Add some private projects

soundcloud/soundcloud_problem_statement/go/main.go

@@ -0,0 +1,187 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"strconv"
+	"strings"
+)
+
+const eventPort = 9090
+const clientPort = 9099
+
+func main() {
+	clientPool := make(map[int]net.Conn)
+	followRegistry := map[int]map[int]bool{}
+
+	seqNoToMessage := make(map[int][]string)
+
+	go func() {
+		lastSeqNo := 0
+
+		eventListener, err := net.Listen("tcp", fmt.Sprintf("127.0.0.1:%d", eventPort))
+		if err != nil {
+			log.Fatal(err)
+		}
+		defer eventListener.Close()
+
+		fmt.Printf("Listening for events on %d\n", eventPort)
+
+	outer:
+		for {
+			conn, err := eventListener.Accept()
+
+			if err != nil {
+				log.Fatal(err)
+			}
+			defer conn.Close()
+
+			reader := bufio.NewReader(conn)
+
+			for {
+				payloadRaw, err := reader.ReadString('\n')
+
+				if err == io.EOF {
+					conn.Close()
+					continue outer
+
+				} else if err != nil {
+					log.Fatal(err)
+				}
+
+				payload := strings.TrimSpace(payloadRaw)
+
+				fmt.Printf("Message received: %s\n", payload)
+
+				payloadParts := strings.Split(payload, "|")
+
+				incomingSeqNo, err := strconv.Atoi(payloadParts[0])
+				if err != nil {
+					log.Fatal(err)
+				}
+
+				seqNoToMessage[incomingSeqNo] = payloadParts
+
+				for {
+
+					nextMessage, ok := seqNoToMessage[lastSeqNo+1]
+					delete(seqNoToMessage, lastSeqNo+1)
+
+					if !ok {
+						break
+					}
+
+					nextPayload := strings.Join(nextMessage, "|") + "\n"
+					kind := strings.TrimSpace(nextMessage[1])
+
+					switch kind {
+					case "F":
+						fromUserID, err := strconv.Atoi(nextMessage[2])
+						if err != nil {
+							log.Fatal(err)
+						}
+						toUserID, err := strconv.Atoi(nextMessage[3])
+						if err != nil {
+							log.Fatal(err)
+						}
+
+						if _, ok := followRegistry[toUserID]; !ok {
+							followRegistry[toUserID] = make(map[int]bool)
+						}
+
+						followers, _ := followRegistry[toUserID]
+						followers[fromUserID] = true
+
+						clientConn, ok := clientPool[toUserID]
+						if ok {
+							fmt.Fprint(clientConn, nextPayload)
+						}
+
+					case "U":
+						fromUserID, err := strconv.Atoi(nextMessage[2])
+						if err != nil {
+							log.Fatal(err)
+						}
+						toUserID, err := strconv.Atoi(nextMessage[3])
+						if err != nil {
+							log.Fatal(err)
+						}
+
+						if followers, ok := followRegistry[toUserID]; ok {
+							delete(followers, fromUserID)
+						}
+
+					case "P":
+						toUserID, err := strconv.Atoi(nextMessage[3])
+						if err != nil {
+							log.Fatal(err)
+						}
+
+						if clientConn, ok := clientPool[toUserID]; ok {
+							fmt.Fprint(clientConn, nextPayload)
+						}
+
+					case "B":
+						for _, clientConn := range clientPool {
+							fmt.Fprint(clientConn, nextPayload)
+						}
+
+					case "S":
+						fromUserID, err := strconv.Atoi(nextMessage[2])
+						if err != nil {
+							log.Fatal(err)
+						}
+
+						if followers, ok := followRegistry[fromUserID]; ok {
+							for follower := range followers {
+								clientConn, ok := clientPool[follower]
+								if ok {
+									fmt.Fprint(clientConn, nextPayload)
+								}
+							}
+						}
+					}
+
+					lastSeqNo = lastSeqNo + 1
+				}
+			}
+		}
+	}()
+
+	eventListener, err := net.Listen("tcp", fmt.Sprintf("127.0.0.1:%d", clientPort))
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer eventListener.Close()
+
+	fmt.Printf("Listening for client requests on %d\n", clientPort)
+
+	for {
+		conn, err := eventListener.Accept()
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		reader := bufio.NewReader(conn)
+
+		userIDRaw, err := reader.ReadString('\n')
+
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		userIDStr := strings.TrimSpace(userIDRaw)
+
+		userID, err := strconv.Atoi(userIDStr)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		clientPool[userID] = conn
+
+		fmt.Printf("User connected: %d (%d total)\n", userID, len(clientPool))
+	}
+}