package mq

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net"
	"time"

	"github.com/oarkflow/xid"
	"github.com/oarkflow/xsync"

	"github.com/oarkflow/mq/utils"
)

type Handler func(context.Context, Task) Result

type Broker struct {
	queues       *xsync.MapOf[string, *Queue]
	taskCallback func(context.Context, *Task) error
}

type Queue struct {
	name     string
	conn     map[net.Conn]struct{}
	messages *xsync.MapOf[string, *Task]
	deferred *xsync.MapOf[string, *Task]
}

type Task struct {
	ID           string          `json:"id"`
	Payload      json.RawMessage `json:"payload"`
	CreatedAt    time.Time       `json:"created_at"`
	ProcessedAt  time.Time       `json:"processed_at"`
	CurrentQueue string          `json:"current_queue"`
	Result       json.RawMessage `json:"result"`
	Status       string          `json:"status"`
	Error        error           `json:"error"`
}

type CMD int

const (
	SUBSCRIBE CMD = iota + 1
	STOP
)

type Command struct {
	Command   CMD    `json:"command"`
	Queue     string `json:"queue"`
	MessageID string `json:"message_id"`
	Error     string `json:"error,omitempty"`
}

type Result struct {
	Command   string          `json:"command"`
	Payload   json.RawMessage `json:"payload"`
	Queue     string          `json:"queue"`
	MessageID string          `json:"message_id"`
	Error     error           `json:"error"`
	Status    string          `json:"status"`
}

func NewBroker(callback ...func(context.Context, *Task) error) *Broker {
	broker := &Broker{
		queues: xsync.NewMap[string, *Queue](),
	}
	if len(callback) > 0 {
		broker.taskCallback = callback[0]
	}
	return broker
}

func (b *Broker) NewQueue(qName string) {
	if _, ok := b.queues.Get(qName); !ok {
		b.queues.Set(qName, &Queue{
			name:     qName,
			messages: xsync.NewMap[string, *Task](),
			deferred: xsync.NewMap[string, *Task](),
		})
	}
}

func (b *Broker) Send(ctx context.Context, cmd Command) error {
	queue, ok := b.queues.Get(cmd.Queue)
	if !ok || queue == nil {
		return errors.New("invalid queue or not exists")
	}
	for client := range queue.conn {
		err := utils.Write(ctx, client, cmd)
		if err != nil {
			return err
		}
	}
	return nil
}

func (b *Broker) Publish(ctx context.Context, message Task, queueName string) error {
	queue, err := b.AddMessageToQueue(&message, queueName)
	if err != nil {
		return err
	}
	if len(queue.conn) == 0 {
		queue.deferred.Set(xid.New().String(), &message)
		fmt.Println("task deferred as no conn are connected", queueName)
		return nil
	}
	for client := range queue.conn {
		err = utils.Write(ctx, client, message)
		if err != nil {
			return err
		}
	}
	return nil
}

func (b *Broker) AddMessageToQueue(message *Task, queueName string) (*Queue, error) {
	queue, ok := b.queues.Get(queueName)
	if !ok {
		return nil, fmt.Errorf("queue %s not found", queueName)
	}
	if message.ID == "" {
		message.ID = xid.New().String()
	}
	if queueName != "" {
		message.CurrentQueue = queueName
	}
	message.CreatedAt = time.Now()
	queue.messages.Set(message.ID, message)
	return queue, nil
}

func (b *Broker) handleCommandMessage(ctx context.Context, conn net.Conn, msg Command) error {
	switch msg.Command {
	case SUBSCRIBE:
		b.subscribe(ctx, msg.Queue, conn)
	default:
		return fmt.Errorf("unknown command: %d", msg.Command)
	}
	return nil
}

func (b *Broker) handleTaskMessage(ctx context.Context, _ net.Conn, msg Result) error {
	return b.HandleProcessedMessage(ctx, msg)
}

func (b *Broker) readMessage(ctx context.Context, conn net.Conn, message []byte) error {
	var cmdMsg Command
	var resultMsg Result
	err := json.Unmarshal(message, &cmdMsg)
	if err == nil {
		return b.handleCommandMessage(ctx, conn, cmdMsg)
	}
	err = json.Unmarshal(message, &resultMsg)
	if err == nil {
		return b.handleTaskMessage(ctx, conn, resultMsg)
	}
	return nil
}

func (b *Broker) HandleProcessedMessage(ctx context.Context, clientMsg Result) error {
	if queue, ok := b.queues.Get(clientMsg.Queue); ok {
		if msg, ok := queue.messages.Get(clientMsg.MessageID); ok {
			msg.ProcessedAt = time.Now()
			msg.Status = clientMsg.Status
			msg.Result = clientMsg.Payload
			msg.Error = clientMsg.Error
			msg.CurrentQueue = clientMsg.Queue
			if clientMsg.Error != nil {
				msg.Status = "error"
			}
			if b.taskCallback != nil {
				return b.taskCallback(ctx, msg)
			}
		}
	}
	return nil
}

func (b *Broker) subscribe(ctx context.Context, queueName string, conn net.Conn) {
	q, ok := b.queues.Get(queueName)
	if !ok {
		q = &Queue{
			conn: make(map[net.Conn]struct{}),
		}
		q.conn[conn] = struct{}{}
		b.queues.Set(queueName, q)
	}
	if q.conn == nil {
		q.conn = make(map[net.Conn]struct{})
	}
	q.conn[conn] = struct{}{}
	if q.deferred == nil {
		q.deferred = xsync.NewMap[string, *Task]()
	}
	q.deferred.ForEach(func(_ string, message *Task) bool {
		err := b.Publish(ctx, *message, queueName)
		if err != nil {
			return false
		}
		return true
	})
	q.deferred = nil
}

func (b *Broker) Start(ctx context.Context, addr string) error {
	listener, err := net.Listen("tcp", addr)
	if err != nil {
		return err
	}
	defer func() {
		_ = listener.Close()
	}()
	fmt.Println("Broker server started on", addr)
	for {
		conn, err := listener.Accept()
		if err != nil {
			fmt.Println("Error accepting connection:", err)
			continue
		}
		go utils.ReadFromConn(ctx, conn, b.readMessage)
	}
}