package main

import (
	"fmt"
	"log/slog"
	"sort"
	"strings"
	"time"

	"github.com/xuri/excelize/v2"
)

type DailySummary struct {
	Date          string
	Day           string
	WorkStart     string
	WorkEnd       string
	BreakDuration time.Duration
	WorkDuration  time.Duration
	Tag           string
}

type ExcelEntry struct {
	Date          string
	Day           string
	WorkStart     string
	WorkEnd       string
	BreakDuration string
	Tag           string
}

func aggregateEntriesToDailySummaries(entries []TimeEntry, yearStart, yearEnd time.Time) (map[string]*DailySummary, error) {
	dailyMap := make(map[string]*DailySummary)
	location := yearStart.Location()
	now := time.Now().In(location)

	currentDay := yearStart
	for currentDay.Before(yearEnd) {
		dayStr := currentDay.Format("2006-01-02")
		weekday := currentDay.Weekday()
		tag := ""
		if weekday == time.Saturday || weekday == time.Sunday {
			tag = "free"
		}

		dailyMap[dayStr] = &DailySummary{
			Date: dayStr,
			Day:  weekday.String()[:3],
			Tag:  tag,
		}
		currentDay = currentDay.Add(24 * time.Hour)
	}

	fullDayTags := make(map[string]string)

	for _, entry := range entries {
		if entry.StartTime.IsZero() {
			slog.Warn(fmt.Sprintf("Skipping entry with zero start time (ID: %d)", entry.ID))
			continue
		}

		startTime := entry.StartTime.In(location)
		endTime := entry.EndTime.Time.In(location)
		validEndTime := entry.EndTime.Valid
		if !validEndTime {
			endTime = now
		}

		if endTime.Before(yearStart) || startTime.After(yearEnd) {
			continue
		}

		lowerTag := strings.ToLower(entry.Tag)
		isPotentiallyFullDaySpecialTag := false
		switch lowerTag {
		case "urlaub", "krank", "feiertag", "uni", "free":
			isPotentiallyFullDaySpecialTag = true
		}

		if isPotentiallyFullDaySpecialTag {
			loopTimeForTag := startTime
			for loopTimeForTag.Before(endTime) || loopTimeForTag.Equal(endTime) {
				dayStr := loopTimeForTag.Format("2006-01-02")
				if _, exists := dailyMap[dayStr]; exists {
					existingTag := fullDayTags[dayStr]
					if shouldOverwriteTag(existingTag, lowerTag) {
						fullDayTags[dayStr] = lowerTag
					}
				}
				loopTimeForTag = time.Date(loopTimeForTag.Year(), loopTimeForTag.Month(), loopTimeForTag.Day(), 0, 0, 0, 0, location).Add(24 * time.Hour)
			}
		}

		loopTime := startTime
		for loopTime.Before(endTime) {
			dayStr := loopTime.Format("2006-01-02")
			dayStart := time.Date(loopTime.Year(), loopTime.Month(), loopTime.Day(), 0, 0, 0, 0, location)
			dayEnd := dayStart.Add(24 * time.Hour)

			summary, exists := dailyMap[dayStr]
			if !exists {
				slog.Warn(fmt.Sprintf("Day %s not found in initial map during entry processing (ID: %d)", dayStr, entry.ID))
				loopTime = dayEnd
				continue
			}

			segmentStart := loopTime
			segmentEnd := endTime
			if segmentEnd.After(dayEnd) {
				segmentEnd = dayEnd
			}

			segmentDuration := segmentEnd.Sub(segmentStart)
			if segmentDuration <= 0 {
				loopTime = dayEnd
				continue
			}

			timeStr := segmentStart.Format("15:04:05")

