fix(app-lib): delay account skin data deletion to next reboot

This gives users an opportunity to not unexpectedly lose skin data in
case they log off on accident.

packages/app-lib/.sqlx/query-e9449930a74c6a6151c3d868042b878b6789927df5adf50986fe642c8afcb681.json

@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "DELETE FROM default_minecraft_capes WHERE minecraft_user_uuid NOT IN (SELECT uuid FROM minecraft_users)",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": []
+  },
+  "hash": "e9449930a74c6a6151c3d868042b878b6789927df5adf50986fe642c8afcb681"
+}

packages/app-lib/.sqlx/query-fd494269d944b179ade61876669d1821b46d60f5cb79685c489aaebf13b35d24.json

@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "DELETE FROM custom_minecraft_skins WHERE minecraft_user_uuid NOT IN (SELECT uuid FROM minecraft_users)",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 0
+    },
+    "nullable": []
+  },
+  "hash": "fd494269d944b179ade61876669d1821b46d60f5cb79685c489aaebf13b35d24"
+}

packages/app-lib/migrations/20250413162050_skin-selector.sql

@@ -2,11 +2,34 @@ CREATE TABLE default_minecraft_capes (
     minecraft_user_uuid TEXT NOT NULL,
     id TEXT NOT NULL,
 
-    PRIMARY KEY (minecraft_user_uuid, id),
-    FOREIGN KEY (minecraft_user_uuid) REFERENCES minecraft_users(uuid)
-        ON DELETE CASCADE ON UPDATE CASCADE
+    PRIMARY KEY (minecraft_user_uuid, id)
 );
 
+-- Emulate a ON UPDATE CASCADE foreign key constraint for the user UUID on the default_minecraft_capes table,
+-- but allowing deletion of the user UUID in the minecraft_users table. This allows the application to temporarily
+-- keep skin state around for logged-out users, allowing them to retain their skins under the right conditions
+CREATE TRIGGER default_minecraft_capes_user_uuid_insert_check
+    BEFORE INSERT ON default_minecraft_capes FOR EACH ROW
+    BEGIN
+        SELECT CASE WHEN NOT EXISTS (
+            SELECT 1 FROM minecraft_users WHERE uuid = NEW.minecraft_user_uuid
+        ) THEN RAISE(ABORT, 'Cannot add a default cape for an unknown Minecraft user UUID') END;
+    END;
+
+CREATE TRIGGER default_minecraft_capes_user_uuid_update_check
+    BEFORE UPDATE ON default_minecraft_capes FOR EACH ROW
+    BEGIN
+        SELECT CASE WHEN NOT EXISTS (
+            SELECT 1 FROM minecraft_users WHERE uuid = NEW.minecraft_user_uuid
+        ) THEN RAISE(ABORT, 'Cannot change a default cape to refer to an unknown Minecraft user UUID') END;
+    END;
+
+CREATE TRIGGER default_minecraft_capes_user_uuid_update_cascade
+    AFTER UPDATE OF uuid ON minecraft_users FOR EACH ROW
+    BEGIN
+        UPDATE default_minecraft_capes SET minecraft_user_uuid = NEW.uuid WHERE minecraft_user_uuid = OLD.uuid;
+    END;
+
 CREATE TABLE custom_minecraft_skins (
     minecraft_user_uuid TEXT NOT NULL,
     texture_key TEXT NOT NULL,
@@ -14,12 +37,33 @@ CREATE TABLE custom_minecraft_skins (
     cape_id TEXT,
 
     PRIMARY KEY (minecraft_user_uuid, texture_key, variant, cape_id),
-    FOREIGN KEY (minecraft_user_uuid) REFERENCES minecraft_users(uuid)
-        ON DELETE CASCADE ON UPDATE CASCADE,
     FOREIGN KEY (texture_key) REFERENCES custom_minecraft_skin_textures(texture_key)
         ON DELETE CASCADE ON UPDATE CASCADE DEFERRABLE INITIALLY DEFERRED
 );
 
+-- Similar partial foreign key emulation as above
+CREATE TRIGGER custom_minecraft_skins_user_uuid_insert_check
+    BEFORE INSERT ON custom_minecraft_skins FOR EACH ROW
+    BEGIN
+        SELECT CASE WHEN NOT EXISTS (
+            SELECT 1 FROM minecraft_users WHERE uuid = NEW.minecraft_user_uuid
+        ) THEN RAISE(ABORT, 'Cannot add a custom skin for an unknown Minecraft user UUID') END;
+    END;
+
+CREATE TRIGGER custom_minecraft_skins_user_uuid_update_check
+    BEFORE UPDATE ON custom_minecraft_skins FOR EACH ROW
+    BEGIN
+        SELECT CASE WHEN NOT EXISTS (
+            SELECT 1 FROM minecraft_users WHERE uuid = NEW.minecraft_user_uuid
+        ) THEN RAISE(ABORT, 'Cannot change a custom skin to refer to an unknown Minecraft user UUID') END;
+    END;
+
+CREATE TRIGGER custom_minecraft_skins_user_uuid_update_cascade
+    AFTER UPDATE OF uuid ON minecraft_users FOR EACH ROW
+    BEGIN
+        UPDATE custom_minecraft_skins SET minecraft_user_uuid = NEW.uuid WHERE minecraft_user_uuid = OLD.uuid;
+    END;
+
 CREATE TABLE custom_minecraft_skin_textures (
     texture_key TEXT NOT NULL,
     texture PNG BLOB NOT NULL,

packages/app-lib/src/api/settings.rs

@@ -24,6 +24,8 @@ pub async fn set(settings: Settings) -> crate::Result<()> {
 
 #[tracing::instrument]
 pub async fn cancel_directory_change() -> crate::Result<()> {
+    // This is called to handle state initialization errors due to folder migrations
+    // failing, so fetching a DB connection pool from `State::get` is not reliable here
     let pool = crate::state::db::connect().await?;
     let mut settings = Settings::get(&pool).await?;
 

packages/app-lib/src/state/db.rs

@@ -36,5 +36,33 @@ pub(crate) async fn connect() -> crate::Result<Pool<Sqlite>> {
 
     sqlx::migrate!().run(&pool).await?;
 
+    if let Err(err) = stale_data_cleanup(&pool).await {
+        tracing::warn!(
+            "Failed to clean up stale data from state database: {err}"
+        );
+    }
+
     Ok(pool)
 }
+
+/// Cleans up data from the database that is no longer referenced, but must be
+/// kept around for a little while to allow users to recover from accidental
+/// deletions.
+async fn stale_data_cleanup(pool: &Pool<Sqlite>) -> crate::Result<()> {
+    let mut tx = pool.begin().await?;
+
+    sqlx::query!(
+        "DELETE FROM default_minecraft_capes WHERE minecraft_user_uuid NOT IN (SELECT uuid FROM minecraft_users)"
+    )
+    .execute(&mut *tx)
+    .await?;
+    sqlx::query!(
+        "DELETE FROM custom_minecraft_skins WHERE minecraft_user_uuid NOT IN (SELECT uuid FROM minecraft_users)"
+    )
+    .execute(&mut *tx)
+    .await?;
+
+    tx.commit().await?;
+
+    Ok(())
+}