                        Icon(Icons.Default.Settings, contentDescription = "Settings")
                    }
                    IconButton(onClick = { menuExpanded = true }) {
                        Icon(Icons.Default.MoreVert, contentDescription = "More")
                    }
                    DropdownMenu(expanded = menuExpanded, onDismissRequest = { menuExpanded = false }) {
                        DropdownMenuItem(
                            text = { Text("Import OPML") },
                            onClick = { menuExpanded = false; onAddFeed() }
                        )
                    }
                }
            )
        },
        floatingActionButton = {
            FloatingActionButton(onClick = onAddFeed) {
                Icon(Icons.Default.Add, contentDescription = "Add feed")
            }
        },
        snackbarHost = { SnackbarHost(snackbarHostState) }
    ) { padding ->
        LazyColumn(modifier = Modifier.fillMaxSize().padding(padding)) {
            item {
                ListItem(
                    headlineContent = { Text("Unread") },
                    trailingContent = { Text(recentUnreadCount.toString()) },
                    modifier = Modifier.fillMaxWidth().clickable { onOpenUnread() }
                )
                HorizontalDivider()
                // The rest of the unread backlog, older than RECENT_WINDOW_MS -- kept
                // out of the main Unread view so a large backlog doesn't bury what's new.
                ListItem(
                    headlineContent = { Text("Older") },
                    trailingContent = { Text(olderUnreadCount.toString()) },
                    modifier = Modifier.fillMaxWidth().clickable { onOpenOlder() }
                )
                HorizontalDivider()
                ListItem(
                    headlineContent = { Text("Saved") },
                    trailingContent = { Text(savedCount.toString()) },
                    modifier = Modifier.fillMaxWidth().clickable { onOpenSaved() }
                )
                SectionHeader("Feeds")
            }

            val failedFeeds = feeds.filter { it.first.lastError != null }
            val okFeeds = feeds.filter { it.first.lastError == null }
            val groupedByFolder = okFeeds.groupBy { it.first.folder }
            val folderNames = groupedByFolder.keys.filterNotNull().sortedBy { it.lowercase() }
            val ungrouped = groupedByFolder[null].orEmpty()

            fun feedRowItems(rows: List<Pair<FeedEntity, Int>>) {
                items(rows, key = { it.first.id }) { (feed, unreadCount) ->
                    FeedRow(
                        feed = feed,
                        unreadCount = unreadCount,
                        onClick = { onOpenFeed(feed.id) },
                        onDelete = { pendingDelete = feed },
                        onToggleReaderMode = {
                            val newEnabled = !feed.readerModeEnabled
                            scope.launch {
                                val message = db.feedDao().setReaderModeEnabled(feed, newEnabled)
                                snackbarHostState.showSnackbar(message)
                            }
                        }
                    )
                    HorizontalDivider()
                }
            }

            if (failedFeeds.isNotEmpty()) {
                item { SectionHeader("Last fetch failed") }
                feedRowItems(failedFeeds)
            }
            for (folder in folderNames) {
                val isExpanded = folder in expandedFolders
                val folderFeeds = groupedByFolder.getValue(folder)
                item {
                    FolderHeader(
                        title = folder,
                        expanded = isExpanded,
                        unreadCount = folderFeeds.sumOf { it.second },
                        onClick = {
                            expandedFolders = if (isExpanded) expandedFolders - folder else expandedFolders + folder
                        }
                    )
                }
                if (isExpanded) feedRowItems(folderFeeds)
            }
            if (ungrouped.isNotEmpty()) {
                if (folderNames.isNotEmpty() || failedFeeds.isNotEmpty()) item { SectionHeader("Other") }
                feedRowItems(ungrouped)
            }
        }
    }
}

@Composable
private fun SectionHeader(title: String) {
    Text(
        title,
        style = MaterialTheme.typography.labelLarge,
        color = MaterialTheme.colorScheme.primary,
        modifier = Modifier.fillMaxWidth().padding(horizontal = 16.dp, vertical = 8.dp)
    )
}

@Composable
private fun FolderHeader(title: String, expanded: Boolean, unreadCount: Int, onClick: () -> Unit) {
    Row(
        verticalAlignment = Alignment.CenterVertically,
        modifier = Modifier.fillMaxWidth().clickable(onClick = onClick).padding(horizontal = 8.dp, vertical = 4.dp)
    ) {
        Icon(
            if (expanded) Icons.Default.ExpandLess else Icons.Default.ExpandMore,
            contentDescription = if (expanded) "Collapse" else "Expand",
            tint = MaterialTheme.colorScheme.primary
        )
        Text(
            title,
            style = MaterialTheme.typography.labelLarge,
            color = MaterialTheme.colorScheme.primary,
            modifier = Modifier.weight(1f).padding(horizontal = 8.dp, vertical = 4.dp)
        )
        // A folder collapsed hides its per-feed unread badges too -- show the total here so
        // collapsing doesn't also hide "is there anything new in here."
        if (unreadCount > 0) {
            Text(unreadCount.toString(), color = MaterialTheme.colorScheme.primary)
            Spacer(modifier = Modifier.width(8.dp))
        }
    }
}

@Composable
private fun FeedRow(
    feed: FeedEntity,
    unreadCount: Int,
    onClick: () -> Unit,
    onDelete: () -> Unit,
    onToggleReaderMode: () -> Unit
) {
    ListItem(
        headlineContent = { Text(feed.title.ifBlank { feed.id }) },
        supportingContent = {
            if (feed.lastError != null) {
                Text("Last fetch failed: ${feed.lastError}")
            }
        },
        trailingContent = {
            Row(verticalAlignment = Alignment.CenterVertically) {
                if (unreadCount > 0) {
                    Text(unreadCount.toString())
                    Spacer(modifier = Modifier.width(8.dp))
                }
                IconButton(onClick = onToggleReaderMode) {
                    Icon(
                        if (feed.readerModeEnabled) Icons.Filled.Article else Icons.Outlined.Article,
                        contentDescription = if (feed.readerModeEnabled)
                            "Reader mode enabled for this feed -- tap to disable"
                        else
                            "Reader mode disabled for this feed -- tap to enable"
                    )
                }
                IconButton(onClick = onDelete) {
                    Icon(Icons.Default.Delete, contentDescription = "Unsubscribe")
                }
            }
        },
        modifier = Modifier.fillMaxWidth().clickable { onClick() }
    )
}