import { context, type WithRefOpts } from '../../provider';
import { createAttrs } from '$uix/morfo';
import { boolToEmptyStrOrUndef } from '$adom';
import { readableActive, state, type ActiveProps, type StateProps } from '$libs/reactive';
import type { SomaKeyboardEvent, SomaMouseEvent, OnChangeFn } from '../../types';
import { KEYS, getDirectionalKeys } from '../../keyboard';
import { Soma } from '../../core/soma.svelte';
import { CALENDAR_LANGS } from './langs';
import {
	type DateValue,
	type DateMatcher,
	type Month,
	type WeekStartsOn,
	type DateOrder,
	isSameDay,
	startOfMonth,
	endOfMonth,
	getLocalTimeZone,
	CalendarDate,
	today,
	resolveDateOrder
} from '$libs/days';
import {
	applyMultipleSelection,
	applySingleSelection,
	computeDateFlags,
	createMonths,
	getIsoWeekNumber,
	getSimpleWeekNumber,
	getWeekdays,
	isOutsideMonth,
	isToday,
	isWeekend,
	shiftDate,
	validateCalendarBounds
} from './helpers';
import type {
	CalendarCellSnippetProps,
	CalendarDaySnippetProps,
	CalendarMonthSelectSnippetProps,
	CalendarView,
	CalendarYearSelectSnippetProps
} from './types';

// ── Contract ─────────────────────────────────────────────────────────────────

import { calendarMorfo } from '../../../morfo/components/calendar';
import type { SomaRuntime, SomaRuntimePart } from '../../runtime.svelte';

const attrs = createAttrs(calendarMorfo);

// ── Root ────────────────────────────────────────────────────────────────────

export interface CalendarOpts
	extends
		WithRefOpts,
		StateProps<{
			placeholder: DateValue;
			value: DateValue | DateValue[] | undefined;
		}>,
		ActiveProps<{
			type: 'single' | 'multiple';
			preventDeselect: boolean;
			minValue: DateValue | undefined;
			maxValue: DateValue | undefined;
			minViewValue: DateValue | undefined;
			maxViewValue: DateValue | undefined;
			disabled: boolean;
			pagedNavigation: boolean;
			weekStartsOn: WeekStartsOn | undefined;
			weekdayFormat: Intl.DateTimeFormatOptions['weekday'];
			isDateDisabled: DateMatcher | undefined;
			isDateUnavailable: DateMatcher | undefined;
			isDateHoliday: DateMatcher | undefined;
			fixedWeeks: boolean;
			numberOfMonths: number;
			calendarLabel: string | undefined;
			readonly: boolean;
			disableDaysOutsideMonth: boolean;
			maxDays: number | undefined;
			monthFormat: Intl.DateTimeFormatOptions['month'] | ((month: number) => string);
			yearFormat: Intl.DateTimeFormatOptions['year'] | ((year: number) => string);
			showWeekNumbers: boolean;
			weekNumberFormat: 'iso' | 'simple';
			announceNavigation: boolean;
			initialFocus: boolean;
			dir: 'ltr' | 'rtl';
			locale: string;
		}> {
	onValueChange?: OnChangeFn<DateValue | DateValue[] | undefined>;
}

/**
 * Resolve the initial placeholder when the consumer has not supplied one.
 * Prefers the current selection, falls back to today. Exposed so the wrapper
 * can stay thin instead of mutating props.
 */
export function resolveInitialCalendarPlaceholder(
	placeholder: DateValue | undefined,
	value: DateValue | DateValue[] | undefined,
	type: 'single' | 'multiple'
): DateValue {
	if (placeholder) return placeholder;
	if (type === 'single' && value && !Array.isArray(value)) return value;
	if (type === 'multiple' && Array.isArray(value) && value.length > 0) {
		return value[value.length - 1];
	}
	const t = today(getLocalTimeZone());
	return new CalendarDate(t.year, t.month, t.day);
}

function sameDateArray(a: DateValue[], b: DateValue[]): boolean {
	if (a.length !== b.length) return false;
	return a.every((date, index) => isSameDay(date, b[index]));
}

export class CalendarProvider {
	readonly opts: CalendarOpts;
	readonly runtimePart: SomaRuntimePart;
	readonly soma: Soma;
	readonly runtime: SomaRuntime;
	static readonly ctx = context<CalendarProvider>('Calendar');
	static get(): CalendarProvider | undefined {
		return this.ctx.getOr(undefined) as CalendarProvider | undefined;
	}
	static require(): CalendarProvider {
		return this.ctx.get();
	}
	static create(opts: CalendarOpts) {
		return new CalendarProvider(opts);
	}

