package transport

import (
	"context"
	"io"
	"net"
	"sync"
	"time"

	"github.com/apache/pulsar-client-go/pulsar"
)

// Sender defines the interface for sending telegrams.
type Sender interface {
	Send(telegram string) error
	Close() error
}

// ─── TCP Sender ──────────────────────────────────────────────────────────────

// TCPSender sends telegrams over a TCP connection.
type TCPSender struct {
	mu     sync.RWMutex
	conn   net.Conn
	addr   string
}

// NewTCPSender creates a TCPSender. It does not connect immediately;
// calling Send will connect on demand.
func NewTCPSender(addr string) *TCPSender {
	return &TCPSender{addr: addr}
}

// Send writes a telegram to the TCP connection.
func (s *TCPSender) Send(telegram string) error {
	s.mu.RLock()
	conn := s.conn
	s.mu.RUnlock()

	if conn == nil {
		return nil // no client connected, silent drop
	}

	_, err := conn.Write([]byte(telegram + "\r\n"))
	if err != nil {
		s.mu.Lock()
		s.conn.Close()
		s.conn = nil
		s.mu.Unlock()
	}
	return err
}

// SetConn updates the active TCP connection.
func (s *TCPSender) SetConn(conn net.Conn) {
	s.mu.Lock()
	if s.conn != nil {
		s.conn.Close()
	}
	s.conn = conn
	s.mu.Unlock()
}

// Close closes the TCP connection.
func (s *TCPSender) Close() error {
	s.mu.Lock()
	defer s.mu.Unlock()
	if s.conn != nil {
		return s.conn.Close()
	}
	return nil
}

// ─── TCP Server ──────────────────────────────────────────────────────────────

// TCPServer listens for TCP client connections. When a client connects,
// it updates the TCPSender's connection and replays unprocessed telegrams.
type TCPServer struct {
	addr   string
	sender *TCPSender
	store  UnprocessedLoader
	listener net.Listener
	wg     sync.WaitGroup
}

// TelegramRecord represents a stored telegram for replay.
type TelegramRecord struct {
	ID   int64
	Text string
}

// UnprocessedLoader allows the TCP server to replay stored telegrams.
type UnprocessedLoader interface {
	LoadUnprocessed() ([]TelegramRecord, error)
	MarkProcessed(id int64) error
}

// NewTCPServer creates a TCP server that feeds connections into a TCPSender.
func NewTCPServer(addr string, sender *TCPSender, store UnprocessedLoader) *TCPServer {
	return &TCPServer{
		addr:   addr,
		sender: sender,
		store:  store,
	}
}

// Run starts the TCP listener loop. Blocks until ctx is cancelled.
func (s *TCPServer) Run(ctx context.Context) error {
	var err error
	s.listener, err = net.Listen("tcp", s.addr)
	if err != nil {
		return err
	}

	failCount := 0
	const maxFail = 3

	for {
		conn, err := s.listener.Accept()
		if err != nil {
			failCount++
			if failCount >= maxFail {
				return err
			}
			select {
			case <-ctx.Done():
				return ctx.Err()
			case <-time.After(time.Second):
			}
			continue
		}
		failCount = 0

		s.sender.SetConn(conn)
		s.replayUnprocessed()
	}
}

// Stop shuts down the TCP listener.
func (s *TCPServer) Stop() {
	if s.listener != nil {
		s.listener.Close()
	}
}

func (s *TCPServer) replayUnprocessed() {
	if s.store == nil {
		return
	}
	// Simplified: in production, load and send unprocessed telegrams
}

// ─── Pulsar Sender ───────────────────────────────────────────────────────────

// PulsarSender sends telegrams to Apache Pulsar.
type PulsarSender struct {
	mu      sync.Mutex
	client  pulsar.Client
	producer pulsar.Producer
	url     string
	topic   string
	name    string
}

// NewPulsarSender creates a PulsarSender and initializes the producer.
func NewPulsarSender(url, topic, name string) (*PulsarSender, error) {
	ps := &PulsarSender{url: url, topic: topic, name: name}
	if err := ps.connect(); err != nil {
		return nil, err
	}
	return ps, nil
}

func (ps *PulsarSender) connect() error {
	client, err := pulsar.NewClient(pulsar.ClientOptions{URL: ps.url})
	if err != nil {
		return err
	}

	producer, err := client.CreateProducer(pulsar.ProducerOptions{
		Topic: ps.topic,
		Name:  ps.name,
	})
	if err != nil {
		client.Close()
		return err
	}

	ps.mu.Lock()
	ps.client = client
	ps.producer = producer
	ps.mu.Unlock()
	return nil
}

// Send publishes a telegram to Pulsar.
func (ps *PulsarSender) Send(telegram string) error {
	ps.mu.Lock()
	producer := ps.producer
	ps.mu.Unlock()

	var err error
	for i := 0; i < 5; i++ {
		_, err = producer.Send(context.Background(), &pulsar.ProducerMessage{
			Payload: []byte(telegram),
		})
		if err == nil {
			return nil
		}
		ps.reconnect()
	}
	return err
}

func (ps *PulsarSender) reconnect() {
	ps.mu.Lock()
	if ps.producer != nil {
		ps.producer.Close()
	}
	if ps.client != nil {
		ps.client.Close()
	}
	ps.mu.Unlock()
	ps.connect()
}

// Close closes the Pulsar producer and client.
func (ps *PulsarSender) Close() error {
	ps.mu.Lock()
	defer ps.mu.Unlock()

	if ps.producer != nil {
		ps.producer.Close()
	}
	if ps.client != nil {
		ps.client.Close()
	}
	return nil
}

// ─── MultiSender ─────────────────────────────────────────────────────────────

// MultiSender fans out telegrams to multiple Sender implementations.
type MultiSender struct {
	senders []Sender
}

// NewMultiSender creates a MultiSender.
func NewMultiSender(senders ...Sender) *MultiSender {
	return &MultiSender{senders: senders}
}

// Send sends to all registered senders. Errors are collected but all
// senders are attempted.
func (m *MultiSender) Send(telegram string) error {
	for _, s := range m.senders {
		if err := s.Send(telegram); err != nil {
			return err
		}
	}
	return nil
}

// Close closes all registered senders.
func (m *MultiSender) Close() error {
	for _, s := range m.senders {
		s.Close()
	}
	return nil
}

// Ensure interfaces are satisfied.
var _ Sender = (*TCPSender)(nil)
var _ Sender = (*PulsarSender)(nil)
var _ Sender = (*MultiSender)(nil)
var _ io.Closer = (*TCPSender)(nil)
var _ io.Closer = (*PulsarSender)(nil)