package main

import (
	"encoding/json"
	"fmt"
	"net/http"
	"regexp"
	"time"
)

type CalendarWorkingHoursDay struct {
	Enabled bool   `json:"enabled"`
	Start   string `json:"start"`
	End     string `json:"end"`
}

type CalendarCoreWorkingHours struct {
	Monday    CalendarWorkingHoursDay `json:"monday"`
	Tuesday   CalendarWorkingHoursDay `json:"tuesday"`
	Wednesday CalendarWorkingHoursDay `json:"wednesday"`
	Thursday  CalendarWorkingHoursDay `json:"thursday"`
	Friday    CalendarWorkingHoursDay `json:"friday"`
	Saturday  CalendarWorkingHoursDay `json:"saturday"`
	Sunday    CalendarWorkingHoursDay `json:"sunday"`
}

type CalendarSettings struct {
	CoreWorkingHours CalendarCoreWorkingHours `json:"coreWorkingHours"`
	UpdatedAt        *time.Time               `json:"updatedAt,omitempty"`
}

var calendarTimePattern = regexp.MustCompile(`^\d{2}:\d{2}$`)

func defaultCalendarCoreWorkingHours() CalendarCoreWorkingHours {
	workingDay := CalendarWorkingHoursDay{
		Enabled: true,
		Start:   "08:00",
		End:     "17:00",
	}
	dayOff := CalendarWorkingHoursDay{
		Enabled: false,
		Start:   "08:00",
		End:     "17:00",
	}

	return CalendarCoreWorkingHours{
		Monday:    workingDay,
		Tuesday:   workingDay,
		Wednesday: workingDay,
		Thursday:  workingDay,
		Friday:    workingDay,
		Saturday:  dayOff,
		Sunday:    dayOff,
	}
}

func (s *Server) ensureCalendarSettingsTable(r *http.Request) error {
	defaultHours, err := json.Marshal(defaultCalendarCoreWorkingHours())
	if err != nil {
		return err
	}

	_, err = s.db.Exec(
		r.Context(),
		`
		CREATE TABLE IF NOT EXISTS calendar_settings (
			id SMALLINT PRIMARY KEY CHECK (id = 1),
			core_working_hours JSONB NOT NULL,
			created_at TIMESTAMPTZ NOT NULL DEFAULT now(),
			updated_at TIMESTAMPTZ NOT NULL DEFAULT now()
		)
		`,
	)
	if err != nil {
		return err
	}

	_, err = s.db.Exec(
		r.Context(),
		`
		INSERT INTO calendar_settings (id, core_working_hours)
		VALUES (1, $1::JSONB)
		ON CONFLICT (id) DO NOTHING
		`,
		string(defaultHours),
	)
	return err
}

func (s *Server) loadCalendarSettings(r *http.Request) (CalendarSettings, error) {
	if err := s.ensureCalendarSettingsTable(r); err != nil {
		return CalendarSettings{}, err
	}

	var rawHours []byte
	var settings CalendarSettings
	var updatedAt time.Time

	err := s.db.QueryRow(
		r.Context(),
		`
		SELECT core_working_hours, updated_at
		FROM calendar_settings
		WHERE id = 1
		`,
	).Scan(&rawHours, &updatedAt)
	if err != nil {
		return CalendarSettings{}, err
	}

	if err := json.Unmarshal(rawHours, &settings.CoreWorkingHours); err != nil {
		return CalendarSettings{}, err
	}

	settings.UpdatedAt = &updatedAt
	return settings, nil
}

func validateCalendarWorkingHours(hours CalendarCoreWorkingHours) error {
	days := []struct {
		name  string
		hours CalendarWorkingHoursDay
	}{
		{name: "Montag", hours: hours.Monday},
		{name: "Dienstag", hours: hours.Tuesday},
		{name: "Mittwoch", hours: hours.Wednesday},
		{name: "Donnerstag", hours: hours.Thursday},
		{name: "Freitag", hours: hours.Friday},
		{name: "Samstag", hours: hours.Saturday},
		{name: "Sonntag", hours: hours.Sunday},
	}

	for _, day := range days {
		if !calendarTimePattern.MatchString(day.hours.Start) ||
			!calendarTimePattern.MatchString(day.hours.End) {
			return fmt.Errorf("%s: Beginn und Ende müssen im Format HH:MM angegeben werden", day.name)
		}

		start, startErr := time.Parse("15:04", day.hours.Start)
		end, endErr := time.Parse("15:04", day.hours.End)
		if startErr != nil || endErr != nil {
			return fmt.Errorf("%s: ungültige Uhrzeit", day.name)
		}

		if day.hours.Enabled && !end.After(start) {
			return fmt.Errorf("%s: das Ende muss nach dem Beginn liegen", day.name)
		}
	}

	return nil
}

func (s *Server) handleGetCalendarSettings(w http.ResponseWriter, r *http.Request) {
	settings, err := s.loadCalendarSettings(r)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Kalender-Einstellungen konnten nicht geladen werden")
		return
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"settings": settings,
	})
}

func (s *Server) handleUpdateCalendarSettings(w http.ResponseWriter, r *http.Request) {
	var payload struct {
		CoreWorkingHours CalendarCoreWorkingHours `json:"coreWorkingHours"`
	}

	if err := readJSON(r, &payload); err != nil {
		writeError(w, http.StatusBadRequest, "Ungültige Anfrage")
		return
	}

	if err := validateCalendarWorkingHours(payload.CoreWorkingHours); err != nil {
		writeError(w, http.StatusBadRequest, err.Error())
		return
	}

	if err := s.ensureCalendarSettingsTable(r); err != nil {
		writeError(w, http.StatusInternalServerError, "Kalender-Einstellungen konnten nicht vorbereitet werden")
		return
	}

	rawHours, err := json.Marshal(payload.CoreWorkingHours)
	if err != nil {
		writeError(w, http.StatusBadRequest, "Kalender-Einstellungen sind ungültig")
		return
	}

	_, err = s.db.Exec(
		r.Context(),
		`
		INSERT INTO calendar_settings (id, core_working_hours)
		VALUES (1, $1::JSONB)
		ON CONFLICT (id) DO UPDATE SET
			core_working_hours = EXCLUDED.core_working_hours,
			updated_at = now()
		`,
		string(rawHours),
	)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Kalender-Einstellungen konnten nicht gespeichert werden")
		return
	}

	settings, err := s.loadCalendarSettings(r)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Kalender-Einstellungen wurden gespeichert, konnten aber nicht neu geladen werden")
		return
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"message":  "Kalender-Einstellungen gespeichert",
		"settings": settings,
	})
}