Working order book with passing tests

orderBook.js

@@ -0,0 +1,46 @@
+function reconcileOrder(existingBook, incomingOrder) {
+  let updatedBook = []
+  let newOrders = []
+
+  if (!existingBook.length) {
+    let updatedBook = existingBook.concat({ ...incomingOrder })
+
+    return updatedBook
+  }
+
+  for (let i = 0; i < existingBook.length; i++) {
+    const bookType = existingBook[i].type
+    const bookPrice = existingBook[i].price
+    const orderType = incomingOrder.type
+    let orderPrice = incomingOrder.price
+    let bookQuantity = existingBook[i].quantity
+    let orderQuantity = incomingOrder.quantity
+
+    if (bookType !== orderType &&
+        bookPrice === orderPrice &&
+        bookQuantity === orderQuantity) {
+      incomingOrder.price = true
+    } else if (bookType !== orderType &&
+        bookPrice === orderPrice &&
+        bookQuantity !== orderQuantity) {
+      if (bookQuantity > orderQuantity) {
+        existingBook[i].quantity -= orderQuantity
+        incomingOrder.quantity = false
+        newOrders.push(existingBook[i])
+      } else {
+        incomingOrder.quantity -= bookQuantity
+      }
+    } else {
+      updatedBook.push(existingBook[i])
+    }
+  }
+  if (incomingOrder.quantity !== false &&
+      incomingOrder.price !== true) {
+    updatedBook.push(incomingOrder)
+  }
+
+  return updatedBook.concat(newOrders)
+}
+
+module.exports = reconcileOrder
+