//Calendar implementation for the HTWK Leipzig timetable. Evaluation and display of the individual dates in iCal format.
//Copyright (C) 2024 HTWKalender support@htwkalender.de

//This program is free software: you can redistribute it and/or modify
//it under the terms of the GNU Affero General Public License as published by
//the Free Software Foundation, either version 3 of the License, or
//(at your option) any later version.

//This program is distributed in the hope that it will be useful,
//but WITHOUT ANY WARRANTY; without even the implied warranty of
//MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//GNU Affero General Public License for more details.

//You should have received a copy of the GNU Affero General Public License
//along with this program.  If not, see <https://www.gnu.org/licenses/>.

package functions

import (
	"time"
)

const START_OF_SUMMER_SEMESTER_MONTH = time.April
const START_OF_WINTER_SEMESTER_MONTH = time.October

// GetCurrentSemesterString returns the current semester as string
// if current month is between 10 and 03 -> winter semester "ws"
func GetCurrentSemesterString() string {

	if now := time.Now(); isBeforeSummerSemester(now) || isAfterSummerSemester(now) {
		return "ws"
	} else {
		return "ss"
	}
}

// GetSemesterStart gibt das Startdatum des aktuellen Semesters zurück
func GetSemesterStart(date time.Time) time.Time {
	if isBeforeSummerSemester(date) {
		return time.Date(date.Year()-1, START_OF_WINTER_SEMESTER_MONTH, 1, 0, 0, 0, 0, date.Location())
	} else if isAfterSummerSemester(date) {
		return time.Date(date.Year(), START_OF_WINTER_SEMESTER_MONTH, 1, 0, 0, 0, 0, date.Location())
	} else {
		return time.Date(date.Year(), START_OF_SUMMER_SEMESTER_MONTH, 1, 0, 0, 0, 0, date.Location())
	}
}

// Check if is in last month of semester
func IsLastMonthOfSemester(date time.Time) bool {
	return date.Month() == START_OF_WINTER_SEMESTER_MONTH-1 || date.Month() == START_OF_SUMMER_SEMESTER_MONTH-1
}

// Check if the given date is before the start of summer semester
func isBeforeSummerSemester(date time.Time) bool {
	return date.Month() < START_OF_SUMMER_SEMESTER_MONTH
}

// Check if the given date is after the end of summer semester
func isAfterSummerSemester(date time.Time) bool {
	return date.Month() >= START_OF_WINTER_SEMESTER_MONTH
}