From 3b127a4a1b0cab0dbe8cf11b2190d7a0b8800f3f Mon Sep 17 00:00:00 2001
From: Zade Viggers <zade@viggers.net>
Date: Fri, 6 Oct 2023 22:55:52 +1300
Subject: [PATCH] Fix day of year calculation

---
 package.json       |  2 +-
 src/miniseed.ts    | 14 ++------------
 src/utils.ts       | 21 +++++++++++++++++++++
 tests/vaid.test.ts |  2 +-
 4 files changed, 25 insertions(+), 14 deletions(-)
 create mode 100644 src/utils.ts

diff --git a/package.json b/package.json
index e1962ff..4e2b965 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
 	"name": "miniseed",
-	"version": "0.1.4",
+	"version": "0.1.5",
 	"type": "module",
 	"scripts": {
 		"build": "vite build",
diff --git a/src/miniseed.ts b/src/miniseed.ts
index e75f84f..0e02bf0 100644
--- a/src/miniseed.ts
+++ b/src/miniseed.ts
@@ -1,5 +1,6 @@
 import { jDataView } from "z-jdataview-temp-publish";
 import { buf as bufToCRC } from "crc-32/crc32c";
+import { getDayOfYear } from "./utils";
 
 const encodingTypes = {
 	text: { code: 0, byteSize: 1 },
@@ -56,20 +57,9 @@ export function serialiseToMiniSEEDBuffer<T extends keyof typeof encodingTypes>(
 
 	if (metadata.startTime instanceof Date) {
 		// From https://stackoverflow.com/a/8619946
-		const start = new Date(metadata.startTime.getFullYear(), 0, 0);
-		const diff =
-			metadata.startTime.valueOf() -
-			start.valueOf() +
-			(start.getTimezoneOffset() -
-				metadata.startTime.getTimezoneOffset()) *
-				60 *
-				1000;
-		const oneDay = 1000 * 60 * 60 * 24;
-		const dayOfYear = Math.floor(diff / oneDay);
-
 		metadata.startTime = {
 			year: metadata.startTime.getFullYear(),
-			dayOfYear,
+			dayOfYear: getDayOfYear(metadata.startTime),
 			hour: metadata.startTime.getHours(),
 			minute: metadata.startTime.getMinutes(),
 			second: metadata.startTime.getSeconds(),
diff --git a/src/utils.ts b/src/utils.ts
new file mode 100644
index 0000000..68f2651
--- /dev/null
+++ b/src/utils.ts
@@ -0,0 +1,21 @@
+/**
+ * Returns a number 1-366 representing how far through the year the date is.
+ * Ideally port this to Temporal when it comes out.
+ *
+ * Credit to https://stackoverflow.com/a/26426761
+ */
+export function getDayOfYear(date: Date): number {
+	// Get Day of Year
+	var dayCount = [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334];
+	var mn = date.getMonth();
+	var dn = date.getDate();
+	var dayOfYear = dayCount[mn] + dn;
+	if (mn > 1 && isLeapYear(date)) dayOfYear++;
+	return dayOfYear;
+}
+
+function isLeapYear(date: Date): boolean {
+	const year = date.getFullYear();
+	if ((year & 3) != 0) return false;
+	return year % 100 != 0 || year % 400 == 0;
+}
diff --git a/tests/vaid.test.ts b/tests/vaid.test.ts
index 94cfd49..c2455f0 100644
--- a/tests/vaid.test.ts
+++ b/tests/vaid.test.ts
@@ -14,7 +14,7 @@ beforeAll(async () => {
 });
 
 afterAll(async () => {
-	// await rm(tempFolder, { recursive: true });
+	await rm(tempFolder, { recursive: true });
 });
 
 describe("Generated data validity", () => {