			switch lowerTag {
			case TagWork:
				summary.WorkDuration += segmentDuration
				if summary.WorkStart == "" || timeStr < summary.WorkStart {
					summary.WorkStart = timeStr
				}
				entryEndTimeOnThisDay := endTime
				if !endTime.Truncate(24 * time.Hour).Equal(dayStart) {
					entryEndTimeOnThisDay = segmentEnd
				}
				entryEndTimeOnThisDayStr := entryEndTimeOnThisDay.Format("15:04:05")
				if summary.WorkEnd == "" || entryEndTimeOnThisDayStr > summary.WorkEnd {
					summary.WorkEnd = entryEndTimeOnThisDayStr
				}

				if summary.Tag == "" || summary.Tag == "free" {
					summary.Tag = TagWork
				}

			case TagBreak:
				summary.BreakDuration += segmentDuration
			default:
				slog.Info(fmt.Sprintf("Encountered unknown tag '%s' during interval processing for entry ID %d on %s. Counting duration as 'work'.", entry.Tag, entry.ID, dayStr))
				summary.WorkDuration += segmentDuration
				if summary.WorkStart == "" || timeStr < summary.WorkStart {
					summary.WorkStart = timeStr
				}
				entryEndTimeOnThisDay := endTime
				if !endTime.Truncate(24 * time.Hour).Equal(dayStart) {
					entryEndTimeOnThisDay = segmentEnd
				}
				entryEndTimeOnThisDayStr := entryEndTimeOnThisDay.Format("15:04:05")
				if summary.WorkEnd == "" || entryEndTimeOnThisDayStr > summary.WorkEnd {
					summary.WorkEnd = entryEndTimeOnThisDayStr
				}
				if summary.Tag == "" || summary.Tag == "free" {
					summary.Tag = TagWork
				}
			}

			loopTime = dayEnd
		}
	}

	for dayStr, specialTag := range fullDayTags {
		if summary, exists := dailyMap[dayStr]; exists {
			if shouldOverwriteTag(summary.Tag, specialTag) {
				summary.Tag = specialTag
				summary.WorkStart = ""
				summary.WorkEnd = ""
				summary.WorkDuration = 0
				summary.BreakDuration = 0
			}
		}
	}

	return dailyMap, nil
}

func shouldOverwriteTag(existingTag, newTag string) bool {
	if newTag != "" && (existingTag == "" || strings.ToLower(existingTag) == "free") {
		return true
	}
	if newTag == "" {
		return false
	}

	priority := map[string]int{
		"krank":    1,
		"feiertag": 1,
		"urlaub":   1,
		"uni":      2,
		"work":     3,
		"break":    99,
		"free":     100,
	}
	prioExisting, okExisting := priority[strings.ToLower(existingTag)]
	if !okExisting {
		prioExisting = 999
	}
	prioNew, okNew := priority[strings.ToLower(newTag)]
	if !okNew {
		prioNew = 999
	}

	return prioNew < prioExisting || (prioNew == prioExisting && strings.ToLower(newTag) != "work")
}

func convertDailyToExcelEntries(dailySummaries map[string]*DailySummary) []ExcelEntry {
	excelEntries := make([]ExcelEntry, 0, len(dailySummaries))

	dates := make([]string, 0, len(dailySummaries))
	for d := range dailySummaries {
		dates = append(dates, d)
	}
	sort.Strings(dates)

	for _, dateStr := range dates {
		summary := dailySummaries[dateStr]
		entry := ExcelEntry{
			Date:          summary.Date,
			Day:           summary.Day,
			WorkStart:     summary.WorkStart,
			WorkEnd:       summary.WorkEnd,
			BreakDuration: formatDuration(summary.BreakDuration),
			Tag:           summary.Tag,
		}
		excelEntries = append(excelEntries, entry)
	}
	return excelEntries
}

