//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 sport

import (
	"errors"
	"github.com/google/uuid"
	"github.com/pocketbase/pocketbase"
	"github.com/pocketbase/pocketbase/tools/types"
	"htwkalender/model"
	"htwkalender/service/db"
	"htwkalender/service/functions"
	"io"
	"log/slog"
	"net/http"
	"regexp"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/PuerkitoBio/goquery"
)

// FetchAndUpdateSportEvents fetches all sport events from the HTWK sport website
// it deletes them first and then saves them to the database
// It returns all saved events
func FetchAndUpdateSportEvents(app *pocketbase.PocketBase) ([]model.Event, error) {

	sportCourseLinks, err := fetchAllAvailableSportCourses()

	if err != nil {
		return nil, err
	}

	sportEntries := fetchHTWKSportCourses(sportCourseLinks)
	events := formatEntriesToEvents(sportEntries)

	var earliestDate time.Time
	var latestDate time.Time

	// find earliest and latest date in events
	for _, event := range events {
		if event.Start.Time().Before(earliestDate) {
			earliestDate = event.Start.Time()
		}
		if event.End.Time().After(latestDate) {
			latestDate = event.End.Time()
		}
	}

	// get all events from database where name = Feiertage und lehrveranstaltungsfreie Tage
	holidays, err := db.GetAllModulesByNameAndDateRange(app, "Feiertage und lehrveranstaltungsfreie Tage", earliestDate, latestDate)
	if err != nil {
		return nil, err
	}

	// remove all events that have same year, month and day as items in holidays
	for _, holiday := range holidays {
		for i, event := range events {
			if event.Start.Time().Year() == holiday.Start.Time().Year() &&
				event.Start.Time().Month() == holiday.Start.Time().Month() &&
				event.Start.Time().Day() == holiday.Start.Time().Day() {
				events = append(events[:i], events[i+1:]...)
			}
		}
	}

	// @TODO: delete and save events in one transaction and it only should delete events that are not in the new events list and save events that are not in the database
	err = db.DeleteAllEventsByCourse(app, "Sport", functions.GetCurrentSemesterString())
	if err != nil {
		return nil, err
	}

	// save events to database
	savedEvents, err := db.SaveEvents(events, app)

	if err != nil {
		return nil, err
	}

	return savedEvents, nil

}

func formatEntriesToEvents(entries []model.SportEntry) []model.Event {

	var events []model.Event

	for _, entry := range entries {
		eventStarts, eventEnds := getWeekEvents(entry.Details.DateRange.Start, entry.Details.DateRange.End, entry.Details.Cycle)
		for j := range eventStarts {

			start, _ := types.ParseDateTime(eventStarts[j].In(time.UTC))
			end, _ := types.ParseDateTime(eventEnds[j].In(time.UTC))

			var event = model.Event{
				UUID:      uuid.NewSHA1(uuid.NameSpaceDNS, []byte(entry.Title+entry.ID+entry.Details.Type)).String(),
				Day:       toGermanWeekdayString(start.Time().Weekday()),
				Week:      strconv.Itoa(23),
				Start:     start,
				End:       end,
				Name:      entry.Title + " (" + entry.ID + ")",
				EventType: entry.Details.Type,
				Prof:      entry.Details.CourseLead.Name,
				Rooms:     entry.Details.Location.Name,
				Notes:     entry.AdditionalNote,
				BookedAt:  "",
				Course:    "Sport",
				Semester:  checkSemester(entry.Details.DateRange.Start),
			}
			events = append(events, event)
		}
	}
	return events
}

func getDayInt(weekDay string) (int, error) {
	var weekDayInt int
	var err error = nil
	switch weekDay {
	case "Mo":
		weekDayInt = 1
	case "Di":
		weekDayInt = 2
	case "Mi":
		weekDayInt = 3
	case "Do":
		weekDayInt = 4
	case "Fr":
		weekDayInt = 5
	case "Sa":
		weekDayInt = 6
	case "So":
		weekDayInt = 0
	default:
		{
			err = errors.New("no day found")
			weekDayInt = -1
		}
	}
	return weekDayInt, err
}

func toGermanWeekdayString(weekday time.Weekday) string {
	switch weekday {
	case time.Monday:
		return "Montag"
	case time.Tuesday:
		return "Dienstag"
	case time.Wednesday:
		return "Mittwoch"
	case time.Thursday:
		return "Donnerstag"
	case time.Friday:
		return "Freitag"
	case time.Saturday:
		return "Samstag"
	case time.Sunday:
		return "Sonntag"
	default:
		return ""
	}
}

func extractStartAndEndTime(cycle string) (int, int, int, int) {
	timeRegExp, _ := regexp.Compile("[0-9]{2}:[0-9]{2}")
	times := timeRegExp.FindAllString(cycle, 2)
	startHour, _ := strconv.Atoi(times[0][0:2])
	startMinute, _ := strconv.Atoi(times[0][3:5])

	endHour, _ := strconv.Atoi(times[1][0:2])
	endMinute, _ := strconv.Atoi(times[1][3:5])
	return startHour, startMinute, endHour, endMinute
}

func getWeekEvents(start time.Time, end time.Time, cycle string) ([]time.Time, []time.Time) {
	var weekEvents []model.SportDayStartEnd
	// split by regexp to get the cycle parts
	var cycleParts = splitByCommaWithTime(cycle)
	for _, cyclePart := range cycleParts {

