package irc

import data.ServerConfig
import kotlinx.coroutines.*
import kotlinx.coroutines.channels.Channel
import java.io.BufferedReader
import java.io.InputStreamReader
import java.io.OutputStreamWriter
import java.io.PrintWriter
import java.net.Socket
import javax.net.ssl.SSLSocket
import javax.net.ssl.SSLSocketFactory

// TEMP DEBUG (see task: closed-channel-doesn't-receive-messages investigation) - remove
// once the overnight rejoin issue is confirmed fixed. Prefixed so it's easy to grep out.
private fun ircDebug(serverId: String, msg: String) {
    println("[irc-debug][$serverId] $msg")
}

// Extra buffer after end-of-MOTD (376/422) before actually sending on-connect commands -
// see runPostRegistration(). Some networks' services genuinely aren't ready the same
// instant MOTD ends; this is cheap insurance on top of that already-real trigger.
private const val POST_MOTD_IDENTIFY_DELAY_MS = 1500L

// on-connect commands are meant to be raw IRC protocol lines (e.g.
// "PRIVMSG NickServ :IDENTIFY password"), but the app's own chat window teaches
// "/msg NickServ IDENTIFY password" as the correct thing to type (it IS correct there -
// ChannelWindow.kt's onSend translates that shorthand before sending) - an easy, natural
// mistake to reuse that exact phrasing in the on-connect-commands field, which has no such
// translation and just writes the string to the socket byte-for-byte. A real network
// confirmed this: the raw line got rejected outright with "421 Unknown command" before
// NickServ ever saw it, since IRC servers have no "/msg" command. This makes on-connect
// commands tolerant of that shorthand too, so either form works.
private fun translateOnConnectCommand(cmd: String): String {
    val trimmed = cmd.trim()
    if (!trimmed.startsWith("/msg ", ignoreCase = true)) return cmd
    val rest = trimmed.substring(5).trim()
    val spaceIdx = rest.indexOf(' ')
    if (spaceIdx <= 0) return cmd
    val target = rest.substring(0, spaceIdx)
    val message = rest.substring(spaceIdx + 1).trim()
    if (message.isEmpty()) return cmd
    return "PRIVMSG $target :$message"
}

/**
 * Owns one socket to one IRC server. Emits raw parsed lines via onLine.
 * Handles registration (NICK/USER), and basic auto-reconnect with backoff.
 */
class IrcConnection(
    val config: ServerConfig,
    private val scope: CoroutineScope,
    // Channels to rejoin on top of config.autoJoinChannels - the ones a previous connection
    // to this server was in (see ConnectionManager.connect).
    initialChannels: Collection<String> = emptyList(),
    private val onLine: (ParsedLine) -> Unit,
    private val onStatus: (String) -> Unit
) {
    // @Volatile: read from the outbox-consumer coroutine, written from the read-loop
    // coroutine - without it there's no cross-thread visibility guarantee, so the outbox
    // consumer could keep observing a stale non-null `writer` from a socket that already
    // closed (or a stale null after a new one connected), silently mis-routing sends.
    @Volatile private var socket: Socket? = null
    @Volatile private var writer: PrintWriter? = null
    private var readJob: Job? = null
    // @Volatile: disconnect() clears it from the UI thread while the read loop checks it on
    // an IO thread - it's what stops the loop from auto-reconnecting after a /quit.
    @Volatile private var wantConnected = false
    private var backoffMillis = 2000L

    // Every channel we're currently in, whether from config.autoJoinChannels or joined
    // manually mid-session - so a reconnect rejoins everything, not just the original
    // auto-join list.
    private val joinedChannels = java.util.concurrent.CopyOnWriteArraySet<String>(initialChannels)

    fun trackedChannels(): Set<String> = joinedChannels.toSet()

    // Guards runPostRegistration() against running twice for the same connection cycle
    // (376 and 422 are mutually exclusive per RFC, but this is cheap insurance) - reset
    // to false at the top of every connect attempt so a reconnect re-arms it.
    @Volatile private var registeredHandled = false

