feat: Add paths.ts with tests

Author: MichaelCurrin

src/generate/paths.ts

@@ -0,0 +1,60 @@
+/**
+ * Find common parent directory of paths.
+ * 
+ * From: http://rosettacode.org/wiki/Find_common_directory_path#JavaScript
+ * 
+ * JS does not have a builtin function like Python does.
+ */
+
+/**
+ * Given an array of strings, return an array of arrays, containing the
+ * strings split at the given separator
+ * 
+ * @param {!Array<!string>} a
+ * @param {string} sep
+ * @returns {!Array<!Array<string>>}
+ */
+const splitStrings = (a: any[], sep = '/') =>
+  a.map((i: string) => i.split(sep));
+
+/**
+ * Given an index number, return a function that takes an array and returns the
+ * element at the given index
+ * 
+ * @param {number} i
+ * @return {function(!Array<*>): *}
+ */
+function elAt(i: number) {
+  return (a: { [x: string]: any }) => a[i];
+}
+
+/**
+ * Transpose an array of arrays:
+ * 
+ * Example:
+ *   [['a', 'b', 'c'], ['A', 'B', 'C'], [1, 2, 3]] ->
+ *   [['a', 'A', 1], ['b', 'B', 2], ['c', 'C', 3]]
+ * 
+ * @param {!Array<!Array<*>>} a
+ * @return {!Array<!Array<*>>}
+ */
+function rotate(a: any[]) {
+  return a[0].map((e: any, i: any) => a.map(elAt(i)));
+}
+
+/**
+ * Checks of all the elements in the array are the same.
+ * 
+ * @param {!Array<*>} arr
+ * @return {boolean}
+ */
+function allElementsEqual(arr: any[]) {
+  return arr.every((e: any) => e === arr[0]);
+}
+
+export function commonPath(input: string[], sep = '/') {
+  return rotate(splitStrings(input, sep))
+    .filter(allElementsEqual)
+    .map(elAt(0))
+    .join(sep);
+}

src/test/paths.test.ts

@@ -0,0 +1,29 @@
+import * as assert from 'assert';
+
+import { commonPath } from '../generate/paths';
+
+describe('Path handling', function() {
+  describe('#commonPath()', function() {
+    it('should give the highest common parent directory for 3 related paths', function() {
+      const paths = [
+        '/home/user1/tmp/coverage/test',
+        '/home/user1/tmp/covert/operator',
+        '/home/user1/tmp/coven/members'
+      ];
+
+      assert.equal(commonPath(paths), '/home/user1/tmp');
+    });
+
+    it('should give the highest common parent directory for two different paths', function() {
+      const paths = [ '/foo/test', '/foo/bar/test' ];
+
+      assert.equal(commonPath(paths), '/foo');
+    });
+
+    it('should give the highest common parent directory for two similar', function() {
+      const paths = [ '/fizz', '/buzz' ];
+
+      assert.equal(commonPath(paths), '');
+    });
+  });
+});