package main

import (
	"context"
	"flag"
	"fmt"
	"log"
	"net/http"
	"net/url"
	"os"
	"os/signal"
	"slices"
	"strings"
	"syscall"
	"time"

	"github.com/gen2brain/beeep"
)

func main() {
	ctx, can := signal.NotifyContext(context.Background(), syscall.SIGINT)
	defer can()

	fs := flag.NewFlagSet(os.Args[0], flag.ContinueOnError)
	gcal := fs.Bool("gcal", false, "wait for google cal events")
	ntfy := fs.String("http", "", "https://squeaky2x3:dYbtypGkHXFtq1E00k2H42SPGUowi@ntfy.home.blapointe.com/alerts-render")
	if err := fs.Parse(os.Args[1:]); err != nil {
		panic(err)
	}

	alerts, err := alerts(ctx, *gcal, fs.Args())
	if err != nil {
		panic(err)
	}

	for alert := range alerts {
		if ctx.Err() != nil {
			break
		}
		if err := alertAt(ctx, *ntfy, time.Now(), alert, time.Now().Format("15:04")); err != nil && ctx.Err() == nil {
			panic(err)
		}
		if ctx.Err() != nil {
			break
		}
	}

	if err := ctx.Err(); err != nil {
		os.Exit(1)
	}
}

func alerts(ctx context.Context, gcal bool, args []string) (chan string, error) {
	if gcal {
		return alertsGCal(ctx)
	}
	duration, err := time.ParseDuration(args[0])
	if err != nil {
		return nil, err
	}
	msg := "alerting after " + duration.String()
	if len(args) > 1 {
		msg = fmt.Sprintf("%s (%s)", args[1], duration.String())
	}
	return alertsAfter(ctx, duration, msg)
}

func alertsAfter(ctx context.Context, dur time.Duration, msg string) (chan string, error) {
	ch := make(chan string)
	deadline := time.Now().Add(dur)
	go func() {
		defer close(ch)
		var prev string
		for ctx.Err() == nil && time.Now().Before(deadline) {
			seconds := int(time.Until(deadline).Seconds())

			cur := fmt.Sprintf("%v", time.Duration(seconds)*time.Second)
			if prev != "" {
				fmt.Printf("\r%s\r", strings.Repeat(" ", len(prev)))
			}
			fmt.Printf("%s", cur)
			prev = cur

			select {
			case <-ctx.Done():
			case <-time.After(time.Second):
			}
		}
		if ctx.Err() == nil {
			fmt.Println(msg)
		}
		ch <- msg
	}()
	return ch, nil
}

func alertsGCal(ctx context.Context) (chan string, error) {
	gcal := NewGCal()
	if err := gcal.Login(ctx); err != nil {
		return nil, err
	}

	var events []Event
	refresh := func() error {
		es, err := gcal.EventsToday(ctx)
		es = slices.DeleteFunc(es, func(s Event) bool {
			return time.Now().After(s.Time)
		})
		if !slices.Equal(es, events) {
			events = es
			if len(events) > 0 {
				log.Println("alerting about", events[0].Name, "at", events[0].Time.Format("15:04"), "(", time.Until(events[0].Time), ")")
			}
		}
		return err
	}
	if err := refresh(); err != nil {
		return nil, err
	}

	ch := make(chan string)
	go func() {
		defer close(ch)

		c := time.NewTicker(time.Minute * 13)
		defer c.Stop()
		for ctx.Err() == nil && len(events) > 0 {
			select {
			case <-c.C:
				if err := refresh(); err != nil {
					panic(err)
				}
			case <-time.After(time.Until(events[0].Time)):
				select {
				case <-ctx.Done():
				case ch <- events[0].Name:
					if events[0].Duration > 0 {
						select {
						case <-ctx.Done():
						case <-time.After(events[0].Duration):
							select {
							case <-ctx.Done():
							case ch <- "/" + events[0].Name:
							}
						}
					}
				}
				events = events[1:]
			case <-ctx.Done():
			}
		}
	}()

	return ch, nil
}

func alertAt(ctx context.Context, ntfy string, deadline time.Time, title, msg string) error {
	c := time.NewTicker(time.Second)
	defer c.Stop()
	func() {
		ctx, can := context.WithDeadline(ctx, deadline)
		defer can()
		for ctx.Err() == nil {
			select {
			case <-c.C:
			case <-ctx.Done():
				return
			}
			fmt.Printf("\r%s   ", deadline.Sub(time.Now()))
		}
	}()
	fmt.Println()

	if err := ctx.Err(); err == nil {
		beeep.Alert(title, msg, "/dev/null")
		if ntfy != "" {
			u, _ := url.Parse(ntfy)
			req, _ := http.NewRequest(http.MethodPost, u.String(), strings.NewReader(fmt.Sprintf("%s: %s", title, msg)))
			req = req.WithContext(ctx)
			http.DefaultClient.Do(req)
		}
	}

	return ctx.Err()
}