	/** Child ids exposed so the Grid can wire aria-labelledby. */
	headingId = state('');
	/** Live-region text for announcements. */
	announcement = $state('');
	/**
	 * Navigation view (Ark/Mantine/MUI pattern): the day grid switches in-place
	 * to a month grid then a year grid for fast navigation — no native `<select>`,
	 * no nested popover. The `MonthView` / `YearView` parts render the reused
	 * `MonthGrid` / `YearGrid` when active; the `Heading` advances the view.
	 */
	view = $state<CalendarView>('day');
	private lastLoggedValidationKey: string | null = null;

	private constructor(opts: CalendarOpts) {
		this.opts = opts;
		this.soma = Soma.require();
		this.runtime = this.soma.runtime(calendarMorfo, {});
		this.runtimePart = this.runtime.part('provider', {
			id: opts.id,
			ref: opts.ref,
			owner: this,
			context: CalendarProvider.ctx,
			// Source for the morfo's `aria-disabled` (propRef('disabled')) so
			// renderProps() resolves it instead of the provider re-declaring it.
			props: { disabled: () => opts.disabled.current }
		});

		// Initial focus management used to live in the wrapper. Move it here so
		// the wrapper stays thin and the focus contract is centralized.
		$effect(() => {
			if (!opts.initialFocus.current) return;
			const root = opts.ref.current;
			if (!root) return;
			queueMicrotask(() => {
				const el = root.querySelector<HTMLElement>(`[${attrs.day}][data-focused]`);
				this.soma.dom.focus(el);
			});
		});

		$effect(() => {
			const status = this.validationStatus;
			if (status === false) {
				this.lastLoggedValidationKey = null;
				return;
			}
			const key =
				status.reason === 'selection-bounds'
					? `${status.reason}:${status.minValue.toString()}:${status.maxValue.toString()}`
					: `${status.reason}:${status.minViewValue.toString()}:${status.maxViewValue.toString()}`;
			if (key === this.lastLoggedValidationKey) return;
			this.lastLoggedValidationKey = key;
			this.soma.logger.error('soma.calendar', status.message, {
				context:
					status.reason === 'selection-bounds'
						? {
								reason: status.reason,
								minValue: status.minValue.toString(),
								maxValue: status.maxValue.toString()
							}
						: {
								reason: status.reason,
								minViewValue: status.minViewValue.toString(),
								maxViewValue: status.maxViewValue.toString()
							}
			});
		});
	}

	// ── Derived reactive model ────────────────────────────────────────────────

	readonly effectiveLocale = $derived.by(
		() => this.opts.locale.current || this.soma.langs.getLocale() || 'en'
	);

	readonly months: Month<DateValue>[] = $derived.by(() =>
		createMonths(this.opts.placeholder.current, {
			numberOfMonths: Math.max(1, this.opts.numberOfMonths.current),
			weekStartsOn: this.opts.weekStartsOn.current,
			fixedWeeks: this.opts.fixedWeeks.current,
			locale: this.effectiveLocale
		})
	);

	readonly weekStartsOnResolved = $derived.by(() => {
		const custom = this.opts.weekStartsOn.current;
		if (custom !== undefined) return custom;
		// Locale default — derive from the first cell produced by the month
		// generator (its day-of-week in en-US is the start).
		const first = this.months[0]?.weeks[0]?.[0];
		if (!first) return 0;
		const dow = first.toDate(getLocalTimeZone()).getDay();
		return dow as WeekStartsOn;
	});

	readonly weekdays = $derived.by(() =>
		getWeekdays(this.effectiveLocale, this.weekStartsOnResolved, this.opts.weekdayFormat.current)
	);

	/**
	 * Resolved date-segment order:
	 *   1. explicit `locale` prop → resolve from that locale (prop wins)
	 *   2. app-wide `soma.dates.getDateOrder()` (when no prop)
	 *   3. derive from the effective locale as last fallback
	 * Matches the precedence used by DateField so a prop-driven Calendar
	 * formats consistently with its sibling DateField in the same locale.
	 */
	readonly dateOrder: DateOrder = $derived.by(() => {
		if (this.opts.locale.current) return resolveDateOrder(this.effectiveLocale);
		const fromService = this.soma.dates?.getDateOrder?.();
		if (fromService) return fromService as DateOrder;
		return resolveDateOrder(this.effectiveLocale);
	});

	/**
	 * Visible months as bare DateValues (first day of month). Used for
	 * prev/next button bound checks so we don't need to recreate
	 * `months` just for comparisons.
	 */
	readonly visibleMonths = $derived.by(() => this.months.map((m) => m.value));

	/** Current value normalized to an array for uniform operations. */
	readonly selectedDates: DateValue[] = $derived.by(() => {
		const v = this.opts.value.current;
		if (!v) return [];
		return Array.isArray(v) ? v : [v];
	});

	readonly boundsValidationStatus = $derived.by(() =>
		validateCalendarBounds({
			minValue: this.opts.minValue.current,
			maxValue: this.opts.maxValue.current,
			minViewValue: this.opts.minViewValue.current,
			maxViewValue: this.opts.maxViewValue.current
		})
	);

	readonly validationStatus = $derived.by(() => this.boundsValidationStatus);

	readonly validationMessage = $derived.by(() =>
		this.validationStatus === false ? undefined : this.validationStatus.message
	);

	readonly selectionInvalid = $derived.by(() => {
		for (const d of this.selectedDates) {
			const flags = this.computeFlags(d);
			if (flags.disabled || flags.unavailable) return true;
		}
		return false;
	});

	readonly isInvalid = $derived.by(() => this.validationStatus !== false || this.selectionInvalid);

	readonly headingValue = $derived.by(() => {
		const first = this.visibleMonths[0];
		if (!first) return '';
		const month = this.formatMonth(first.month);
		const year = this.formatYear(first.year);
		if (this.visibleMonths.length > 1) {
			const last = this.visibleMonths[this.visibleMonths.length - 1];
			const lastMonth = this.formatMonth(last.month);
			const lastYear = this.formatYear(last.year);
			return `${month} ${year} – ${lastMonth} ${lastYear}`;
		}
		return `${month} ${year}`;
	});

	readonly fullCalendarLabel = $derived.by(() => {
		const base =
			this.opts.calendarLabel.current ?? this.soma.langs.ts(CALENDAR_LANGS.LABEL) ?? 'Calendar';
		return `${base}, ${this.headingValue}`;
	});

