add money tracker

src/lib/money-tracker/charts.ts

@@ -0,0 +1,89 @@
+export type ChartPoint = { date: string; value: number };
+export type ChartSeries = { label: string; color: string; points: ChartPoint[] };
+
+export function balanceSeries(
+	accounts: { id: number; name: string; openingBalanceCents: number }[],
+	transactions: { accountId: number; date: string; amountCents: number }[]
+): ChartSeries[] {
+	const palette = ['#0070f3', '#e5484d', '#46a758', '#ad7f00', '#8e4ec6', '#0091ad', '#e56910'];
+	const lastDate = transactions.at(-1)?.date;
+	return accounts.map((account, index) => {
+		let balance = account.openingBalanceCents;
+		const entries = transactions.filter((transaction) => transaction.accountId === account.id);
+		const points: ChartPoint[] = [];
+		if (entries.length) points.push({ date: entries[0].date, value: balance });
+		for (const entry of entries) {
+			balance += entry.amountCents;
+			points.push({ date: entry.date, value: balance });
+		}
+		if (lastDate && entries.length && lastDate > entries.at(-1)!.date)
+			points.push({ date: lastDate, value: balance });
+		return { label: account.name, color: palette[index % palette.length], points };
+	});
+}
+
+export function accountBalances(
+	accounts: { id: number; openingBalanceCents: number }[],
+	transactions: { accountId: number; amountCents: number }[]
+): Map<number, number> {
+	const balances = new Map(accounts.map((account) => [account.id, account.openingBalanceCents]));
+	for (const transaction of transactions)
+		balances.set(
+			transaction.accountId,
+			(balances.get(transaction.accountId) ?? 0) + transaction.amountCents
+		);
+	return balances;
+}
+
+export function monthlyCents(amountCents: number, cadence: string): number {
+	return cadence === 'weekly'
+		? (amountCents * 52) / 12
+		: cadence === 'yearly'
+			? amountCents / 12
+			: amountCents;
+}
+
+export function forecastSeries(
+	currentCents: number,
+	forecasts: { date: string; amountCents: number }[],
+	today: string
+): ChartSeries[] {
+	let projected = currentCents;
+	const points: ChartPoint[] = [{ date: today, value: currentCents }];
+	for (const item of forecasts
+		.filter((entry) => entry.date >= today)
+		.sort((a, b) => a.date.localeCompare(b.date))) {
+		projected += item.amountCents;
+		points.push({ date: item.date, value: projected });
+	}
+	return [{ label: 'Projected total', color: '#0070f3', points }];
+}
+
+export function utilityEstimate(
+	readings: { date: string; reading: string; kind: string }[],
+	kind: string,
+	ratePerUnit: string,
+	monthlyAdvanceCents: number,
+	billingStart?: string | null
+) {
+	const byKind = readings.filter(
+		(reading) => reading.kind === kind && (!billingStart || reading.date >= billingStart)
+	);
+	if (byKind.length < 2) return null;
+	const first = byKind[0];
+	const last = byKind.at(-1)!;
+	const usage = Number(last.reading) - Number(first.reading);
+	const months =
+		(Date.parse(`${last.date}T12:00:00Z`) - Date.parse(`${first.date}T12:00:00Z`)) /
+		((365.25 / 12) * 86_400_000);
+	if (months <= 0 || usage < 0) return null;
+	const estimatedCents = Math.round(usage * Number(ratePerUnit) * 100);
+	const advancesCents = Math.round(months * monthlyAdvanceCents);
+	return {
+		usage,
+		months,
+		estimatedCents,
+		advancesCents,
+		differenceCents: advancesCents - estimatedCents
+	};
+}