From 339f38c1b03047e62679c7e0f105162dc85bd742 Mon Sep 17 00:00:00 2001
From: Danielv123 <tranen.bananen@gmail.com>
Date: Tue, 19 Sep 2017 08:35:55 +0200
Subject: [PATCH] Moved string hashing function away from main files

---
 lib/stringUtils.js      | 14 ++++++++++++
 lib/stringUtils.spec.js | 48 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+)
 create mode 100644 lib/stringUtils.js
 create mode 100644 lib/stringUtils.spec.js

diff --git a/lib/stringUtils.js b/lib/stringUtils.js
new file mode 100644
index 00000000..6d73348e
--- /dev/null
+++ b/lib/stringUtils.js
@@ -0,0 +1,14 @@
+function hashCode(string){
+	if(typeof string !== "string") throw "ERROR: Not a string";
+	var hash = 0;
+	if (string.length == 0) return hash;
+	for (let i = 0; i < string.length; i++) {
+		char = string.charCodeAt(i);
+		hash = ((hash << 5) - hash) + char;
+		hash = hash & hash; // Convert to 32bit integer
+	}
+	return hash;
+}
+module.exports = {
+	hashCode: hashCode,
+}
\ No newline at end of file
diff --git a/lib/stringUtils.spec.js b/lib/stringUtils.spec.js
new file mode 100644
index 00000000..f16f19ca
--- /dev/null
+++ b/lib/stringUtils.spec.js
@@ -0,0 +1,48 @@
+const assert = require("assert");
+const stringUtils = require("./stringUtils");
+
+describe("stringUtils.js", function(){
+	describe("hashCode", function(){
+		it("Produces a 32bit signed int hash from a string", function(){
+			let x = stringUtils.hashCode("whatever");
+			let y = stringUtils.hashCode(" a much longer string to prove this works for long strings as well and also special characters &!¤(#)¤");
+			
+			assert(typeof x == "number", "hashCode should be returning a 32 bit signed int");
+			assert(x.toString() == "1934383586");
+			assert(y.toString() == "1648886132");
+		});
+		let permutations = 1000;
+		it("Rarely produces same hash for different strings ("+permutations+" hashes with collision check)", function(){
+			let keyHashPairs = [];
+			for(let i = 0; i < permutations; i++){
+				let string = Math.random().toString();
+				keyHashPairs.push({
+					key:string,
+					hash:stringUtils.hashCode(string),
+				});
+			}
+			
+			for(let i = 0; i < permutations; i++){
+				for(let o = 0; o < permutations; o++){
+					assert(i == o || keyHashPairs[o].key != keyHashPairs[i].key, "Woha, Math.random() generated 2 equal numbers???");
+					assert(i == o || keyHashPairs[o].hash != keyHashPairs[i].hash, "Hash collision, as long at it doesn't happen again its fine.");
+				}
+			}
+		});
+		it("Returns 0 for 0 length strings", function(){
+			let x = stringUtils.hashCode("");
+			assert.deepEqual(x, 0);
+		});
+		it("Throws when supplied with anything other than a string", function(){
+			assert.throws(function(){
+				stringUtils.hashCode([]);
+			}, "ERROR: Not a string")
+			assert.throws(function(){
+				stringUtils.hashCode({});
+			}, "ERROR: Not a string")
+			assert.throws(function(){
+				stringUtils.hashCode(0);
+			}, "ERROR: Not a string")
+		});
+	});
+});
\ No newline at end of file