Implement workaround for series deletion

So this is super annoying. The endpoint in opencast will
start `republish metadata` workflows for each event in the
series. This takes roughly 10 second **per video**.
Not in parallel but.. in.. series (pun intended? idk).

So long story short, it could take several minutes to return,
at which point it probably just responds with a `503`.
The series is still being deleted though, so I don't know how
to handle that case.

Anyway, this workaround will send the request, mark the series
as deleted and then just return without waiting. If it fails,
it will **eventually** become apparent, but until then it's just
showing as `deletion pending`, or sth. Actually, depending on
the configured interval, it will already show `deletion failed`
after a couple of minutes or sooner, when the "deletion process"
is still running in Opencast. So all in all a poor solution but
idk what else to do here other than an Opencast rewrite™.

backend/src/api/model/event.rs

@@ -764,10 +764,3 @@ define_sort_column_and_order!(
     };
     pub struct VideosSortOrder
 );
-
-
-#[derive(juniper::GraphQLObject)]
-#[graphql(Context = Context)]
-pub(crate) struct RemovedEvent {
-    id: Id,
-}

backend/src/api/model/series.rs

@@ -38,6 +38,7 @@ use super::{
 };
 
 
+#[derive(Clone)]
 pub(crate) struct Series {
     pub(crate) key: Key,
     pub(crate) opencast_id: String,
@@ -53,7 +54,7 @@ pub(crate) struct Series {
     pub(crate) tobira_deletion_timestamp: Option<DateTime<Utc>>,
 }
 
-#[derive(GraphQLObject)]
+#[derive(Clone, GraphQLObject)]
 pub(crate) struct SyncedSeriesData {
     description: Option<String>,
 }
@@ -491,32 +492,49 @@ impl Series {
             )
         ).await?;
 
-        let response = context
-            .oc_client
-            .delete(&series)
-            .await
-            .map_err(|e| {
-                error!("Failed to send delete request: {}", e);
-                err::opencast_unavailable!("Failed to communicate with Opencast")
-            })?;
+        info!(series_id = %id, "Attempting to send request to delete series in Opencast");
+
+        context.db.execute("\
+            update all_series \
+            set tobira_deletion_timestamp = current_timestamp \
+            where id = $1 \
+        ", &[&series.key]).await?;
+        // Todo: Consider optimistically updating events as well.
+
+
+        let oc_client = context.oc_client.clone();
+        let series_clone = series.clone();
+
+        // Unfortunately we can't wait for the http response. The Opencast delete endpoint will
+        // automatically start `republish metadata` workflows for all events in the series, which
+        // takes roughly 10 seconds per event, and only returns once all have finished.
+        // This would block the request for a long time.
+        tokio::spawn(async move {
+            let response = match oc_client.delete(&series_clone).await {
+                Ok(response) => response,
+                Err(e) => {
+                    error!("Failed to send delete request: {}", e);
+                    return;
+                }
+            };
+
+            if response.status() == StatusCode::NO_CONTENT {
+                info!(series_id = %id, "Deletion successfully requested");
+            } else {
+                // This is kinda pointless. Depending on the number of videos, the request takes
+                // super long to respond and will potentially return with `504 Gateway Timeout`.
+                // This is not necessarily an error in this case as the deletion could still be
+                // in progress.
+                warn!(
+                    series_id = %id,
+                    "Failed to delete series, Opencast returned status: {}",
+                    response.status()
+                );
+            }
+            // Todo: Consider reverting DB changes on error or unexpected response.
+        });
 
-        if response.status() == StatusCode::NO_CONTENT {
-            // 204: The series has been deleted
-            info!(series_id = %id, "Requested deletion of series");
-            context.db.execute("\
-                update all_series \
-                set tobira_deletion_timestamp = current_timestamp \
-                where id = $1 \
-            ", &[&series.key]).await?;
-            Ok(series)
-        } else {
-            warn!(
-                series_id = %id,
-                "Failed to delete series, OC returned status: {}",
-                response.status()
-            );
-            Err(err::opencast_unavailable!("Opencast API error: {}", response.status()))
-        }
+        Ok(series)
     }
 }
 
@@ -665,3 +683,4 @@ define_sort_column_and_order!(
     };
     pub struct SeriesSortOrder
 );
+

backend/src/api/mutation.rs

@@ -82,7 +82,7 @@ impl Mutation {
     /// The series is marked as "deletion pending" in Tobira and fully removed once Opencast
     /// finished deleting the series.
     ///
-    /// Returns the deletion timestamp in case of success and errors otherwise.
+    /// Returns the preliminary deletion timestamp.
     async fn delete_series(id: Id, context: &Context) -> ApiResult<Series> {
         Series::delete(id, context).await
     }

backend/src/model/event/mod.rs

@@ -6,7 +6,7 @@ use crate::{auth::AuthContext, HasRoles};
 
 
 /// Information necessary to render a thumbnail.
-#[derive(Debug, GraphQLObject)]
+#[derive(Debug, GraphQLObject, Clone)]
 pub(crate) struct ThumbnailInfo {
     pub(crate) url: Option<String>,
     pub(crate) live: bool,

backend/src/model/extra_metadata.rs

@@ -16,7 +16,7 @@ use crate::prelude::*;
 /// `"dcterms"` for the dc terms (most common namespace). The value for each
 /// namespace is a simple string-key map where each value is an array of string
 /// values.
-#[derive(Debug, Serialize, Deserialize, Default, GraphQLScalar)]
+#[derive(Clone, Debug, Serialize, Deserialize, Default, GraphQLScalar)]
 #[cfg_attr(test, derive(PartialEq, Eq))]
 #[graphql(
     description = "Arbitrary metadata for events/series. Serialized as JSON object.",

backend/src/model/series/mod.rs

@@ -3,7 +3,7 @@ use juniper::GraphQLObject;
 use super::ThumbnailInfo;
 
 
-#[derive(Debug, GraphQLObject)]
+#[derive(Debug, GraphQLObject, Clone)]
 pub(crate) struct SeriesThumbnailStack {
     pub(crate) thumbnails: Vec<ThumbnailInfo>,
 }

frontend/src/schema.graphql

@@ -392,7 +392,7 @@ type Mutation {
     The series is marked as "deletion pending" in Tobira and fully removed once Opencast
     finished deleting the series.
 
-    Returns the deletion timestamp in case of success and errors otherwise.
+    Returns the preliminary deletion timestamp.
   """
   deleteSeries(id: ID!): Series!
   """