From 84b3cd3d31e9aa9fd67c7746c5e011e12c0ddc81 Mon Sep 17 00:00:00 2001
From: Garrett Mills <shout@garrettmills.dev>
Date: Tue, 22 Jun 2021 01:15:42 +0000
Subject: [PATCH] Add 'finance.js'

---
 finance.js | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 finance.js

diff --git a/finance.js b/finance.js
new file mode 100644
index 0000000..bd7c954
--- /dev/null
+++ b/finance.js
@@ -0,0 +1,25 @@
+/**
+ * Calculate the # of periods to break-even on an initial investment,
+ * given some array of cash flows for as many periods.
+ *
+ * Returns -1 if never break even.
+ */
+function payback_period(initial, flows = []) {
+    let balance = -initial;
+    let periods = 0;
+
+    for ( const flow of flows ) {
+        console.log({flow, balance, periods})
+        if ( balance + flow > 0 ) {
+            periods += (Math.abs(balance)) / flow;
+            return periods;
+        } else {
+            balance += flow;
+            periods += 1;
+        }
+    }
+
+    return -1;
+}
+
+module.exports = exports = { payback_period }
\ No newline at end of file