Improve floating elements, add form inputs for date and time with a full datepicker.

+ Add datepicker form input.
+ Add datepicker component.
+ Add calendar component.
+ Add timepicker form input.
* Change Popover to Float, with a better library and general behavior, and some fixes.
* Floating elements visual improvements.

demo/DemoApp.tsx

@@ -1,4 +1,4 @@
-import React from "react";
+import React, {useState} from "react";
 import "../index";
 import {Checkbox} from "../src/Components/Forms/Checkbox";
 import { Radio } from "../src/Components/Forms/Radio";
@@ -6,11 +6,15 @@ import {FloppyDisk, TrashSimple, XCircle} from "@phosphor-icons/react";
 import {Card} from "../src/Components/Card";
 import {PasswordInput} from "../src/Components/Forms/PasswordInput";
 import {RequiredField} from "../src/Components/Forms/RequiredField";
-import {Popover} from "../src/Components/Popovers/Popover";
-import {Tooltip} from "../src/Components/Popovers/Tooltip";
+import {Float} from "../src/Components/Floating/Float";
+import {Tooltip} from "../src/Components/Floating/Tooltip";
+import {DatepickerInput} from "../src/Components/Forms/DatepickerInput";
+import {TimepickerInput} from "../src/Components/Forms/TimepickerInput";
 
 export function DemoApp()
 {
+	const [datetime, setDatetime] = useState(null);
+
 	return (
 		<main className={"app"}>
 			<h1>KernelUI</h1>
@@ -73,6 +77,16 @@ export function DemoApp()
 					Test password
 				</PasswordInput>
 
+				<DatepickerInput value={datetime} onChange={setDatetime}>
+					Date test
+				</DatepickerInput>
+
+				<TimepickerInput value={datetime} onChange={setDatetime}>
+					Time test
+				</TimepickerInput>
+
+				<p>Currently selected datetime: <strong>{datetime ? datetime.toISOString() : "none"}</strong></p>
+
 				<Checkbox>Checkbox demo</Checkbox>
 				<Radio name={"radio-test"}>Radio box test</Radio>
 				<Radio name={"radio-test"}>Radio box test</Radio>
@@ -183,33 +197,33 @@ export function DemoApp()
 
 			<h2>Popovers</h2>
 
-			<Popover mode={"hover"} content={"Do you see me?"}>
+			<Float mode={"hover"} content={"Do you see me?"}>
 				<button type={"button"}>Hover me!</button>
-			</Popover>
+			</Float>
 
-			<Popover mode={"focus"} content={<>I am <strong>focused</strong></>}>
+			<Float mode={"focus"} content={<>I am <strong>focused</strong></>}>
 				<button>Focus me!</button>
-			</Popover>
+			</Float>
 
-			<Popover mode={"click"} content={(
+			<Float mode={"click"} content={(
 				<div>
 					You can add complex (clickable) content in me.
 					<button type={"button"}>OK</button>
 				</div>
 			)}>
 				<button>Click me!</button>
-			</Popover>
+			</Float>
 
-			<Popover content={"I am always shown."} popperOptions={{ placement: "top" }}>
+			<Float mode={"always"} content={"I am always shown."} floatingOptions={{ placement: "top" }}>
 				<button>Why always me?</button>
-			</Popover>
+			</Float>
 
 			<div>
-				<Popover mode={"managed"} content={(show, hide) => (<button onClick={hide}>I can hide the popover!</button>)}>
+				<Float mode={"managed"} content={(show, hide) => (<button onClick={hide}>I can hide the popover!</button>)}>
 					{(show, hide) => (
 						<button type={"button"} onClick={show}>Customized behavior</button>
 					)}
-				</Popover>
+				</Float>
 			</div>
 
 			<h2>Tooltips</h2>

package.json

@@ -11,13 +11,13 @@
   "types": "lib/index.d.ts",
   "main": "lib/index.js",
   "dependencies": {
+    "@floating-ui/react": "^0.26.17",
     "@fontsource-variable/jetbrains-mono": "^5.0.21",
     "@fontsource-variable/manrope": "^5.0.20",
     "@fontsource-variable/source-serif-4": "^5.0.19",
     "@phosphor-icons/react": "^2.1.5",
-    "@popperjs/core": "^2.11.8",
     "react": "^18.3.1",
-    "react-popper": "^2.3.0"
+    "react-merge-refs": "^2.1.1"
   },
   "devDependencies": {
     "@types/react": "^18.3.3",

