use crate::db::Db;
use chrono::TimeZone;
use std::collections::HashSet;
use std::sync::Mutex;
use std::time::Duration;
use tauri::{AppHandle, Manager};
use tauri_plugin_notification::NotificationExt;

const POLL_INTERVAL_SECS: u64 = 30;
/// Only fire a reminder whose trigger moment is this recent — avoids a flood of
/// stale notifications for reminders that elapsed while the app was closed.
const FRESHNESS_WINDOW_SECS: i64 = 300;
const LOOKAHEAD_SECS: i64 = 2 * 86400;

pub fn spawn_poller(app: AppHandle) {
    tauri::async_runtime::spawn(async move {
        let notified: Mutex<HashSet<String>> = Mutex::new(HashSet::new());
        let mut interval = tokio::time::interval(Duration::from_secs(POLL_INTERVAL_SECS));
        loop {
            interval.tick().await;
            poll_once(&app, &notified);
        }
    });
}

fn poll_once(app: &AppHandle, notified: &Mutex<HashSet<String>>) {
    let db = app.state::<Db>();
    let Ok(events) = db.list_events_with_reminders() else { return };
    let now = chrono::Utc::now().timestamp();

    for base in events {
        let Some(reminder_min) = base.reminder_minutes else { continue };
        let occurrences = if let Some(rule) = &base.rrule {
            let exdates: Vec<i64> = base.exdates.as_deref().unwrap_or("").split(',').filter_map(|s| s.trim().parse().ok()).collect();
            crate::recurrence::expand(base.start_ts, base.end_ts, rule, now - 3600, now + LOOKAHEAD_SECS, &exdates)
        } else {
            vec![(base.start_ts, base.end_ts)]
        };

        for (occ_start, _) in occurrences {
            let trigger_ts = occ_start - i64::from(reminder_min) * 60;
            if trigger_ts > now || now - trigger_ts >= FRESHNESS_WINDOW_SECS {
                continue;
            }
            let key = format!("{}#{}", base.id, occ_start);
            {
                let mut set = notified.lock().unwrap();
                if !set.insert(key) {
                    continue;
                }
            }
            let when = chrono::Local
                .timestamp_opt(occ_start, 0)
                .single()
                .map(|d| d.format("um %H:%M").to_string())
                .unwrap_or_default();
            let body = if base.all_day {
                "Heute".to_string()
            } else {
                format!("Beginnt {when}")
            };
            let _ = app
                .notification()
                .builder()
                .title(format!("Erinnerung: {}", base.title))
                .body(body)
                .show();
        }
    }
}