package com.example.aiapp

import androidx.activity.compose.BackHandler
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.combinedClickable
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Column
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.height
import androidx.compose.foundation.layout.heightIn
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.width
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.material3.AlertDialog
import androidx.compose.material3.CardDefaults
import androidx.compose.material3.CircularProgressIndicator
import androidx.compose.material3.LocalContentColor
import androidx.compose.material3.MaterialTheme
import androidx.compose.material3.OutlinedCard
import androidx.compose.material3.Text
import androidx.compose.material3.TextButton
import androidx.compose.runtime.Composable
import androidx.compose.runtime.LaunchedEffect
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableIntStateOf
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.Dispatchers
import kotlinx.coroutines.launch
import kotlinx.coroutines.withContext

/**
 * What a session has running beside the turn you are reading: its background tasks, then its
 * subagents, in the panel [SidePanels] slides over it from the right.
 *
 * [active] is whether the panel is being looked at: the lists are fetched then rather than on
 * composition, since the panel is composed for every session whether or not anybody opens it.
 *
 * [backgroundTasks] is the live count from the session's own event stream, and is what the
 * background list is refetched against: a card for work that has since finished is a stale
 * measurement drawn as a current one, which is the one thing a list of what is running now must not
 * do.
 *
 * Both lists are items of one lazy column rather than two stacked scrollers, so expanding the
 * background section pushes the subagents down without either being able to run off the panel.
 */
@Composable
fun SubagentPanel(
    settings: ServerSettings,
    summary: SessionSummary,
    active: Boolean,
    backgroundTasks: Int,
    onClose: () -> Unit,
    onOpenSubagent: (SubagentSummary) -> Unit,
) {
    val scope = rememberCoroutineScope()
    val context = LocalContext.current
    val transcriptCache = remember(settings) { TranscriptCache(cacheRoot(context, settings)) }
    var rows by
        remember(summary.id) { mutableStateOf<LoadState<List<SubagentSummary>>>(LoadState.Loading) }
    var selected by remember(summary.id) { mutableStateOf(setOf<String>()) }
    var deleting by remember(summary.id) { mutableStateOf(setOf<String>()) }
    var deleteError by remember(summary.id) { mutableStateOf<String?>(null) }
    var confirming by remember(summary.id) { mutableStateOf<List<SubagentSummary>?>(null) }
    var refreshToken by remember(summary.id) { mutableIntStateOf(0) }
    var background by
        remember(summary.id) {
            mutableStateOf<LoadState<List<BackgroundTaskSummary>?>>(LoadState.Loading)
        }
    var backgroundExpanded by remember(summary.id) { mutableStateOf(false) }

    LaunchedEffect(active, refreshToken) {
        if (!active) return@LaunchedEffect
        rows = LoadState.Loading
        rows =
            try {
                val fetched = withContext(Dispatchers.IO) { fetchSubagents(settings, summary.id) }
                selected = selected intersect fetched.mapTo(mutableSetOf()) { it.id }
                LoadState.Loaded(fetched)
            } catch (e: ApiException) {
                LoadState.failed(e)
            }
    }

    // No reset to Loading on a refetch: the spinner belongs to the first fetch, and one flashed
    // over the list at every start and end would blink precisely when something happened.
    LaunchedEffect(active, backgroundTasks, refreshToken) {
        if (!active || backgroundTasks == 0) return@LaunchedEffect
        background =
            try {
                LoadState.Loaded(
                    withContext(Dispatchers.IO) { fetchBackgroundTasks(settings, summary.id) }
                )
            } catch (e: ApiException) {
                LoadState.failed(e)
            }
    }

    BackHandler(enabled = selected.isNotEmpty()) { selected = emptySet() }

    val ordered = (rows as? LoadState.Loaded)?.value?.let(::subagentOrder)

    Column(Modifier.fillMaxSize()) {
        Row(
            horizontalArrangement = Arrangement.End,
            verticalAlignment = Alignment.CenterVertically,
            modifier = Modifier.fillMaxWidth().padding(horizontal = 16.dp),
        ) {
            MarkButton("Close panel", onClose) { Chevron(Pointing.Right) }
        }

        LazyColumn(
            verticalArrangement = Arrangement.spacedBy(8.dp),
            modifier = Modifier.weight(1f).padding(horizontal = 16.dp),
        ) {
            backgroundTaskSection(
                count = backgroundTasks,
                tasks = background,
                expanded = backgroundExpanded,
                onToggle = { backgroundExpanded = !backgroundExpanded },
                onRetry = { refreshToken++ },
            )
            item(key = "subagents-heading") { PanelSectionHeading("Subagents") }
            when (val state = rows) {
                is LoadState.Loading ->
                    item(key = "subagents-loading") {
                        CircularProgressIndicator(modifier = Modifier.width(24.dp).height(24.dp))
                    }
                is LoadState.Error ->
                    item(key = "subagents-error") {
                        Column {
                            Text(
                                state.message,
                                color = MaterialTheme.colorScheme.error,
                                style = MaterialTheme.typography.bodySmall,
                            )
                            TextButton(onClick = { refreshToken++ }) { Text("Try again") }
                        }
                    }
                is LoadState.Loaded ->
                    if (ordered.isNullOrEmpty()) {
                        item(key = "subagents-empty") {
                            Text(
                                "No subagents in this session.",
                                color = MaterialTheme.colorScheme.onSurfaceVariant,
                                style = MaterialTheme.typography.bodyMedium,
                            )
                        }
                    } else {
                        uniqueItems(ordered, key = { it.id }) { subagent ->
                            SubagentCard(
                                subagent = subagent,
                                selected = subagent.id in selected,
                                selecting = selected.isNotEmpty(),
                                deleting = subagent.id in deleting,
                                onClick = { onOpenSubagent(subagent) },
                                onSelect = {
                                    selected =
                                        if (subagent.id in selected) selected - subagent.id
                                        else selected + subagent.id
                                },
                            )
                        }
                    }
            }
        }