src/Components/Dates/Calendar.tsx

@@ -0,0 +1,107 @@
+import React, {useMemo} from "react";
+
+/**
+ * Calendar component.
+ */
+export function Calendar({date, onDateSelected, locale, className, ...tableProps}: {
+	date: Date;
+	onDateSelected: (date: Date) => void;
+	locale?: string;
+} & React.TableHTMLAttributes<HTMLTableElement>): React.ReactElement
+{
+	locale = useMemo(() => (locale ?? "fr"), [locale]);
+
+	const currentMonthHeader = useMemo(() => (
+		<tr>
+			{ // For each day of the week, showing its name.
+				[1, 2, 3, 4, 5, 6, 7].map(day => {
+					// Getting a date with the right day of the week.
+					const dayOfWeek = new Date(1970, 0, 4 + day);
+
+					return (
+						<th key={day}>
+							{(new Intl.DateTimeFormat(locale, {weekday: "short"})).format(dayOfWeek)}
+						</th>
+					);
+				})
+			}
+		</tr>
+	), [date]);
+
+	const currentMonthTable = useMemo(() => {
+		// Initialize weeks.
+		const weeksRows = [];
+		let currentWeek = [];
+
+		// Get start date of the calendar.
+		let currentDate = new Date(date);
+		currentDate.setDate(1); // First day of the month.
+		currentDate.setDate(currentDate.getDate() - (currentDate.getDay() - 1 + 7) % 7); // Searching the start of the first week of the current month.
+
+		// Get last day of the calendar.
+		const lastDate = new Date(date);
+		lastDate.setMonth(lastDate.getMonth() + 1, 0); // Get the last day of the month.
+		lastDate.setDate(lastDate.getDate() + (7 - lastDate.getDay())); // Searching the end of the last week of the current month.
+
+
+		while (currentDate.getTime() <= lastDate.getTime() || weeksRows.length < 6)
+		{ // While the current date is before or is the last day of the current view,
+			// adding the current day to the current week.
+			currentWeek.push(
+				<Day key={`${currentDate.getFullYear()}-${currentDate.getMonth()}-${currentDate.getDate()}`}
+				     date={new Date(currentDate)}
+				     faded={date.getMonth() != currentDate.getMonth()}
+				     selected={date.getTime() == currentDate.getTime()}
+				     onClick={onDateSelected} />
+			);
+
+			// We're on sunday, adding the current week and creating a new one.
+			if (currentDate.getDay() == 0)
+			{ // The current week is ended, adding it and creating a new one.
+				weeksRows.push(
+					<tr key={`${currentDate.getFullYear()}-${currentDate.getMonth()}-${currentDate.getDate()}`}>
+						{currentWeek}
+					</tr>
+				);
+				currentWeek = []; // Reset the current week to a new one.
+			}
+
+			// Get the next day.
+			currentDate.setDate(currentDate.getDate() + 1);
+		}
+
+		// Return generated weeks rows.
+		return weeksRows;
+	}, [date, onDateSelected]);
+
+	return (
+		<table className={`calendar${className ? ` ${className}` : ""}`} {...tableProps}>
+			<thead>
+			{currentMonthHeader}
+			</thead>
+			<tbody>
+			{currentMonthTable}
+			</tbody>
+		</table>
+	);
+}
+
+/**
+ * Calendar day component.
+ */
+function Day({date, onClick, faded, selected}: {
+	date: Date;
+	onClick?: (date: Date) => void;
+	faded: boolean;
+	selected: boolean;
+}): React.ReactElement
+{
+	return (
+		<td key={`${date.getFullYear()}-${date.getMonth()}-${date.getDate()}`}>
+			<a className={`day${faded ? " faded" : ""}${selected ? " selected" : ""}`}
+			   onClick={() => onClick?.(date)}>
+				{date.getDate()}
+			</a>
+		</td>
+	);
+}

src/Components/Dates/Datepicker.tsx

@@ -0,0 +1,64 @@
+import React, {useCallback, useMemo} from "react";
+import {CaretLeft, CaretRight} from "@phosphor-icons/react";
+import {Tooltip} from "../Floating/Tooltip";
+import {Calendar} from "./Calendar";
+
+/**
+ * Datepicker component.
+ */
+export function Datepicker({date, onDateSelected, locale, className, ...divProps}: {
+	date: Date;
+	onDateSelected: (date: Date) => void;
+	locale?: string;
+} & React.HTMLAttributes<HTMLDivElement>): React.ReactElement
+{
+	locale = useMemo(() => (locale ?? "fr"), [locale]);
+
+	// Get previous month name.
+	const previousMonthName = useMemo(() => {
+		// Copy the current date and get back one month earlier.
+		const previousMonthDate = new Date(date);
+		previousMonthDate.setMonth(previousMonthDate.getMonth() - 1);
+		return (new Intl.DateTimeFormat(locale, { month: "long", year: "numeric" })).format(previousMonthDate);
+	}, [date]);
+	// Get next month name.
+	const nextMonthName = useMemo(() => {
+		// Copy the current date and go to one month later.
+		const nextMonthDate = new Date(date);
+		nextMonthDate.setMonth(nextMonthDate.getMonth() + 1);
+		return (new Intl.DateTimeFormat(locale, { month: "long", year: "numeric" })).format(nextMonthDate);
+	}, [date]);
+
+	return (
+		<div className={`datepicker${className ? ` ${className}` : ""}`} {...divProps}>
+			<div className={"year-month"}>
+				{(new Intl.DateTimeFormat(locale, {month: "long", year: "numeric"})).format(date)}
+			</div>
+
+			<Calendar date={date} onDateSelected={onDateSelected} />
+
+			<Tooltip content={previousMonthName}>
+				<button type={"button"} className={"previous-month"} onClick={
+					useCallback((event) => {
+						const newDate = new Date(date);
+						newDate.setMonth(newDate.getMonth() - 1);
+						onDateSelected(newDate);
+					}, [date, onDateSelected])
+				}>
+					<CaretLeft weight={"bold"}/>
+				</button>
+			</Tooltip>
+			<Tooltip content={nextMonthName}>
+				<button type={"button"} className={"next-month"} onClick={
+					useCallback((event) => {
+						const newDate = new Date(date);
+						newDate.setMonth(newDate.getMonth() + 1);
+						onDateSelected(newDate);
+					}, [date, onDateSelected])
+				}>
+					<CaretRight weight={"bold"}/>
+				</button>
+			</Tooltip>
+		</div>
+	);
+}

