From 4874c88bb126c42563940460ca2637af14ad1823 Mon Sep 17 00:00:00 2001
From: elioat <elioat@tilde.institute>
Date: Mon, 14 Oct 2024 10:38:49 -0400
Subject: *

---
 js/little-regex.js | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 js/little-regex.js

diff --git a/js/little-regex.js b/js/little-regex.js
new file mode 100644
index 0000000..8b19aff
--- /dev/null
+++ b/js/little-regex.js
@@ -0,0 +1,52 @@
+// Inspired by https://www.cs.princeton.edu/courses/archive/spr09/cos333/beautiful.html
+const matchHere = (pattern, text) => {
+    if (pattern.length === 0) return true;
+    
+    // If pattern ends with $, match end of string
+    if (pattern[0] === '$' && pattern.length === 1) return text.length === 0;
+
+    // If next char is '*', match zero or more occurrences of prev char
+    if (pattern[1] === '*') return matchStar(pattern[0], pattern.slice(2), text);
+
+    // Match . or literal character
+    if (text.length !== 0 && (pattern[0] === '.' || pattern[0] === text[0])) {
+        return matchHere(pattern.slice(1), text.slice(1));
+    }
+
+    return false;
+};
+
+const matchStar = (prevChar, pattern, text) => {
+    // Try matching zero occurrences first
+    if (matchHere(pattern, text)) return true;
+
+    // Then, match one or more occurrences of prevChar
+    while (text.length > 0 && (text[0] === prevChar || prevChar === '.')) {
+        text = text.slice(1);
+        if (matchHere(pattern, text)) return true;
+    }
+
+    return false;
+};
+
+const match = (pattern, text) => {
+    // Handle ^ anchor at the beginning
+    if (pattern[0] === '^') {
+        return matchHere(pattern.slice(1), text);
+    }
+
+    // Otherwise, check the entire string
+    for (let i = 0; i <= text.length; i++) {
+        if (matchHere(pattern, text.slice(i))) return true;
+    }
+
+    return false;
+};
+
+const assertEqual = (actual, expected, testName) => 
+    console.log(actual === expected ? `Passed: ${testName}` : `Failed: ${testName}. Expected ${expected} but got ${actual}`);
+
+assertEqual(match("ab*c", "ac"), true, "Star match 'ab*c' vs 'ac' (zero occurrences)");
+assertEqual(match("ab*c", "abbbc"), true, "Star match 'ab*c' vs 'abbbc' (multiple occurrences)");
+assertEqual(match("^ab.*c$", "abc"), true, "Complex match '^ab.*c$' vs 'abc'");
+assertEqual(match("^ab.*c$", "abcd"), false, "Complex mismatch '^ab.*c$' vs 'abcd'");
-- 
cgit 1.4.1-2-gfad0