        if (selected.isNotEmpty()) {
            val picked = ordered.orEmpty().filter { it.id in selected }
            SubagentSelectionBar(
                picked = picked,
                onDelete = { confirming = picked },
                modifier = Modifier.padding(horizontal = 16.dp),
            )
        }
        deleteError?.let {
            Text(
                it,
                color = MaterialTheme.colorScheme.error,
                style = MaterialTheme.typography.bodySmall,
                modifier = Modifier.padding(horizontal = 16.dp, vertical = 8.dp),
            )
        }
    }

    confirming?.let { picked ->
        AlertDialog(
            onDismissRequest = { confirming = null },
            title = {
                Text(
                    if (picked.size == 1) "Delete this subagent?"
                    else "Delete ${picked.size} subagents?"
                )
            },
            text = {
                Text(
                    (if (picked.size == 1) "\"${picked.first().title}\"\n\n" else "") +
                        "A subagent's transcript is the only record of what it did: the session " +
                        "that started it kept just the Task call. Nothing else has a copy, so " +
                        "this can't be undone. The session itself is untouched."
                )
            },
            confirmButton = {
                TextButton(
                    onClick = {
                        confirming = null
                        selected = emptySet()
                        val ids = picked.map { it.id }
                        val gone = ids.toSet()
                        deleting += gone
                        deleteError = null
                        scope.launch {
                            try {
                                withContext(Dispatchers.IO) {
                                    deleteSubagents(settings, summary.id, ids)
                                    gone.forEach {
                                        transcriptCache
                                            .session(TranscriptAddress(summary.id, it))
                                            .purge()
                                    }
                                }
                                val loaded = rows
                                if (loaded is LoadState.Loaded) {
                                    rows =
                                        LoadState.Loaded(loaded.value.filterNot { it.id in gone })
                                }
                            } catch (e: ApiException) {
                                deleteError = e.message ?: "Delete failed"
                            } finally {
                                deleting -= gone
                            }
                        }
                    }
                ) {
                    Text("Delete", color = MaterialTheme.colorScheme.error)
                }
            },
            dismissButton = { TextButton(onClick = { confirming = null }) { Text("Cancel") } },
        )
    }
}

private fun subagentOrder(rows: List<SubagentSummary>): List<SubagentSummary> =
    rows.sortedWith(
        compareByDescending<SubagentSummary> { it.status == "running" }
            .thenByDescending { it.lastActivity }
    )

@OptIn(ExperimentalFoundationApi::class)
@Composable
private fun SubagentCard(
    subagent: SubagentSummary,
    selected: Boolean,
    selecting: Boolean,
    deleting: Boolean,
    onClick: () -> Unit,
    onSelect: () -> Unit,
) {
    BusyItem(label = if (deleting) "deleting" else null) {
        OutlinedCard(
            colors =
                if (selected)
                    CardDefaults.outlinedCardColors(
                        containerColor = MaterialTheme.colorScheme.secondaryContainer,
                        contentColor = MaterialTheme.colorScheme.onSecondaryContainer,
                    )
                else CardDefaults.outlinedCardColors(),
            modifier =
                Modifier.fillMaxWidth()
                    .combinedClickable(
                        enabled = !deleting,
                        onClick = { if (selecting) onSelect() else onClick() },
                        onLongClick = onSelect,
                    ),
        ) {
            Column(Modifier.padding(horizontal = 12.dp, vertical = 8.dp)) {
                Text(subagent.title, style = MaterialTheme.typography.titleSmall)
                Spacer(Modifier.height(2.dp))
                Row(Modifier.fillMaxWidth()) {
                    Text(
                        subagentStatusLabel(subagent.status),
                        style = MaterialTheme.typography.bodySmall,
                        color = MaterialTheme.colorScheme.onSurfaceVariant,
                        modifier = Modifier.weight(1f),
                    )
                    Text(
                        relativeTime(subagent.lastActivity),
                        style = MaterialTheme.typography.bodySmall,
                        color = MaterialTheme.colorScheme.onSurfaceVariant,
                    )
                }
            }
        }
    }
}

@Composable
private fun SubagentSelectionBar(
    picked: List<SubagentSummary>,
    onDelete: () -> Unit,
    modifier: Modifier = Modifier,
) {
    val running = picked.count { it.status == "running" }
    Row(
        verticalAlignment = Alignment.CenterVertically,
        modifier = modifier.fillMaxWidth().heightIn(min = 48.dp),
    ) {
        Text(
            if (running == 0) "${picked.size} selected" else "$running still running",
            style = MaterialTheme.typography.bodySmall,
            color = MaterialTheme.colorScheme.onSurfaceVariant,
            modifier = Modifier.weight(1f),
        )
        TextButton(onClick = onDelete, enabled = running == 0) {
            Text(
                "Delete",
                color =
                    if (running == 0) MaterialTheme.colorScheme.error
                    else LocalContentColor.current,
            )
        }
    }
}

private fun subagentStatusLabel(status: String) =
    when (status) {
        "running" -> "running"
        "exited" -> "finished"
        else -> "unknown"
    }