Scontrini-Web-Client/api.go

package main

import (
	"encoding/binary"
	"encoding/json"
	"fmt"
	"net"
)

var (
	printer_server_IP   = net.ParseIP("127.0.0.1")
	printer_server_port = 4444
)

// Commands to give to the API
type JSONCommand interface {
	PrintCommand | PizzaCommand | GetPizzasCommand
}

type PrintCommand struct {
	Command string `json:"command"`
	Text    string `json:"text"`
}

type PizzaCommand struct {
	Command string  `json:"command"`
	Pizzas  []Pizza `json:"pizzas"`
}

type GetPizzasCommand struct {
	Command string `json:"command"`
}

// What to receive from the API
type JSONReceived interface {
	ReceivePizzas | ReceivePrice
}

type ReceivePizzas struct {
	Pizzas []Pizza `json:"pizzas"`
}

type ReceivePrice struct {
	TotalPrice int `json:"total_price"`
}

/**
* All messages from and to the API must have the first 4 bytes set to represent
* the length of the message, followed by the message itself
 */
func sendJSONToServer[T JSONCommand](socket *net.TCPConn, json_command T) (*net.TCPConn, error) {
	json_data, err := json.Marshal(json_command)

	if err != nil {
		return nil, err
	}

	// in case a socket doesn't already exist create a new one
	if socket == nil {
		socket, err = net.DialTCP("tcp4", nil, &net.TCPAddr{printer_server_IP, printer_server_port, ""})
	}

	if err != nil {
		return nil, err
	}

	// the first 4 bytes must be the length of the message
	to_send := make([]byte, 4)
	binary.LittleEndian.PutUint32(to_send, uint32(len(json_data)))

	to_send = append(to_send, json_data...)
	socket.Write([]byte(to_send))

	return socket, nil
}

func receiveJSONFromServer[T JSONReceived](socket *net.TCPConn, json_received *T) (*net.TCPConn, error) {
	var err error

	// in case a socket doesn't already exist create a new one
	if socket == nil {
		fmt.Println("nil")
		socket, err = net.DialTCP("tcp4", nil, &net.TCPAddr{printer_server_IP, printer_server_port, ""})
	}

	if err != nil {
		return nil, err
	}

	// the first 4 bytes are the length of the message
	b := make([]byte, 4)
	_, err = socket.Read(b[0:])

	if err != nil {
		return nil, err
	}

	body_length := binary.LittleEndian.Uint32(b)

	body := make([]byte, body_length)
	_, err = socket.Read(body[0:])

	err = json.Unmarshal(body, json_received)

	if err != nil {
		return nil, err
	}

	return socket, nil
}