package events

import (
	"context"
	"fmt"
	"log"
	"strconv"
	"time"

	"velox-bot/internal/db/services"

	"github.com/bwmarrin/discordgo"
)

// StartScheduleReminderLoop runs a background loop that periodically checks for
// upcoming sessions and sends DM reminders to all participants.
func StartScheduleReminderLoop(s *discordgo.Session, svc *services.Services) {
	if svc == nil || svc.Schedule == nil || s == nil {
		return
	}

	const (
		interval       = time.Minute      // check every minute
		remindBefore   = 10 * time.Minute // remind 10 minutes before
		initialDelay   = 10 * time.Second
	)

	go func() {
		// small delay so the bot can fully start
		time.Sleep(initialDelay)

		ticker := time.NewTicker(interval)
		defer ticker.Stop()

		for range ticker.C {
			now := time.Now().UTC()
			ctx := context.Background()

			// Find all sessions that start in the next `remindBefore` window and haven't been reminded.
			schedules, err := svc.Schedule.ListDueForReminder(ctx, now, remindBefore)
			if err != nil {
				log.Printf("schedule: reminder query failed: %v", err)
				continue
			}
			for _, sch := range schedules {
				if sch == nil {
					continue
				}

				// Build reminder text
				whenStr := sch.ScheduledAt.UTC().Format("2006-01-02 15:04")
				base := fmt.Sprintf("Reminder: you have a scheduled session at %s UTC with <@%d>.", whenStr, sch.InviteeID)
				desc := sch.Description
				if desc != "" {
					base += "\nTopic: " + desc
				}

				// Notify requester
				if err := dmUser(s, sch.RequesterID, base); err != nil {
					log.Printf("schedule: failed to DM requester reminder: %v", err)
				}

				// Notify invitee (mirror text with requester mention)
				baseInvitee := fmt.Sprintf("Reminder: you have a scheduled session at %s UTC with <@%d>.", whenStr, sch.RequesterID)
				if desc != "" {
					baseInvitee += "\nTopic: " + desc
				}
				if err := dmUser(s, sch.InviteeID, baseInvitee); err != nil {
					log.Printf("schedule: failed to DM invitee reminder: %v", err)
				}

				if err := svc.Schedule.MarkReminded(ctx, sch.ID); err != nil {
					log.Printf("schedule: failed to mark reminder sent for id=%d: %v", sch.ID, err)
				}
			}
		}
	}()
}

func dmUser(s *discordgo.Session, userID int64, content string) error {
	if s == nil || userID == 0 {
		return nil
	}
	uid := strconv.FormatInt(userID, 10)
	ch, err := s.UserChannelCreate(uid)
	if err != nil {
		return err
	}
	_, err = s.ChannelMessageSend(ch.ID, content)
	return err
}