ferretirc-client/src/main/kotlin/com/shr4pnel/ferretirc/net/MessageParser.kt

package com.shr4pnel.ferretirc.net

import com.shr4pnel.ferretirc.net.messages.ServerMessage
import io.github.oshai.kotlinlogging.KotlinLogging
import io.github.oshai.kotlinlogging.slf4j.logger
import kotlinx.coroutines.channels.Channel
import org.slf4j.helpers.NOPLogger

class MessageParser(val incoming: Channel<String>, enableLogging: Boolean = false) {
    val incomingParsedMessages = Channel<ServerMessage>()
    private val logger = if (enableLogging) KotlinLogging.logger {} else KotlinLogging.logger(NOPLogger.NOP_LOGGER)

    class MessageBuilder {
        private var tags: String? = null
        private var prefix: String? = null
        private lateinit var command: Command

        abstract class Command(open val command: String, open val parameters: List<String>) {
            abstract fun toServerMessage(): ServerMessage

            fun getTrailingParameterIndex() = parameters.indexOfFirst { it.startsWith(":") }

            fun getTrailingParameterString() =
                parameters
                    .subList(getTrailingParameterIndex(), parameters.size)
                    .joinToString(" ")
                    .removePrefix(":")

            fun getNonTrailingParameterString() =
                parameters
                    .subList(0, getTrailingParameterIndex())
                    .joinToString(" ")
                    .removePrefix(":")

            fun getNonTrailingParameters() = getNonTrailingParameterString().split(" ")

            class NamedCommand(override val command: String, override val parameters: List<String>) : Command(command, parameters) {
                override fun toServerMessage() =
                    when (command.uppercase()) {
                        "PONG" -> ServerMessage.Pong(getTrailingParameterString().removePrefix(":"))

                        // TODO MODE, CHANMODE, LOCALMODE
                        "MODE" ->
                            ServerMessage.Mode(
                                parameters.first(),
                                parameters.last().removePrefix(":"),
                            )

                        "NOTICE" ->
                            ServerMessage.Notice(
                                getNonTrailingParameters(),
                                getTrailingParameterString(),
                            )

                        "PRIVMSG" ->
                            ServerMessage.PrivMsg(
                                getNonTrailingParameters(),
                                getTrailingParameterString(),
                            )

                        else -> ServerMessage.UNIMPLEMENTED("$command ${parameters.joinToString(" ")}")
                    }
            }

            class NumericCommand(override val command: String, override val parameters: List<String>) : Command(command, parameters) {
                private enum class RPL(val underlying: Int) {
                    ISUPPORT(5),
                    LISTSTART(321),
                    LIST(322),
                    LISTEND(323),
                    NONE(0xbeef), ;

                    companion object {
                        val rplMap = RPL.entries.associateBy { it.underlying }
                        infix fun from(value: Int) = rplMap[value] ?: NONE
                        infix fun from(value: String) = from(value.toInt())
                    }
                }

                override fun toServerMessage() =
                    when (RPL from command) {
                        RPL.ISUPPORT -> ServerMessage.Numeric.RPL_ISUPPORT(getNonTrailingParameterString())
                        RPL.LISTSTART -> ServerMessage.Numeric.RPL_LISTSTART()
                        RPL.LIST -> ServerMessage.Numeric.RPL_LIST(
                            parameters[1],
                            parameters[2].toInt(),
                            getTrailingParameterString(),
                        )
                        RPL.LISTEND -> ServerMessage.Numeric.RPL_LISTEND()
                        RPL.NONE -> ServerMessage.UNIMPLEMENTED(parameters.toString())
                    }
            }
        }

        /**
         * Messages have this format, as rough ABNF:
         *
         *   message         ::= ['@' <tags> SPACE] [':' <source> SPACE] <command> <parameters> <crlf>
         *   SPACE           ::=  %x20 *( %x20 )   ; space character(s)
         *   crlf            ::=  %x0D %x0A        ; "carriage return" "linefeed"
         *
         * The specific parts of an IRC message are:
         *
         * tags: Optional metadata on a message, starting with ('@', 0x40).
         *
         * source: Optional note of where the message came from, starting with (':', 0x3A).
         *
         * command: The specific command this message represents.
         *
         * parameters: If it exists, data relevant to this specific command.
         *
         * ===================
         *
         * Convert line from server into tokens split on strings and remove elements that belong
         * to different segments of the IRC message e.g. tags, prefixes etc
         */
        fun build(commandList: List<String>): ServerMessage {
            val tokens = commandList.toMutableList()

            // remove tags from strlist if present
            tags =
                if (tokens.first().startsWith("@")) {
                    tokens.removeFirst()
                } else {
                    null
                }

            // remove client prefix (nick&opt hostname) if present
            prefix =
                if (tokens.first().startsWith(":")) {
                    tokens.removeFirst()
                } else {
                    null
                }

            // get command e.g. PING
            val commandStr = tokens.removeFirst()

            // Check if command is a numeric (RPL/ERR) or named
            command =
                if (commandStr.toIntOrNull() == null) {
                    Command.NamedCommand(commandStr, tokens)
                } else {
                    Command.NumericCommand(commandStr, tokens)
                }

            return command.toServerMessage()
        }

        fun build(command: String) = build(command.split(" "))
    }

    suspend fun start() {
        val builder = MessageBuilder()
        for (msg in incoming) {
            logger.debug { "Receiving: $msg" }
            incomingParsedMessages.send(builder.build(msg))
        }
    }
}