		//cut string at the first integer/number
		cyclePartWithDaysOnly := cyclePart[0:strings.IndexFunc(cyclePart, func(r rune) bool { return r >= '0' && r <= '9' })]

		// check if cycle has multiple days by checking if it has a plus sign
		if strings.Contains(cyclePartWithDaysOnly, "+") {
			// find all days in cycle part by regexp
			dayRegExp, _ := regexp.Compile("[A-Z][a-z]")
			days := dayRegExp.FindAllString(cyclePart, -1)
			startHour, startMinute, endHour, endMinute := extractStartAndEndTime(cyclePart)

			// creating a SportDayStartEnd for each day in the cycle
			for _, day := range days {
				weekDay, err := getDayInt(day)
				if err != nil {
					slog.Error("Error while getting day int: "+day+" ", "error", err)
				} else {
					weekEvents = append(weekEvents, model.SportDayStartEnd{
						Start: time.Date(start.Year(), start.Month(), start.Day(), startHour, startMinute, 0, 0, start.Location()),
						End:   time.Date(end.Year(), end.Month(), end.Day(), endHour, endMinute, 0, 0, end.Location()),
						Day:   time.Weekday(weekDay),
					})
				}
			}

		}

		// check if cycle has multiple days by checking if it has a minus sign
		if strings.Contains(cyclePartWithDaysOnly, "-") {
			// find all days in cycle part by regexp
			dayRegExp, _ := regexp.Compile("[A-Z][a-z]")
			days := dayRegExp.FindAllString(cyclePart, 2)
			startHour, startMinute, endHour, endMinute := extractStartAndEndTime(cyclePart)

			var startI, endI int
			var endIErr, startIErr error
			startI, startIErr = getDayInt(days[0])
			endI, endIErr = getDayInt(days[1])

			if endIErr != nil || startIErr != nil {
				slog.Error("Error while getting day int: "+days[0]+" - "+days[1]+" :", "error", startIErr)
				slog.Error("Error while getting day int endErr: ", "error", endIErr)
			} else {
				//create an int array with all days from start to end day
				var daysBetween []int
				for i := startI; i <= endI; i++ {
					daysBetween = append(daysBetween, i)
				}

				// creating a SportDayStartEnd for each day in the cycle
				weekEvents = createEventListFromStartToEndMatchingDay23(daysBetween, start, startHour, startMinute, end, endHour, endMinute)
			}
		}

		// check if cycle has only one day
		if !strings.Contains(cyclePartWithDaysOnly, "-") && !strings.Contains(cyclePartWithDaysOnly, "+") {
			// find all days in cycle part by regexp
			dayRegExp, _ := regexp.Compile("[A-Z][a-z]")
			days := dayRegExp.FindAllString(cyclePart, -1)
			startHour, startMinute, endHour, endMinute := extractStartAndEndTime(cyclePart)

			var dayNumbers []int
			for _, day := range days {

				dayInt, err := getDayInt(day)
				if err != nil {
					slog.Error("Error while getting day int: "+day+" ", "error", err)
				} else {
					dayNumbers = append(dayNumbers, dayInt)
				}
			}

			// creating a SportDayStartEnd for each day in the cycle
			weekEvents = append(weekEvents, createEventListFromStartToEndMatchingDay23(dayNumbers, start, startHour, startMinute, end, endHour, endMinute)...)
			for _, day := range days {

				weekDay, err := getDayInt(day)
				if err != nil {
					slog.Error("Error while getting day int: "+day+" ", "error", err)
				} else {
					weekEvents = append(weekEvents, model.SportDayStartEnd{
						Start: time.Date(start.Year(), start.Month(), start.Day(), startHour, startMinute, 0, 0, start.Location()),
						End:   time.Date(end.Year(), end.Month(), end.Day(), endHour, endMinute, 0, 0, end.Location()),
						Day:   time.Weekday(weekDay),
					})
				}
			}
		}
	}

	var startDatesList []time.Time
	var endDatesList []time.Time

	for _, weekEvent := range weekEvents {
		startDates, endDates := createEventListFromStartToEndMatchingDay(weekEvent)
		startDatesList = append(startDatesList, startDates...)
		endDatesList = append(endDatesList, endDates...)
	}

