feat: add reminder source (#126)

packages/freya-source-reminders/src/recurrence.ts

@@ -0,0 +1,392 @@
+import type {
+	Reminder,
+	ReminderOccurrence,
+	ReminderOccurrenceOverride,
+	ReminderOccurrencePatch,
+	ReminderRecurrence,
+	ReminderWeekday,
+} from "./types.ts"
+
+import { ReminderRecurrenceFrequency } from "./types.ts"
+
+interface ZonedDateTimeParts {
+	year: number
+	month: number
+	day: number
+	hour: number
+	minute: number
+	second: number
+	millisecond: number
+}
+
+interface ExpandReminderOccurrencesOptions {
+	from: Date
+	to: Date
+	includeCompleted: boolean
+	overrides?: readonly ReminderOccurrenceOverride[]
+}
+
+export function createReminderOccurrenceId(originalDueAt: Date): string {
+	return originalDueAt.toISOString()
+}
+
+export function expandReminderOccurrences(
+	reminder: Reminder,
+	options: ExpandReminderOccurrencesOptions,
+): ReminderOccurrence[] {
+	const originalDueAts = new Map<string, Date>()
+	for (const dueAt of expandReminderOriginalDueAts(reminder, options.from, options.to)) {
+		originalDueAts.set(createReminderOccurrenceId(dueAt), dueAt)
+	}
+
+	const overrideById = new Map<string, ReminderOccurrenceOverride>()
+	for (const override of options.overrides ?? []) {
+		if (override.reminderId !== reminder.id) continue
+		if (!isCurrentOriginalDueAt(reminder, override.originalDueAt)) continue
+		overrideById.set(override.occurrenceId, override)
+		originalDueAts.set(override.occurrenceId, override.originalDueAt)
+	}
+
+	const occurrences: ReminderOccurrence[] = []
+	const originals = Array.from(originalDueAts.values()).sort(compareDates)
+
+	for (const originalDueAt of originals) {
+		const occurrenceId = createReminderOccurrenceId(originalDueAt)
+		const override = overrideById.get(occurrenceId)
+		if (override?.deletedAt) continue
+
+		const occurrence = createOccurrence(reminder, originalDueAt, override)
+		if (occurrence.dueAt < options.from || occurrence.dueAt > options.to) continue
+		if (!options.includeCompleted && occurrence.completedAt) continue
+
+		occurrences.push(occurrence)
+	}
+
+	return occurrences.sort(compareOccurrences)
+}
+
+export function expandReminderOriginalDueAts(reminder: Reminder, from: Date, to: Date): Date[] {
+	if (to < reminder.dueAt) return []
+
+	if (!reminder.recurrence) {
+		return reminder.dueAt >= from && reminder.dueAt <= to ? [reminder.dueAt] : []
+	}
+
+	switch (reminder.recurrence.frequency) {
+		case ReminderRecurrenceFrequency.Daily:
+			return expandDaily(reminder, from, to)
+		case ReminderRecurrenceFrequency.Weekly:
+			return expandWeekly(reminder, from, to)
+		case ReminderRecurrenceFrequency.Monthly:
+			return expandMonthly(reminder, from, to)
+		case ReminderRecurrenceFrequency.Yearly:
+			return expandYearly(reminder, from, to)
+	}
+}
+
+export function findReminderOccurrenceIndex(
+	reminder: Reminder,
+	occurrenceDueAt: Date,
+): number | null {
+	if (!reminder.recurrence) {
+		return reminder.dueAt.getTime() === occurrenceDueAt.getTime() ? 0 : null
+	}
+
+	const originals = expandReminderOriginalDueAts(reminder, reminder.dueAt, occurrenceDueAt)
+	for (let index = 0; index < originals.length; index++) {
+		if (originals[index]!.getTime() === occurrenceDueAt.getTime()) {
+			return index
+		}
+	}
+
+	return null
+}
+
+function isCurrentOriginalDueAt(reminder: Reminder, originalDueAt: Date): boolean {
+	return findReminderOccurrenceIndex(reminder, originalDueAt) !== null
+}
+
+export function stopRecurrenceAfterOccurrenceCount(
+	recurrence: ReminderRecurrence,
+	count: number,
+): ReminderRecurrence | null {
+	if (count <= 0) return null
+	return { ...recurrence, count }
+}
+