	// ── Navigation ────────────────────────────────────────────────────────────

	private canShowPlaceholder(next: DateValue): boolean {
		const min = this.opts.minViewValue.current;
		if (min && endOfMonth(next).compare(min) < 0) return false;
		const max = this.opts.maxViewValue.current;
		if (!max) return true;
		const last = next.add({ months: Math.max(1, this.opts.numberOfMonths.current) - 1 });
		return last.compare(max) <= 0;
	}

	private setPlaceholder(next: DateValue, target?: HTMLElement): void {
		const nextMonth = startOfMonth(next);
		if (!this.canShowPlaceholder(nextMonth)) return;
		if (this.opts.placeholder.current.compare(nextMonth) === 0) return;
		this.opts.placeholder.current = nextMonth;
		this.announceNavigation();
		void this.runtime.trigger('shift-navigate', target ? { fallbackTarget: target } : undefined);
	}

	prevPage(target?: HTMLElement): void {
		const step = this.opts.pagedNavigation.current
			? Math.max(1, this.opts.numberOfMonths.current)
			: 1;
		this.setPlaceholder(
			startOfMonth(this.opts.placeholder.current.subtract({ months: step })),
			target
		);
	}

	nextPage(target?: HTMLElement): void {
		const step = this.opts.pagedNavigation.current
			? Math.max(1, this.opts.numberOfMonths.current)
			: 1;
		this.setPlaceholder(startOfMonth(this.opts.placeholder.current.add({ months: step })), target);
	}

	prevYear(target?: HTMLElement): void {
		this.setPlaceholder(this.opts.placeholder.current.subtract({ years: 1 }), target);
	}

	nextYear(target?: HTMLElement): void {
		this.setPlaceholder(this.opts.placeholder.current.add({ years: 1 }), target);
	}

	setMonth(month: number, target?: HTMLElement): void {
		this.setPlaceholder(this.opts.placeholder.current.set({ month }), target);
	}

	setYear(year: number, target?: HTMLElement): void {
		this.setPlaceholder(this.opts.placeholder.current.set({ year }), target);
	}

	// ── Navigation view (day ↔ month ↔ year) ──────────────────────────────────

	setView(view: CalendarView): void {
		this.view = view;
	}

	/** Heading click: drill UP one level (day → month → year). */
	advanceView(): void {
		this.view = this.view === 'day' ? 'month' : 'year';
	}

	/** Month grid select: set the placeholder year+month and drill back DOWN to days. */
	selectMonthView(year: number, month: number, target?: HTMLElement): void {
		this.setPlaceholder(this.opts.placeholder.current.set({ year, month }), target);
		this.view = 'day';
	}

	/** Year grid select: set the placeholder year and drill back DOWN to months. */
	selectYearView(year: number, target?: HTMLElement): void {
		this.setYear(year, target);
		this.view = 'month';
	}

	private announceNavigation(): void {
		if (!this.opts.announceNavigation.current) return;
		this.announcement = this.headingValue;
	}

	// ── Bound checks ──────────────────────────────────────────────────────────

	readonly isPrevButtonDisabled = $derived.by(() => {
		if (this.opts.disabled.current) return true;
		const min = this.opts.minViewValue.current;
		if (!min) return false;
		const prev = this.visibleMonths[0]?.subtract({ months: 1 });
		return prev ? endOfMonth(prev).compare(min) < 0 : false;
	});

	readonly isNextButtonDisabled = $derived.by(() => {
		if (this.opts.disabled.current) return true;
		const max = this.opts.maxViewValue.current;
		if (!max) return false;
		const last = this.visibleMonths[this.visibleMonths.length - 1];
		const next = last?.add({ months: 1 });
		return next ? next.compare(max) > 0 : false;
	});