func formatDuration(d time.Duration) string {
	if d < 0 {
		d = -d
		sign := "-"
		d = d.Round(time.Second)
		h := int64(d.Hours())
		m := int64(d.Minutes()) % 60
		s := int64(d.Seconds()) % 60
		return fmt.Sprintf("%s%02d:%02d:%02d", sign, h, m, s)
	}
	d = d.Round(time.Second)
	h := int64(d.Hours())
	m := int64(d.Minutes()) % 60
	s := int64(d.Seconds()) % 60
	return fmt.Sprintf("%02d:%02d:%02d", h, m, s)
}

func getSollExcelTime(dayOfWeek string) any {
	var sollString string
	switch dayOfWeek {
	case "Mon", "Tue", "Thu", "Fri":
		sollString = "08:00"
	case "Wed":
		sollString = "04:00"
	default:
		return nil
	}

	sollDur, err := time.Parse("15:04", sollString)
	if err != nil {
		slog.Error(fmt.Sprintf("Could not parse hardcoded soll string '%s': %v", sollString, err))
		return nil
	}
	return float64(sollDur.Hour())/24.0 + float64(sollDur.Minute())/(24.0*60.0)
}

func writeExcelSheet(entries []ExcelEntry, name string) error {
	f := excelize.NewFile()
	defer func() {
		if err := f.Close(); err != nil {
			slog.Error(fmt.Sprintf("Failed to close excel file handle: %v", err))
		}
	}()

	sheetName := "Zeiten"
	if len(entries) > 0 {
		if t, err := time.Parse("2006-01-02", entries[0].Date); err == nil {
			sheetName = fmt.Sprintf("%d", t.Year())
		}
	}

	index, err := f.NewSheet(sheetName)
	if err != nil {
		existingIndex, _ := f.GetSheetIndex(sheetName)
		if existingIndex == -1 {
			sheetName = "Sheet1"
			index, _ = f.GetSheetIndex(sheetName)
			if index == -1 {
				return fmt.Errorf("could not create or find sheet '%s' or 'Sheet1': %w", sheetName, err)
			}
		} else {
			index = existingIndex
		}
	}

	defaultSheetName := "Sheet1"
	defaultSheetIndex, _ := f.GetSheetIndex(defaultSheetName)
	if sheetName != defaultSheetName && defaultSheetIndex != -1 {
		f.DeleteSheet(defaultSheetName)
	}

	f.SetCellValue(sheetName, "B1", "Arbeitszeiten "+sheetName)
	f.MergeCell(sheetName, "B1", "O1")

	f.SetCellValue(sheetName, "B3", "Datum")
	f.SetCellValue(sheetName, "C3", "Tag")
	f.SetCellValue(sheetName, "D3", "Status / Zeit")
	f.MergeCell(sheetName, "D3", "E3")
	f.SetCellValue(sheetName, "G3", "Dauer")
	f.MergeCell(sheetName, "G3", "H3")
	f.SetCellValue(sheetName, "I3", "Pause")
	f.SetCellValue(sheetName, "J3", "Netto")
	f.SetCellValue(sheetName, "K3", "Soll")
	f.SetCellValue(sheetName, "L3", "Saldo")
	f.SetCellValue(sheetName, "N3", "Saldo Kumuliert")
	f.MergeCell(sheetName, "N3", "O3")

	f.SetCellValue(sheetName, "D4", "von / Status")
	f.SetCellValue(sheetName, "E4", "bis")
	f.SetCellValue(sheetName, "G4", "brutto")
	f.SetCellValue(sheetName, "H4", "")
	f.SetCellValue(sheetName, "J4", "Ist (Netto)")
	f.SetCellValue(sheetName, "K4", "")
	f.SetCellValue(sheetName, "L4", "Tag")
	f.SetCellValue(sheetName, "N4", "Total")
	f.SetCellValue(sheetName, "O4", "")

