//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 v1

import (
	"fmt"
	"github.com/google/uuid"
	"github.com/pocketbase/pocketbase/tools/types"
	"golang.org/x/net/html"
	"htwkalender/data-manager/model"
	"htwkalender/data-manager/service/date"
	"htwkalender/data-manager/service/fetch"
	"htwkalender/data-manager/service/functions"
	"log/slog"
	"regexp"
	"strconv"
	"strings"
	"time"
)

func ReplaceEmptyEventNames(group model.SeminarGroup) model.SeminarGroup {
	for j, event := range group.Events {
		if functions.OnlyWhitespace(event.Name) {
			group.Events[j].Name = "Sonderveranstaltungen"
		}
	}
	return group
}

func fetchHTMLFromURL(semester, seminarGroupLabel string) (string, error) {
	// check that semester and seminarGroupLabel are not empty
	if semester == "" || seminarGroupLabel == "" {
		return "", fmt.Errorf("semester or seminarGroupLabel is empty")
	}

	url := "https://stundenplan.htwk-leipzig.de/" + semester + "/Berichte/Text-Listen;Studenten-Sets;name;" + seminarGroupLabel + "?template=sws_semgrp&weeks=1-65"
	result, err := fetch.GetHTML(url)
	if err != nil {
		slog.Error("Error occurred while fetching the HTML document:", "error", err)
		return "", err
	}
	return result, nil
}

func isSummerSemester(month time.Month) bool {
	return month >= 3 && month <= 10
}

func isWinterSemester(month time.Month) bool {
	return month >= 9 || month <= 4
}

func FetchAndParse(season, label string) (model.SeminarGroup, error) {
	result, err := fetchHTMLFromURL(season, label)
	if err != nil {
		return model.SeminarGroup{}, err
	}
	return parseSeminarGroup(result, season), nil
}

func SplitEventType(events []model.Event) ([]model.Event, error) {
	re, err := regexp.Compile("^([VPS])([wp])$")
	if err != nil {
		return nil, err
	}

	for i, event := range events {
		matched := re.Match([]byte(event.EventType))
		if matched {
			eventType := event.EventType
			event.EventType = eventType[0:1]
			event.Compulsory = eventType[1:2]
			events[i] = event
		}
	}
	return events, nil
}

func parseSeminarGroup(result string, semester string) model.SeminarGroup {
	doc, err := html.Parse(strings.NewReader(result))
	if err != nil {
		fmt.Printf("Error occurred while parsing the HTML document: %s\n", err.Error())
		return model.SeminarGroup{}
	}

	table := findFirstTable(doc)
	allDayLabels := getAllDayLabels(doc)
	eventTables := getEventTables(doc, allDayLabels)

	if table == nil {
		slog.Error("Failed to find first table")
		return model.SeminarGroup{}
	}

	course := findFirstSpanWithClass(table, "header-2-0-1").FirstChild.Data
	semesterString := findFirstSpanWithClass(table, "header-0-2-0").FirstChild.Data
	semester, year := extractSemesterAndYear(semesterString)

	if eventTables == nil || allDayLabels == nil {
		return model.SeminarGroup{
			University: findFirstSpanWithClass(table, "header-1-0-0").FirstChild.Data,
			Course:     course,
			Events:     []model.Event{},
		}
	}

	eventsWithCombinedWeeks := toEvents(eventTables, course)
	splitEventsByWeekVal := splitEventsByWeek(eventsWithCombinedWeeks)
	events := splitEventsBySingleWeek(splitEventsByWeekVal)
	events = convertWeeksToDates(events, semester, year)
	events = generateUUIDs(events, course)
	events, err = SplitEventType(events)

	if err != nil {
		slog.Error("Error occurred while splitting event types:", "error", err)
		return model.SeminarGroup{}
	}

	var seminarGroup = model.SeminarGroup{
		University: findFirstSpanWithClass(table, "header-1-0-0").FirstChild.Data,
		Course:     course,
		Events:     events,
		Semester:   semester,
	}
	return seminarGroup
}

func generateUUIDs(events []model.Event, course string) []model.Event {
	for i, event := range events {
		// generate a hash value from the event name, course and semester
		hash := uuid.NewSHA1(uuid.NameSpaceOID, []byte(event.Name+course))
		events[i].UUID = hash.String()
	}
	return events
}

// convertWeeksToDates converts the week and year to a date
// The date is calculated based on the week and the year
// The time is unset and 23:00 is used as default
// Additionally the semester is added to the event

func convertWeeksToDates(events []model.Event, semester string, year string) []model.Event {
	var newEvents []model.Event
	eventYear, _ := strconv.Atoi(year)