src/Components/Floating/Float.tsx

@@ -0,0 +1,122 @@
+import React, {useCallback, useMemo, useState} from "react";
+import {Card} from "../Card";
+import {
+	shift,
+	useClick,
+	useFloating,
+	useFocus,
+	useHover,
+	useInteractions, useTransitionStyles
+} from "@floating-ui/react";
+import {UseFloatingOptions} from "@floating-ui/react/dist/floating-ui.react";
+import {mergeRefs} from "react-merge-refs";
+
+/**
+ * Fully managed floating content function.
+ */
+export type Managed<T = React.ReactElement|React.ReactNode> = (show: () => void, hide: () => void) => T;
+
+/**
+ * Allowed floating modes.
+ */
+export type FloatingMode = "always"|"click"|"hover"|"focus"|"managed";
+
+/**
+ * A component to show something floating next to an element.
+ */
+export function Float({children, content, className, mode, floatingOptions}: {
+	children: (React.ReactElement & React.ClassAttributes<HTMLElement>)|Managed<(React.ReactElement & React.ClassAttributes<HTMLElement>)>;
+	content?: React.ReactNode|Managed<React.ReactNode>;
+	className?: string;
+	mode?: FloatingMode;
+	floatingOptions?: UseFloatingOptions;
+}): React.ReactElement
+{
+	// By default, use "always" mode.
+	if (!mode) mode = "always";
+
+	// Followed show status.
+	const [shown, setShown] = useState(false);
+
+	// Create show / hide functions.
+	const show = useCallback(() => setShown(true), [setShown]);
+	const hide = useCallback(() => setShown(false), [setShown]);
+
+	// If show mode is "always", always show the floating part after render.
+	if (mode == "always")
+	{
+		setTimeout(() => {
+			setShown(true);
+		}, 0);
+	}
+
+	// Floating initialization.
+	const { refs, floatingStyles, context } = useFloating(
+		useMemo(() => (Object.assign({
+			open: shown,
+			onOpenChange: setShown,
+			middleware: [shift()],
+		} as UseFloatingOptions, floatingOptions)), [floatingOptions, shown, setShown])
+	);
+
+	// Interactions initialization.
+	const hover = useHover(context, useMemo(() => ({ enabled: mode == "hover" }), [mode]));
+	const focus = useFocus(context, useMemo(() => ({ enabled: mode == "focus", visibleOnly: false }), [mode]));
+	const click = useClick(context, useMemo(() => ({ enabled: mode == "click" }), [mode]));
+	const {getReferenceProps, getFloatingProps} = useInteractions([hover, focus, click]);
+
+	// Transition configuration.
+	const {isMounted, styles: transitionStyles} = useTransitionStyles(context, {
+		duration: 200,
+		common: ({side}) => ({
+			transformOrigin: {
+				top: "bottom",
+				bottom: "top",
+				left: "right",
+				right: "left",
+			}[side],
+		}),
+		initial: {
+			transform: "scale(0.66)",
+			opacity: "0",
+		},
+	});
+
+	// Change the child element to use the reference and the interactions properties.
+	const referencedChild = useMemo(() => {
+		// Render the children if a managed floating function is passed.
+		const child = typeof children == "function" ? children(show, hide) : children;
+
+		return React.cloneElement(child,
+			Object.assign(
+				{
+					// Pass references.
+					ref: mergeRefs([refs.setReference, child?.ref]),
+				},
+				// Get interaction properties.
+				getReferenceProps(),
+			),
+		);
+	}, [children, show, hide, refs.setReference, getReferenceProps]);
+
+	// Update floating content.
+	const floatingContent = useMemo(() => (
+		// Render the children if a managed floating function is passed.
+		typeof content == "function" ? content(show, hide) : content
+	), [shown, show, hide, content]);
+
+	return (
+		<>
+			{referencedChild}
+
+			{ // Showing floating element if the state says to do so.
+				isMounted &&
+				<div ref={refs.setFloating} style={floatingStyles} {...getFloatingProps()} className={"floating"}>
+					<Card style={transitionStyles} className={`floating${className ? ` ${className}` : ""}`}>
+						{floatingContent}
+					</Card>
+				</div>
+			}
+		</>
+	);
+}

src/Components/Floating/Tooltip.tsx

@@ -1,5 +1,5 @@
 import React from "react";
-import {Popover} from "./Popover";
+import {Float} from "./Float";
 
 export function Tooltip({children, content}: {
 	children: React.ReactElement;
@@ -7,8 +7,8 @@ export function Tooltip({children, content}: {
 }): React.ReactElement
 {
 	return (
-		<Popover mode={"hover"} content={content} className={"tooltip"} popperOptions={{ placement: "top" }}>
+		<Float mode={"hover"} content={content} className={"tooltip"} floatingOptions={{ placement: "top" }}>
 			{children}
-		</Popover>
+		</Float>
 	);
 }

