From 73d1cea28612677b42b4e506402533abe4cd893e Mon Sep 17 00:00:00 2001
From: Tsah <tsah@Tsahs-MBP.lan>
Date: Mon, 10 Aug 2026 09:53:27 +0300
Subject: [PATCH] feat: add collection helpers and email validation

---
 node/collections.js | 16 ++++++++++++++++
 python/emails.py    | 14 ++++++++++++++
 2 files changed, 30 insertions(+)
 create mode 100644 node/collections.js
 create mode 100644 python/emails.py

diff --git a/node/collections.js b/node/collections.js
new file mode 100644
index 0000000..a1e9ca7
--- /dev/null
+++ b/node/collections.js
@@ -0,0 +1,16 @@
+export function groupBy(items, keyFn) {
+  return items.reduce((acc, item) => {
+    const key = keyFn(item);
+    (acc[key] ||= []).push(item);
+    return acc;
+  }, {});
+}
+
+export function partition(items, predicate) {
+  const pass = [];
+  const fail = [];
+  for (const item of items) {
+    (predicate(item) ? pass : fail).push(item);
+  }
+  return [pass, fail];
+}
diff --git a/python/emails.py b/python/emails.py
new file mode 100644
index 0000000..f284367
--- /dev/null
+++ b/python/emails.py
@@ -0,0 +1,14 @@
+import re
+
+EMAIL_RE = re.compile(r"^[^@\s]+@[^@\s]+\.[^@\s]+$")
+
+
+def is_valid_email(value):
+    return bool(EMAIL_RE.match(value))
+
+
+def normalize_email(value):
+    if not is_valid_email(value):
+        raise ValueError("invalid email address")
+    local, domain = value.split("@", 1)
+    return f"{local}@{domain.lower()}"