1 files changed, 50 insertions, 0 deletions
diff --git a/src/misc/format-time-string.ts b/src/misc/format-time-string.ts
new file mode 100644
index 0000000000..caa31780ba
--- /dev/null
+++ b/src/misc/format-time-string.ts
@@ -0,0 +1,50 @@
+const defaultLocaleStringFormats: {[index: string]: string} = {
+	'weekday': 'narrow',
+	'era': 'narrow',
+	'year': 'numeric',
+	'month': 'numeric',
+	'day': 'numeric',
+	'hour': 'numeric',
+	'minute': 'numeric',
+	'second': 'numeric',
+	'timeZoneName': 'short'
+};
+
+function formatLocaleString(date: Date, format: string): string {
+	return format.replace(/\{\{(\w+)(:(\w+))?\}\}/g, (match: string, kind: string, unused?, option?: string) => {
+		if (['weekday', 'era', 'year', 'month', 'day', 'hour', 'minute', 'second', 'timeZoneName'].includes(kind)) {
+			return date.toLocaleString(window.navigator.language, {[kind]: option ? option : defaultLocaleStringFormats[kind]});
+		} else {
+			return match;
+		}
+	});
+}
+
+function formatDateTimeString(date: Date, format: string): string {
+	return format
+		.replace(/yyyy/g, date.getFullYear().toString())
+		.replace(/yy/g, date.getFullYear().toString().slice(-2))
+		.replace(/MMMM/g, date.toLocaleString(window.navigator.language, { month: 'long'}))
+		.replace(/MMM/g, date.toLocaleString(window.navigator.language, { month: 'short'}))
+		.replace(/MM/g, (`0${date.getMonth() + 1}`).slice(-2))
+		.replace(/M/g, (date.getMonth() + 1).toString())
+		.replace(/dd/g, (`0${date.getDate()}`).slice(-2))
+		.replace(/d/g, date.getDate().toString())
+		.replace(/HH/g, (`0${date.getHours()}`).slice(-2))
+		.replace(/H/g, date.getHours().toString())
+		.replace(/hh/g, (`0${(date.getHours() % 12) || 12}`).slice(-2))
+		.replace(/h/g, ((date.getHours() % 12) || 12).toString())
+		.replace(/mm/g, (`0${date.getMinutes()}`).slice(-2))
+		.replace(/m/g, date.getMinutes().toString())
+		.replace(/ss/g, (`0${date.getSeconds()}`).slice(-2))
+		.replace(/s/g, date.getSeconds().toString())
+		.replace(/tt/g, date.getHours() >= 12 ? 'PM' : 'AM');
+}
+
+export function formatTimeString(date: Date, format: string): string {
+	return format.replace(/\[(([^\[]|\[\])*)\]|(([yMdHhmst])\4{0,3})/g, (match: string, localeformat?: string, unused?, datetimeformat?: string) => {
+		if (localeformat) return formatLocaleString(date, localeformat);
+		if (datetimeformat) return formatDateTimeString(date, datetimeformat);
+		return match;
+	});
+}