	// for each event we need to calculate the start and end date based on the week and the year
	for _, event := range events {
		eventWeek, _ := strconv.Atoi(event.Week)
		eventDay, _ := date.GetDateFromWeekNumber(eventYear, eventWeek, event.Day)
		start := replaceTimeForDate(eventDay, event.Start.Time())
		end := replaceTimeForDate(eventDay, event.End.Time())

		//Check if end is before start
		if end.Before(start) {
			end = end.AddDate(0, 0, 1)
		}

		newEvent := event
		newEvent.Start, _ = types.ParseDateTime(start.In(time.UTC))
		newEvent.End, _ = types.ParseDateTime(end.In(time.UTC))
		newEvent.Semester = semester
		newEvents = append(newEvents, newEvent)
	}
	return newEvents
}

// replaceTimeForDate replaces hour, minute, second, nsec for the selected date
func replaceTimeForDate(date time.Time, replacementTime time.Time) time.Time {
	return time.Date(date.Year(), date.Month(), date.Day(), replacementTime.Hour(), replacementTime.Minute(), replacementTime.Second(), replacementTime.Nanosecond(), date.Location())
}

func extractSemesterAndYear(semesterString string) (string, string) {
	winterPattern := "Wintersemester"
	summerPattern := "Sommersemester"

	winterMatch := strings.Contains(semesterString, winterPattern)
	summerMatch := strings.Contains(semesterString, summerPattern)

	semester := ""
	semesterShortcut := ""

	if winterMatch {
		semester = "Wintersemester"
		semesterShortcut = "ws"
	} else if summerMatch {
		semester = "Sommersemester"
		semesterShortcut = "ss"
	} else {
		return "", ""
	}

	yearPattern := `\d{4}`
	combinedPattern := semester + `\s` + yearPattern
	re := regexp.MustCompile(combinedPattern)
	match := re.FindString(semesterString)
	year := ""

	if match != "" {
		reYear := regexp.MustCompile(yearPattern)
		year = reYear.FindString(match)
	}
	return semesterShortcut, year
}

func toEvents(tables map[string][]*html.Node, course string) []model.Event {
	var events []model.Event

	for day := range tables {
		for row := range tables[day] {

			tableData := findTableData(tables[day][row])
			if len(tableData) > 0 {
				start, _ := types.ParseDateTime(createTimeFromHourAndMinuteString(getTextContent(tableData[1])))
				end, _ := types.ParseDateTime(createTimeFromHourAndMinuteString(getTextContent(tableData[2])))
				events = append(events, model.Event{
					Day:       day,
					Week:      getTextContent(tableData[0]),
					Start:     start,
					End:       end,
					Name:      getTextContent(tableData[3]),
					EventType: getTextContent(tableData[4]),
					Prof:      getTextContent(tableData[5]),
					Rooms:     getTextContent(tableData[6]),
					Notes:     getTextContent(tableData[7]),
					BookedAt:  getTextContent(tableData[8]),
					Course:    course,
				})
			}
		}

	}
	return events
}

// createEventFromTableData should create an event from the table data
// tableTime represents Hour and Minute like HH:MM
// tableDate returns a Time
func createTimeFromHourAndMinuteString(tableTime string) time.Time {
	timeParts := strings.Split(tableTime, ":")
	hour, _ := strconv.Atoi(timeParts[0])
	minute, _ := strconv.Atoi(timeParts[1])
	return time.Date(0, 0, 0, hour, minute, 0, 0, time.UTC)
}

func splitEventsByWeek(events []model.Event) []model.Event {
	var newEvents []model.Event

	for _, event := range events {
		weeks := strings.Split(event.Week, ",")
		for _, week := range weeks {
			newEvent := event
			newEvent.Week = strings.TrimSpace(week)
			newEvents = append(newEvents, newEvent)
		}
	}
	return newEvents
}

func splitEventsBySingleWeek(events []model.Event) []model.Event {
	var newEvents []model.Event

	for _, event := range events {
		if strings.Contains(event.Week, "-") {
			weeks := splitWeekRange(event.Week)
			for _, week := range weeks {
				newEvent := event
				newEvent.Week = week
				newEvents = append(newEvents, newEvent)
			}
		} else {
			newEvents = append(newEvents, event)
		}
	}
	return newEvents
}

func splitWeekRange(weekRange string) []string {
	parts := strings.Split(weekRange, "-")
	if len(parts) != 2 {
		return nil // Invalid format
	}

	start, errStart := strconv.Atoi(strings.TrimSpace(parts[0]))
	end, errEnd := strconv.Atoi(strings.TrimSpace(parts[1]))

	if errStart != nil || errEnd != nil {
		return nil // Error converting to integers
	}

	var weeks []string
	for i := start; i <= end; i++ {
		weeks = append(weeks, strconv.Itoa(i))
	}

	return weeks
}