src/Components/Forms/DatepickerInput.tsx

@@ -0,0 +1,155 @@
+import React, {useCallback, useEffect, useMemo, useRef, useState} from "react";
+import {formatDate, Modify} from "../../Utils";
+import {Float} from "../Floating/Float";
+import {Datepicker} from "../Dates/Datepicker";
+
+/**
+ * A form input for a date with a datepicker.
+ */
+export function DatepickerInput(
+	{
+		children, className,
+		value, onChange,
+		// Properties to pass down.
+		onKeyUp, onBlur,
+		// Already set properties.
+		type, placeholder,
+		...props}: React.PropsWithChildren<Modify<React.InputHTMLAttributes<HTMLInputElement>, {
+		/**
+		 * The current date value.
+		 */
+		value?: Date|null;
+
+		/**
+		 * Called when picked date is changed.
+		 * @param newDate The new date.
+		 */
+		onChange: (newDate: Date) => void;
+
+		// Already set properties.
+		type?: never;
+		placeholder?: never;
+	}>>): React.ReactElement
+{
+	// Date text state.
+	const [dateText, setDateText] = useState("");
+
+	// Update date text when date value has changed.
+	useEffect(() => {
+		if (value && value instanceof Date && !isNaN(value.getTime()))
+			setDateText(formatDate(value));
+	}, [value]);
+
+	// Check if date is valid.
+	const invalidDate = useMemo(() => !(value && value instanceof Date && !isNaN(value.getTime())) && dateText.length > 0, [value, dateText]);
+	const dateValue = useMemo(() => invalidDate ? new Date() : (value ?? new Date()), [invalidDate, value]);
+
+	const inputRef = useRef<HTMLInputElement>();
+
+	/**
+	 * Submit a new date from its raw text.
+	 */
+	const submitDate = useCallback((customDateText?: string) => {
+		// Get the current date text status.
+		const dateTextMatch = (customDateText ?? dateText).match(/^([0-9]?[0-9])\/([0-9]?[0-9])\/([0-9]?[0-9]?[0-9]?[0-9])$/);
+
+		if (dateTextMatch)
+		{
+			// Parse day.
+			let day = dateTextMatch[1];
+			if (day.length < 2) day = "0" + day;
+			if (parseInt(day) <= 0) day = "01";
+
+			// Parse month.
+			let month = dateTextMatch[2];
+			if (month.length < 2) month = "0" + month;
+			if (parseInt(month) <= 0) month = "01";
+
+			// Parse year.
+			let year = parseInt(dateTextMatch[3]);
+			if (year < 100)
+			{
+				year += 1900;
+				if ((new Date()).getFullYear() - year > 96) year += 100;
+			}
+			if (year < 1000) year += 1000;
+
+			// Try to build the structurally valid date.
+			const date = new Date(year + "-" + month + "-" + day);
+
+			if (!isNaN(date.getTime()))
+			{ // Date is valid, checking that it uses the right month (to fix the behavior when we go change 31/03 to 31/02, we want 28/02 or 29/02 and not 01/03).
+				if ((date.getMonth() + 1) > parseInt(month))
+				{ // Current date month is not valid, we're getting back to it.
+					date.setDate(date.getDate() - 1);
+				}
+				if ((date.getMonth() + 1) < parseInt(month))
+				{ // Current date month is not valid, we're getting back to it.
+					date.setDate(date.getDate() + 1);
+				}
+			}
+
+			// Try to keep original hours.
+			date.setHours(value?.getHours() ?? 0, value?.getMinutes() ?? 0, value?.getSeconds() ?? 0, value?.getMilliseconds() ?? 0);
+
+			// Set the structurally valid date.
+			onChange?.(date);
+		}
+		else
+			// No structurally valid date, removing it.
+			onChange?.(null);
+	}, [dateText, onChange]);
+
+	return (
+		<label className={`datepicker-input${invalidDate ? " error" : ""}${className ? ` ${className}` : ""}`}
+			     // Keeping focus on the input when something else in the label takes it.
+			     onFocus={useCallback(() => inputRef.current?.focus(), [inputRef])}>
+			{children}
+
+			<Float mode={"focus"} className={"datepicker"} content={
+				<Datepicker date={dateValue} onDateSelected={onChange} />
+			}>
+				<input type={"text"} ref={inputRef} placeholder={"DD/MM/AAAA"} value={dateText}
+				       onChange={useCallback((event) => {
+					       let dateText = event.currentTarget.value;
+
+					       // Add first '/' if missing.
+					       if (dateText.match(/^[0-9]{2}[^\/]*$/))
+						       dateText = dateText.substring(0, 2) + "/" + dateText.substring(2);
+
+					       // Add second '/' if missing.
+					       if (dateText.match(/^[0-9]{2}\/[0-9]{2}[^\/]*$/))
+						       dateText = dateText.substring(0, 5) + "/" + dateText.substring(5);
+
+					       // Set the new date text.
+					       setDateText(dateText);
+
+					       // If a full date has been entered, reading it.
+					       const fullDateMatch = dateText.match(/^([0-9]{2})\/([0-9]{2})\/([0-9]{4})$/);
+					       if (fullDateMatch)
+					       { // We have a structurally valid date, submitting it.
+						       submitDate(dateText);
+					       }
+				       }, [submitDate])}
+				       onKeyUp={useCallback((event) => {
+					       if (event.key == "Enter")
+						       // Submit date when enter is pressed.
+						       submitDate();
+								 return onKeyUp?.(event);
+				       }, [submitDate, onKeyUp])}
+					     onBlur={useCallback((event) => {
+						     // Submit date when leaving form input.
+								 submitDate();
+								 return onBlur?.(event);
+							 }, [submitDate, onBlur])}
+					     {...props} />
+			</Float>
+
+			{ // The date is invalid, showing a subtext to say so.
+				invalidDate && (
+					<span className={"error subtext"}>Invalid date.</span>
+				)
+			}
+		</label>
+	);
+}

