Start work on #34

Started work on the garbage-collection module. This for now just loads the stored demo ids
and checks if they are also found in the database, logging every demo that could not be found
and should at some point delete these demos

backend/src/gc.rs

@@ -0,0 +1,36 @@
+use diesel::prelude::*;
+use diesel_async::RunQueryDsl;
+
+#[tracing::instrument(skip(storage))]
+pub async fn run_gc(storage: &mut dyn crate::storage::DemoStorage) -> Result<(), ()> {
+    let stored_demos = match storage.list_demos().await {
+        Ok(ds) => ds,
+        Err(e) => return Err(()),
+    };
+
+    tracing::info!("Found {} demos in storage", stored_demos.len());
+
+    let mut db_con = crate::db_connection().await;
+
+    let db_res = db_con
+        .build_transaction()
+        .run(move |con| {
+            Box::pin(async move {
+                for demo in stored_demos {
+                    let query = crate::schema::demos::dsl::demos
+                        .filter(crate::schema::demos::dsl::demo_id.eq(&demo)).select(crate::models::Demo::as_select());
+                    
+                    let matching: Vec<crate::models::Demo> = query.load(con).await?;
+
+                    if matching.is_empty() {
+                        tracing::debug!("Should delete old demo {:?}", demo);
+                    }
+                }
+
+                Ok::<(), diesel::result::Error>(())
+            })
+        })
+        .await;
+
+    db_res.map_err(|e| ())
+}