Reschedule the reminders when adding a new one

The thread handling the reminders is unparked and reschedules the
execution of sending out reminders.

src/main.rs

@@ -6,7 +6,7 @@ use diesel::{
     r2d2::{ConnectionManager, Pool},
 };
 use lettre::{Message, SmtpTransport, Transport};
-use std::{env, net::SocketAddr, time::Duration};
+use std::{env, net::SocketAddr, sync::Arc, thread::JoinHandle, time::Duration};
 use time::OffsetDateTime;
 use tower::ServiceBuilder;
 use tower_http::trace::TraceLayer;
@@ -80,6 +80,12 @@ fn remind(
     Ok(())
 }
 
+#[derive(Clone)]
+pub struct AppState {
+    db_pool: Pool<ConnectionManager<PgConnection>>,
+    reminder: Arc<JoinHandle<Result<(), Error>>>,
+}
+
 #[tokio::main]
 async fn main() -> Result<()> {
     let args = Args::parse();
@@ -97,25 +103,23 @@ async fn main() -> Result<()> {
     );
 
     let config = Config::load_config(args.config)?;
-
     let mut db_pool = get_connection_pool(&config)?;
-
-    std::thread::spawn(move || -> Result<(), Error> {
+    let reminder = std::thread::spawn(move || -> Result<(), Error> {
         let mailer = SmtpTransport::unencrypted_localhost();
 
         loop {
             remind(&mut db_pool, &mailer)?;
         }
     });
-
     let db_pool = get_connection_pool(&config)?;
-
     let app = Router::new()
         .route("/v1/reminder", post(api::create_reminder))
         .layer(ServiceBuilder::new().layer(TraceLayer::new_for_http()))
         .fallback(api::not_found)
-        .with_state(db_pool);
-
+        .with_state(AppState {
+            db_pool,
+            reminder: Arc::new(reminder),
+        });
     let addr = SocketAddr::from((config.server.address, config.server.port));
 
     info!("{} listening on {}", env!("CARGO_PKG_NAME"), addr);