	// ── Selection ────────────────────────────────────────────────────────────

	/**
	 * Handle activation of a date (click or Enter/Space on a Day). Respects
	 * readonly, disabled, unavailable. Dispatches to single/multiple handler
	 * and calls the `onValueChange` callback configured in the wrapper.
	 */
	select(date: DateValue, target?: HTMLElement): void {
		if (this.opts.readonly.current || this.opts.disabled.current) return;
		const flags = this.computeFlags(date);
		if (flags.disabled || flags.unavailable) return;

		const type = this.opts.type.current;
		const preventDeselect = this.opts.preventDeselect.current;
		let eventName: 'commit-select' | 'commit-unselect';
		if (type === 'single') {
			const prev = this.opts.value.current as DateValue | undefined;
			const next = applySingleSelection(prev, date, preventDeselect);
			if (prev && next && isSameDay(prev, next)) return;
			if (!prev && !next) return;
			this.opts.value.current = next;
			eventName = next ? 'commit-select' : 'commit-unselect';
		} else {
			const prev = (this.opts.value.current as DateValue[] | undefined) ?? [];
			const next = applyMultipleSelection(prev, date, preventDeselect, this.opts.maxDays.current);
			if (sameDateArray(prev, next)) return;
			this.opts.value.current = next;
			eventName = next.some((d) => isSameDay(d, date)) ? 'commit-select' : 'commit-unselect';
		}
		void this.runtime.trigger(eventName, target ? { fallbackTarget: target } : undefined);
	}

	isSelected(date: DateValue): boolean {
		for (const d of this.selectedDates) if (isSameDay(d, date)) return true;
		return false;
	}

	computeFlags(date: DateValue) {
		return computeDateFlags(date, {
			minValue: this.opts.minValue.current,
			maxValue: this.opts.maxValue.current,
			disabled: this.opts.disabled.current,
			isDateDisabled: this.opts.isDateDisabled.current,
			isDateUnavailable: this.opts.isDateUnavailable.current,
			isDateHoliday: this.opts.isDateHoliday.current
		});
	}

	// ── Keyboard ──────────────────────────────────────────────────────────────

	/**
	 * Keyboard routing for the root element — delegated to by Day onkeydown.
	 * Returns true when the event was handled (caller must preventDefault).
	 */
	handleDayKeydown(e: SomaKeyboardEvent<HTMLElement>, date: DateValue): boolean {
		const { nextKey: horizNext, prevKey: horizPrev } = getDirectionalKeys(
			this.opts.dir.current,
			'horizontal'
		);

		let target: DateValue | undefined;
		if (e.key === horizNext) target = shiftDate(date, 1);
		else if (e.key === horizPrev) target = shiftDate(date, -1);
		else if (e.key === KEYS.ARROW_DOWN) target = shiftDate(date, 7);
		else if (e.key === KEYS.ARROW_UP) target = shiftDate(date, -7);
		else if (e.key === KEYS.HOME) {
			const monthStart = startOfMonth(date);
			target = monthStart;
		} else if (e.key === KEYS.END) {
			target = endOfMonth(date);
		} else if (e.key === KEYS.PAGE_UP) {
			target = e.shiftKey ? date.subtract({ years: 1 }) : date.subtract({ months: 1 });
		} else if (e.key === KEYS.PAGE_DOWN) {
			target = e.shiftKey ? date.add({ years: 1 }) : date.add({ months: 1 });
		} else if (e.key === KEYS.ENTER || e.key === ' ') {
			e.preventDefault();
			this.select(date, e.currentTarget as HTMLElement);
			return true;
		}

		if (!target) return false;
		e.preventDefault();

		// If target is outside the visible months, advance the placeholder
		// so the focused cell renders.
		if (
			isOutsideMonth(target, this.visibleMonths[0]) &&
			(this.visibleMonths.length === 1 ||
				target.compare(this.visibleMonths[this.visibleMonths.length - 1]) < 0 ||
				target.compare(this.visibleMonths[0]) < 0)
		) {
			this.setPlaceholder(startOfMonth(target), e.currentTarget as HTMLElement);
		}

		// Move focus after the DOM updates.
		queueMicrotask(() => {
			const root = this.opts.ref.current;
			if (!root) return;
			const el = root.querySelector<HTMLElement>(
				`[data-calendar-day][data-value="${target!.toString()}"]`
			);
			this.soma.dom.focus(el);
		});

		return true;
	}

	// ── Formatters ────────────────────────────────────────────────────────────

	formatMonth(month: number): string {
		const fmt = this.opts.monthFormat.current;
		if (typeof fmt === 'function') return fmt(month);
		const anchor = new Date(Date.UTC(2024, month - 1, 15));
		return new Intl.DateTimeFormat(this.effectiveLocale, { month: fmt ?? 'long' }).format(anchor);
	}

	formatYear(year: number): string {
		const fmt = this.opts.yearFormat.current;
		if (typeof fmt === 'function') return fmt(year);
		const anchor = new Date(Date.UTC(year, 5, 15));
		return new Intl.DateTimeFormat(this.effectiveLocale, { year: fmt ?? 'numeric' }).format(anchor);
	}

	formatDay(date: DateValue): string {
		return new Intl.DateTimeFormat(this.effectiveLocale, { day: 'numeric' }).format(
			date.toDate(getLocalTimeZone())
		);
	}

	// ── Week numbers ──────────────────────────────────────────────────────────

	getWeekNumber(weekFirstDate: DateValue): number {
		return this.opts.weekNumberFormat.current === 'iso'
			? getIsoWeekNumber(weekFirstDate)
			: getSimpleWeekNumber(weekFirstDate, this.weekStartsOnResolved, this.effectiveLocale);
	}