src/Components/Forms/TimepickerInput.tsx

@@ -0,0 +1,117 @@
+import React, {useCallback, useEffect, useMemo, useState} from "react";
+import {formatTime, Modify} from "../../Utils";
+
+export function TimepickerInput(
+	{
+		children, className,
+		value, onChange,
+		// Properties to pass down.
+		onKeyUp, onBlur,
+		// Already set properties.
+		type, placeholder,
+		...props
+	}: React.PropsWithChildren<Modify<React.InputHTMLAttributes<HTMLInputElement>, {
+		value?: Date|null;
+
+		onChange: (newDateTime: Date) => void;
+
+		// Already set properties.
+		type?: never;
+		placeholder?: never;
+	}>>): React.ReactElement
+{
+	// Time text state.
+	const [timeText, setTimeText] = useState("");
+
+	// Update time text when datetime value has changed.
+	useEffect(() => {
+		if (value && value instanceof Date && !isNaN(value.getTime()))
+			setTimeText(formatTime(value));
+	}, [value]);
+
+	// Check if time is valid.
+	const invalidTime = useMemo(() => !(value && value instanceof Date && !isNaN(value.getTime())) && timeText.length > 0, [value, timeText]);
+	const timeValue = useMemo(() => invalidTime ? new Date() : (value ?? new Date()), [invalidTime, value]);
+
+	/**
+	 * Submit a new time from its raw text.
+	 */
+	const submitTime = useCallback((customTimeText?: string) => {
+		// Get the current date text status.
+		const timeTextMatch = (customTimeText ?? timeText).match(/^([0-2]?[0-9]):([0-5]?[0-9])$/);
+
+		if (timeTextMatch)
+		{
+			// Parse hours.
+			let rawHours = timeTextMatch[1];
+			if (rawHours.length < 2) rawHours = "0" + rawHours;
+			let hours = parseInt(rawHours);
+			if (isNaN(hours)) hours = 0;
+
+			// Parse minutes.
+			let rawMinutes = timeTextMatch[2];
+			if (rawMinutes.length < 2) rawMinutes = "0" + rawMinutes;
+			let minutes = parseInt(rawMinutes);
+			if (isNaN(minutes)) minutes = 0;
+
+			//TODO
+			// Parse seconds?
+
+			// Try to build the structurally valid date with this time.
+			//TODO
+			const datetime = new Date(timeValue);
+			datetime.setHours(hours, minutes);
+			// Put the date back, if it changed to another day.
+			datetime.setFullYear(timeValue.getFullYear(), timeValue.getMonth(), timeValue.getDate());
+
+			// Set the structurally valid date.
+			onChange?.(datetime);
+		}
+		else
+			// No structurally valid date, removing it.
+			onChange?.(null);
+	}, [timeText, timeValue, onChange]);
+
+	return (
+		<label className={`timepicker${className ? ` ${className}` : ""}`}>
+			{children}
+
+			<input type={"text"} placeholder={"HH:MM"} value={timeText}
+			       onChange={useCallback((event) => {
+				       let timeText = event.currentTarget.value;
+
+				       // Add first ':' if missing.
+				       if (timeText.match(/^[0-9]{2}[^:]*$/))
+					       timeText = timeText.substring(0, 2) + ":" + timeText.substring(2);
+
+				       // Set the new time text.
+				       setTimeText(timeText);
+
+				       // If a full time has been entered, reading it.
+				       const fullTimeMatch = timeText.match(/^([0-2][0-9]):([0-5][0-9])$/);
+				       if (fullTimeMatch)
+				       { // We have a structurally valid time, submitting it.
+					       submitTime(timeText);
+				       }
+			       }, [submitTime])}
+			       onKeyUp={useCallback((event) => {
+				       if (event.key == "Enter")
+					       // Submit time when enter is pressed.
+					       submitTime();
+				       return onKeyUp?.(event);
+			       }, [submitTime, onKeyUp])}
+			       onBlur={useCallback((event) => {
+				       // Submit time when leaving form input.
+				       submitTime();
+				       return onBlur?.(event);
+			       }, [submitTime, onBlur])}
+			       {...props} />
+
+			{ // The date is invalid, showing a subtext to say so.
+				invalidTime && (
+					<span className={"error subtext"}>Invalid time.</span>
+				)
+			}
+		</label>
+	);
+}

