feat: implemented backend updates for email casing issue

backend/src/db/migrations/20250430174352_email-case-change.ts

@@ -0,0 +1,47 @@
+import { Knex } from "knex";
+
+import { TableName } from "../schemas";
+
+export async function up(knex: Knex): Promise<void> {
+  const hasEmail = await knex.schema.hasColumn(TableName.Users, "email");
+  const hasUsername = await knex.schema.hasColumn(TableName.Users, "username");
+  if (hasEmail) {
+    await knex(TableName.Users)
+      .where({ isGhost: false })
+      .update({
+        // @ts-expect-error email assume string this is expected
+        email: knex.raw("lower(email)")
+      });
+  }
+  if (hasUsername) {
+    await knex.schema.raw(`
+      CREATE INDEX IF NOT EXISTS ${TableName.Users}_lower_username_idx 
+      ON ${TableName.Users} (LOWER(username))
+    `);
+
+    const duplicatesSubquery = knex(TableName.Users)
+      .select(knex.raw("lower(username) as lowercase_username"))
+      .groupBy("lowercase_username")
+      .having(knex.raw("count(*)"), ">", 1);
+
+    // Update usernames to lowercase where they won't create duplicates
+    await knex(TableName.Users)
+      .where({ isGhost: false })
+      .whereRaw("username <> lower(username)") // Only update if not already lowercase
+      // @ts-expect-error username assume string this is expected
+      .whereNotIn(knex.raw("lower(username)"), duplicatesSubquery)
+      .update({
+        // @ts-expect-error username assume string this is expected
+        username: knex.raw("lower(username)")
+      });
+  }
+}
+
+export async function down(knex: Knex): Promise<void> {
+  const hasUsername = await knex.schema.hasColumn(TableName.Users, "username");
+  if (hasUsername) {
+    await knex.schema.raw(`
+  DROP INDEX IF EXISTS ${TableName.Users}_lower_username_idx
+`);
+  }
+}