From e9bd10f4c50998bbfe6cc9d0442062e4636442c3 Mon Sep 17 00:00:00 2001
From: Adam Laycock <aml@lhs.lancs.sch.uk>
Date: Tue, 28 Mar 2023 15:38:45 +0100
Subject: [PATCH] feat: add rndFromString and invertString

---
 src/functions/strings.spec.ts | 16 +++++++++++++
 src/functions/strings.ts      | 43 +++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)
 create mode 100644 src/functions/strings.spec.ts
 create mode 100644 src/functions/strings.ts

diff --git a/src/functions/strings.spec.ts b/src/functions/strings.spec.ts
new file mode 100644
index 0000000..c33753e
--- /dev/null
+++ b/src/functions/strings.spec.ts
@@ -0,0 +1,16 @@
+import {rndFromString, invertString} from './strings'
+
+describe('Strings', () => {
+  it('should generate a random number from a string', () => {
+    expect(rndFromString('foo')).toBe(0)
+    expect(rndFromString('foo', 10)).toBe(3)
+    // Test that it always returns the same
+    expect(rndFromString('foo', 10)).toBe(3)
+  })
+
+  it('should invert strings', () => {
+    expect(invertString('abc')).toBe('zyx')
+    expect(invertString('AbC')).toBe('ZyX')
+    expect(invertString('Alpha!')).toBe('Zoksz!')
+  })
+})
diff --git a/src/functions/strings.ts b/src/functions/strings.ts
new file mode 100644
index 0000000..1df0ee6
--- /dev/null
+++ b/src/functions/strings.ts
@@ -0,0 +1,43 @@
+/**
+ * Returns a random number seeded using the supplied string. A given string will always return the same number
+ *
+ * @param string The string to seed with
+ * @param base The maximum number to produce. Defaults to `1`.
+ * @returns A random number
+ */
+export const rndFromString = (string: string, base: number = 1) => {
+  const seed = string.split('').reduce((count, char) => {
+    return count + char.charCodeAt(0)
+  }, 0)
+
+  const n = Math.sin(seed) * 10000
+
+  return Math.round((n - Math.floor(n)) * base)
+}
+
+export const invertString = (string: string) => {
+  return string
+    .split('')
+    .map(char => {
+      const charCode = char.charCodeAt(0)
+
+      if (
+        !(
+          (charCode >= 65 && charCode <= 90) ||
+          (charCode >= 97 && charCode <= 122)
+        )
+      ) {
+        return char
+      }
+
+      const alpha = charCode < 97 ? 65 : 97
+      const zeta = charCode < 97 ? 90 : 122
+
+      const letterCode = charCode - alpha
+
+      return String.fromCharCode(zeta - letterCode)
+    })
+    .join('')
+}
+
+// {rndFromString, invertString}