	// ── Props ─────────────────────────────────────────────────────────────────

	readonly props = $derived.by(() =>
		this.runtimePart.assert({
			// role + aria-disabled are morfo-declared, resolved via renderProps.
			...this.runtimePart.renderProps(),
			dir: this.opts.dir.current,
			// Computed accessible name (calendarLabel + heading) — overrides the
			// morfo's raw `ariaLabel` propRef (which the provider doesn't source).
			'aria-label': this.fullCalendarLabel,
			// Soma-owned data values (the morfo declares these attrs without a value).
			'data-type': this.opts.type.current,
			'data-readonly': boolToEmptyStrOrUndef(this.opts.readonly.current),
			'data-disabled': boolToEmptyStrOrUndef(this.opts.disabled.current),
			'data-invalid': boolToEmptyStrOrUndef(this.isInvalid)
		} as const)
	);
}

// ── Header ───────────────────────────────────────────────────────────────────

export class CalendarHeaderProvider {
	readonly opts: WithRefOpts;
	readonly runtimePart: SomaRuntimePart;
	static create(opts: WithRefOpts) {
		return new CalendarHeaderProvider(opts);
	}

	private constructor(opts: WithRefOpts) {
		this.opts = opts;
		const provider = CalendarProvider.require();
		this.runtimePart = provider.runtime.part('header', {
			id: opts.id,
			ref: opts.ref,
			owner: this
		});
	}

	readonly props = $derived.by(() =>
		this.runtimePart.assert({ ...this.runtimePart.props } as const)
	);
}

// ── Heading ──────────────────────────────────────────────────────────────────

export interface CalendarHeadingOpts
	extends
		WithRefOpts,
		ActiveProps<{
			value: DateValue | undefined;
		}> {}

export class CalendarHeadingProvider {
	readonly opts: CalendarHeadingOpts;
	readonly runtimePart: SomaRuntimePart;
	static create(opts: CalendarHeadingOpts) {
		return new CalendarHeadingProvider(opts);
	}

	readonly provider: CalendarProvider;

	private constructor(opts: CalendarHeadingOpts) {
		this.opts = opts;
		this.provider = CalendarProvider.require();
		this.runtimePart = this.provider.runtime.part('heading', {
			id: opts.id,
			ref: opts.ref,
			owner: this
		});
		if (!opts.value.current) this.provider.headingId.current = opts.id.current;
	}

	readonly headingValue = $derived.by(() => {
		const value = this.opts.value.current;
		if (!value) return this.provider.headingValue;
		return `${this.provider.formatMonth(value.month)} ${this.provider.formatYear(value.year)}`;
	});

	readonly props = $derived.by(() =>
		this.runtimePart.assert({ ...this.runtimePart.props, 'aria-hidden': true as const } as const)
	);
}

// ── Prev / Next Buttons ─────────────────────────────────────────────────────

abstract class CalendarPaginationButtonProvider {
	readonly opts: WithRefOpts;
	readonly runtimePart: SomaRuntimePart;
	readonly provider: CalendarProvider;
	protected abstract disabled(): boolean;
	protected abstract trigger(target?: HTMLElement): void;

	protected constructor(opts: WithRefOpts, part: 'prev-button' | 'next-button') {
		this.opts = opts;
		this.provider = CalendarProvider.require();
		this.runtimePart = this.provider.runtime.part(part, {
			id: opts.id,
			ref: opts.ref,
			owner: this,
			// Source for the morfo's `aria-disabled` (propRef('disabled')) — the
			// button-local bound check (isPrev/isNextButtonDisabled).
			props: { disabled: () => this.disabled() }
		});
	}

	readonly onclick = (e: SomaMouseEvent<HTMLButtonElement>) => {
		if (this.disabled()) return;
		this.trigger(e.currentTarget as HTMLElement);
	};

	readonly props = $derived.by(() => {
		const disabled = this.disabled();
		return this.runtimePart.assert({
			// type, aria-label (commonRef calendar.prev/next-month) and
			// aria-disabled are morfo-declared, resolved via renderProps.
			...this.runtimePart.renderProps(),
			'data-disabled': boolToEmptyStrOrUndef(disabled),
			disabled,
			onclick: this.onclick
		} as const);
	});
}

export class CalendarPrevButtonProvider extends CalendarPaginationButtonProvider {
	static create(opts: WithRefOpts) {
		return new CalendarPrevButtonProvider(opts);
	}
	private constructor(opts: WithRefOpts) {
		super(opts, 'prev-button');
	}
	protected disabled() {
		return this.provider.isPrevButtonDisabled;
	}
	protected trigger(target?: HTMLElement) {
		this.provider.prevPage(target);
	}
}

export class CalendarNextButtonProvider extends CalendarPaginationButtonProvider {
	static create(opts: WithRefOpts) {
		return new CalendarNextButtonProvider(opts);
	}
	private constructor(opts: WithRefOpts) {
		super(opts, 'next-button');
	}
	protected disabled() {
		return this.provider.isNextButtonDisabled;
	}
	protected trigger(target?: HTMLElement) {
		this.provider.nextPage(target);
	}
}

