add script to delete message ids from unlinked channels from db

bridge/src/data_deletion.ts

@@ -0,0 +1,50 @@
+/**
+ * When executed, this file scans the entire `messages` database collection
+ * and deletes entries belonging to channels which do no longer have a bridge
+ * configuration associated. Reads mongo URI from $DB_STRING env var.
+ */
+
+import Mongo from 'mongodb';
+
+if (!process.env.DB_STRING) {
+    console.error('$DB_STRING not provided.');
+    process.exit(1);
+}
+
+const mongo = new Mongo.MongoClient(process.env.DB_STRING);
+
+(async () => {
+    await mongo.connect();
+    const client = mongo.db();
+    const messages = client.collection('bridged_messages');
+
+    const res = messages.aggregate([{
+        $lookup: {
+            from: 'bridge_config',
+            localField: 'channels.discord',
+            foreignField: 'discord',
+            as: 'bridgeConfig',
+        }
+    }]);
+
+    let buf: string[] = [];
+
+    const execute = async () => {
+        const ids = [ ...buf ];
+        buf.length = 0;
+
+        if (ids.length) {
+            console.log('Deleting ' + ids.length + ' entries');
+            await messages.deleteMany({ _id: { $in: ids } });
+        }
+    }
+
+    res.on('data', data => {
+        if (!data.bridgeConfig?.length) buf.push(data._id);
+        if (buf.length >= 500) execute();
+    });
+
+    res.on('end', () => {
+        execute().then(() => process.exit(0));
+    });
+})();