package bot

import (
	"fmt"
	"time"

	"github.com/xuri/excelize/v2"

	"worktimeBot/internal/db"
)

// GenerateMonthlyReport creates an Excel spreadsheet for the given month.
func GenerateMonthlyReport(store *db.Store, year int, month time.Month) ([]byte, error) {
	f := excelize.NewFile()
	defer func() { _ = f.Close() }()

	sheet := "Report"
	// Create a new sheet
	index, err := f.NewSheet(sheet)
	if err != nil {
		return nil, err
	}
	f.SetActiveSheet(index)

	// Header row
	headers := []string{"Date", "Work Duration (h)", "Pairs"}
	for i, h := range headers {
		cell, _ := excelize.CoordinatesToCellName(i+1, 1)
		if err := f.SetCellValue(sheet, cell, h); err != nil {
			return nil, err
		}
	}

	row := 2
	loc := time.Now().Location()
	firstDay := time.Date(year, month, 1, 0, 0, 0, 0, loc)
	lastDay := firstDay.AddDate(0, 1, -1)

	for d := firstDay; d.Before(lastDay.AddDate(0, 0, 1)); d = d.AddDate(0, 0, 1) {
		dateStr := d.Format("2006-01-02")
		isOff, err := store.IsDayOff(dateStr)
		if err != nil {
			return nil, err
		}
		if isOff {
			continue // skip day‑offs
		}
		events, err := store.EventsForDay(dateStr)
		if err != nil {
			return nil, err
		}
		totals := ComputeDailyTotals(events)
		hours := float64(totals.TotalSeconds) / 3600.0

		cellDate, _ := excelize.CoordinatesToCellName(1, row)
		cellHours, _ := excelize.CoordinatesToCellName(2, row)
		cellPairs, _ := excelize.CoordinatesToCellName(3, row)

		if err := f.SetCellValue(sheet, cellDate, dateStr); err != nil {
			return nil, err
		}
		if err := f.SetCellValue(sheet, cellHours, fmt.Sprintf("%.2f", hours)); err != nil {
			return nil, err
		}
		if err := f.SetCellValue(sheet, cellPairs, totals.PairCount); err != nil {
			return nil, err
		}
		row++
	}

	buf, err := f.WriteToBuffer()
	if err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}