package main

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

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

var calName = flag.String("calendar", "", "name of calendar")
var days = flag.Int("days", 0, "number of days in the future")

func main() {
	flag.Parse()

	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)
	}

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

	calendars, err := srv.CalendarList.List().Do()
	if err != nil {
		log.Fatal(err)
	}
	var myCal *calendar.CalendarListEntry
	for _, item := range calendars.Items {
		if item.Summary == *calName {
			myCal = item
			break
		}
	}
	if myCal == nil {
		log.Fatalf("calendar '%s' not found", *calName)
	}

	loc, err := time.LoadLocation("US/Pacific")
	if err != nil {
		log.Fatal(err)
	}

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

	for i := 0; i < *days; i++ {
		date := now.Add(time.Duration(i * 24) * time.Hour)

		eventMap, err := getDayEvents(srv, myCal.Id, date)
		if err != nil {
			log.Fatal(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 := srv.Events.Insert(myCal.Id, ev).Do()
				if err != nil {
					log.Fatal(err)
				}
			} else {
				if !eventsEqual(old, ev) {
					log.Printf("upd: [%s] %s", ev.Start.DateTime, ev.Summary)
					_, err := srv.Events.Update(myCal.Id, old.Id, ev).Do()
					if err != nil {
						log.Fatal(err)
					}
				}
			}
		}
	}
}

func getDayEvents(srv *calendar.Service, 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 := srv.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
}