From 31792a3a432f792f2228f1ec1cd85f8eea3d3c10 Mon Sep 17 00:00:00 2001
From: KitAmbraid <128903658+KitAmbraid@users.noreply.github.com>
Date: Sat, 22 Feb 2025 12:00:54 +0100
Subject: [PATCH] space lua: os.date add support for %U, %V and %W (#1250)

---
 common/space_lua/stdlib/os.ts       | 33 +++++++++++++++++++++++++++--
 common/space_lua/stdlib/os_test.lua |  6 +++++-
 website/API/os.md                   |  3 +++
 3 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/common/space_lua/stdlib/os.ts b/common/space_lua/stdlib/os.ts
index 947e975f..2dea449c 100644
--- a/common/space_lua/stdlib/os.ts
+++ b/common/space_lua/stdlib/os.ts
@@ -1,5 +1,31 @@
 import { LuaBuiltinFunction, LuaTable } from "$common/space_lua/runtime.ts";
 
+const ONE_DAY = 1000 * 60 * 60 * 24;
+
+// weekStartDay: 0 for Sunday, 1 for Monday
+// iso: if true, week 01 contains Jan. 4th and prior week is week 52 or 53 of year prior
+//      if false, week 01 starts on first weekStartDay of the year and prior week is week 00
+function weekNumber(inDate: Date, weekStartDay: number, iso: boolean): number {
+  const year = inDate.getFullYear();
+  const jan1 = new Date(year, 0, 1);
+
+  let jan1Week: number;
+  if (iso) {
+    jan1Week = (jan1.getDay() - weekStartDay + 7) % 7 < 3 ? 1 : 0;
+  } else jan1Week = jan1.getDay() == weekStartDay ? 1 : 0;
+
+  const week = Math.floor(
+    ((inDate.getTime() - jan1.getTime() + ONE_DAY) / ONE_DAY) / 7,
+  ) + jan1Week;
+
+  if (iso && week == 0) {
+    const dec31 = new Date(inDate.getFullYear() - 1, 11, 31);
+    return weekNumber(dec31, weekStartDay, iso);
+  }
+
+  return week;
+}
+
 export const osApi = new LuaTable({
   time: new LuaBuiltinFunction((_sf, tbl?: LuaTable) => {
     if (tbl) {
@@ -69,10 +95,13 @@ export const osApi = new LuaTable({
       "%j": () => {
         const start = new Date(date.getFullYear(), 0, 0);
         const diff = date.getTime() - start.getTime();
-        const oneDay = 1000 * 60 * 60 * 24;
-        const dayOfYear = Math.floor(diff / oneDay);
+        const dayOfYear = Math.floor(diff / ONE_DAY);
         return dayOfYear.toString().padStart(3, "0");
       },
+      // Week
+      "%U": () => weekNumber(date, 0, false).toString().padStart(2, "0"),
+      "%W": () => weekNumber(date, 1, false).toString().padStart(2, "0"),
+      "%V": () => weekNumber(date, 1, true).toString().padStart(2, "0"),
       // Time zone
       "%Z": () => {
         const match = date.toTimeString().match(/\((.*)\)/);
diff --git a/common/space_lua/stdlib/os_test.lua b/common/space_lua/stdlib/os_test.lua
index 85c7d35e..bf907a6d 100644
--- a/common/space_lua/stdlib/os_test.lua
+++ b/common/space_lua/stdlib/os_test.lua
@@ -6,4 +6,8 @@ end
 
 -- Basic OS functions
 assert(os.time() > 0)
-assert(os.date("%Y-%m-%d", os.time({ year = 2020, month = 1, day = 1 })) == "2020-01-01") 
\ No newline at end of file
+assert(os.date("%Y-%m-%d", os.time({ year = 2020, month = 1, day = 1 })) == "2020-01-01")
+
+-- Week calculations
+assert(os.date("%U %V %W", os.time({ year = 2051, month = 1, day = 1 })) == "01 52 00")
+assert(os.date("%U %V %W", os.time({ year = 2025, month = 2, day = 18})) == "07 08 07")
diff --git a/website/API/os.md b/website/API/os.md
index 6d59e773..1fe578c2 100644
--- a/website/API/os.md
+++ b/website/API/os.md
@@ -35,6 +35,9 @@ Format specifiers:
 - `%A`: Full weekday name (e.g., "Sunday")
 - `%a`: Abbreviated weekday name (e.g., "Sun")
 - `%w`: Weekday (0-6, Sunday is 0)
+- `%U`: Week of the year, starting with the first Sunday as the first day of week 01 (00-53)
+- `%W`: Week of the year, starting with the first Monday as the first day of week 01 (00-53)
+- `%V`: ISO 8601 week of the year (01-53) (see [Wikipedia](https://en.wikipedia.org/wiki/ISO_week_date))
 - `%j`: Day of year (001-366)
 - `%Z`: Time zone name
 - `%z`: Time zone offset from UTC