package main

import (
	"fmt"
	"io"
	"log/slog"
	"net"
	"os"
	"strconv"
	"strings"
)

type Message struct {
	ID   int
	Data []string
}

func ParseMsg(msg string) (*Message, error) {
	parts := strings.Split(msg, ",")
	msgIdStr := parts[0]
	if !strings.HasPrefix(msgIdStr, "M") {
		return nil, fmt.Errorf("message must start with 'M' prefix")
	}
	msgIdStr = strings.TrimPrefix(msgIdStr, "M")
	msgId, err := strconv.Atoi(msgIdStr)
	if err != nil {
		return nil, err
	}
	msgData := make([]string, len(parts)-1)
	for i, data := range parts[1:] {
		msgData[i] = strings.TrimSpace(data)
	}
	message := &Message{
		ID:   msgId,
		Data: msgData,
	}
	return message, nil
}

func main() {
	// Initialize JSON logger
	logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
	slog.SetDefault(logger)

	addr := "0.0.0.0:8080"
	slog.Info("Starting TCP server", "address", addr)

	//Resolve address
	addr_, err := net.ResolveTCPAddr("tcp", addr)
	if err != nil {
		slog.Error("Error resolving address", "error", err)
		return
	}

	//Listen for incoming connections
	listener, err := net.ListenTCP("tcp", addr_)
	if err != nil {
		slog.Error("Error starting server", "error", err)
		return
	}
	defer listener.Close()

	for {
		//Accept incoming connection
		conn, err := listener.AcceptTCP()
		if err != nil {
			slog.Error("Error accepting connection", "error", err)
			continue
		}
		go handleConnection(conn)
	}
}

func handleConnection(conn *net.TCPConn) {
	defer conn.Close()
	slog.Info("New connection", "remote_addr", conn.RemoteAddr().String())

	buffer := make([]byte, 1024)
	for {
		//Read up to 1024 bytes
		n, err := conn.Read(buffer)
		if err != nil {
			if err == io.EOF {
				slog.Info("Connection closed by client", "remote_addr", conn.RemoteAddr().String())
			} else {
				slog.Error("Error reading from connection", "error", err)
			}
			return
		}
		if n == 0 {
			return
		}
		msgStr := string(buffer[:n])
		slog.Info("Received message", "message", msgStr, "bytes", n)
		msg, err := ParseMsg(msgStr)
		if err != nil {
			slog.Error("Error parsing message", "error", err)
			return
		}
		slog.Info("Parsed message", "message", msg)

		//Echo message back
		// _, err = conn.Write(buffer[:n])
		_, err = conn.Write([]byte("1"))
		if err != nil {
			slog.Error("Error writing to connection", "error", err)
			return
		}
	}
}