// ── MonthSelect ──────────────────────────────────────────────────────────────

export interface CalendarMonthSelectOpts
	extends
		WithRefOpts,
		ActiveProps<{
			months: number[];
			monthFormat: Intl.DateTimeFormatOptions['month'] | ((month: number) => string) | undefined;
			disabled: boolean;
		}> {}

export class CalendarMonthSelectProvider {
	readonly opts: CalendarMonthSelectOpts;
	readonly runtimePart: SomaRuntimePart;
	static create(opts: CalendarMonthSelectOpts) {
		return new CalendarMonthSelectProvider(opts);
	}

	readonly provider: CalendarProvider;

	private constructor(opts: CalendarMonthSelectOpts) {
		this.opts = opts;
		this.provider = CalendarProvider.require();
		this.runtimePart = this.provider.runtime.part('month-select', {
			id: opts.id,
			ref: opts.ref,
			owner: this,
			// Source for the morfo's `aria-disabled` (propRef('disabled')) — the
			// combined own-or-provider disabled state.
			props: { disabled: () => this.isDisabled }
		});
	}

	readonly isDisabled = $derived.by(
		() => this.opts.disabled.current || this.provider.opts.disabled.current
	);

	readonly monthItems: CalendarMonthSelectSnippetProps['monthItems'] = $derived.by(() => {
		const customFmt = this.opts.monthFormat.current;
		const formatter = (m: number) => {
			if (typeof customFmt === 'function') return customFmt(m);
			if (typeof customFmt === 'string') {
				const anchor = new Date(Date.UTC(2024, m - 1, 15));
				return new Intl.DateTimeFormat(this.provider.effectiveLocale, {
					month: customFmt
				}).format(anchor);
			}
			return this.provider.formatMonth(m);
		};
		return this.opts.months.current.map((value) => ({ value, label: formatter(value) }));
	});

	readonly selectedMonthItem = $derived.by(() => {
		const month = this.provider.opts.placeholder.current.month;
		return (
			this.monthItems.find((i) => i.value === month) ??
			this.monthItems[0] ?? { value: month, label: String(month) }
		);
	});

	readonly onchange = (e: Event) => {
		const target = e.currentTarget as HTMLSelectElement;
		const month = Number.parseInt(target.value, 10);
		if (!Number.isNaN(month)) this.provider.setMonth(month, target);
	};

	readonly props = $derived.by(() => {
		const disabled = this.isDisabled;
		return this.runtimePart.assert({
			// aria-label (commonRef calendar.month-select) and aria-disabled are
			// morfo-declared, resolved via renderProps.
			...this.runtimePart.renderProps(),
			'data-disabled': boolToEmptyStrOrUndef(disabled),
			disabled,
			value: String(this.selectedMonthItem.value),
			onchange: this.onchange
		} as const);
	});
}

// ── YearSelect ───────────────────────────────────────────────────────────────

export interface CalendarYearSelectOpts
	extends
		WithRefOpts,
		ActiveProps<{
			years: number[];
			yearFormat: Intl.DateTimeFormatOptions['year'] | ((year: number) => string) | undefined;
			disabled: boolean;
		}> {}

export class CalendarYearSelectProvider {
	readonly opts: CalendarYearSelectOpts;
	readonly runtimePart: SomaRuntimePart;
	static create(opts: CalendarYearSelectOpts) {
		return new CalendarYearSelectProvider(opts);
	}

	readonly provider: CalendarProvider;

	private constructor(opts: CalendarYearSelectOpts) {
		this.opts = opts;
		this.provider = CalendarProvider.require();
		this.runtimePart = this.provider.runtime.part('year-select', {
			id: opts.id,
			ref: opts.ref,
			owner: this,
			// Source for the morfo's `aria-disabled` (propRef('disabled')) — the
			// combined own-or-provider disabled state.
			props: { disabled: () => this.isDisabled }
		});
	}

	readonly isDisabled = $derived.by(
		() => this.opts.disabled.current || this.provider.opts.disabled.current
	);

	readonly yearItems: CalendarYearSelectSnippetProps['yearItems'] = $derived.by(() => {
		const customFmt = this.opts.yearFormat.current;
		const formatter = (y: number) => {
			if (typeof customFmt === 'function') return customFmt(y);
			if (typeof customFmt === 'string') {
				const anchor = new Date(Date.UTC(y, 5, 15));
				return new Intl.DateTimeFormat(this.provider.effectiveLocale, {
					year: customFmt
				}).format(anchor);
			}
			return this.provider.formatYear(y);
		};
		return this.opts.years.current.map((value) => ({ value, label: formatter(value) }));
	});

	readonly selectedYearItem = $derived.by(() => {
		const year = this.provider.opts.placeholder.current.year;
		return (
			this.yearItems.find((i) => i.value === year) ??
			this.yearItems[0] ?? { value: year, label: String(year) }
		);
	});

	readonly onchange = (e: Event) => {
		const target = e.currentTarget as HTMLSelectElement;
		const year = Number.parseInt(target.value, 10);
		if (!Number.isNaN(year)) this.provider.setYear(year, target);
	};

	readonly props = $derived.by(() => {
		const disabled = this.isDisabled;
		return this.runtimePart.assert({
			// aria-label (commonRef calendar.year-select) and aria-disabled are
			// morfo-declared, resolved via renderProps.
			...this.runtimePart.renderProps(),
			'data-disabled': boolToEmptyStrOrUndef(disabled),
			disabled,
			value: String(this.selectedYearItem.value),
			onchange: this.onchange
		} as const);
	});
}