src/Components/Popovers/Popover.tsx

@@ -1,96 +0,0 @@
-import React, {useMemo, useRef, useState} from "react";
-import {usePopper} from "react-popper";
-import * as PopperJS from "@popperjs/core";
-import {Card} from "../Card";
-
-/**
- * Fully managed popover content function.
- */
-export type Managed<T = React.ReactElement|React.ReactNode> = (show: () => void, hide: () => void) => T;
-
-/**
- * Allowed popover modes.
- */
-export type PopoverMode = "always"|"click"|"hover"|"focus"|"managed";
-
-/**
- * A component to show something next to an element.
- */
-export function Popover({children, content, className, mode, popperOptions}: {
-	children: React.ReactElement|Managed<React.ReactElement>;
-	content?: React.ReactNode|Managed<React.ReactNode>;
-	className?: string;
-	mode?: PopoverMode;
-	popperOptions?: Partial<PopperJS.Options>;
-}): React.ReactElement
-{
-	// By default, use "always" mode.
-	if (!mode) mode = "always";
-
-	// Followed show status.
-	const [shown, setShown] = useState(false);
-
-	// Create show / hide functions.
-	const show = useMemo(() => (!shown ? () => setShown(true) : () => {}), [shown]);
-	const hide = useMemo(() => (shown ? () => setShown(false) : () => {}), [shown]);
-
-	// If show mode is "always", always show the popover after render.
-	setTimeout(() => {
-		if (mode == "always") setShown(true);
-	}, 0);
-
-	// HTML elements references.
-	const referenceElement = useRef();
-	const popperElement = useRef();
-
-	// Change the child element to use the reference.
-	const referencedChild = useMemo(() => (
-		React.cloneElement(
-			// Render the children if a managed popover function is passed.
-			typeof children == "function" ? children(show, hide) : children,
-			Object.assign(
-				{
-					ref: referenceElement,
-				},
-				// Pass click event if click mode is enabled.
-				mode == "click" ? {
-					onClick: (event: React.MouseEvent): void => {
-						setShown(!shown);
-					},
-				} : {},
-				// Pass focus events if focus mode is enabled.
-				mode == "focus" ? {
-					onFocus: show,
-					onBlur: hide,
-				} : {},
-				// Pass the hover event if hover mode is enabled.
-				mode == "hover" ? {
-					onMouseEnter: show,
-					onMouseOut: hide,
-				} : {},
-			))
-	), [mode, shown, show, hide, children]);
-
-	// Update popover content.
-	const popoverContent = useMemo(() => (
-		// Render the children if a managed popover function is passed.
-		typeof content == "function" ? content(show, hide) : content
-	), [shown, show, hide, content]);
-
-	// Initialize popper.
-	const { styles, attributes } = usePopper(
-		referenceElement?.current, popperElement?.current, popperOptions
-	);
-
-	return (
-		<>
-			{referencedChild}
-
-			<div ref={popperElement} style={styles.popper} {...attributes.popper} className={"popover"} hidden={!shown}>
-				<Card className={`popover${className ? ` ${className}` : ""}`}>
-					{popoverContent}
-				</Card>
-			</div>
-		</>
-	);
-}

src/Utils.tsx

@@ -0,0 +1,12 @@
+
+export type Modify<T, R> = Omit<T, keyof R> & R;
+
+export function formatDate(date: Date): string
+{
+	return ((date.getDate() < 10 ? "0" : "") + date.getDate()) + "/" + (((date.getMonth() + 1) < 10 ? "0" : "") + (date.getMonth() + 1)) + "/" + date.getFullYear();
+}
+
+export function formatTime(date: Date): string
+{
+	return (date.getHours() < 10 ? "0" : "") + date.getHours() + ":" + (date.getMinutes() < 10 ? "0" : "") + date.getMinutes();
+}

src/styles/_components.less

@@ -1,10 +1,11 @@
 
 @import "components/_button";
 @import "components/_card";
+@import "components/_dates";
 @import "components/_form";
 @import "components/_headings";
 @import "components/_link";
 @import "components/_list";
-@import "components/_popover";
+@import "components/_floating";
 @import "components/_steps";
 @import "components/_table";

src/styles/components/_card.less

@@ -30,7 +30,7 @@
 		margin-bottom: 0;
 	}
 
-	&.popover
+	&.floating
 	{
 		width: 20em;
 	}

src/styles/components/_dates.less

@@ -0,0 +1,3 @@
+
+@import "dates/_calendar";
+@import "dates/_datepicker";

src/styles/components/_floating.less

@@ -0,0 +1,2 @@
+@import "floating/_floating";
+@import "floating/_tooltip";

src/styles/components/_form.less

@@ -1,5 +1,6 @@
 
 @import "forms/_box";
+@import "forms/_datepicker-input";
 @import "forms/_input";
 @import "forms/_label";
 @import "forms/_password-input";

src/styles/components/_popover.less

@@ -1,2 +0,0 @@
-@import "popovers/_popover";
-@import "popovers/_tooltip";

src/styles/components/dates/_calendar.less

@@ -0,0 +1,57 @@
+table.calendar
+{
+	thead th
+	{
+		text-align: center;
+	}
+
+	tbody > tr
+	{
+		border-bottom: none;
+
+		&:nth-child(even) { background: transparent; }
+		&:hover { background: transparent; }
+
+		> td
+		{
+			padding: 0;
+			text-align: center;
+		}
+	}
+
+	a.day
+	{
+		transition: background 0.15s ease;
+
+		display: inline-flex;
+		align-items: center;
+		justify-content: center;
+
+		width: 2.2em;
+		height: 2.2em;
+		border-radius: 50%;
+
+		background: transparent;
+		color: var(--foreground);
+
+		font-weight: 400;
+		text-align: center;
+		cursor: pointer;
+
+		&:hover
+		{
+			background: var(--background-darker);
+		}
+
+		&.selected
+		{
+			background: var(--primary);
+			color: var(--background);
+		}
+
+		&.faded
+		{
+			opacity: 0.4;
+		}
+	}
+}

