res_levis_backend/cmd/server/main.go

package main

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"strings"
	"time"

	"github.com/AFASystems/presence/internal/pkg/kafkaclient"
	"github.com/AFASystems/presence/internal/pkg/model"
	"github.com/gorilla/handlers"
	"github.com/gorilla/mux"
	"github.com/gorilla/websocket"
	"github.com/redis/go-redis/v9"
	"github.com/segmentio/kafka-go"
)

var upgrader = websocket.Upgrader{
	CheckOrigin: func(r *http.Request) bool { return true },
}

func main() {
	HttpServer("0.0.0.0:1902")
}

func HttpServer(addr string) {
	headersOk := handlers.AllowedHeaders([]string{"X-Requested-With"})
	originsOk := handlers.AllowedOrigins([]string{"*"})
	methodsOk := handlers.AllowedMethods([]string{"GET", "HEAD", "POST", "PUT", "DELETE", "OPTIONS"})

	// Kafka writer that relays messages
	writer := kafkaclient.KafkaWriter("kafka:9092", "apibeacons")
	defer writer.Close()

	settingsWriter := kafkaclient.KafkaWriter("kafka:9092", "settings")
	defer settingsWriter.Close()

	// Define if maybe ws writer should have more topics
	wsWriter := kafkaclient.KafkaWriter("kafka:9092", "wsmessages")
	defer wsWriter.Close()

	r := mux.NewRouter()

	client := redis.NewClient(&redis.Options{
		Addr:     "valkey:6379",
		Password: "",
	})

	// declare WS clients list | do I need it though? or will locations worker send message
	// to kafka and then only this service (server) is being used for communication with the clients
	clients := make(map[*websocket.Conn]bool)

	// Declare broadcast channel
	broadcast := make(chan model.Message)

	// For now just add beacon DELETE / GET / POST / PUT methods
	r.HandleFunc("/api/beacons/{beacon_id}", beaconsDeleteHandler(writer)).Methods("DELETE")
	r.HandleFunc("/api/beacons", beaconsListHandler(client)).Methods("GET")
	r.HandleFunc("/api/beacons", beaconsAddHandler(writer)).Methods("POST")
	r.HandleFunc("/api/beacons", beaconsAddHandler(writer)).Methods("PUT")

	r.HandleFunc("/api/settings", settingsListHandler(client)).Methods("GET")
	r.HandleFunc("/api/settings", settingsEditHandler(settingsWriter)).Methods("POST")

	// Handler for WS messages
	// No point in having seperate route for each message type, better to handle different message types in one connection
	r.HandleFunc("/ws/api/beacons", serveWs(client))
	r.HandleFunc("/ws/api/beacons/latest", serveLatestBeaconsWs(client))
	r.HandleFunc("/ws/broadcast", handleConnections(clients, broadcast))

	http.ListenAndServe(addr, handlers.CORS(originsOk, headersOk, methodsOk)(r))
}

// Probably define value as interface and then reuse this writer in all of the functions
func sendKafkaMessage(writer *kafka.Writer, value *model.ApiUpdate) bool {
	valueStr, err := json.Marshal(&value)
	if err != nil {
		fmt.Println("error in encoding: ", err)
		return false
	}
	msg := kafka.Message{
		Value: valueStr,
	}

	err = writer.WriteMessages(context.Background(), msg)
	if err != nil {
		fmt.Println("Error in sending kafka message: ")
		return false
	}

	return true
}

func beaconsDeleteHandler(writer *kafka.Writer) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		vars := mux.Vars(r)
		beaconId := vars["beacon_id"]
		apiUpdate := model.ApiUpdate{
			Method: "DELETE",
			ID:     beaconId,
		}

		flag := sendKafkaMessage(writer, &apiUpdate)
		if !flag {
			fmt.Println("error in sending Kafka message")
			http.Error(w, "Error in sending kafka message", 500)
			return
		}

		w.Write([]byte("ok"))
	}
}

func beaconsAddHandler(writer *kafka.Writer) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		decoder := json.NewDecoder(r.Body)
		var inBeacon model.Beacon
		err := decoder.Decode(&inBeacon)

		if err != nil {
			http.Error(w, err.Error(), 400)
			return
		}

		if (len(strings.TrimSpace(inBeacon.Name)) == 0) || (len(strings.TrimSpace(inBeacon.Beacon_id)) == 0) {
			http.Error(w, "name and beacon_id cannot be blank", 400)
			return
		}

		apiUpdate := model.ApiUpdate{
			Method: "POST",
			Beacon: inBeacon,
		}

		flag := sendKafkaMessage(writer, &apiUpdate)
		if !flag {
			fmt.Println("error in sending Kafka message")
			http.Error(w, "Error in sending kafka message", 500)
			return
		}

		w.Write([]byte("ok"))
	}
}

func beaconsListHandler(client *redis.Client) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		beaconsList, err := client.Get(context.Background(), "beaconsList").Result()
		if err == redis.Nil {
			fmt.Println("no beacons list, starting empty")
			http.Error(w, "list is empty", 500)
		} else if err != nil {
			http.Error(w, "Internal server error", 500)
			panic(err)
		} else {
			w.Write([]byte(beaconsList))
		}
	}
}