// ── Grid / GridHead / GridBody / GridRow / HeadCell (presentational) ────────

export interface CalendarGridOpts
	extends
		WithRefOpts,
		ActiveProps<{
			labelledBy: string | undefined;
		}> {}

export class CalendarGridProvider {
	readonly opts: CalendarGridOpts;
	readonly runtimePart: SomaRuntimePart;
	static create(opts: CalendarGridOpts) {
		return new CalendarGridProvider(opts);
	}

	readonly provider: CalendarProvider;

	private constructor(opts: CalendarGridOpts) {
		this.opts = opts;
		this.provider = CalendarProvider.require();
		this.runtimePart = this.provider.runtime.part('grid', {
			id: opts.id,
			ref: opts.ref,
			owner: this,
			// Sources for the morfo's `aria-readonly`/`aria-disabled`
			// (propRef('readonly')/propRef('disabled')) so renderProps resolves them.
			props: {
				readonly: () => this.provider.opts.readonly.current,
				disabled: () => this.provider.opts.disabled.current
			}
		});
	}

	readonly props = $derived.by(() => {
		const headingId = this.opts.labelledBy.current ?? this.provider.headingId.current;
		return this.runtimePart.assert({
			// role, aria-readonly and aria-disabled are morfo-declared, resolved
			// via renderProps.
			...this.runtimePart.renderProps(),
			// Computed: honours the `labelledBy` prop override + the registered
			// heading id (overrides the morfo's raw partRef('heading')).
			'aria-labelledby': headingId || undefined
		} as const);
	});
}

export class CalendarGridHeadProvider {
	readonly opts: WithRefOpts;
	readonly runtimePart: SomaRuntimePart;
	static create(opts: WithRefOpts) {
		return new CalendarGridHeadProvider(opts);
	}
	private constructor(opts: WithRefOpts) {
		this.opts = opts;
		const provider = CalendarProvider.require();
		this.runtimePart = provider.runtime.part('grid-head', {
			id: opts.id,
			ref: opts.ref,
			owner: this
		});
	}
	readonly props = $derived.by(() =>
		this.runtimePart.assert({ ...this.runtimePart.props } as const)
	);
}

export class CalendarGridBodyProvider {
	readonly opts: WithRefOpts;
	readonly runtimePart: SomaRuntimePart;
	static create(opts: WithRefOpts) {
		return new CalendarGridBodyProvider(opts);
	}
	private constructor(opts: WithRefOpts) {
		this.opts = opts;
		const provider = CalendarProvider.require();
		this.runtimePart = provider.runtime.part('grid-body', {
			id: opts.id,
			ref: opts.ref,
			owner: this
		});
	}
	readonly props = $derived.by(() =>
		this.runtimePart.assert({ ...this.runtimePart.props } as const)
	);
}

export class CalendarGridRowProvider {
	readonly opts: WithRefOpts;
	readonly runtimePart: SomaRuntimePart;
	static create(opts: WithRefOpts) {
		return new CalendarGridRowProvider(opts);
	}
	private constructor(opts: WithRefOpts) {
		this.opts = opts;
		const provider = CalendarProvider.require();
		this.runtimePart = provider.runtime.part('grid-row', {
			id: opts.id,
			ref: opts.ref,
			owner: this
		});
	}
	readonly props = $derived.by(() =>
		this.runtimePart.assert({ ...this.runtimePart.props, role: 'row' as const } as const)
	);
}

export class CalendarHeadCellProvider {
	readonly opts: WithRefOpts;
	readonly runtimePart: SomaRuntimePart;
	static create(opts: WithRefOpts) {
		return new CalendarHeadCellProvider(opts);
	}
	private constructor(opts: WithRefOpts) {
		this.opts = opts;
		const provider = CalendarProvider.require();
		this.runtimePart = provider.runtime.part('head-cell', {
			id: opts.id,
			ref: opts.ref,
			owner: this
		});
	}
	readonly props = $derived.by(() =>
		this.runtimePart.assert({ ...this.runtimePart.props, scope: 'col' as const } as const)
	);
}

// ── Cell ─────────────────────────────────────────────────────────────────────

export interface CalendarCellOpts
	extends WithRefOpts, ActiveProps<{ date: DateValue; month: DateValue }> {}

export class CalendarCellProvider {
	readonly opts: CalendarCellOpts;
	readonly runtimePart: SomaRuntimePart;
	static readonly ctx = context<CalendarCellProvider>('CalendarCell');
	static get(): CalendarCellProvider | undefined {
		return this.ctx.getOr(undefined) as CalendarCellProvider | undefined;
	}
	static require(): CalendarCellProvider {
		return this.ctx.get();
	}
	static create(opts: CalendarCellOpts) {
		return new CalendarCellProvider(opts);
	}

	readonly provider: CalendarProvider;

