//
//  XPCClient.swift
//  kordophone2
//
//  Created by James Magahern on 8/24/25.
//

import Foundation
import ServiceManagement
import XPC

private let serviceName = "net.buzzert.kordophonecd"

final class XPCClient
{
    private var connection: xpc_connection_t?
    private let connectionQueue = DispatchQueue(label: "net.buzzert.kordophone.xpc.connection")
    private var isReconnecting: Bool = false
    private var reconnectAttempt: Int = 0
    private let signalLock = NSLock()
    private var signalSinks: [UUID: (Signal) -> Void] = [:]
    private var didSubscribeSignals: Bool = false
    
    static let appService: SMAppService = {
        do {
            let service = SMAppService.agent(plistName: "net.buzzert.kordophonecd.plist")
            if service.status != .enabled {
                try service.register()
            }
            
            return service
        } catch {
            print("Unable to register agent: \(error)")
            fatalError()
        }
    }()

    init() {
        _ = Self.appService
        connect()
    }
    
    public func eventStream() -> AsyncStream<Signal> {
        // Auto-subscribe on first stream creation
        if !didSubscribeSignals {
            didSubscribeSignals = true
            Task {
                try? await subscribeToSignals()
            }
        }

        return AsyncStream { continuation in
            let id = UUID()
            signalLock.withLock {
                signalSinks[id] = { signal in
                    continuation.yield(signal)
                }
            }

            continuation.onTermination = { [weak self] _ in
                guard let self else { return }
                _ = self.signalLock.withLock {
                    self.signalSinks.removeValue(forKey: id)
                }
            }
        }
    }
    
    public func getVersion() async throws -> String {
        let req = makeRequest(method: "GetVersion")
        guard let reply = try await sendSync(req), xpc_get_type(reply) == XPC_TYPE_DICTIONARY else { throw Error.typeError }
        if let cstr = xpc_dictionary_get_string(reply, "version") {
            return String(cString: cstr)
        }
        
        throw Error.typeError
    }

    public func getConversations(limit: Int = 100, offset: Int = 0) async throws -> [Serialized.Conversation] {
        var args: [String: xpc_object_t] = [:]
        args["limit"] = xpcString(String(limit))
        args["offset"] = xpcString(String(offset))

        let req = makeRequest(method: "GetConversations", arguments: args)
        guard let reply = try await sendSync(req), xpc_get_type(reply) == XPC_TYPE_DICTIONARY else { return [] }
        guard let items = xpc_dictionary_get_value(reply, "conversations"), xpc_get_type(items) == XPC_TYPE_ARRAY else { return [] }

        var results: [Serialized.Conversation] = []
        xpc_array_apply(items) { _, element in
            if xpc_get_type(element) == XPC_TYPE_DICTIONARY, let conv = Serialized.Conversation(xpc: element) {
                results.append(conv)
            }
            
            return true
        }
        return results
    }

    public func syncConversation(conversationId: String) async throws {
        let req = makeRequest(method: "SyncConversation", arguments: ["conversation_id": xpcString(conversationId)])
        _ = try await sendSync(req)
    }

    public func syncConversationList() async throws {
        let req = makeRequest(method: "SyncConversationList")
        _ = try await sendSync(req)
    }

    public func markConversationAsRead(conversationId: String) async throws {
        let req = makeRequest(method: "MarkConversationAsRead", arguments: ["conversation_id": xpcString(conversationId)])
        _ = try await sendSync(req)
    }

    public func getMessages(conversationId: String, limit: Int = 100, offset: Int = 0) async throws -> [Serialized.Message] {
        var args: [String: xpc_object_t] = [:]
        args["conversation_id"] = xpcString(conversationId)
        args["limit"] = xpcString(String(limit))
        args["offset"] = xpcString(String(offset))

        let req = makeRequest(method: "GetMessages", arguments: args)
        guard let reply = try await sendSync(req), xpc_get_type(reply) == XPC_TYPE_DICTIONARY else { return [] }
        guard let items = xpc_dictionary_get_value(reply, "messages"), xpc_get_type(items) == XPC_TYPE_ARRAY else { return [] }

        var results: [Serialized.Message] = []
        xpc_array_apply(items) { _, element in
            if xpc_get_type(element) == XPC_TYPE_DICTIONARY, let msg = Serialized.Message(xpc: element) {
                results.append(msg)
            }
            
            return true
        }

        return results
    }

    public func sendMessage(conversationId: String, message: String, transferGuids: Set<String>) async throws {
        var args: [String: xpc_object_t] = [:]
        args["conversation_id"] = xpcString(conversationId)
        args["text"] = xpcString(message)
        
