semester.ts

import { z } from "zod";
import { getMonth } from "date-fns";

export const SeasonEnum = z.enum(["FALL", "SPRING"]);
export type Season = z.TypeOf<typeof SeasonEnum>;

export const SemesterSchema = z.object({
	season: SeasonEnum,
	year: z.number().min(2000).max(2050),
});
export type Semester = z.infer<typeof SemesterSchema>;

const semesterRanges: Record<Season, [number, number]> = {
	[SeasonEnum.enum.FALL]: [8, 12],
	[SeasonEnum.enum.SPRING]: [0, 4],
};

/**
 * Given a date, retrieve the season it resides within.
 * @param time The date to operate on. Assumed UTC.
 * @return {Season|null} The season, if the date is in one. If no seasons match, null is returned.
 */
export const getSeason = (time: Date): Season | null => {
	const semesterEntry = Object.entries(semesterRanges).find(([, [startMonth, endMonth]]) => {
		const month = getMonth(time);
		console.log({ month, startMonth, endMonth });
		return month >= startMonth && month <= endMonth;
	});
	return semesterEntry != null ? (semesterEntry[0] as Season) : null;
};

/**
 * Given the date of a specific event, identify the semester it occurs within.
 * @param time {Date} The date to operate on. Assumed UTC.
 * @return {Semester|null} The semester (season & year) the date occurs within. If no seasons match, null is returned.
 */
export const getSemester = (time: Date): Semester | null => {
	const season = getSeason(time);
	return season != null ? SemesterSchema.parse({ season, year: time.getUTCFullYear() }) : null;
};

/**
 * Calculate the start and end dates for a given Semester.
 * This is useful for generating min/max values while filtering events in the database.
 * @param season {Season} The season to use the range of. Spring, for example, might be January to May.
 * @param year {number|null} The year of the date range. If null, it will default to the current year (UTC).
 */
export const getSemesterRange = (
	season: Season,
	year: number | null = null
): { start: Date; end: Date } => {
	if (year == null) year = new Date().getUTCFullYear();
	const [startMonth, endMonth] = semesterRanges[season];
	return {
		start: new Date(year, startMonth),
		end: new Date(year, endMonth),
	};
};