src/styles/components/dates/_datepicker.less

@@ -0,0 +1,44 @@
+.datepicker
+{
+	position: relative;
+	padding: 0 1em;
+	background: var(--background-lighter);
+	font-size: 0.9em;
+
+	.year-month
+	{
+		font-size: 1.1em;
+		text-align: center;
+	}
+
+	button
+	{
+		&.previous-month, &.next-month
+		{
+			position: absolute;
+			top: 0;
+			bottom: 0;
+
+			display: flex;
+			align-items: center;
+			justify-content: center;
+
+			margin: auto;
+			padding: 0;
+			width: 2em;
+			height: 2em;
+
+			svg
+			{ margin: 0; }
+		}
+
+		&.previous-month
+		{
+			left: -1.1em;
+		}
+		&.next-month
+		{
+			right: -1.1em;
+		}
+	}
+}

src/styles/components/floating/_floating.less

@@ -0,0 +1,10 @@
+:not(.card).floating
+{
+	display: block;
+	z-index: 1;
+
+	> .card.floating
+	{
+		margin: 0.4em;
+	}
+}

src/styles/components/floating/_tooltip.less

@@ -1,4 +1,4 @@
-.card.popover.tooltip
+.card.floating.tooltip
 {
 	width: unset;
 	max-width: 20em;

src/styles/components/forms/_datepicker-input.less

@@ -0,0 +1,9 @@
+label.datepicker-input
+{
+	.card.datepicker
+	{
+		padding: 0.2em;
+		width: fit-content;
+		max-width: unset;
+	}
+}

src/styles/components/forms/_label.less

@@ -11,4 +11,21 @@ label
 	{
 		&::after { content: "*"; color: var(--red); font-weight: 600; }
 	}
+
+	&.error
+	{
+		input, textarea, select { border-color: var(--red); }
+	}
+
+	span.subtext
+	{
+		display: block;
+		font-size: 0.9em;
+		text-align: center;
+
+		&.error
+		{
+			color: var(--red);
+		}
+	}
 }

src/styles/components/popovers/_popover.less

@@ -1,27 +0,0 @@
-:not(.card).popover
-{
-	transition: opacity 0.2s ease;
-
-	display: flex;
-	z-index: 1;
-
-	opacity: 1;
-
-	&[data-popper-placement="top"], &[data-popper-placement="bottom"]
-	{ justify-content: center; }
-	&[data-popper-placement="right"]
-	{ justify-content: left; }
-	&[data-popper-placement="left"]
-	{ justify-content: right; }
-
-	> .card.popover
-	{
-		margin: 0.4em;
-	}
-
-	&[hidden]
-	{
-		opacity: 0;
-		pointer-events: none;
-	}
-}

yarn.lock

@@ -430,6 +430,58 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@floating-ui/core@npm:^1.0.0":
+  version: 1.6.2
+  resolution: "@floating-ui/core@npm:1.6.2"
+  dependencies:
+    "@floating-ui/utils": "npm:^0.2.0"
+  checksum: 10c0/db2621dc682e7f043d6f118d087ae6a6bfdacf40b26ede561760dd53548c16e2e7c59031e013e37283801fa307b55e6de65bf3b316b96a054e4a6a7cb937c59e
+  languageName: node
+  linkType: hard
+
+"@floating-ui/dom@npm:^1.0.0":
+  version: 1.6.5
+  resolution: "@floating-ui/dom@npm:1.6.5"
+  dependencies:
+    "@floating-ui/core": "npm:^1.0.0"
+    "@floating-ui/utils": "npm:^0.2.0"
+  checksum: 10c0/ebdc14806f786e60df8e7cc2c30bf9cd4d75fe734f06d755588bbdef2f60d0a0f21dffb14abdc58dea96e5577e2e366feca6d66ba962018efd1bc91a3ece4526
+  languageName: node
+  linkType: hard
+
+"@floating-ui/react-dom@npm:^2.1.0":
+  version: 2.1.0
+  resolution: "@floating-ui/react-dom@npm:2.1.0"
+  dependencies:
+    "@floating-ui/dom": "npm:^1.0.0"
+  peerDependencies:
+    react: ">=16.8.0"
+    react-dom: ">=16.8.0"
+  checksum: 10c0/9ee44dfeb27f585fb1e0114cbe37c72ff5d34149900f4f3013f6b0abf8c3365eab13286c360f97fbe0c44bb91a745e7a4c18b82d111990b45a7a7796dc55e461
+  languageName: node
+  linkType: hard
+
+"@floating-ui/react@npm:^0.26.17":
+  version: 0.26.17
+  resolution: "@floating-ui/react@npm:0.26.17"
+  dependencies:
+    "@floating-ui/react-dom": "npm:^2.1.0"
+    "@floating-ui/utils": "npm:^0.2.0"
+    tabbable: "npm:^6.0.0"
+  peerDependencies:
+    react: ">=16.8.0"
+    react-dom: ">=16.8.0"
+  checksum: 10c0/3d3a995aff5e905acd1fc4a3a7c92beba801b1d241f5ee1a05667c98dc1fcb9a0cc6ec82d4330fd84a0fd9b9fafa50f76dee886819659c49371733caa8d48b12
+  languageName: node
+  linkType: hard
+
+"@floating-ui/utils@npm:^0.2.0":
+  version: 0.2.2
+  resolution: "@floating-ui/utils@npm:0.2.2"
+  checksum: 10c0/b2becdcafdf395af1641348da0031ff1eaad2bc60c22e14bd3abad4acfe2c8401e03097173d89a2f646a99b75819a78ef21ebb2572cab0042a56dd654b0065cd
+  languageName: node
+  linkType: hard
+
 "@fontsource-variable/jetbrains-mono@npm:^5.0.21":
   version: 5.0.21
   resolution: "@fontsource-variable/jetbrains-mono@npm:5.0.21"
@@ -599,13 +651,6 @@ __metadata:
   languageName: node
   linkType: hard
 