	private constructor(opts: CalendarCellOpts) {
		this.opts = opts;
		this.provider = CalendarProvider.require();
		this.runtimePart = this.provider.runtime.part('cell', {
			id: opts.id,
			ref: opts.ref,
			owner: this,
			context: CalendarCellProvider.ctx,
			// Sources for the morfo's `aria-selected`/`aria-disabled`
			// (propRef('selected')/propRef('disabled')) — the cell-local flags.
			props: {
				selected: () => this.selected,
				disabled: () => this.isDisabled
			}
		});
	}

	readonly flags = $derived.by(() => this.provider.computeFlags(this.opts.date.current));
	readonly selected = $derived.by(() => this.provider.isSelected(this.opts.date.current));
	readonly outside = $derived.by(() =>
		isOutsideMonth(this.opts.date.current, this.opts.month.current)
	);
	readonly todayFlag = $derived.by(() => isToday(this.opts.date.current));
	readonly weekendFlag = $derived.by(() => isWeekend(this.opts.date.current));

	readonly isDisabled = $derived.by(() => {
		const base = this.flags.disabled;
		if (base) return true;
		return this.outside && this.provider.opts.disableDaysOutsideMonth.current;
	});

	readonly snippetProps: CalendarCellSnippetProps = $derived.by(() => ({
		disabled: this.isDisabled,
		unavailable: this.flags.unavailable,
		selected: this.selected,
		today: this.todayFlag,
		weekend: this.weekendFlag,
		holiday: this.flags.holiday,
		outsideMonth: this.outside
	}));

	readonly props = $derived.by(() =>
		this.runtimePart.assert({
			// role, aria-selected and aria-disabled are morfo-declared, resolved
			// via renderProps.
			...this.runtimePart.renderProps(),
			// Soma-owned data values (the morfo declares these attrs without a value).
			'data-selected': boolToEmptyStrOrUndef(this.selected),
			'data-disabled': boolToEmptyStrOrUndef(this.isDisabled),
			'data-unavailable': boolToEmptyStrOrUndef(this.flags.unavailable),
			'data-today': boolToEmptyStrOrUndef(this.todayFlag),
			'data-weekend': boolToEmptyStrOrUndef(this.weekendFlag),
			'data-holiday': boolToEmptyStrOrUndef(this.flags.holiday),
			'data-outside-month': boolToEmptyStrOrUndef(this.outside),
			'data-value': this.opts.date.current.toString()
		} as const)
	);
}

// ── Day ──────────────────────────────────────────────────────────────────────

export class CalendarDayProvider {
	readonly opts: WithRefOpts;
	readonly runtimePart: SomaRuntimePart;
	static create(opts: WithRefOpts) {
		return new CalendarDayProvider(opts);
	}

	readonly provider: CalendarProvider;
	readonly cell: CalendarCellProvider;

	private constructor(opts: WithRefOpts) {
		this.opts = opts;
		this.provider = CalendarProvider.require();
		this.cell = CalendarCellProvider.require();
		this.runtimePart = this.provider.runtime.part('day', {
			id: opts.id,
			ref: opts.ref,
			owner: this,
			// Sources for the morfo's `aria-disabled`/`aria-selected`
			// (propRef('disabled')/propRef('selected')) — the cell's resolved flags.
			props: {
				disabled: () => this.cell.snippetProps.disabled,
				selected: () => this.cell.snippetProps.selected
			}
		});
	}

	readonly focused = $derived.by(() =>
		isSameDay(this.cell.opts.date.current, this.provider.opts.placeholder.current)
	);

	readonly day = $derived.by(() => this.provider.formatDay(this.cell.opts.date.current));

	readonly snippetProps: CalendarDaySnippetProps = $derived.by(() => ({
		...this.cell.snippetProps,
		day: this.day
	}));

	readonly onclick = (e: SomaMouseEvent<HTMLElement>) => {
		const date = this.cell.opts.date.current;
		this.provider.select(date, e.currentTarget as HTMLElement);
	};

	readonly onkeydown = (e: SomaKeyboardEvent<HTMLElement>) => {
		this.provider.handleDayKeydown(e, this.cell.opts.date.current);
	};

	readonly props = $derived.by(() => {
		const s = this.cell.snippetProps;
		const tabindex = this.focused && !s.disabled ? 0 : -1;
		return this.runtimePart.assert({
			// role, aria-disabled and aria-selected are morfo-declared, resolved
			// via renderProps.
			...this.runtimePart.renderProps(),
			tabindex,
			// Soma-owned data values (the morfo declares these attrs without a value).
			'data-selected': boolToEmptyStrOrUndef(s.selected),
			'data-disabled': boolToEmptyStrOrUndef(s.disabled),
			'data-unavailable': boolToEmptyStrOrUndef(s.unavailable),
			'data-today': boolToEmptyStrOrUndef(s.today),
			'data-weekend': boolToEmptyStrOrUndef(s.weekend),
			'data-holiday': boolToEmptyStrOrUndef(s.holiday),
			'data-outside-month': boolToEmptyStrOrUndef(s.outsideMonth),
			'data-focused': boolToEmptyStrOrUndef(this.focused),
			'data-value': this.cell.opts.date.current.toString(),
			onclick: this.onclick,
			onkeydown: this.onkeydown
		} as const);
	});
}