import { preferredScheduleSemester } from './schedule-period.js';

export function academicYearsFromSemesters(semesters = []) {
    const years = new Map();
    semesters.forEach(semester => {
        const id = String(semester?.academicYearId ?? '');
        if (!id || years.has(id)) return;
        years.set(id, {
            id,
            title: semester.academicYearTitle || `Учебный год ${id}`
        });
    });
    return [...years.values()];
}

export function semestersForAcademicYear(semesters = [], academicYearId = '') {
    return semesters.filter(semester =>
        String(semester?.academicYearId ?? '') === String(academicYearId)
    );
}

export function resolveAcademicPeriod(semesters = [], options = {}) {
    if (!semesters.length) return { academicYearId: '', semesterId: '' };

    const requestedSemester = semesters.find(semester =>
        String(semester.id) === String(options.semesterId || '')
    );
    const availableYearIds = new Set(academicYearsFromSemesters(semesters).map(year => year.id));
    const requestedYearId = availableYearIds.has(String(options.academicYearId || ''))
        ? String(options.academicYearId)
        : '';
    const preferred = preferredScheduleSemester(semesters, options.date || isoToday()) || semesters[0];
    const academicYearId = requestedSemester
        ? String(requestedSemester.academicYearId)
        : (requestedYearId || String(preferred?.academicYearId || semesters[0].academicYearId));
    const yearSemesters = semestersForAcademicYear(semesters, academicYearId);
    const semester = requestedSemester && String(requestedSemester.academicYearId) === academicYearId
        ? requestedSemester
        : (preferredScheduleSemester(yearSemesters, options.date || isoToday()) || yearSemesters[0]);

    return {
        academicYearId,
        semesterId: String(semester?.id || '')
    };
}

function isoToday() {
    const date = new Date();
    const offset = date.getTimezoneOffset() * 60_000;
    return new Date(date.getTime() - offset).toISOString().slice(0, 10);
}