	timeStyleCode := "hh:mm"
	timeStyle, _ := f.NewStyle(&excelize.Style{CustomNumFmt: &timeStyleCode})
	dateStyleCode := "dd.mm.yyyy"
	dateStyle, _ := f.NewStyle(&excelize.Style{CustomNumFmt: &dateStyleCode})
	saldoStyleCode := "[h]:mm;[RED]-[h]:mm"
	saldoStyle, _ := f.NewStyle(&excelize.Style{CustomNumFmt: &saldoStyleCode})
	headerStyle, _ := f.NewStyle(&excelize.Style{
		Font:      &excelize.Font{Bold: true},
		Alignment: &excelize.Alignment{Horizontal: "center"},
	})
	centerStyle, _ := f.NewStyle(&excelize.Style{Alignment: &excelize.Alignment{Horizontal: "center"}})

	f.SetCellStyle(sheetName, "B3", "O4", headerStyle)
	f.SetCellStyle(sheetName, "B1", "O1", headerStyle)

	startRow := 6
	for i, entry := range entries {
		row := startRow + i
		rowStr := fmt.Sprintf("%d", row)
		tagLower := strings.ToLower(entry.Tag)

		dateValue, err := time.Parse("2006-01-02", entry.Date)
		if err == nil {
			f.SetCellValue(sheetName, "B"+rowStr, dateValue)
			f.SetCellStyle(sheetName, "B"+rowStr, "B"+rowStr, dateStyle)
		} else {
			f.SetCellValue(sheetName, "B"+rowStr, entry.Date)
		}
		f.SetCellValue(sheetName, "C"+rowStr, entry.Day)

		sollExcelTime := getSollExcelTime(entry.Day)
		if sollExcelTime != nil {
			f.SetCellValue(sheetName, "K"+rowStr, sollExcelTime)
			f.SetCellStyle(sheetName, "K"+rowStr, "K"+rowStr, timeStyle)
		} else {
			f.SetCellValue(sheetName, "K"+rowStr, "")
		}

		switch tagLower {
		case TagWork, "":
			if entry.WorkStart != "" && entry.WorkEnd != "" {
				startTime, _ := time.Parse("15:04:05", entry.WorkStart)
				endTime, _ := time.Parse("15:04:05", entry.WorkEnd)
				startExcelTime := float64(startTime.Hour())/24.0 + float64(startTime.Minute())/(24.0*60.0) + float64(startTime.Second())/(24.0*60.0*60.0)
				endExcelTime := float64(endTime.Hour())/24.0 + float64(endTime.Minute())/(24.0*60.0) + float64(endTime.Second())/(24.0*60.0*60.0)
				if endExcelTime < startExcelTime {
					endExcelTime += 1.0
				}

				f.SetCellValue(sheetName, "D"+rowStr, startExcelTime)
				f.SetCellStyle(sheetName, "D"+rowStr, "D"+rowStr, timeStyle)
				f.SetCellValue(sheetName, "E"+rowStr, endExcelTime)
				f.SetCellStyle(sheetName, "E"+rowStr, "E"+rowStr, timeStyle)

				f.SetCellFormula(sheetName, "G"+rowStr, fmt.Sprintf("E%d-D%d", row, row))
				f.SetCellStyle(sheetName, "G"+rowStr, "H"+rowStr, saldoStyle) // Saldo-Style für Dauer

				breakDur, _ := time.Parse("15:04:05", entry.BreakDuration)
				breakExcelTime := float64(breakDur.Hour())/24.0 + float64(breakDur.Minute())/(24.0*60.0) + float64(breakDur.Second())/(24.0*60.0*60.0)
				thirtyMinBreak := float64(30) / (24 * 60)
				if breakExcelTime < thirtyMinBreak {
					breakExcelTime = thirtyMinBreak
				}
				f.SetCellValue(sheetName, "I"+rowStr, breakExcelTime)
				f.SetCellStyle(sheetName, "I"+rowStr, "I"+rowStr, timeStyle)

				f.SetCellFormula(sheetName, "J"+rowStr, fmt.Sprintf("MAX(0, G%d-I%d)", row, row))
				f.SetCellStyle(sheetName, "J"+rowStr, "J"+rowStr, saldoStyle)

