export interface USFestival {
name: string;
rule: FixedDateRule | NthWeekdayRule;
}
interface FixedDateRule {
type: "fixed";
month: number;
day: number;
}
interface NthWeekdayRule {
type: "nth_weekday";
month: number;
weekday: number; // 0=Sunday, 1=Monday, ...
n: number; // which occurrence (1-based), -1 for last
}
export const US_FESTIVALS: USFestival[] = [
{ name: "New Year's Day", rule: { type: "fixed", month: 1, day: 1 } },
{ name: "Martin Luther King Jr. Day", rule: { type: "nth_weekday", month: 1, weekday: 1, n: 3 } },
{ name: "Presidents' Day", rule: { type: "nth_weekday", month: 2, weekday: 1, n: 3 } },
{ name: "Memorial Day", rule: { type: "nth_weekday", month: 5, weekday: 1, n: -1 } },
{ name: "Independence Day", rule: { type: "fixed", month: 7, day: 4 } },
{ name: "Labor Day", rule: { type: "nth_weekday", month: 9, weekday: 1, n: 1 } },
{ name: "Columbus Day", rule: { type: "nth_weekday", month: 10, weekday: 1, n: 2 } },
{ name: "Veterans Day", rule: { type: "fixed", month: 11, day: 11 } },
{ name: "Thanksgiving", rule: { type: "nth_weekday", month: 11, weekday: 4, n: 4 } },
{ name: "Christmas", rule: { type: "fixed", month: 12, day: 25 } },
];
/**
* Resolve a US festival name to a { month, day } for a given year.
* Returns null if not found.
*/
export function resolveUSFestivalDate(name: string, year: number): { month: number; day: number } | null {
const festival = US_FESTIVALS.find(f => f.name.toLowerCase() === name.toLowerCase());
if (!festival) return null;
const rule = festival.rule;
if (rule.type === "fixed") {
return { month: rule.month, day: rule.day };
}
// nth_weekday
if (rule.n === -1) {
// Last occurrence of weekday in month
// Start from last day of month and go backward
const lastDay = new Date(year, rule.month, 0).getDate();
for (let d = lastDay; d >= 1; d--) {
const dt = new Date(year, rule.month - 1, d);
if (dt.getDay() === rule.weekday) {
return { month: rule.month, day: d };
}
}
} else {
// Nth occurrence
let count = 0;
const daysInMonth = new Date(year, rule.month, 0).getDate();
for (let d = 1; d <= daysInMonth; d++) {
const dt = new Date(year, rule.month - 1, d);
if (dt.getDay() === rule.weekday) {
count++;
if (count === rule.n) {
return { month: rule.month, day: d };
}
}
}
}
return null;
}