        if !transferGuids.isEmpty {
            args["attachment_guids"] = xpcStringArray(transferGuids)
        }

        let req = makeRequest(method: "SendMessage", arguments: args)
        guard let reply = try await sendSync(req), xpc_get_type(reply) == XPC_TYPE_DICTIONARY else { throw Error.typeError }
    }

    public func getAttachmentInfo(attachmentId: String) async throws -> AttachmentInfo {
        var args: [String: xpc_object_t] = [:]
        args["attachment_id"] = xpcString(attachmentId)

        let req = makeRequest(method: "GetAttachmentInfo", arguments: args)
        guard let reply = try await sendSync(req), xpc_get_type(reply) == XPC_TYPE_DICTIONARY else { throw Error.typeError }
        
        return AttachmentInfo(
            path: reply["path"] ?? "",
            previewPath: reply["preview_path"] ?? "",
            isDownloaded: reply["is_downloaded"] ?? false,
            isPreviewDownloaded: reply["is_preview_downloaded"] ?? false
        )
    }

    public func downloadAttachment(attachmentId: String, preview: Bool, awaitCompletion: Bool = false) async throws {
        var args: [String: xpc_object_t] = [:]
        args["attachment_id"] = xpcString(attachmentId)
        args["preview"] = xpcString(preview ? "true" : "false")

        let req = makeRequest(method: "DownloadAttachment", arguments: args)
        _ = try await sendSync(req)

        if awaitCompletion {
            // Wait for downloaded event
            let _ = await eventStream().first { $0 == .attachmentDownloaded(attachmentId: attachmentId) }
        }
    }
    
    public func uploadAttachment(path: String) async throws -> String {
        var args: [String: xpc_object_t] = [:]
        args["path"] = xpcString(path)

        let req = makeRequest(method: "UploadAttachment", arguments: args)
        guard let reply = try await sendSync(req), xpc_get_type(reply) == XPC_TYPE_DICTIONARY else { throw Error.typeError }
        guard let guid: String = reply["upload_guid"] else { throw Error.encodingError }
        return guid
    }

    public func openAttachmentFileHandle(attachmentId: String, preview: Bool) async throws -> FileHandle {
        var args: [String: xpc_object_t] = [:]
        args["attachment_id"] = xpcString(attachmentId)
        args["preview"] = xpcString(preview ? "true" : "false")

        let req = makeRequest(method: "OpenAttachmentFd", arguments: args)
        guard let reply = try await sendSync(req), xpc_get_type(reply) == XPC_TYPE_DICTIONARY else { throw Error.typeError }

        let fd = xpc_dictionary_dup_fd(reply, "fd")
        let fileHandler = FileHandle(fileDescriptor: fd, closeOnDealloc: true)
        
        if fd < 0 { throw Error.badFileHandle }
        
        return fileHandler
    }

    public func getSettings() async throws -> Serialized.Settings {
        let req = makeRequest(method: "GetAllSettings")
        guard let reply = try await sendSync(req), xpc_get_type(reply) == XPC_TYPE_DICTIONARY else { throw Error.typeError }
        return Serialized.Settings.fromXPC(reply) ?? Serialized.Settings(serverUrl: "", username: "")
    }

    public func setSettings(settings: Serialized.Settings) async throws {
        let req = makeRequest(
            method: "UpdateSettings", 
            arguments: [
                "server_url": xpcString(settings.serverUrl), 
                "username": xpcString(settings.username),
            ]
        )
        
        _ = try await sendSync(req)
    }
    
    // MARK: - Types

    struct AttachmentInfo: Decodable
    {
        let path: String
        let previewPath: String
        let isDownloaded: Bool
        let isPreviewDownloaded: Bool
    }
    
    enum Error: Swift.Error
    {
        case typeError
        case encodingError
        case badFileHandle
        case connectionError
    }
    
    enum Signal: Equatable
    {
        case conversationsUpdated
        case messagesUpdated(conversationId: String)
        case attachmentDownloaded(attachmentId: String)
        case attachmentUploaded(uploadGuid: String, attachmentGuid: String)
        case updateStreamReconnected
    }
}

extension XPCClient
{
    private func connect() {
        connectionQueue.async { [weak self] in
            guard let self else { return }
            
            if let existing = connection {
                xpc_connection_cancel(existing)
                connection = nil
            }

            let newConn = xpc_connection_create_mach_service(serviceName, nil, 0)
            let handler: xpc_handler_t = { [weak self] event in
                self?.handleIncomingXPCEvent(event)
            }
            xpc_connection_set_event_handler(newConn, handler)
            xpc_connection_resume(newConn)