+export function recurrenceAfterSplit(
+	recurrence: ReminderRecurrence,
+	occurrenceIndex: number,
+): ReminderRecurrence | null {
+	if (recurrence.count === undefined) {
+		return { ...recurrence }
+	}
+
+	const remainingCount = recurrence.count - occurrenceIndex
+	if (remainingCount <= 1) return null
+
+	return { ...recurrence, count: remainingCount }
+}
+
+function expandDaily(reminder: Reminder, from: Date, to: Date): Date[] {
+	return expandStepped(reminder, from, to, function addDaily(parts, step) {
+		return addDays(parts, step)
+	})
+}
+
+function expandMonthly(reminder: Reminder, from: Date, to: Date): Date[] {
+	const anchor = getZonedParts(reminder.dueAt, reminder.timeZone).day
+	return expandStepped(reminder, from, to, function addMonthly(parts, step) {
+		return addMonths(parts, step, anchor)
+	})
+}
+
+function expandYearly(reminder: Reminder, from: Date, to: Date): Date[] {
+	const anchor = getZonedParts(reminder.dueAt, reminder.timeZone).day
+	return expandStepped(reminder, from, to, function addYearly(parts, step) {
+		return addMonths(parts, step * 12, anchor)
+	})
+}
+
+function expandStepped(
+	reminder: Reminder,
+	from: Date,
+	to: Date,
+	addStep: (parts: ZonedDateTimeParts, step: number) => ZonedDateTimeParts,
+): Date[] {
+	const recurrence = reminder.recurrence
+	if (!recurrence) return []
+
+	const dates: Date[] = []
+	const start = getZonedParts(reminder.dueAt, reminder.timeZone)
+	let emitted = 0
+	let index = 0
+
+	while (true) {
+		const parts = addStep(start, index * recurrence.interval)
+		const dueAt = zonedPartsToDate(parts, reminder.timeZone)
+		if (isAfterRecurrenceEnd(dueAt, recurrence, emitted)) break
+		if (dueAt > to) break
+
+		if (dueAt >= from) {
+			dates.push(dueAt)
+		}
+
+		emitted++
+		index++
+	}
+
+	return dates
+}
+
+function expandWeekly(reminder: Reminder, from: Date, to: Date): Date[] {
+	const recurrence = reminder.recurrence
+	if (!recurrence) return []
+
+	const start = getZonedParts(reminder.dueAt, reminder.timeZone)
+	const startWeekday = weekdayForParts(start)
+	const weekStart = addDays(start, -startWeekday)
+	const weekdays = recurrence.weekdays?.length
+		? Array.from(new Set(recurrence.weekdays)).sort(compareNumbers)
+		: [startWeekday as ReminderWeekday]
+
+	const dates: Date[] = []
+	let emitted = 0
+	let weekIndex = 0
+
+	while (true) {
+		let weekHadFutureDate = false
+
+		for (const weekday of weekdays) {
+			const parts = addDays(weekStart, weekIndex * recurrence.interval * 7 + weekday)
+			const dueAt = zonedPartsToDate(parts, reminder.timeZone)
+			if (dueAt < reminder.dueAt) continue
+			if (isAfterRecurrenceEnd(dueAt, recurrence, emitted)) return dates
+			if (dueAt > to) {
+				weekHadFutureDate = true
+				continue
+			}
+
+			if (dueAt >= from) {
+				dates.push(dueAt)
+			}
+
+			emitted++
+		}
+
+		if (weekHadFutureDate) break
+		weekIndex++
+	}
+
+	return dates.sort(compareDates)
+}
+
+function createOccurrence(
+	reminder: Reminder,
+	originalDueAt: Date,
+	override: ReminderOccurrenceOverride | undefined,
+): ReminderOccurrence {
+	const patch = override?.patch
+
+	return {
+		reminderId: reminder.id,
+		occurrenceId: createReminderOccurrenceId(originalDueAt),
+		title: patch?.title ?? reminder.title,
+		notes: valueWithNullableOverride(reminder.notes, patch, "notes"),
+		originalDueAt,
+		dueAt: patch?.dueAt ?? originalDueAt,
+		timeZone: patch?.timeZone ?? reminder.timeZone,
+		recurrence: reminder.recurrence,
+		priority: patch?.priority ?? reminder.priority,
+		completedAt: override?.completedAt ?? null,
+	}
+}
+
+function valueWithNullableOverride(
+	fallback: string | null,
+	patch: ReminderOccurrencePatch | undefined,
