Payment chain now works as intended

index.js

@@ -8,29 +8,42 @@ app.use(bodyParser.json({
   limit: '100mb',
   type: 'application/json'
 }))
+
 app.get('/help', function (req, res) {
   res.send('https://github.com/binhonglee/Breakups')
 })
+
 app.post('/total', function (req, res) {
   input = req.body
   var toReturn = { 'total': 0 }
   toReturn.total = total(input.users)
   res.json(toReturn)
 })
+
 app.post('/perPerson', function (req, res) {
   input = req.body
   var toReturn = { 'perPerson': 0 }
   toReturn.perPerson = (total(input.users)) / input.users.length
   res.json(toReturn)
 })
+
 app.post('/oweChart', function (req, res) {
   input = req.body
-  var perPerson = total(input.users) / input.users.length
-  for (var i = 0; i < input.users.length; i++) {
-    input.users[i].amount -= perPerson
-  }
-  res.json(input)
+  input.users = oweChart(input.users)
+  res.send(input)
+})
+
+app.post('/sortedOweChart', function (req, res) {
+  input = req.body
+  input.users = mergeSort(oweChart(input.users))
+  res.send(input)
 })
+
+app.post('/paymentChain', function (req, res) {
+  input = req.body
+  res.json(paymentChain(mergeSort(oweChart(input.users))))
+})
+
 // app.listen(3000)
 app.listen(process.env.PORT)
 
@@ -42,3 +55,65 @@ function total (input) {
 
   return total
 }
+
+function oweChart (users) {
+  var perPerson = total(users) / users.length
+  for (var i = 0; i < users.length; i++) {
+    users[i].amount -= perPerson
+  }
+
+  return users
+}
+
+function mergeSort (users) {
+  if (users.length < 2) {
+    return users
+  }
+
+  var middle = Math.floor(users.length / 2)
+  var left = users.slice(0, middle)
+  var right = users.slice(middle)
+
+  return merge(mergeSort(left), mergeSort(right))
+}
+
+function merge (left, right) {
+  var result = []
+  var il = 0
+  var ir = 0
+
+  while (il < left.length && ir < right.length) {
+    if (left[il].amount < 0 && right[ir].amount < 0) {
+      if (left[il].amount > right[ir].amount) {
+        result.push(left[il++])
+      } else {
+        result.push(right[ir++])
+      }
+    } else {
+      if (left[il].amount < right[ir].amount) {
+        result.push(left[il++])
+      } else {
+        result.push(right[ir++])
+      }
+    }
+  }
+
+  return result.concat(left.slice(il)).concat(right.slice(ir))
+}
+
+function paymentChain (users) {
+  var chain = []
+  var stack = 0
+
+  for (var i = 0; i < users.length - 1; i++) {
+    var item = {'from': '', 'to': '', 'amount': 0}
+    item['from'] = users[i].name
+    item['to'] = users[i + 1].name
+    var amount = users[i].amount * -1
+    stack += amount
+    item['amount'] = stack
+    chain.push(item)
+  }
+
+  return chain
+}