Add some private projects

soundcloud/soundcloud_problem_statement/js/index.js

@@ -0,0 +1,124 @@
+const net = require("net");
+const readline = require("readline");
+
+const EVENT_PORT = 9090;
+const CLIENT_PORT = 9099;
+
+const clientPool = {};
+const followRegistry = {};
+
+let lastSeqNo = 0;
+
+net
+  .createServer(socket => {
+    const seqNoToMessage = {};
+    const readInterface = readline.createInterface({ input: socket });
+    readInterface.on("line", payload => {
+      console.log(`Message received: ${payload}`);
+
+      const payloadParts = payload.split("|");
+      seqNoToMessage[parseInt(payloadParts[0])] = payloadParts;
+
+      while (seqNoToMessage[lastSeqNo + 1]) {
+        const nextMessage = seqNoToMessage[lastSeqNo + 1];
+        const nextPayload = nextMessage.join("|");
+
+        const seqNo = parseInt(nextMessage[0]);
+        const kind = nextMessage[1];
+
+        switch (kind) {
+          case "F":
+            {
+              const fromUserId = parseInt(nextMessage[2]);
+              const toUserId = parseInt(nextMessage[3]);
+
+              const followers = followRegistry[toUserId] || new Set([]);
+              followers.add(fromUserId);
+              followRegistry[toUserId] = followers;
+
+              const socket = clientPool[toUserId];
+              if (socket) {
+                socket.write(nextPayload + "\n");
+              }
+            }
+            break;
+
+          case "U":
+            {
+              const fromUserId = parseInt(nextMessage[2]);
+              const toUserId = parseInt(nextMessage[3]);
+
+              const followers = followRegistry[toUserId] || new Set([]);
+              followers.delete(fromUserId);
+              followRegistry[toUserId] = followers;
+            }
+            break;
+
+          case "P":
+            {
+              const toUserId = parseInt(nextMessage[3]);
+
+              const socket = clientPool[toUserId];
+              if (socket) {
+                socket.write(nextPayload + "\n");
+              }
+            }
+            break;
+
+          case "B":
+            {
+              for (let toUserId in clientPool) {
+                const socket = clientPool[toUserId];
+                if (socket) {
+                  socket.write(nextPayload + "\n");
+                }
+              }
+            }
+            break;
+
+          case "S":
+            {
+              const fromUserId = parseInt(nextMessage[2]);
+
+              const followers = followRegistry[fromUserId] || new Set([]);
+
+              followers.forEach(follower => {
+                const socket = clientPool[follower];
+                if (socket) {
+                  socket.write(nextPayload + "\n");
+                }
+              });
+            }
+            break;
+        }
+
+        lastSeqNo = seqNo;
+      }
+    });
+  })
+  .listen(EVENT_PORT, "127.0.0.1", err => {
+    if (err) {
+      throw err;
+    }
+    console.log(`Listening for events on ${EVENT_PORT}`);
+  });
+
+net
+  .createServer(clientSocket => {
+    const readInterface = readline.createInterface({ input: clientSocket });
+    readInterface.on("line", userIdString => {
+      if (userIdString != null) {
+        clientPool[parseInt(userIdString)] = clientSocket;
+
+        console.log(
+          `User connected: ${userIdString} (${clientPool.length} total)`
+        );
+      }
+    });
+  })
+  .listen(CLIENT_PORT, "127.0.0.1", err => {
+    if (err) {
+      throw err;
+    }
+    console.log(`Listening for client requests on ${CLIENT_PORT}`);
+  });