// SPDX-License-Identifier: MIT
// SPDX-FileCopyrightText: 2023 mysubarumq
// SPDX-FileContributor: alex-savin

package app

import (
	"context"
	"errors"
	"log/slog"
	"runtime"
	"sync/atomic"
	"time"

	"git.savin.nyc/alex/mysubaru-mq/bus"
	"git.savin.nyc/alex/mysubaru-mq/config"
	"git.savin.nyc/alex/mysubaru-mq/listeners"
	"git.savin.nyc/alex/mysubaru-mq/system"
	"git.savin.nyc/alex/mysubaru-mq/workers"
)

const (
	AppVersion = "1.0.1"      // the current application version.
	AppName    = "mysubarumq" // the short app name
)

var (
	ErrWorkerIDExists   = errors.New("worker id already exists")
	ErrListenerIDExists = errors.New("listener id already exists")
)

type App struct {
	Options   *config.Config       // configurable server options
	Workers   *workers.Workers     // worker are network interfaces which listen for new connections
	Listeners *listeners.Listeners // listeners are network interfaces which listen for new connections
	Info      *system.Info         // values about the server commonly known as $SYS topics
	Log       *slog.Logger         // minimal no-alloc logger
	bus       *bus.Bus             //
	hooks     *Hooks               // hooks contains hooks for extra functionality such as auth and persistent storage
	loop      *loop                // loop contains tickers for the system event loop
	cancel    context.CancelFunc   //
	// done    chan bool          // indicate that the server is ending
}

// loop contains interval tickers for the system events loop.
type loop struct {
	sysInfo *time.Ticker // interval ticker for sending updating $SYS topics
}
type Info struct {
	AppVersion  string `json:"version"`      // the current version of the server
	Started     int64  `json:"started"`      // the time the server started in unix seconds
	MemoryAlloc int64  `json:"memory_alloc"` // memory currently allocated
	Threads     int64  `json:"threads"`      // number of active goroutines, named as threads for platform ambiguity
	Time        int64  `json:"time"`         // current time on the server
	Uptime      int64  `json:"uptime"`       // the number of seconds the server has been online
}

// EstablishConnection establishes a new client when a listener accepts a new connection.
// func (a *App) EstablishConnection(listener string, c net.Conn) error {
// 	cl := a.NewClient(c, listener, "", false)
// 	return a.attachClient(cl, listener)
// }

// New returns a new instance of mochi mqtt broker. Optional parameters
// can be specified to override some default settings (see Options).
func New(opts *config.Config, bus *bus.Bus, logger *slog.Logger) *App {
	if opts == nil {
		slog.Error("empty config")
	}

	ctx, cancel := context.WithCancel(context.Background())

	var m runtime.MemStats
	runtime.ReadMemStats(&m)
	a := &App{
		Options:   opts,
		Workers:   workers.New(),
		Listeners: listeners.New(),
		Info: &system.Info{
			Version:     AppVersion,
			Started:     time.Now().Unix(),
			MemoryAlloc: int64(m.HeapInuse),
			Threads:     int64(runtime.NumGoroutine()),
			// Time:        time.Now().Unix(),
			// Uptime:      time.Now().Unix() - atomic.LoadInt64(&a.Started),
		},
		Log: logger,
		bus: bus,
		hooks: &Hooks{
			Log: logger,
		},
		loop: &loop{
			sysInfo: time.NewTicker(time.Second * time.Duration(1)),
		},
		cancel: cancel,
		// done:   make(chan bool),
	}

	chAppWorker, err := a.bus.Subscribe("app:connected", "mysubarumq", a.Options.SubscriptionSize["app:connected"])
	if err != nil {
		a.Log.Error("couldn't subscribe to a channel", "error", err.Error())
	}

	go a.eventLoop(ctx, chAppWorker)

	return a
}

// AddHook attaches a new Hook to the server. Ideally, this should be called
// before the server is started with s.Serve().
func (a *App) AddHook(hook Hook, config any) error {
	nl := a.Log.With("hook", hook.ID())
	hook.SetOpts(nl)

	a.Log.Info("added hook", "hook", hook.ID())
	return a.hooks.Add(hook, config)
}

// AddListener adds a new network listener to the server, for receiving incoming client connections.
func (a *App) AddWorker(w workers.Worker) error {
	if _, ok := a.Workers.Get(w.ID()); ok {
		return ErrWorkerIDExists
	}

	nl := a.Log.With(slog.String("worker", w.ID()))
	err := w.Init(nl)
	if err != nil {
		return err
	}

	a.Workers.Add(w)

	a.Log.Info("attached worker", "id", w.ID(), "type", w.Type())
	return nil
}

// AddListener adds a new network listener to the server, for receiving incoming client connections.
func (a *App) AddListener(l listeners.Listener) error {
	if _, ok := a.Listeners.Get(l.ID()); ok {
		return ErrListenerIDExists
	}

	nl := a.Log.With(slog.String("listener", l.ID()))
	err := l.Init(nl)
	if err != nil {
		return err
	}

	a.Listeners.Add(l)

	a.Log.Info("attached listener", "id", l.ID(), "protocol", l.Protocol(), "address", l.Address())
	return nil
}

// Serve starts the event loops responsible for establishing client connections
// on all attached listeners, publishing the system topics, and starting all hooks.
func (a *App) Serve() error {
	a.Log.Info("mysubarumq starting", "version", AppVersion)
	defer a.Log.Info("mysubarumq started")

	a.Workers.ServeAll()   // start listening on all workers.
	a.Listeners.ServeAll() // start listening on all listeners.
	a.publishSysTopics()
	a.hooks.OnStarted()

	return nil
}

// Close attempts to gracefully shut down the server, all listeners, clients, and stores.
func (a *App) Close() error {
	// close(a.done)
	a.cancel()
	a.Log.Info("gracefully stopping mysubarumq")
	a.Workers.CloseAll()
	a.Listeners.CloseAll()
	a.hooks.OnStopped()
	a.hooks.Stop()

	a.Log.Info("mysubarumq stopped")
	return nil
}

// eventLoop loops forever
func (a *App) eventLoop(ctx context.Context, chAppWorker chan bus.Event) {
	a.Log.Info("app communication event loop started")
	defer a.Log.Info("app communication event loop halted")

	for {
		select {
		case <-a.loop.sysInfo.C:
			a.publishSysTopics()
		case event := <-chAppWorker:
			message := event.Data.(*bus.ConnectionStatus)
			a.Log.Info("got a message from worker", "worker", message.WorkerID, "type", message.WorkerType, "isconnected", message.IsConnected)
			if !message.IsConnected {
				a.hooks.OnWorkerDisconnected()
				a.Workers.Close(message.WorkerID)
			}
			a.hooks.OnWorkerConnected()
		case <-ctx.Done():
			a.Log.Info("stopping app communication event loop")
			return
		}
	}
}

// publishSysTopics publishes the current values to the server $SYS topics.
// Due to the int to string conversions this method is not as cheap as
// some of the others so the publishing interval should be set appropriately.
func (a *App) publishSysTopics() {
	var m runtime.MemStats
	runtime.ReadMemStats(&m)
	atomic.StoreInt64(&a.Info.MemoryAlloc, int64(m.HeapInuse))
	atomic.StoreInt64(&a.Info.Threads, int64(runtime.NumGoroutine()))
	atomic.StoreInt64(&a.Info.Time, time.Now().Unix())
	atomic.StoreInt64(&a.Info.Uptime, time.Now().Unix()-atomic.LoadInt64(&a.Info.Started))

	a.hooks.OnSysInfoTick(a.Info)
}