    // Outgoing lines go through a single serial consumer instead of one
    // scope.launch(Dispatchers.IO) per send() call. That old approach had two problems:
    // (1) no ordering guarantee between independently-scheduled coroutines on a thread
    // pool dispatcher, and (2) if the socket dropped between a send() call being made and
    // its coroutine actually running, `writer` would already be null and the line was
    // silently discarded with no trace - which made a dropped JOIN indistinguishable from
    // one that was never requested. This queue preserves order and gives a single place
    // to log what actually made it onto the wire vs. what got dropped.
    private val outbox = Channel<String>(Channel.UNLIMITED)

    init {
        scope.launch(Dispatchers.IO) {
            for (raw in outbox) {
                val w = writer
                if (w == null) {
                    // Kept (unlike the old per-line CHECKPOINT4 write-confirmation logging,
                    // removed - it fired on every single outbound line and was real
                    // console-I/O overhead under busy-channel volume, per println being
                    // synchronized/blocking) - this specific case should be rare and is
                    // worth knowing about if it ever happens.
                    ircDebug(config.id, "DROPPED (writer is null - not connected): \"$raw\"")
                } else {
                    w.println(raw)
                }
            }
        }
    }

    fun connect() {
        wantConnected = true
        readJob?.cancel()
        readJob = scope.launch(Dispatchers.IO) {
            while (wantConnected && isActive) {
                var fallbackJob: Job? = null
                try {
                    onStatus("Connecting to ${config.host}:${config.port}...")
                    ircDebug(config.id, "connecting to ${config.host}:${config.port} (tracked channels: $joinedChannels)")
                    val sock: Socket = if (config.useTls) {
                        val sslSocket = SSLSocketFactory.getDefault().createSocket(config.host, config.port) as SSLSocket
                        val sslParams = sslSocket.sslParameters
                        sslParams.endpointIdentificationAlgorithm = "HTTPS"
                        sslSocket.sslParameters = sslParams
                        sslSocket.startHandshake()
                        sslSocket
                    } else {
                        Socket(config.host, config.port)
                    }
                    socket = sock
                    // disconnect() can't interrupt a socket that's still being opened, so
                    // check here before registering on a connection nobody wants anymore.
                    ensureActive()
                    val out = PrintWriter(OutputStreamWriter(sock.getOutputStream(), Charsets.UTF_8), true)
                    writer = out

                    // Used to send "CAP REQ :sasl" here whenever config.saslUser was set, but
                    // there was never any AUTHENTICATE/CAP END follow-through - SASL isn't
                    // actually implemented (there's no UI to even set saslUser/saslPass). Per
                    // the IRCv3 CAP spec, a compliant server MUST hold off sending 001 until
                    // it sees CAP END, so starting a negotiation the client can never finish
                    // risked silently stalling registration forever on strict servers -
                    // meaning 001/376/422 (and therefore the on-connect identify command)
                    // would never fire at all. Removed until SASL is actually implemented
                    // end-to-end.
                    out.println("NICK ${config.nick}")
                    out.println("USER ${config.nick} 0 * :${config.nick}")

                    backoffMillis = 2000L
                    onStatus("Connected, registering...")
                    registeredHandled = false
                    // On-connect commands (identify, etc.) used to fire straight off 001 -
                    // technically "registered" but too early on plenty of real networks:
                    // NickServ/services in general aren't guaranteed ready for PRIVMSGs the
                    // instant 001 lands, which is exactly why real clients (mIRC, HexChat,
                    // irssi) fire "perform"/on-connect scripts off end-of-MOTD (376/422)
                    // instead - see runPostRegistration(). This matches that convention, with
                    // an 8s fallback in case a server never sends either (rare, but some
                    // minimal/bouncer-style endpoints omit MOTD numerics entirely).
                    fallbackJob = scope.launch {
                        delay(8000)
                        if (!registeredHandled) {
                            ircDebug(config.id, "no 376/422 within 8s of connecting - running perform+rejoin anyway (fallback)")
                            runPostRegistration()
                        }
                    }

                    val reader = BufferedReader(InputStreamReader(sock.getInputStream(), Charsets.UTF_8))
                    while (isActive) {
                        val line = reader.readLine() ?: break
                        handleRawLine(line)
                    }
                } catch (e: Exception) {
                    // After disconnect() the read fails because we closed the socket
                    // ourselves - that's not an error worth reporting.
                    if (!wantConnected) break
                    onStatus("Connection error: ${e.message}")
                    ircDebug(config.id, "connection dropped: ${e.message} - tracked channels at drop time: $joinedChannels")
                } finally {
                    fallbackJob?.cancel()
                    closeSocketQuietly()
                }

                if (wantConnected) {
                    onStatus("Reconnecting in ${backoffMillis / 1000}s...")
                    ircDebug(config.id, "reconnecting in ${backoffMillis}ms")
                    delay(backoffMillis)
                    backoffMillis = (backoffMillis * 2).coerceAtMost(60_000L)
                }
            }
        }
    }

    private fun handleRawLine(line: String) {
        // Used to log every single raw line here (RECV: "...") - removed. It was the
        // single highest-volume debug line in the app: one per incoming line, every line,
        // forever, and println is synchronized/blocking - a real, measurable cost in a
        // busy channel, not just noise. The specific 001/376/422 confirmations below are
        // once-per-connect and stay.
        if (line.startsWith("PING")) {
            val token = line.substringAfter("PING ")
            send("PONG $token")
            return
        }
        val parsed = parseIrcLine(line) ?: return