            self.connection = newConn
            self.isReconnecting = false
            self.reconnectAttempt = 0
        }

        if didSubscribeSignals {
            Task { try? await subscribeToSignals() }
        }
    }

    private func scheduleReconnect() {
        connectionQueue.async { [weak self] in
            guard let self else { return }
            
            if self.isReconnecting { return }
            self.isReconnecting = true

            let attempt = self.reconnectAttempt
            self.reconnectAttempt += 1
            
            let delaySeconds = min(pow(2.0, Double(attempt)), 30.0)
            self.connectionQueue.asyncAfter(deadline: .now() + delaySeconds) { [weak self] in
                self?.connect()
            }
        }
    }

    private func subscribeToSignals() async throws {
        let req = makeRequest(method: "SubscribeSignals")
        _ = try await sendSync(req)
    }

    private func makeRequest(method: String, arguments: [String: xpc_object_t]? = nil) -> xpc_object_t {
        let dict = xpc_dictionary_create(nil, nil, 0)
        xpc_dictionary_set_string(dict, "method", method)
        if let args = arguments {
            let argsDict = xpc_dictionary_create(nil, nil, 0)
            for (k, v) in args {
                k.withCString { cKey in
                    xpc_dictionary_set_value(argsDict, cKey, v)
                }
            }
            xpc_dictionary_set_value(dict, "arguments", argsDict)
        }
        return dict
    }

    private func xpcString(_ s: String) -> xpc_object_t {
        return s.withCString { ptr in xpc_string_create(ptr) }
    }

    private func xpcStringArray(_ set: Set<String>) -> xpc_object_t {
        let array = xpc_array_create(nil, 0)
        for str in set {
            xpc_array_append_value(array, xpcString(str))
        }
        
        return array
    }

    private func sendSync(_ request: xpc_object_t) async throws -> xpc_object_t? {
        try await withCheckedThrowingContinuation { continuation in
            let conn: xpc_connection_t? = self.connectionQueue.sync { self.connection }
            guard let conn else {
                self.scheduleReconnect()
                continuation.resume(throwing: Error.connectionError)
                return
            }

            xpc_connection_send_message_with_reply(conn, request, DispatchQueue.global(qos: .userInitiated)) { r in
                switch xpc_get_type(r) {
                    case XPC_TYPE_ERROR:
                        if r.isInterruptionError {
                            self.scheduleReconnect()
                            continuation.resume(throwing: Error.connectionError)
                        } else {
                            continuation.resume(throwing: Error.typeError)
                        }

                    case XPC_TYPE_DICTIONARY:
                        continuation.resume(returning: r)
                        
                    default:
                        continuation.resume(throwing: Error.typeError)
                }
            }
        }
    }

    private func handleIncomingXPCEvent(_ event: xpc_object_t) {
        switch xpc_get_type(event) {
        case XPC_TYPE_DICTIONARY:
            guard let eventDict = XPCDictionary(event), let name: String = eventDict["name"] else { return }

            let args = eventDict.object("arguments").flatMap { XPCDictionary($0) }
            let signal: Signal? = {
                switch name {
                case "ConversationsUpdated":
                    return .conversationsUpdated
                case "MessagesUpdated":
                    if let args, let cid: String = args["conversation_id"] { return .messagesUpdated(conversationId: cid) }
                    return nil
                case "AttachmentDownloadCompleted":
                    if let args, let aid: String = args["attachment_id"] { return .attachmentDownloaded(attachmentId: aid) }
                    return nil
                case "AttachmentUploadCompleted":
                    if let args,
                       let uploadGuid: String = args["upload_guid"],
                       let attachmentGuid: String = args["attachment_guid"] {
                        return .attachmentUploaded(uploadGuid: uploadGuid, attachmentGuid: attachmentGuid)
                    }
                    return nil
                case "UpdateStreamReconnected":
                    return .updateStreamReconnected
                default:
                    return nil
                }
            }()

            if let signal {
                signalLock.lock()
                let sinks = signalSinks.values
                signalLock.unlock()
                for sink in sinks { sink(signal) }
            }

        case XPC_TYPE_ERROR:
            if event.isInterruptionError {
                scheduleReconnect()
            }
        default:
            break
        }
    }
}

extension xpc_object_t
{
    var isInterruptionError: Bool {
        return (
            xpc_equal(self, XPC_ERROR_CONNECTION_INTERRUPTED) ||
            xpc_equal(self, XPC_ERROR_CONNECTION_INVALID) ||
            xpc_equal(self, XPC_ERROR_TERMINATION_IMMINENT)
         )
    }
}