From 8482a412afd06a5a67ec8e3d664ab3cb6cdf6b11 Mon Sep 17 00:00:00 2001
From: Daniel Cassidy <mail@danielcassidy.me.uk>
Date: Mon, 17 Jan 2022 14:17:35 +0000
Subject: [PATCH] feat(prefixmatch): add prefixMatch function

---
 index.test.ts |  9 +++++++++
 index.ts      | 25 +++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/index.test.ts b/index.test.ts
index 6d2da170..da36b848 100644
--- a/index.test.ts
+++ b/index.test.ts
@@ -39,6 +39,7 @@ import {
     or,
     partition,
     partitionWhile,
+    prefixMatch,
     prepend,
     product,
     remove,
@@ -169,6 +170,14 @@ test("equal", t => {
     );
 });
 
+test("prefixMatch", t => {
+    t.true(prefixMatch([], []));
+    t.true(prefixMatch([1, 2, 3], []));
+    t.true(prefixMatch([1, 2, 3, 4], [1, 2]));
+    t.false(prefixMatch([1, 3, 4], [1, 2]));
+    t.false(prefixMatch([], [1]));
+});
+
 test("map", t => {
     t.deepEqual(
         map([1, 2, 3], e => e + 1),
diff --git a/index.ts b/index.ts
index 3f2af280..f0bd5f16 100644
--- a/index.ts
+++ b/index.ts
@@ -254,6 +254,31 @@ export function notEqualFn<T>(
     return a => notEqual(a, b, elementsEqual);
 }
 
+export function prefixMatch<T>(
+    a: ArrayLike<T>,
+    b: ArrayLike<T>,
+    elementsEqual: (a: T, b: T) => boolean = defaultEqual
+): boolean {
+    if (a.length < b.length) {
+        return false;
+    }
+
+    for (let i = 0; i < b.length; ++i) {
+        if (a[i] !== b[i]) {
+            return false;
+        }
+    }
+
+    return true;
+}
+
+export function prefixMatchFn<T>(
+    b: ArrayLike<T>,
+    elementsEqual: (a: T, b: T) => boolean = defaultEqual
+): (a: ArrayLike<T>) => boolean {
+    return a => prefixMatch(a, b, elementsEqual);
+}
+
 function defaultEqual(a: unknown, b: unknown): boolean {
     return a === b;
 }