			} else {
				f.SetCellValue(sheetName, "J"+rowStr, 0.0)
				f.SetCellStyle(sheetName, "J"+rowStr, "J"+rowStr, saldoStyle)
			}

		case "urlaub", "uni":
			text := ""
			if tagLower == "urlaub" {
				text = "Urlaub"
			} else {
				text = "Hochschule"
			}
			f.SetCellValue(sheetName, "D"+rowStr, text)
			f.MergeCell(sheetName, "D"+rowStr, "I"+rowStr)
			f.SetCellStyle(sheetName, "D"+rowStr, "I"+rowStr, centerStyle)

			if sollExcelTime != nil {
				f.SetCellValue(sheetName, "J"+rowStr, sollExcelTime)
			} else {
				f.SetCellValue(sheetName, "J"+rowStr, 0.0)
			}
			f.SetCellStyle(sheetName, "J"+rowStr, "J"+rowStr, saldoStyle)

		case "feiertag", "krank":
			text := ""
			if tagLower == "feiertag" {
				text = "Feiertag"
			} else {
				text = "Krank"
			}
			f.SetCellValue(sheetName, "D"+rowStr, text)
			f.MergeCell(sheetName, "D"+rowStr, "I"+rowStr)
			f.SetCellStyle(sheetName, "D"+rowStr, "I"+rowStr, centerStyle)

			if sollExcelTime != nil {
				f.SetCellValue(sheetName, "J"+rowStr, sollExcelTime)
			} else {
				f.SetCellValue(sheetName, "J"+rowStr, 0.0)
			}
			f.SetCellStyle(sheetName, "J"+rowStr, "J"+rowStr, saldoStyle)

		case "free":
			f.SetCellValue(sheetName, "D"+rowStr, "")
			f.MergeCell(sheetName, "D"+rowStr, "I"+rowStr)
			f.SetCellStyle(sheetName, "D"+rowStr, "I"+rowStr, centerStyle)
			f.SetCellValue(sheetName, "J"+rowStr, 0.0)
			f.SetCellStyle(sheetName, "J"+rowStr, "J"+rowStr, saldoStyle)

		default:
			f.SetCellValue(sheetName, "J"+rowStr, 0.0)
			f.SetCellStyle(sheetName, "J"+rowStr, "J"+rowStr, saldoStyle)
		}

		f.SetCellFormula(sheetName, "L"+rowStr, fmt.Sprintf("J%d-K%d", row, row))
		f.SetCellStyle(sheetName, "L"+rowStr, "M"+rowStr, saldoStyle)

		if i == 0 {
			f.SetCellFormula(sheetName, "N"+rowStr, fmt.Sprintf("L%d", row))
		} else {
			prevSaldoTotalCell := fmt.Sprintf("N%d", row-1)
			f.SetCellFormula(sheetName, "N"+rowStr, fmt.Sprintf("%s+L%d", prevSaldoTotalCell, row))
		}
		f.SetCellStyle(sheetName, "N"+rowStr, "O"+rowStr, saldoStyle)
	}

	f.SetColWidth(sheetName, "B", "B", 12)
	f.SetColWidth(sheetName, "C", "C", 5)
	f.SetColWidth(sheetName, "D", "E", 10)
	f.SetColWidth(sheetName, "F", "F", 2)
	f.SetColWidth(sheetName, "G", "H", 9)
	f.SetColWidth(sheetName, "I", "I", 9)
	f.SetColWidth(sheetName, "J", "J", 9)
	f.SetColWidth(sheetName, "K", "K", 9)
	f.SetColWidth(sheetName, "L", "M", 9)
	f.SetColWidth(sheetName, "N", "O", 10)

	f.SetActiveSheet(index)
	if err := f.SaveAs(name); err != nil {
		return fmt.Errorf("failed to save excel file as '%s': %w", name, err)
	}

	return nil
}