Shorten the time until the next tick if it's required to send a start notification

src/main.rs

@@ -4,14 +4,16 @@ mod db;
 mod error;
 mod schema;
 
-use std::{env, fs::File, io::BufReader, sync::Arc, time::Duration};
+use std::time::Duration;
+use std::{env, fs::File, io::BufReader, sync::Arc};
 
 use anyhow::Result;
 use async_mutex::Mutex;
 use bot::fetch_and_announce_appointment;
-use chrono::{DateTime, NaiveTime, TimeZone, Utc};
+use chrono::{DateTime, NaiveDateTime, NaiveTime, TimeZone, Utc};
 use chrono_tz::Europe;
 use db::ChatInfo;
+use diesel::result::Error::NotFound;
 use diesel::{Connection, RunQueryDsl, SqliteConnection};
 use diesel::{ExpressionMethods, QueryDsl};
 use diesel_migrations::{embed_migrations, EmbeddedMigrations, MigrationHarness};
@@ -23,7 +25,7 @@ use teloxide::prelude::RequesterExt;
 use teloxide::requests::Requester;
 use teloxide::types::ChatId;
 use teloxide::{adaptors::throttle::Limits, Bot};
-use tokio::time::interval;
+use tokio::time::sleep;
 
 use crate::db::DbChat;
 
@@ -77,11 +79,36 @@ async fn main() {
 	{
 		let db = db.clone();
 		let bot = bot.clone();
+		let poll_duration = Duration::from_secs(config.poll_interval);
 		tokio::task::spawn(async move {
-			let mut interval = interval(Duration::from_secs(config.poll_interval));
-			interval.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Delay);
 			loop {
-				interval.tick().await;
+				let now = Utc::now();
+
+				let next_appointment = db.lock().await.transaction(|db| {
+					use schema::chat::dsl::*;
+					chat.select(next_appointment_start)
+						.filter(next_appointment_start.is_not_null())
+						.filter(next_appointment_start.gt(now.timestamp()))
+						.order(next_appointment_start.asc())
+						.first::<Option<i64>>(db)
+				});
+
+				let next_appointment = match next_appointment {
+					Err(NotFound) => None,
+					Ok(appointment) => appointment,
+					Err(e) => Err(e).unwrap(),
+				};
+
+				let sleep_duration = next_appointment
+					.map(|timestamp| NaiveDateTime::from_timestamp(timestamp, 0))
+					.map(|naive_date_time| DateTime::<Utc>::from_utc(naive_date_time, Utc))
+					.map(|date_time| date_time - now)
+					.map(|duration| duration.to_std().unwrap())
+					.filter(|duration| *duration < poll_duration)
+					.unwrap_or(poll_duration);
+
+				sleep(sleep_duration).await;
+
 				// TODO Log the error and continue instead
 				check_task(&bot, config.reminder_time, &db).await.unwrap();
 			}