From 6e54ce1e4264abe70e7776bb0e6d8cbdcf1d7b87 Mon Sep 17 00:00:00 2001
From: Alex de Leeuw <adeleeuw@andrew.cmu.edu>
Date: Sat, 5 Sep 2026 16:27:25 +0000
Subject: [PATCH] Extract Accept-Language parsing to remove duplication in
 middleware.ts

---
 packages/web/package.json           |  3 ++-
 packages/web/src/i18n/locales.ts    | 34 ++++++++++++++++++++++++
 packages/web/src/middleware.test.ts | 40 +++++++++++++++++++++++++++++
 packages/web/src/middleware.ts      | 32 ++---------------------
 4 files changed, 78 insertions(+), 31 deletions(-)
 create mode 100644 packages/web/src/middleware.test.ts

diff --git a/packages/web/package.json b/packages/web/package.json
index 280a52e6..abb1f7ee 100644
--- a/packages/web/package.json
+++ b/packages/web/package.json
@@ -9,7 +9,8 @@
     "start": "astro dev",
     "build": "astro build",
     "preview": "astro preview",
-    "astro": "astro"
+    "astro": "astro",
+    "test": "bun test"
   },
   "dependencies": {
     "@astrojs/cloudflare": "12.6.3",
diff --git a/packages/web/src/i18n/locales.ts b/packages/web/src/i18n/locales.ts
index d1b3e74d..7f73f853 100644
--- a/packages/web/src/i18n/locales.ts
+++ b/packages/web/src/i18n/locales.ts
@@ -115,3 +115,37 @@ export function matchLocale(input: string) {
 
   return starts.find((item) => value.startsWith(item[0]))?.[1] ?? null
 }
+
+export function parseAcceptLanguage(header: string | null): { lang: string; q: number }[] {
+  if (!header) return []
+
+  return header
+    .split(",")
+    .map((raw) => raw.trim())
+    .filter(Boolean)
+    .map((raw) => {
+      const parts = raw.split(";").map((x) => x.trim())
+      const lang = parts[0] ?? ""
+      const q = parts
+        .slice(1)
+        .find((x) => x.startsWith("q="))
+        ?.slice(2)
+      return {
+        lang,
+        q: q ? Number.parseFloat(q) : 1,
+      }
+    })
+    .sort((a, b) => b.q - a.q)
+}
+
+export function localeFromAcceptLanguage(header: string | null) {
+  const items = parseAcceptLanguage(header)
+
+  const locale = items
+    .map((item) => item.lang)
+    .filter((lang) => lang && lang !== "*")
+    .map((lang) => matchLocale(lang))
+    .find((lang) => lang)
+
+  return locale ?? "root"
+}
\ No newline at end of file
diff --git a/packages/web/src/middleware.test.ts b/packages/web/src/middleware.test.ts
new file mode 100644
index 00000000..4ef61c5e
--- /dev/null
+++ b/packages/web/src/middleware.test.ts
@@ -0,0 +1,40 @@
+import { describe, expect, test } from "bun:test"
+import { parseAcceptLanguage, localeFromAcceptLanguage } from "./i18n/locales"
+
+describe("parseAcceptLanguage", () => {
+  test("returns empty array for null header", () => {
+    expect(parseAcceptLanguage(null)).toEqual([])
+  })
+
+  test("parses a single language with no q value as q=1", () => {
+    expect(parseAcceptLanguage("fr")).toEqual([{ lang: "fr", q: 1 }])
+  })
+
+  test("parses multiple languages and sorts by q value descending", () => {
+    const result = parseAcceptLanguage("en;q=0.5,fr;q=0.9,de")
+    expect(result.map((r) => r.lang)).toEqual(["de", "fr", "en"])
+  })
+
+  test("ignores empty segments from trailing commas", () => {
+    const result = parseAcceptLanguage("en,,fr")
+    expect(result.map((r) => r.lang)).toEqual(["en", "fr"])
+  })
+})
+
+describe("localeFromAcceptLanguage", () => {
+  test("returns 'root' for null header", () => {
+    expect(localeFromAcceptLanguage(null)).toBe("root")
+  })
+
+  test("picks the highest-weighted matching locale", () => {
+    expect(localeFromAcceptLanguage("en;q=0.5,fr;q=0.9")).toBe("fr")
+  })
+
+  test("returns 'root' when no listed language matches a known locale", () => {
+    expect(localeFromAcceptLanguage("xx-XX")).toBe("root")
+  })
+
+  test("skips wildcard entries", () => {
+    expect(localeFromAcceptLanguage("*;q=0.9,de;q=0.5")).toBe("de")
+  })
+})
\ No newline at end of file
diff --git a/packages/web/src/middleware.ts b/packages/web/src/middleware.ts
index cf9f97b0..8671979c 100644
--- a/packages/web/src/middleware.ts
+++ b/packages/web/src/middleware.ts
@@ -1,5 +1,6 @@
 import { defineMiddleware } from "astro:middleware"
-import { exactLocale, matchLocale } from "./i18n/locales"
+import { exactLocale, matchLocale, localeFromAcceptLanguage } from "./i18n/locales"
+
 
 function docsAlias(pathname: string) {
   const hit = /^\/docs\/([^/]+)(\/.*)?$/.exec(pathname)
@@ -47,35 +48,6 @@ function localeFromCookie(header: string | null) {
   return matchLocale(raw)
 }
 
-function localeFromAcceptLanguage(header: string | null) {
-  if (!header) return "root"
-
-  const items = header
-    .split(",")
-    .map((raw) => raw.trim())
-    .filter(Boolean)
-    .map((raw) => {
-      const parts = raw.split(";").map((x) => x.trim())
-      const lang = parts[0] ?? ""
-      const q = parts
-        .slice(1)
-        .find((x) => x.startsWith("q="))
-        ?.slice(2)
-      return {
-        lang,
-        q: q ? Number.parseFloat(q) : 1,
-      }
-    })
-    .sort((a, b) => b.q - a.q)
-
-  const locale = items
-    .map((item) => item.lang)
-    .filter((lang) => lang && lang !== "*")
-    .map((lang) => matchLocale(lang))
-    .find((lang) => lang)
-
-  return locale ?? "root"
-}
 
 export const onRequest = defineMiddleware((ctx, next) => {
   const alias = docsAlias(ctx.url.pathname)