	return startDatesList, endDatesList
}

// creating a SportDayStartEnd for each day in the cycle
func createEventListFromStartToEndMatchingDay23(days []int, start time.Time, startHour int, startMinute int, end time.Time, endHour int, endMinute int) []model.SportDayStartEnd {

	var weekEvents []model.SportDayStartEnd

	for _, day := range days {
		weekEvents = append(weekEvents, model.SportDayStartEnd{
			Start: time.Date(start.Year(), start.Month(), start.Day(), startHour, startMinute, 0, 0, start.Location()),
			End:   time.Date(end.Year(), end.Month(), end.Day(), endHour, endMinute, 0, 0, end.Location()),
			Day:   time.Weekday(day),
		})
	}
	return weekEvents
}

func createEventListFromStartToEndMatchingDay(weekEvent model.SportDayStartEnd) ([]time.Time, []time.Time) {
	var startDates []time.Time
	var endDates []time.Time
	for d := weekEvent.Start; d.Before(weekEvent.End); d = d.AddDate(0, 0, 1) {
		if d.Weekday() == weekEvent.Day {
			startDates = append(startDates, time.Date(d.Year(), d.Month(), d.Day(), weekEvent.Start.Hour(), weekEvent.Start.Minute(), 0, 0, d.Location()))
			endDates = append(endDates, time.Date(d.Year(), d.Month(), d.Day(), weekEvent.End.Hour(), weekEvent.End.Minute(), 0, 0, d.Location()))
		}
	}
	return startDates, endDates
}

func splitByCommaWithTime(input string) []string {
	var result []string

	// Split by comma
	parts := strings.Split(input, ", ")

	// Regular expression to match a day with time
	regex := regexp.MustCompile(`([A-Za-z]{2,}(\+[A-Za-z]{2,})* \d{2}:\d{2}-\d{2}:\d{2})`)

	// Iterate over parts and combine when necessary
	var currentPart string
	for _, part := range parts {
		if regex.MatchString(part) {
			if currentPart != "" {
				currentPart += ", " + part
				result = append(result, currentPart)
				currentPart = ""
			} else {
				result = append(result, part)
			}
			// If the part contains a day with time, start a new currentPart

		} else {
			// If there's no currentPart, start a new one
			if currentPart != "" {
				currentPart += ", " + part
			} else {
				currentPart = part
			}
		}
	}

	// Add the last currentPart to the result
	if currentPart != "" {
		result = append(result, currentPart)
	}

	return result
}

// check if ws or ss
func checkSemester(date time.Time) string {
	if date.Month() >= 4 && date.Month() <= 9 {
		return "ss"
	} else {
		return "ws"
	}
}

// fetch the main page where all sport courses are listed and extract all links to the sport courses
func fetchAllAvailableSportCourses() ([]string, error) {
	var url = "https://sport.htwk-leipzig.de/sportangebote"

	var doc, err = htmlRequest(url)

	if err != nil {
		slog.Error("Error while fetching sport courses from webpage", "error", err)
		return nil, err
	}

	// link list of all sport courses
	var links []string

	// find all links to sport courses with regex https://sport.htwk-leipzig.de/sportangebote/detail/sport/ + [0-9]{1,4}
	doc.Find("a[href]").Each(func(i int, s *goquery.Selection) {
		link, _ := s.Attr("href")
		if strings.HasPrefix(link, "/sportangebote/detail/sport/") {
			links = append(links, link)
		}
	})

	return links, nil
}

// fetchAllHTWKSportCourses fetches all sport courses from the given links.
// to speed up the process, it uses multithreading.

func fetchHTWKSportCourses(links []string) []model.SportEntry {

	//multithreaded webpage requests to speed up the process

	var maxThreads = 10
	var htmlPageArray = make([]*goquery.Document, len(links))
	var hostUrl = "https://sport.htwk-leipzig.de"

	var wg sync.WaitGroup
	wg.Add(maxThreads)
	for i := 0; i < maxThreads; i++ {
		go func(i int) {
			for j := i; j < len(links); j += maxThreads {
				doc, err := htmlRequest(hostUrl + links[j])
				if err == nil {
					htmlPageArray[j] = doc
				}
			}
			wg.Done()
		}(i)
	}
	wg.Wait()

	var events []model.SportEntry

	for _, doc := range htmlPageArray {
		if doc != nil {
			event, err := fetchHtwkSportCourse(doc)
			if err == nil {
				events = append(events, event...)
			}
		}
	}
	return events
}

