feat: implement change timestamp for subscriptions set

src/db/models/subscription.rs

@@ -1,3 +1,5 @@
+use std::collections::HashSet;
+
 use diesel::prelude::*;
 use serde::{Deserialize, Serialize};
 
@@ -10,6 +12,8 @@ pub struct Subscription {
     pub id: i64,
     pub device_id: i64,
     pub url: String,
+    pub time_changed: i64,
+    pub deleted: bool,
 }
 
 #[derive(Deserialize, Insertable)]
@@ -18,6 +22,8 @@ pub struct Subscription {
 pub struct NewSubscription {
     pub device_id: i64,
     pub url: String,
+    pub time_changed: i64,
+    pub deleted: bool,
 }
 
 impl Subscription {
@@ -37,15 +43,76 @@ impl Subscription {
             .get_results(&mut pool.get()?)?)
     }
 
-    pub fn update_for_device(pool: &DbPool, device_id: i64, urls: Vec<String>) -> DbResult<()> {
+    pub fn set_for_device(
+        pool: &DbPool,
+        device_id: i64,
+        urls: Vec<String>,
+        timestamp: i64,
+    ) -> DbResult<()> {
         pool.get()?.transaction(|conn| {
-            diesel::delete(subscriptions::table.filter(subscriptions::device_id.eq(device_id)))
-                .execute(conn)?;
+            // https://github.com/diesel-rs/diesel/discussions/2826
+            // SQLite doesn't support default on conflict set values, so we can't handle this using
+            // on conflict. Therefore, we instead calculate which URLs should be inserted and which
+            // updated, so we avoid conflicts.
+            let urls: HashSet<String> = urls.into_iter().collect();
+            let urls_in_db: HashSet<String> = subscriptions::table
+                .select(subscriptions::url)
+                .filter(subscriptions::device_id.eq(device_id))
+                .get_results(&mut pool.get()?)?
+                .into_iter()
+                .collect();
 
+            // URLs originally in the database that are no longer in the list
+            let urls_to_delete = urls_in_db.difference(&urls);
+
+            // URLs not in the database that are in the new list
+            let urls_to_insert = urls.difference(&urls_in_db);
+
+            // URLs that are in both the database and the new list. For these, those marked as
+            // "deleted" in the database are updated so they're no longer deleted, with their
+            // timestamp updated.
+            let urls_to_update = urls.intersection(&urls_in_db);
+
+            // Mark the URLs to delete as properly deleted
+            diesel::update(
+                subscriptions::table.filter(
+                    subscriptions::device_id
+                        .eq(device_id)
+                        .and(subscriptions::url.eq_any(urls_to_delete)),
+                ),
+            )
+            .set((
+                subscriptions::deleted.eq(true),
+                subscriptions::time_changed.eq(timestamp),
+            ))
+            .execute(conn)?;
+
+            // Update the existing deleted URLs that are reinserted as no longer deleted
+            diesel::update(
+                subscriptions::table.filter(
+                    subscriptions::device_id
+                        .eq(device_id)
+                        .and(subscriptions::url.eq_any(urls_to_update))
+                        .and(subscriptions::deleted.eq(true)),
+                ),
+            )
+            .set((
+                subscriptions::deleted.eq(false),
+                subscriptions::time_changed.eq(timestamp),
+            ))
+            .execute(conn)?;
+
+            // Insert the new values into the database
             diesel::insert_into(subscriptions::table)
                 .values(
-                    urls.into_iter()
-                        .map(|url| NewSubscription { device_id, url })
+                    urls_to_insert
+                        .into_iter()
+                        .map(|url| NewSubscription {
+                            device_id,
+                            url: url.to_string(),
+                            deleted: false,
+                            time_changed: timestamp,
+                        })
                         .collect::<Vec<_>>(),
                 )
                 .execute(conn)?;

src/db/schema.rs

@@ -23,6 +23,8 @@ diesel::table! {
         id -> BigInt,
         device_id -> BigInt,
         url -> Text,
+        time_changed -> BigInt,
+        deleted -> Bool,
     }
 }
 

src/server/gpodder/simple/subscriptions.rs

@@ -85,8 +85,11 @@ pub async fn put_device_subscriptions(
             .insert(&ctx.pool)?
         };
 
-        Ok::<_, AppError>(db::Subscription::update_for_device(
-            &ctx.pool, device.id, urls,
+        Ok::<_, AppError>(db::Subscription::set_for_device(
+            &ctx.pool,
+            device.id,
+            urls,
+            chrono::Utc::now().timestamp(),
         )?)
     })
     .await