Respect timezones when converting dates

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "@ztimson/utils",
-	"version": "0.27.0",
+	"version": "0.27.4",
 	"description": "Utility library",
 	"author": "Zak Timson",
 	"license": "MIT",

src/objects.ts

@@ -1,56 +1,51 @@
 export type Delta = { [key: string]: any | Delta | null };
 
+
 /**
- * Applies deltas in order to modify `target`.
- * @param target - Object to mutate
- * @param deltas - List of deltas to apply
+ * Applies deltas to `target`.
+ * @param base starting point
+ * @param deltas List of deltas to apply
  * @returns Mutated target
  */
-export function applyDeltas(target: any, deltas: Delta[]): any {
-	for(const delta of deltas) {
-		for(const [key, value] of Object.entries(delta)) {
-			if(value === null) {
-				delete target[key]; // Remove
-			} else if(Array.isArray(value)) {
-				target[key] = [...value]; // Array
-			} else if(typeof value === 'object') {
-				if(typeof target[key] !== 'object' || Array.isArray(target[key]) || !target[key])
-					target[key] = {}; // Nested
-				applyDeltas(target[key], [value]); // Recurse
-			} else {
-				target[key] = value; // Primitive
+export function applyDeltas(base: any, ...deltas: any[]): any {
+	function applyDelta(base: any, delta: any): any {
+		if(delta === null) return null;
+		if(typeof base !== 'object' || base === null) return delta === undefined ? base : delta;
+		const result = Array.isArray(base) ? [...base] : { ...base };
+		for(const key in delta) {
+			const val = delta[key];
+			if(val === undefined) delete result[key];
+			else if(typeof val === 'object' && val !== null && !Array.isArray(val)) result[key] = applyDelta(result[key], val);
+			else result[key] = val;
 		}
+		return result;
 	}
-	}
-	return target;
+
+	for(const d of deltas.flat()) base = applyDelta(base, d?.delta ?? d);
+	return base;
 }
 
 /**
  * Creates a nested delta that reverts `target` back to `old`.
  * @param old - Original object
- * @param target - Modified object
- * @returns Delta to revert changes
+ * @param updated - Modified object
+ * @returns New changes
  */
-export function calcDelta(old: any, target: any): Delta {
-	const delta: Delta = {};
-	const keys = new Set([...Object.keys(old || {}), ...Object.keys(target || {})]);
-	for(const key of keys) {
-		const val1 = old?.[key];
-		const val2 = target?.[key];
-		if(!(key in target)) {
-			delta[key] = val1; // Removed
-		} else if(!(key in old)) {
-			delta[key] = null; // Added
-		} else if(Array.isArray(val1) || Array.isArray(val2)) {
-			if(JSON.stringify(val1) !== JSON.stringify(val2)) delta[key] = val1; // Array
-		} else if(typeof val1 === 'object' && typeof val2 === 'object' && val1 && val2) {
-			const nested = calcDelta(val1, val2);
-			if(Object.keys(nested).length) delta[key] = nested; // Nested
-		} else if(val1 !== val2) {
-			delta[key] = val1; // Modified
+export function calcDelta(old: any, updated: any): any {
+	if(updated == null) return null; // full delete
+	const delta: any = {};
+	const isObj = (v: any) => v && typeof v === 'object' && !Array.isArray(v);
+	for (const key of new Set([...(old ? Object.keys(old) : []), ...(updated ? Object.keys(updated) : [])])) {
+		const oldVal = old?.[key];
+		const newVal = updated?.[key];
+		if(isObj(oldVal) && isObj(newVal)) {
+			const nested = calcDelta(oldVal, newVal);
+			if(nested !== null && Object.keys(nested).length > 0) delta[key] = nested;
+		} else if(JSON.stringify(oldVal) !== JSON.stringify(newVal)) {
+			delta[key] = newVal;
 		}
 	}
-	return delta;
+	return Object.keys(delta).length === 0 ? {} : delta;
 }
 
 /**

src/time.ts

@@ -55,23 +55,46 @@ export function formatDate(format: string = 'YYYY-MM-DD H:mm', date: Date | numb
 	}
 
 	let zonedDate = new Date(date);
+	let get: (fn: 'FullYear' | 'Month' | 'Date' | 'Day' | 'Hours' | 'Minutes' | 'Seconds' | 'Milliseconds') => number;
+	const partsMap: Record<string, string> = {};
 	if (!numericTz && tzName !== 'UTC') {
 		const parts = new Intl.DateTimeFormat('en-US', {
 			timeZone: tzName,
-			year: 'numeric', month: '2-digit', day: '2-digit',
+			year: 'numeric', month: '2-digit', day: '2-digit', weekday: 'long',
 			hour: '2-digit', minute: '2-digit', second: '2-digit',
 			hour12: false
 		}).formatToParts(date);
-		const get = (type: string) => parts.find(p => p.type === type)?.value;
-		const build = `${get('year')}-${get('month')}-${get('day')}T${get('hour')}:${get('minute')}:${get('second')}Z`;
-		zonedDate = new Date(build);
-	} else if (numericTz || tzName === 'UTC') {
+		parts.forEach(p => {
+			partsMap[p.type] = p.value;
+		});
+
+		const monthValue = parseInt(partsMap.month) - 1;
+		const dayOfWeekValue = new Date(`${partsMap.year}-${partsMap.month}-${partsMap.day}`).getDay();
+		const hourValue = parseInt(partsMap.hour);
+
+		get = (fn: 'FullYear' | 'Month' | 'Date' | 'Day' | 'Hours' | 'Minutes' | 'Seconds' | 'Milliseconds'): number => {
+			switch (fn) {
+				case 'FullYear': return parseInt(partsMap.year);
+				case 'Month': return monthValue;
+				case 'Date': return parseInt(partsMap.day);
+				case 'Day': return dayOfWeekValue;
+				case 'Hours': return hourValue;
+				case 'Minutes': return parseInt(partsMap.minute);
+				case 'Seconds': return parseInt(partsMap.second);
+				default: return 0;
+			}
+		};
+	} else {
 		const offset = numericTz ? tz as number : 0;
 		zonedDate = new Date(date.getTime() + offset * 60 * 60 * 1000);
+		get = (fn: 'FullYear' | 'Month' | 'Date' | 'Day' | 'Hours' | 'Minutes' | 'Seconds' | 'Milliseconds'): number => zonedDate[`getUTC${fn}`]();
 	}
 
-	const get = (fn: 'FullYear' | 'Month' | 'Date' | 'Day' | 'Hours' | 'Minutes' | 'Seconds' | 'Milliseconds') =>
-		(numericTz || tzName === 'UTC') ? zonedDate[`getUTC${fn}`]() : zonedDate[`get${fn}`]();
+	function numSuffix(n: number): string {
+		const s = ["th", "st", "nd", "rd"];
+		const v = n % 100;
+		return n + (s[(v - 20) % 10] || s[v] || s[0]);
+	}
 
 	function getTZOffset(): string {
 		if (numericTz) {
@@ -119,7 +142,7 @@ export function formatDate(format: string = 'YYYY-MM-DD H:mm', date: Date | numb
 		m: get('Minutes').toString(),
 		ss: get('Seconds').toString().padStart(2, '0'),
 		s: get('Seconds').toString(),
-		SSS: get('Milliseconds').toString().padStart(3, '0'),
+		SSS: (zonedDate[`getUTC${'Milliseconds'}`]()).toString().padStart(3, '0'),
 		A: get('Hours') >= 12 ? 'PM' : 'AM',
 		a: get('Hours') >= 12 ? 'pm' : 'am',
 		ZZ: getTZOffset().replace(':', ''),