        // CTCP requests arrive as a PRIVMSG wrapped in \x01...\x01. VERSION gets
        // handled right here so it never shows up in a channel/PM window - real
        // clients answer these silently too.
        if (parsed.command == "PRIVMSG") {
            val text = parsed.params.getOrNull(1)
            if (text != null && text.startsWith("
") && text.endsWith("
") && text.length > 1) {
                val ctcpBody = text.removePrefix("
").removeSuffix("
")
                val ctcpCommand = ctcpBody.substringBefore(' ').uppercase()
                if (ctcpCommand == "VERSION") {
                    val replyTo = nickFromPrefix(parsed.prefix)
                    if (replyTo != null) {
                        send("NOTICE $replyTo :
VERSION It's an irc client, fucko!
")
                    }
                    return
                }
                // Other CTCP types (ACTION, PING, etc.) fall through to onLine as normal -
                // ACTION in particular still needs to reach ConnectionManager to render as /me.
            }
        }

        if (parsed.command == "001") {
            ircDebug(config.id, "registered (001) - awaiting end-of-MOTD (376/422) before perform+rejoin")
        }
        if (parsed.command == "376" || parsed.command == "422") {
            runPostRegistration()
        }
        onLine(parsed)
    }

    // Runs the on-connect ("perform") commands - NickServ/ChanServ identify, etc. - then
    // rejoins every channel we were actually in (the configured auto-join list plus
    // anything joined manually mid-session, so a reconnect doesn't forget those). Fired
    // off end-of-MOTD rather than bare 001 - see the comment in connect() for why - so
    // identify commands land once the session is actually settled enough for services to
    // reliably act on them.
    private fun runPostRegistration() {
        if (registeredHandled) return
        registeredHandled = true
        // The whole sequence (identify, then rejoin) runs inside this delayed coroutine
        // rather than just delaying the identify send - keeping both here preserves "run
        // identify before joining anything that might require it" (rejoin used to run
        // synchronously right after, which would otherwise now race ahead of a delayed
        // identify send and reach the wire first). The delay itself is a few extra hundred
        // ms of insurance on top of an already-real event (376/422) rather than a fixed
        // guess from connection time - some networks' NickServ genuinely isn't ready to
        // process a command in the same instant MOTD ends.
        scope.launch(Dispatchers.IO) {
            delay(POST_MOTD_IDENTIFY_DELAY_MS)
            config.onConnectCommands.forEach { cmd ->
                if (cmd.isNotBlank()) send(translateOnConnectCommand(cmd))
            }
            val rejoinList = (config.autoJoinChannels + joinedChannels).distinct()
            ircDebug(config.id, "post-registration - rejoining: $rejoinList")
            rejoinList.forEach { ch -> joinChannel(ch) }
        }
    }

    fun send(raw: String) {
        outbox.trySend(raw)
    }

    fun sendMessage(target: String, text: String) {
        send("PRIVMSG $target :$text")
    }

    fun joinChannel(channel: String) {
        joinedChannels.add(channel)
        ircDebug(config.id, "joinChannel($channel) - tracked set now: $joinedChannels")
        send("JOIN $channel")
    }

    fun partChannel(channel: String, reason: String = "") {
        joinedChannels.remove(channel)
        ircDebug(config.id, "partChannel($channel) - tracked set now: $joinedChannels")
        send("PART $channel :$reason")
    }
    fun kick(channel: String, nick: String, reason: String = "") = send("KICK $channel $nick :$reason")
    fun setMode(channel: String, modeChange: String, nick: String) = send("MODE $channel $modeChange $nick")
    fun ban(channel: String, mask: String) = send("MODE $channel +b $mask")

    fun disconnect() {
        wantConnected = false
        scope.launch(Dispatchers.IO) {
            try { writer?.println("QUIT :leaving") } catch (_: Exception) {}
            readJob?.cancel()
            closeSocketQuietly()
            // Ends the outbox consumer - this connection is never reused (a reconnect
            // makes a new IrcConnection), so it would otherwise idle forever.
            outbox.close()
        }
    }

    private fun closeSocketQuietly() {
        try { socket?.close() } catch (_: Exception) {}
        socket = null
        writer = null
    }
}