-"@popperjs/core@npm:^2.11.8":
-  version: 2.11.8
-  resolution: "@popperjs/core@npm:2.11.8"
-  checksum: 10c0/4681e682abc006d25eb380d0cf3efc7557043f53b6aea7a5057d0d1e7df849a00e281cd8ea79c902a35a414d7919621fc2ba293ecec05f413598e0b23d5a1e63
-  languageName: node
-  linkType: hard
-
 "@rollup/pluginutils@npm:^5.1.0":
   version: 5.1.0
   resolution: "@rollup/pluginutils@npm:5.1.0"
@@ -1769,18 +1814,18 @@ __metadata:
   version: 0.0.0-use.local
   resolution: "kernel-ui-core@workspace:."
   dependencies:
+    "@floating-ui/react": "npm:^0.26.17"
     "@fontsource-variable/jetbrains-mono": "npm:^5.0.21"
     "@fontsource-variable/manrope": "npm:^5.0.20"
     "@fontsource-variable/source-serif-4": "npm:^5.0.19"
     "@phosphor-icons/react": "npm:^2.1.5"
-    "@popperjs/core": "npm:^2.11.8"
     "@types/react": "npm:^18.3.3"
     "@types/react-dom": "npm:^18.3.0"
     "@vitejs/plugin-react": "npm:^4.3.0"
     less: "npm:^4.2.0"
     react: "npm:^18.3.1"
     react-dom: "npm:^18.3.1"
-    react-popper: "npm:^2.3.0"
+    react-merge-refs: "npm:^2.1.1"
     typescript: "npm:^5.4.5"
     vite: "npm:^5.2.11"
     vite-plugin-dts: "npm:^3.9.1"
@@ -1850,7 +1895,7 @@ __metadata:
   languageName: node
   linkType: hard
 
-"loose-envify@npm:^1.0.0, loose-envify@npm:^1.1.0":
+"loose-envify@npm:^1.1.0":
   version: 1.4.0
   resolution: "loose-envify@npm:1.4.0"
   dependencies:
@@ -2254,24 +2299,10 @@ __metadata:
   languageName: node
   linkType: hard
 
-"react-fast-compare@npm:^3.0.1":
-  version: 3.2.2
-  resolution: "react-fast-compare@npm:3.2.2"
-  checksum: 10c0/0bbd2f3eb41ab2ff7380daaa55105db698d965c396df73e6874831dbafec8c4b5b08ba36ff09df01526caa3c61595247e3269558c284e37646241cba2b90a367
-  languageName: node
-  linkType: hard
-
-"react-popper@npm:^2.3.0":
-  version: 2.3.0
-  resolution: "react-popper@npm:2.3.0"
-  dependencies:
-    react-fast-compare: "npm:^3.0.1"
-    warning: "npm:^4.0.2"
-  peerDependencies:
-    "@popperjs/core": ^2.0.0
-    react: ^16.8.0 || ^17 || ^18
-    react-dom: ^16.8.0 || ^17 || ^18
-  checksum: 10c0/23f93540537ca4c035425bb8d5e51b11131fbc921d7ac1d041d0ae557feac8c877f3a012d36b94df8787803f52ed81e6df9257ac9e58719875f7805518d6db3f
+"react-merge-refs@npm:^2.1.1":
+  version: 2.1.1
+  resolution: "react-merge-refs@npm:2.1.1"
+  checksum: 10c0/b68cbc4ea51fd96f77247733388738630769d928f32958e63262ce43dff10c6b20f18a0483c6a640a1ffba48f32be26059d4ee9711881cacc63297b01311c8f6
   languageName: node
   linkType: hard
 
@@ -2635,6 +2666,13 @@ __metadata:
   languageName: node
   linkType: hard
 
+"tabbable@npm:^6.0.0":
+  version: 6.2.0
+  resolution: "tabbable@npm:6.2.0"
+  checksum: 10c0/ced8b38f05f2de62cd46836d77c2646c42b8c9713f5bd265daf0e78ff5ac73d3ba48a7ca45f348bafeef29b23da7187c72250742d37627883ef89cbd7fa76898
+  languageName: node
+  linkType: hard
+
 "tar@npm:^6.1.11, tar@npm:^6.1.2":
   version: 6.2.1
   resolution: "tar@npm:6.2.1"
@@ -2844,15 +2882,6 @@ __metadata:
   languageName: node
   linkType: hard
 
-"warning@npm:^4.0.2":
-  version: 4.0.3
-  resolution: "warning@npm:4.0.3"
-  dependencies:
-    loose-envify: "npm:^1.0.0"
-  checksum: 10c0/aebab445129f3e104c271f1637fa38e55eb25f968593e3825bd2f7a12bd58dc3738bb70dc8ec85826621d80b4acfed5a29ebc9da17397c6125864d72301b937e
-  languageName: node
-  linkType: hard
-
 "which@npm:^2.0.1":
   version: 2.0.2
   resolution: "which@npm:2.0.2"