func settingsListHandler(client *redis.Client) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		settings, err := client.Get(context.Background(), "settings").Result()
		if err == redis.Nil {
			fmt.Println("no settings persisted, starting empty")
			http.Error(w, "list is empty", 500)
		} else if err != nil {
			http.Error(w, "Internal server error", 500)
			panic(err)
		} else {
			w.Write([]byte(settings))
		}
	}
}

func settingsEditHandler(writer *kafka.Writer) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		decoder := json.NewDecoder(r.Body)
		var inSettings model.SettingsVal
		if err := decoder.Decode(&inSettings); err != nil {
			http.Error(w, err.Error(), 400)
			fmt.Println("Error in decoding Settings body: ", err)
			return
		}

		if !settingsCheck(inSettings) {
			http.Error(w, "values must be greater than 0", 400)
			fmt.Println("settings values must be greater than 0")
			return
		}

		valueStr, err := json.Marshal(&inSettings)
		if err != nil {
			http.Error(w, "Error in encoding settings", 500)
			fmt.Println("Error in encoding settings: ", err)
			return
		}

		msg := kafka.Message{
			Value: valueStr,
		}

		if err := writer.WriteMessages(context.Background(), msg); err != nil {
			fmt.Println("error in sending Kafka message")
			http.Error(w, "Error in sending kafka message", 500)
			return
		}

		w.Write([]byte("ok"))
	}
}

func settingsCheck(settings model.SettingsVal) bool {
	if settings.Location_confidence <= 0 || settings.Last_seen_threshold <= 0 || settings.HA_send_interval <= 0 {
		return false
	}

	return true
}

func serveWs(client *redis.Client) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		ws, err := upgrader.Upgrade(w, r, nil)
		if err != nil {
			if _, ok := err.(websocket.HandshakeError); !ok {
				log.Println(err)
			}
			return
		}

		go writer(ws, client)
		reader(ws)
	}
}

func writer(ws *websocket.Conn, client *redis.Client) {
	pingTicker := time.NewTicker((60 * time.Second * 9) / 10)
	beaconTicker := time.NewTicker(2 * time.Second)
	defer func() {
		pingTicker.Stop()
		beaconTicker.Stop()
		ws.Close()
	}()
	for {
		select {
		case <-beaconTicker.C:
			httpresults, err := client.Get(context.Background(), "httpresults").Result()
			if err == redis.Nil {
				fmt.Println("no beacons list, starting empty")
			} else if err != nil {
				panic(err)
			} else {
				ws.SetWriteDeadline(time.Now().Add(10 * time.Second))
				if err := ws.WriteMessage(websocket.TextMessage, []byte(httpresults)); err != nil {
					return
				}
			}
		case <-pingTicker.C:
			ws.SetWriteDeadline(time.Now().Add(10 * time.Second))
			if err := ws.WriteMessage(websocket.PingMessage, []byte{}); err != nil {
				return
			}
		}
	}
}

func serveLatestBeaconsWs(client *redis.Client) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		ws, err := upgrader.Upgrade(w, r, nil)
		if err != nil {
			if _, ok := err.(websocket.HandshakeError); !ok {
				log.Println(err)
			}
			return
		}

		go latestBeaconWriter(ws, client)
		reader(ws)
	}
}

// This and writer can be refactored in one function
func latestBeaconWriter(ws *websocket.Conn, client *redis.Client) {
	pingTicker := time.NewTicker((60 * time.Second * 9) / 10)
	beaconTicker := time.NewTicker(2 * time.Second)
	defer func() {
		pingTicker.Stop()
		beaconTicker.Stop()
		ws.Close()
	}()
	for {
		select {
		case <-beaconTicker.C:
			latestbeacons, err := client.Get(context.Background(), "latestbeacons").Result()
			if err == redis.Nil {
				fmt.Println("no beacons list, starting empty")
			} else if err != nil {
				panic(err)
			} else {
				ws.SetWriteDeadline(time.Now().Add(10 * time.Second))
				if err := ws.WriteMessage(websocket.TextMessage, []byte(latestbeacons)); err != nil {
					return
				}
			}
		case <-pingTicker.C:
			ws.SetWriteDeadline(time.Now().Add(10 * time.Second))
			if err := ws.WriteMessage(websocket.PingMessage, []byte{}); err != nil {
				return
			}
		}
	}
}

func reader(ws *websocket.Conn) {
	defer ws.Close()
	ws.SetReadLimit(512)
	ws.SetReadDeadline(time.Now().Add(60 * time.Second))
	ws.SetPongHandler(func(string) error { ws.SetReadDeadline(time.Now().Add(60 * time.Second)); return nil })
	for {
		_, _, err := ws.ReadMessage()
		if err != nil {
			break
		}
	}
}

func handleConnections(clients map[*websocket.Conn]bool, broadcast chan model.Message) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		ws, err := upgrader.Upgrade(w, r, nil)
		if err != nil {
			log.Fatal(err)
		}
		defer ws.Close()
		clients[ws] = true

		for {
			var msg model.Message
			err := ws.ReadJSON(&msg)
			if err != nil {
				log.Printf("error: %v", err)
				delete(clients, ws)
				break
			}
			broadcast <- msg
		}
	}
}