Lucas Winther
de333685a2
Recurrences of 28 and 30 days do not align to months, so the domain needs day-level maths for the first time. It gets it the way months.ts does: an integer ordinal, no Date anywhere. A Date would make 2026-03-29 a different instant per timezone while being the same day everywhere, and a 28-day step must not gain or lose a day at a DST boundary. Hinnant's days_from_civil, which shifts the year to start in March so the leap day is the last day rather than an insertion, removing every special case. No isDayGranular export: nothing in the plan consumes it, later tasks branch on a recurrence kind and import validation uses a regex directly.
84 lines
2.8 KiB
TypeScript
84 lines
2.8 KiB
TypeScript
import { describe, expect, test } from "bun:test";
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import { addDays, fromDayOrdinal, toDayOrdinal, weekdayOf } from "./days.ts";
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describe("day ordinals", () => {
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test("the epoch is day zero", () => {
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expect(toDayOrdinal("1970-01-01")).toBe(0);
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});
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test("known dates convert to known ordinals", () => {
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expect(toDayOrdinal("1969-12-31")).toBe(-1);
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expect(toDayOrdinal("2000-03-01")).toBe(11017);
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expect(toDayOrdinal("2026-09-03")).toBe(20699);
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});
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test("every date in a four-year window round-trips", () => {
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// 2024 is a leap year, 2025 and 2026 are not, so this covers both.
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for (let ordinal = toDayOrdinal("2024-01-01"); ordinal <= toDayOrdinal("2027-12-31"); ordinal++) {
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expect(toDayOrdinal(fromDayOrdinal(ordinal))).toBe(ordinal);
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}
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});
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test("leap day exists in 2024 and not in 2026", () => {
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expect(fromDayOrdinal(toDayOrdinal("2024-02-28") + 1)).toBe("2024-02-29");
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expect(fromDayOrdinal(toDayOrdinal("2026-02-28") + 1)).toBe("2026-03-01");
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});
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test("century rules: 1900 is not a leap year, 2000 is", () => {
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expect(fromDayOrdinal(toDayOrdinal("1900-02-28") + 1)).toBe("1900-03-01");
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expect(fromDayOrdinal(toDayOrdinal("2000-02-28") + 1)).toBe("2000-02-29");
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});
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test("a month-only date is rejected, not silently treated as the first", () => {
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expect(() => toDayOrdinal("2026-09")).toThrow(/day-granular/);
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});
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test("an impossible day is rejected", () => {
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expect(() => toDayOrdinal("2026-02-30")).toThrow();
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expect(() => toDayOrdinal("2026-13-01")).toThrow();
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});
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});
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describe("addDays", () => {
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test("crosses a month boundary", () => {
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expect(addDays("2026-01-30", 3)).toBe("2026-02-02");
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});
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test("crosses a year boundary", () => {
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expect(addDays("2026-12-30", 5)).toBe("2027-01-04");
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});
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test("a 28-day cycle lands on the same weekday every time", () => {
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let date = "2026-01-05";
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const weekday = weekdayOf(date);
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for (let i = 0; i < 13; i++) {
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date = addDays(date, 28);
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expect(weekdayOf(date)).toBe(weekday);
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}
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});
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test("a 30-day cycle drifts through the calendar", () => {
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// The phone bill's shape: 30 days is not a month, so it walks backwards
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// through the month over a year.
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expect(addDays("2026-01-31", 30)).toBe("2026-03-02");
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});
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});
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describe("weekdayOf", () => {
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test("the epoch was a Thursday", () => {
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expect(weekdayOf("1970-01-01")).toBe(4);
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});
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test("known weekdays", () => {
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expect(weekdayOf("2026-09-03")).toBe(4); // Thursday
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expect(weekdayOf("2026-09-06")).toBe(0); // Sunday
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expect(weekdayOf("2026-09-07")).toBe(1); // Monday
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});
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test("seven consecutive days cover every weekday exactly once", () => {
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const seen = new Set<number>();
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for (let i = 0; i < 7; i++) seen.add(weekdayOf(addDays("2026-09-03", i)));
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expect(seen.size).toBe(7);
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});
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});
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