func htmlRequest(url string) (*goquery.Document, error) {
	resp, err := http.Get(url)
	if err != nil {
		return nil, err
	}
	defer func(Body io.ReadCloser) {
		readErr := Body.Close()
		if readErr != nil {
			slog.Error("Error while closing response body from html request", "error", readErr)
			return
		}
	}(resp.Body)

	doc, err := goquery.NewDocumentFromReader(resp.Body)
	if err != nil {
		return nil, err
	}

	return doc, nil
}

// fetchHtwkSportCourse fetches the sport course from the given url and id.
// If the sport course does not exist, it will return an error.
// If the sport course exists, it will return the sport course.
// goquery is used to parse the html. The html structure is not very consistent, so it is hard to parse.
// May be improved in the future.
func fetchHtwkSportCourse(doc *goquery.Document) ([]model.SportEntry, error) {
	var events []model.SportEntry
	germanTime, _ := time.LoadLocation("Europe/Berlin")

	if doc.Find("h1").Text() == "Aktuelle Sportangebote" {
		return nil, errors.New("not a sport course page")
	}

	doc.Find(".eventHead").Each(func(i int, s *goquery.Selection) {
		var event model.SportEntry
		var details model.EventDetails

		fullTitle := strings.TrimSpace(s.Find("h3").Text())
		titleParts := strings.Split(fullTitle, "-")
		if len(titleParts) > 0 {
			event.Title = strings.TrimSpace(titleParts[0])
		}

		if len(titleParts) > 2 {
			details.Type = strings.TrimSpace(titleParts[len(titleParts)-1])
		}

		event.ID = parseEventID(fullTitle)

		s.NextFiltered("table.eventDetails").Find("tr").Each(func(i int, s *goquery.Selection) {
			key := strings.TrimSpace(s.Find("td").First().Text())
			value := strings.TrimSpace(s.Find("td").Last().Text())

			switch key {
			case "Zeitraum":
				dates := strings.Split(value, "-")
				if len(dates) == 2 {
					startDate, _ := time.ParseInLocation("02.01.2006", strings.TrimSpace(dates[0]), germanTime)
					endDate, _ := time.ParseInLocation("02.01.2006", strings.TrimSpace(dates[1]), germanTime)
					details.DateRange = model.DateRange{Start: startDate, End: endDate}
				}
			case "Zyklus":
				details.Cycle = value
			case "Geschlecht":
				details.Gender = value
			case "Leiter":
				leaderName := strings.TrimSpace(s.Find("td a").Text())
				leadersSlice := strings.Split(leaderName, "\n")
				for i, leader := range leadersSlice {
					leadersSlice[i] = strings.TrimSpace(leader)
				}
				formattedLeaders := strings.Join(leadersSlice, ", ")
				leaderLink, _ := s.Find("td a").Attr("href")
				details.CourseLead = model.CourseLead{Name: formattedLeaders, Link: leaderLink}
			case "Ort":
				locationDetails := strings.Split(value, "(")
				if len(locationDetails) == 2 {
					details.Location = model.Location{
						Name:    strings.TrimSpace(locationDetails[0]),
						Address: strings.TrimRight(strings.TrimSpace(locationDetails[1]), ")"),
					}
				}
			case "Teilnehmer":
				parts := strings.Split(value, "/")
				if len(parts) >= 3 {
					bookings, _ := strconv.Atoi(strings.TrimSpace(parts[0]))
					totalPlaces, _ := strconv.Atoi(strings.TrimSpace(parts[1]))
					waitList, _ := strconv.Atoi(strings.TrimSpace(parts[2]))
					details.Participants = model.Participants{Bookings: bookings, TotalPlaces: totalPlaces, WaitList: waitList}
				}
			case "Kosten":
				details.Cost = value // makes no sense since you need to be logged in to see the price
			case "Hinweis":
				var allNotes []string

				s.Find("td").Last().Contents().Each(func(i int, s *goquery.Selection) {
					if s.Is("h4.eventAdvice") || goquery.NodeName(s) == "#text" {
						note := strings.TrimSpace(s.Text())
						if note != "" {
							allNotes = append(allNotes, note)
						}
					}
				})

				event.AdditionalNote = strings.Join(allNotes, " ")
			}
		})

		event.Details = details
		events = append(events, event)
	})

	return events, nil
}

// parseEventID from fulltitle
// the event id is a number in the fulltitle thats not a time like HH:MM and shoudl be found after Nr. or Nr:
func parseEventID(fulltitle string) string {
	var eventID string
	var numberRegExp = regexp.MustCompile("[0-9]{1,4}")
	var fulltitleParts = strings.Split(fulltitle, " ")
	for i, part := range fulltitleParts {
		if part == "Nr." || part == "Nr:" {
			eventID = fulltitleParts[i+1]
			break
		}
	}
	if eventID == "" {
		eventID = numberRegExp.FindString(fulltitle)
	}
	return eventID

}