solution proposal 4

problems/05.md

@@ -9,11 +9,100 @@ we can secure our bank.
 
 ```js
 // bank.js
+var jsonStream = require('duplex-json-stream')
+var net = require('net')
+var fs = require('fs')
+var log = require('./log.json')
+
+function sum() {
+    return log.reduce(
+        function (accu, x) {
+            switch (x.cmd) {
+                case 'deposit':
+                    return accu + x.amount
+                case 'withdraw':
+                    return accu - x.amount
+                default:
+                    return accu
+            }
+        }
+        , 0)
+}
+
+function save() {
+    let data = JSON.stringify(log, null, 2);
+    fs.writeFileSync('log.json', data);
+}
+
+
+var server = net.createServer(function (socket) {
+    socket = jsonStream(socket)
+    socket.on('data', function (msg) {
+        console.log('Bank received:', msg)
+        let amount = Math.abs(parseInt(msg.amount))
+        switch (msg.cmd){
+            case 'balance':
+                socket.write({ cmd: 'balance', balance: sum() })
+                break
+            case 'deposit':
+                log.push({cmd: 'deposit', amount: amount})
+                save()
+                socket.write({ cmd: 'balance', balance: sum() })
+                break
+            case 'withdraw':
+                if(amount<=sum()){
+                    log.push({cmd: 'withdraw', amount: amount})
+                    save()
+                    socket.write({ cmd: 'balance', balance: sum() })
+                } else {
+                    socket.write("insufficient funds")
+                }
+                break
+            default:
+                break
+        }
+
+    })
+})
+
+server.listen(3876)
+
+console.log("started bank")
+
 
 ```
 
 ```js
 // teller.js
+var jsonStream = require('duplex-json-stream')
+var net = require('net')
+
+var client = jsonStream(net.connect(3876))
+
+client.on('data', function (msg) {
+  console.log('Teller received:', msg)
+})
+
+const args = process.argv.slice(2)
+const command = args[0]
+const amount = Math.abs(parseInt(args[1]))
+
+switch (command){
+    case 'balance':
+        client.end({cmd: 'balance'})
+        break
+    case 'deposit':
+        client.end({cmd: 'deposit', amount: amount})
+        break
+    case 'withdraw':
+        client.end({cmd: 'withdraw', amount: amount})
+        break
+    default:
+        break
+}
+
+console.log("started teller")
+
 
 ```