package main

import (
	"fmt"
	"io/ioutil"
	"log"
	"time"

	"golang.org/x/oauth2/google"
	"google.golang.org/api/calendar/v3"
)

var _globalCalService *calendar.Service

func getCalService() *calendar.Service {
	if _globalCalService != nil {
		return _globalCalService
	}

	b, err := ioutil.ReadFile("credentials.json")
	if err != nil {
		log.Fatal(err)
	}

	// If modifying these scopes, delete your previously saved token.json.
	config, err := google.ConfigFromJSON(b, calendar.CalendarScope)
	if err != nil {
		log.Fatal(err)
	}
	client, err := getClient(config)
	if err != nil {
		log.Fatal(err)
	}

	_globalCalService, err := calendar.New(client)
	if err != nil {
		log.Fatal(err)
	}

	return _globalCalService
}

func getCalendarId(calName string) (string, error) {
	client := getCalService()

	calendars, err := client.CalendarList.List().Do()
	if err != nil {
		return "", err
	}

	for _, item := range calendars.Items {
		if item.Summary == calName {
			return item.Id, nil
		}
	}

	return "", fmt.Errorf("calendar '%s' not found", calName)
}

func updateCalendar(calName string, classes []Class, days int) error {
	loc, err := time.LoadLocation("US/Pacific")
	if err != nil {
		return err
	}

	now := time.Now().In(loc)

	calId, err := getCalendarId(calName)
	if err != nil {
		return err
	}

	for i := 0; i < days; i++ {
		date := now.Add(time.Duration(i * 24) * time.Hour)
		err = updateDay(calId, date, classes)
		if err != nil {
			return err
		}
	}
	return nil
}

func updateDay(calId string, date time.Time, classes []Class) error {
	eventMap, err := getDayEvents(calId, date)
	if err != nil {
		return err
	}

	for _, class := range classes {
		if !class.happensOnDay(date) {
			continue
		}

		if !class.tagsMatch(date) {
			continue
		}

		ev := class.buildEvent(date)

		old := eventMap[ev.Summary]

		if old == nil {
			log.Printf("add: [%s] %s", ev.Start.DateTime, ev.Summary)
			_, err := getCalService().Events.Insert(calId, ev).Do()
			if err != nil {
				return err
			}
		} else {
			if !eventsEqual(old, ev) {
				log.Printf("upd: [%s] %s", ev.Start.DateTime, ev.Summary)
				_, err := getCalService().Events.Update(calId, old.Id, ev).Do()
				if err != nil {
					return err
				}
			}
		}
	}

	return nil
}

func getDayEvents(calendarId string, t time.Time) (map[string]*calendar.Event, error) {
	start := time.Date(
		t.Year(),
		t.Month(),
		t.Day(),
		0, 0, 0, 0,
		t.Location())

	// This may be wrong for DST changes, but it's the middle of the night and probably doesn't matter
	end := start.Add(24 * time.Hour)

	events, err := getCalService().Events.List(calendarId).
		ShowDeleted(false).
		SingleEvents(true).
		TimeMin(start.Format(time.RFC3339)).
		TimeMax(end.Format(time.RFC3339)).
		MaxResults(250).
		Do()
	if err != nil {
		return nil, err
	}

	eventMap := map[string]*calendar.Event{}

	for _, item := range events.Items {
		eventMap[item.Summary] = item
	}

	return eventMap, nil
}

func eventsEqual(a *calendar.Event, b *calendar.Event) bool {
	if a.Summary != b.Summary {
		return false
	}

	if a.Description != b.Description {
		return false
	}

	if a.Start.DateTime[:19] != b.Start.DateTime[:19] {
		return false
	}

	if a.End.DateTime[:19] != b.End.DateTime[:19] {
		return false
	}

	if len(a.Attendees) != len(b.Attendees) {
		return false
	}

	emails := map[string]bool{}
	for _, attendee := range a.Attendees {
		emails[attendee.Email] = true
	}
	for _, attendee := range b.Attendees {
		if !emails[attendee.Email] {
			return false
		}
	}

	return true
}