+	key: "notes",
+): string | null {
+	if (!patch) return fallback
+	if (Object.prototype.hasOwnProperty.call(patch, key)) {
+		return patch[key] ?? null
+	}
+	return fallback
+}
+
+function isAfterRecurrenceEnd(
+	dueAt: Date,
+	recurrence: ReminderRecurrence,
+	emittedCount: number,
+): boolean {
+	if (recurrence.count !== undefined && emittedCount >= recurrence.count) {
+		return true
+	}
+	if (recurrence.until !== undefined && dueAt > recurrence.until) {
+		return true
+	}
+	return false
+}
+
+function getZonedParts(date: Date, timeZone: string): ZonedDateTimeParts {
+	const formatter = new Intl.DateTimeFormat("en-US", {
+		timeZone,
+		year: "numeric",
+		month: "2-digit",
+		day: "2-digit",
+		hour: "2-digit",
+		minute: "2-digit",
+		second: "2-digit",
+		hourCycle: "h23",
+	})
+
+	const parts = formatter.formatToParts(date)
+	return {
+		year: numberPart(parts, "year"),
+		month: numberPart(parts, "month"),
+		day: numberPart(parts, "day"),
+		hour: numberPart(parts, "hour"),
+		minute: numberPart(parts, "minute"),
+		second: numberPart(parts, "second"),
+		millisecond: date.getUTCMilliseconds(),
+	}
+}
+
+function zonedPartsToDate(parts: ZonedDateTimeParts, timeZone: string): Date {
+	const localAsUtc = Date.UTC(
+		parts.year,
+		parts.month - 1,
+		parts.day,
+		parts.hour,
+		parts.minute,
+		parts.second,
+		parts.millisecond,
+	)
+	let timestamp = localAsUtc
+
+	for (let i = 0; i < 3; i++) {
+		const offset = getTimeZoneOffsetMs(new Date(timestamp), timeZone)
+		const next = localAsUtc - offset
+		if (next === timestamp) break
+		timestamp = next
+	}
+
+	return new Date(timestamp)
+}
+
+function getTimeZoneOffsetMs(date: Date, timeZone: string): number {
+	const parts = getZonedParts(date, timeZone)
+	const zonedAsUtc = Date.UTC(
+		parts.year,
+		parts.month - 1,
+		parts.day,
+		parts.hour,
+		parts.minute,
+		parts.second,
+		parts.millisecond,
+	)
+
+	return zonedAsUtc - date.getTime()
+}
+
+function numberPart(parts: Intl.DateTimeFormatPart[], type: Intl.DateTimeFormatPartTypes): number {
+	const part = parts.find(function matchesType(value) {
+		return value.type === type
+	})
+	if (!part) {
+		throw new Error(`Missing ${type} part while formatting zoned date`)
+	}
+	return Number(part.value)
+}
+
+function addDays(parts: ZonedDateTimeParts, days: number): ZonedDateTimeParts {
+	const date = new Date(Date.UTC(parts.year, parts.month - 1, parts.day + days))
+	return {
+		...parts,
+		year: date.getUTCFullYear(),
+		month: date.getUTCMonth() + 1,
+		day: date.getUTCDate(),
+	}
+}
+
+function addMonths(
+	parts: ZonedDateTimeParts,
+	months: number,
+	anchorDay: number,
+): ZonedDateTimeParts {
+	const monthIndex = parts.year * 12 + parts.month - 1 + months
+	const year = Math.floor(monthIndex / 12)
+	const month = positiveModulo(monthIndex, 12) + 1
+	const day = Math.min(anchorDay, daysInMonth(year, month))
+
+	return {
+		...parts,
+		year,
+		month,
+		day,
+	}
+}
+
+function daysInMonth(year: number, month: number): number {
+	return new Date(Date.UTC(year, month, 0)).getUTCDate()
+}
+
+function weekdayForParts(parts: ZonedDateTimeParts): number {
+	return new Date(Date.UTC(parts.year, parts.month - 1, parts.day)).getUTCDay()
+}
+
+function positiveModulo(value: number, divisor: number): number {
+	return ((value % divisor) + divisor) % divisor
+}
+
+function compareDates(a: Date, b: Date): number {
+	return a.getTime() - b.getTime()
+}
+
+function compareNumbers(a: number, b: number): number {
+	return a - b
+}
+
+function compareOccurrences(a: ReminderOccurrence, b: ReminderOccurrence): number {
+	return a.dueAt.getTime() - b.dueAt.getTime()
+}